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Wiring Unlimited Contents
1. Introduction and Disclaimer............................................................................................................................ 4 2. Theory ............................................................................................................................................................. 4 2.1 Ohm’s Law..................................................................................................................................................... 4 2.2 Power ............................................................................................................................................................ 4 2.3 Conductivity and resistance .......................................................................................................................... 5 2.4 Current, cable resistance and voltage drop.................................................................................................. 6 2.5 Negative effects of cable voltage drop ......................................................................................................... 8 2.6 DC ripple.................................................................................................................................................. 9 3. Battery bank wiring....................................................................................................................................... 12 3.1 Battery bank.......................................................................................................................................... 12 3.2 Large battery banks..................................................................................................................................... 13 3.3 Parallel battery bank wiring ........................................................................................................................ 14 3.4 Battery bank balancing ............................................................................................................................... 15 3.5 Battery bank midpoint ................................................................................................................................ 16 4. DC wiring ....................................................................................................................................................... 18 4.1 Select the right cable................................................................................................................................... 18 4.2 Busbars........................................................................................................................................................ 20 4.3 Cable connections ....................................................................................................................................... 21 4.4 Fuses............................................................................................................................................................ 23 4.5 Battery isolation.......................................................................................................................................... 24 4.6 Shunt ........................................................................................................................................................... 25 4.7 Parallel and/or 3 phase system DC wiring .................................................................................................. 26 4.8 Large system busbars.................................................................................................................................. 27 4.9 Voltage sensing and compensation ............................................................................................................ 27 4.10 Solar array design...................................................................................................................................... 28 5. AC cabling...................................................................................................................................................... 30 5.1 Power generation........................................................................................................................................ 30 5.2 Distribution networks ................................................................................................................................. 30 5.3 System current VA and Watt....................................................................................................................... 31 5.4 AC wiring ..................................................................................................................................................... 32 5.5 Fuses and circuit breakers........................................................................................................................... 33 5.6 AC bypass switch......................................................................................................................................... 33 5.7 Special considerations for AC wiring of parallel and/or 3 phase inverter/chargers ..................................... 33 6. Grounding, earth leakage and RCD............................................................................................................... 35 6.1 RCD.............................................................................................................................................................. 35
6.2 Mobile or independent installations........................................................................................................... 36 6.3 Inverter/charger combinations................................................................................................................... 38 6.4 Grounding boat parts.................................................................................................................................. 39 6.5 Isolation and grounding of Victron Equipment........................................................................................... 39 6.6 Land based systems .................................................................................................................................... 40 7. Galvanic corrosion......................................................................................................................................... 41 7.1 Preventing galvanic corrosion..................................................................................................................... 42 7.2 The galvanic isolator ................................................................................................................................... 42 7.3 The isolation transformer ........................................................................................................................... 43
1. Introduction and Disclaimer For a trouble-free operation of a system containing inverter/chargers and batteries, it is essential that the wiring in the system is done correctly. Many system problems are due to bad wiring. A system might underperform due to sub-standard wiring on both the DC or the AC side. In this document we aim to explain about wiring, the importance of getting it right and assist the installer in making the correct choices. We would like to acknowledge that electrical wiring regulations are different based on where you are in the world. Local electrical regulations can differ from the wiring advice given in this document. It is your responsibility to always seek professional advice and instruction form local authorities and/or licensed electricians prior to commencing any electrical work. The sole purpose of this document is to aid in the understanding of basic principles behind certain electrical concepts. This document is intended as a guide only. 2. Theory To be able to understand the underlying factors are that determine wiring thickness and fuse ratings. You do need to know some basic electrical theory. You might already know this and can perhaps skip this chapter, but we highly recommend that you at least have a read. 2.1 Ohm’s Law This basic electrical law allows you to be able to calculate the current that runs through a cable or a fuse at different voltages.
Electricity is movement of electrons. When you pass electricity through a material it meets a certain resistance. When the resistance is low the elections move easily, and the current is high. When the resistance is high the electrons move slow or do not move at all and the current is low. The resistance determines how much current runs through a material at a given voltage. This can be represented in a formula. The formula is called Ohm’s Law:
Current (A) = Voltage (V) / Resistance (Ω) I = V/R
2.2 Power
Ohms law can be used to derive other formulas. All possible formulas are listed in the image on the right. Please note that there are two symbols in use in the world that represent Voltage. These are U or V.
Some of these formulas are very useful when calculating current in cables.
One often used formula is this formula.
I = P/V
It calculates the current through a cable when the voltage and the load is known:
An example of how this formula can be used:
Question: If we have a 12V battery that is connected to a 2400 W load. How much current is running through the cable? Answer: V = 12V P = 2400W
I = P/V = 2400/12 = 200 A
2.3 Conductivity and resistance
Some materials conduct electricity better than other materials. Materials with a low resistance conduct electricity well, and materials with a high resistance conduct electricity poorly, or not at all. Metals have a low resistance and they conduct electricity well. These materials are called conductors. This is the reason they are used in electrical cables. Plastic or ceramics have a very high resistance, they do not conduct electricity at all. They are called insulators. This why, for example, plastic or rubber is used on the outside of cables. You will not get an electrical shock when you touch the cable. Insulators are also used to prevent short circuit when two cables touch each other.
Each material has its own specific resistance. This is written down as rho (ρ). In Ω.m. The table on the right on the right lists various conducting materials, their electrical conductivity and their specific resistance. You can see in this table that copper conducts electricity well and has a low resistance. This is the reason why electrical cable is made from copper. But, for example, titanium, does not conduct electricity well and therefor has a higher specific resistance. There are two more factors that determine cable resistance. These are the length and the thickness of the conductor (cable):
• A thin cable has a higher resistance than a thick cable • A long cable has a higher resistance than a short cable
The resistance of a length of cable can be calculated:
𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙ℎ𝑡𝑡 /
𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴
𝑙𝑙 /
𝐴𝐴
Resistance = Rho x
R= ρ x
As you can see there are 3 factors that determine cable resistance. Namely: • The electrical resistance of the used material • The length of the cable (longer cable = more resistance) • The diameter of the cable (thinner cable = more resistance)
It is important to know the resistance of a cable. Cable resistance creates two effects when a current is passed through a cable: • There will be a voltage loss over the cables • The cables heat up
If the current is increased these effects will be worse. The voltage loss increases, and the cable heats up more.
This is how to calculate the resistance of a cable:
Question: What is the resistance of a 1.5-meter-long, 16 mm 2 cable? Given: ρ copper = 1.7 x 10-8 Ω/m l = 1.5 m A = 16 mm2 = 16 x 10-6 m 2 Answer: R = ρ x 𝑙𝑙 / 𝐴𝐴 R = 1.7 x 10 -8 x 1.5/(16 x 10 -6 ) R= 1.7 x 10 -2 x 1.5/16 R = 0.16 x 10 -2 = 1.6 x 10 -3 R = 1.6 m Ω
The effect of cable length: Let’s take above example and now calculate for a 5m long cable. The result will be that the resistance is 5.3 mΩ. If you make the cable longer the resistance increases. The effect of cable thickness: Let’s take the original example and now calculate for a 2.5m 2 cable. The result will be that the resistance is 10.2 mΩ. If you make the cable thinner the resistance increases. Conclusion: Both cable thickness and cable length have a big impact on cable resistance. Please read next chapter what the effect of a high cable resistance is.
2.4 Current, cable resistance and voltage drop
To be able to select the right cable thickness and you will need to know how to much current runs through that cable. The current that flows through a system varies depending on the system voltage. The higher the voltage the lower the current is. Below is an overview of the amount of current that run in 3 systems where to load is the same, but the battery voltage varies:
As we have seen before, a cable has a certain amount of resistance.
When current flows through a resistor, the resistor heats up. These are called cable losses. Power is lost in the form of heat. The lost power can be calculated with the following formula:
Power = Resistance x Current 2 P = R x I²
Another effect of cable losses is that a voltage drop will be created over the cable. The voltage drop can be calculated with the following formula:
Voltage = Resistance x Current V = R x I
We now will add cable resistance to the system we used previously. In the circuit diagram on the right we have added two cables with a 1.6 mΩ resistance. The current that flows through each resistive element in a series electrical circuit remains the same while there will be a voltage drop over each element of which the sum equals the total voltage. This is called the Law of Kirchhoff. Knowing this we can calculate the voltage drop over one cable: • A 2400W load at 12V creates a current of 200 A • The voltage drop over one cable is: V = I x R = 200 x 0.0016 = 0.32 V
Because we have two cables, the total voltage loss in this system is 0.64 V
This also means that the inverter does not get 12V anymore, but 11.4V
The load is a constant in an inverter system, so the battery needs to deliver more current to compensate for the losses. In this example this means that the current will increase to 210 A.
When designing a system, you will always keep in mind that voltage drop varies for different battery voltages.
If we look at the same 2400 W load, but now in a 24V system: • The 2400 W load @ 24V will create a current of 2400/24 = 100A • The total voltage drop will be 2 x 100 x 0.0016 = 0.32 V (= 1.3%)
Battery voltage
Percenta ge drop
Voltage drop
12 V
2.5 %
0.3 V
And at 48V the current is 50A. The voltage drop is 0.16 V (= 0.3%)
24 V
2.5 %
0.6 V
This leads to the next question; how much voltage drop is allowed? The opinions vary somewhat, but we advise to aim for voltage drop no bigger than 2.5 %. For the different voltages this is indicated in the table on the right. It is important to realize that resistance does not only occur in the cable itself, but additional resistance is created by any items in the path of the current. This is a list of possible items that can add to the total resistance: • Fuses • Shunts • Switches • Cable lug crimps • Connections
48 V
2.5 %
1.2 V
And especially watch out for: • Loose connections
• Dirty or corroded contacts • Bad cable lug crimps
Each time a connection is made, or something is placed in the path between battery and inverter resistance is added.
To give you some idea how much these resistances can be:
• Each cable connection: 0.06 mΩ • 500A shunt: 0.10 mΩ • 150A fuse: 0.35 mΩ • 2m 35mm 2 cable: 1.08 mΩ
2.5 Negative effects of cable voltage drop
We now we know that we need to do to keep resistance down to prevent a voltage drop. But what are the negative effects of a high voltage drop in a system? This is a list of the negative effects of a high voltage drop: • Energy is lost and therefore the system efficiency is reduced • All devices connected to the system have a shorter lifetime because of DC ripple. • The system current will increase. This can lead to DC fuses blowing prematurely. • High system currents can lead to premature inverter overloads. • Voltage drop during charging will cause batteries to get undercharged. • The inverter receives a lower battery voltage. This this can potentially trigger low voltage alarms • The battery cables can heat up.
This is how to prevent voltage losses: • Use as short as possible cable lengths • Use cables with sufficient cable thickness • Make tight connections (but not too tight, follow torque recommendations in the manual) • Check that all contacts are clean and not corroded • Use quality battery isolator switches • Reduce the amount of connections within a cable run • Use DC distribution point or busbars
It is good practice to measure the system voltage drop. But Remember that a voltage drop only occurs at high current events. This is when an inverter is loaded with maximum load or when a battery charger is charging at full current. This is how to measure voltage drop: • Load the DC system with maximum power. • Measure with a voltmeter in the negative cable between the connection inside the unit and the battery pole • Repeat this for the positive cable In case of the battery and the unit being too far away or in a different room or enclosure: • Load the DC system with maximum power. • Measure with a voltmeter across the DC connections inside the unit • Measure arcos the battery poles • Compare these readings 2.6DC ripple One of the negative effects of high voltage drop in a system is ripple. Ripple appears in a system were the power source is a battery (DC) and the load is AC device. This is always the case in a system with an inverter. The inverter connects to batteries, but it powers an AC load. Ripple is directly related to the voltage drop over the DC cables when a system is under load and the battery currents are high. A high current causes a high voltage drop and this means that there will be a high ripple in the system.
The mechanism that causes ripple is an alternating voltage drop. The voltage drops when the system is feeding a load. And once the load is turned off the voltage recovers. And then drop again, recovers, drops and so on and on…. The voltage drop can be made worse if lead acid batteries are used, especially when these are too small or
when they are too old or when they are damaged. This process is depicted in the drawing on the right. 1. The voltage measured at the inverter is normal. In this example 12.6V 2. When a large load is turned on the battery voltage drops to 11.5 V 3. When the load is turned off, the battery voltage usually recovers back to 12.6V
How is ripple created? 1. The inverter converts DC voltage into an AC voltage.
2. The load connected to the inverter creates an AC current in the inverter.
3. This AC current causes (via the inverter) a fluctuating DC current on the battery.
4. The result of this fluctuating DC current is the following • When the DC current peaks the battery voltage will drop. • When the DC current drops the battery voltage recovers • When the DC current peaks the battery voltage will drop again • And so on.
The DC voltage will keep going up and down and is not constant anymore. It now is fluctuating. It will go up and down 100 times per second (100Hz). The amount the DC voltage fluctuation is called ripple voltage.
Normal DC looks like this:
DC voltage with ripple looks like this:
It is possible to measure ripple. There are two ways: • Use a Multi meter. Put multimeter in AC mode and measure the DC close to the inverter. • Use VE Configure, it keeps track of ripple When measuring remember that ripple only occurs when the system is under load. The same as for voltage drop, it can only be detected when the system is under full load or is when it is charging at full current.
A small amount of ripple can exist with no measurable impact. However, an excessive ripple can have a negative impact: • The lifetime of the inverter will be reduced. The capacitors in the inverter will try to flatten the ripple as much as possible and as a result the capacitors will age faster. • The lifetime of the other DC equipment in the system will be reduced as well. They too suffer from ripple • The batteries will age prematurely, each ripple acts a mini cycle for the battery. Due to the increase in battery cycles the battery lifetime will reduce • Ripple during charging will reduce the charge power Inverters or inverter/chargers have a built-in ripple alarm. There are two ripple alarm levels: • Ripple pre-alarm: Both the overload and the low battery LEDs blink and the unit will turn of after 20 minutes. • Full ripple alarm: Both the overload and low battery LEDs are on and the unit powers down.
These are the ripple alarm levels for the different voltages:
12V
24V 2.25 3.75
48V
Ripple pre-alarm 1.5V Full ripple alarm 2.5V
3V 5V
The only reason ripple exits is when there is a voltage drop in a system. To fix ripple you will have to reduce the resistance in the path from battery to inverter and back to the inverter. For more seen chapter 2.5.
To fix high ripple in a system do the following:
• Reduce Long battery cables • Use thicker cables
• Check Fuses, shunts and battery isolator switches • Check for loose terminals and loose cable connections
• Check for dirty or corroded connections • Check for bad, old or too small batteries
3. Battery bank wiring
3.1 Battery bank At the heart of any Victron system is the battery. A battery bank can consist out of a single battery but can also consist out of multiple batteries that are connected to form a battery bank. Commonly referred to as the house battery. The reason for doing this is to either increase the battery voltage, increases the battery capacity or both.
A battery bank is when: • When two batteries are connected in series their voltage increases. • When 2 batteries are connected in parallel their capacity increases. • Series/parallel combinations are also possible. Some examples:
Two batteries in series
Single battery
Four batteries in series/parallel
Two batteries in parallel
Four batteries in series
3.2 Large battery banks
When a large battery bank is needed try to avoid numerous series parallel battery banks constructed out of 12V AGM or Gel batteries. In these cases, consider using 2V lead acid batteries, Victron lithium batteries, smart Lithium batteries or smart other chemistry batteries. 2V lead acid batteries 2V OPzV or OPzS batteries are available in a variety of large capacities. You only have to pick the capacity you want and connect them in series. They are supplied with dedicated connection links exactly for that purpose.
Basic Lithium batteries With internal or external BMS.
Smart Lithium batteries Each battery has their own battery management system.
Together they will generate a total state of charge value for the whole battery bank. A Venus monitoring device is needed in the system. More info on what brands can work with Victron see: https://www.victronenergy.com/live/battery_compatibility:start
Other chemistry batteries Flow batteries and other chemistries. Commonly available in 48V. Multiple batteries can connect in parallel without any issues. Each battery has their own battery management system. Together they will generate a total state of charge value for the whole battery bank. A Venus monitoring device is needed in the system. More info on what brands can work with Victron see: https://www.victronenergy.com/live/battery_compatibility:start
3.3 Parallel battery bank wiring
It matters how a battery bank is wired into the system. It is easy to make a mistake. One of the most common mistakes is to parallel all the batteries together and then connect one side of the parallel battery bank to the installation. As indicated in below image. What happens when a load is connected? The power coming from the bottom battery will only travel through the main connection leads. The power from the next battery has to travel through the main connection and through the 2 interconnecting leads to the next battery. The next battery up has to go through 4 sets of interconnecting leads. The top one has to go through 6 sets of interconnecting leads. The top battery will be providing much less current than the bottom battery. What happens if the battery bank is being charged? The bottom battery gets charged with a higher current than the top battery. The top battery gets charged with a lower voltage than the bottom battery. The result is that the bottom battery is worked harder, discharged harder, charged harder. The bottom battery will fail prematurely.
Why is cable resistance important when wiring battery banks? Remember that a cable is a resistor. The longer the cable, the higher the resistance. And cable lugs and battery connections also add to this resistance. To give an indication of this, the total resistance for a 20cm 35 m 2 cable together with its cable lugs is about 1,5 mΩ. You might say that 1.5 mΩ is not much. But the internal resistance of the actual battery is also low. Therefore, it does matter a lot! The internal resistance of a battery is typically between 10 to 3 mΩ. If you construct an electrical diagram it will look like this: Current always chooses the path of least resistance. Most of the current will travel through the bottom battery. And only a small current will travel through the top battery.
The correct way of connecting a multiple parallel battery bank is indicated in below drawings. Use a positive and negative post, connect diagonally or use busbars. The main aim is to make sure the total path of the current into each battery is equal.
3.4 Battery bank balancing
Multiple 12V batteries can be connected in series to create a higher voltage like 24V or 48V. Only batteries are not completely identical and have minute differences in internal resistance. When a series string of batteries is charged you can end up with a variance in terminal voltages on each battery. This will cause the batteries to become unbalanced over time, and one of the batteries in a string will fail prematurely.
To check if cell unbalance is happening in your system: • Charge the battery bank. • Measure at the beginning of the bulk charge stage. This is when the charger is charging at full current. • Measure the individual battery voltages of one battery. • Measure the individual battery voltages of the other battery. • Compare the voltages. • If there is a noticeable difference between these voltages, then the battery bank is unbalanced.
To prevent initial battery unbalance you will need to fully charge each individual battery prior to connecting them in series (and/or parallel). to prevent unbalance in the future as the batteries are aging use a Battery balancer.
The battery balancer balances measures, warns and corrects battery imbalance. When a 24V battery bank is charged, and the voltage has reached 27V, the Battery Balancer will turn on. It will compare the voltage of both batteries and if it detects that the voltage of one battery is higher than the other battery it will draw a current of up to 1 A from the battery until the voltages are the same again. For a 24V system a single battery balancer is needed. And for a 48V system 3 battery balancers are needed, one between each two batteries. For more info see: https://www.victronenergy.com.au/batteries/battery-balancer
3.5 Battery bank midpoint
Battery unbalance can be detected by looking at the midpoint of a battery bank. If the midpoint is monitored it can be used to generate an alarm.
A midpoint alarm can mean the following: • An individual battery has failed, like an open cell or short- circuited cell • End of battery life due to sulfation or shedding of active material • Equalization is needed (only for wet cells) Both the battery balancer and the BMV 702 and 712 can generate a midpoint alarm.
The BMV 702 and 712 have a second voltage input that can be used for midpoint monitoring. It can be wired to the mid-point of the battery bank. The BMV will display the difference between the two voltages or as a percentage. For more info see: https://www.victronenergy.com.au/battery-monitors/bmv-700
In series/parallel battery banks it can be helpful to connect the midpoints of each parallel series string. The reason to do is to eliminate unbalance within the battery bank.
If you connect batteries in series/parallel, like the image on the right, you will see that the individual voltages will vary per series string and they will also vary within the string.
First make sure that each string has the same voltages by using a common negative and positive connection point or busbar
Once each string voltage is equal the midpoints can be connected. Make sure that the midpoint cabling is able to carry the full current between the batteries.
Once the midpoint of the battery bank is connected one battery balancer can be used, instead of using 3 battery balancers (one for each string). Also, a single BMV can be used for midpoint monitoring of the entire batetry bank.
But please be aware, that the only reason to use the midpoints of a battery bank is for balancing and/or monitoring purposes. It is not allowed to connect loads to the midpoint of a battery bank in order to be able to run loads that require a lower voltage. Doing so will create a large imbalance in a battery bank. This imbalance is bigger than a battery balancer can rectify (larger than 1A). The battery that is used to provide the lower voltage will fail prematurely.
For example, do not do this:
But instead use an Orion DC /DC converter:
4. DC wiring
4.1 Select the right cable It is important to use the correct cable thickness in a system. The correct cable can only be selected once you know the currents in a system. This is an example of what cable size belong to these currents. Providing the cable distance is less than 5 meters.
In order to avoid very thick cables, the first thing you should consider is to increase the system voltage. Large systems mean large currents. If you increase the system voltage the current will drop. The preferred upper inverter power limits per system voltage are: • 12V: up to 3000VA • 24V: up to 5000VA • 48V: 5000 VA and up Remember, that in case you have some loads or charge sources that only can deal with 12V, you can use DC/DC converters, rather than to choose a low voltage for the entire system. As explained already, it is very important to always use the right cable thickness. The correct cable thickness as mentioned in the product manual. Using too thin cabling has a direct effect on system performance. Generally, cable core thickness is indicated in mm². This indicates the surface area of the cable core. But other annotations are used as well. Like AWG (American Wire gauge) is used. In that case see here for a conversion table.
To find out the core dimeter of a stranded core cable, look on the cable insulation. There will be markings on the cable that indicate cable core thickness. Be aware that some cables can have very thick insulation and they may appear thicker than they are.
In a solid cable you can calculate the surface area if you measure the diameter of the cable core, but in a stranded cable this might not possible. (Please note that we do not recommend using solid core cables).
Surface area = π x raduis 2 Surface area = π x (diameter/2) 2 A = π x (d/2) 2
If you cannot find the right cable, double up. Use two cables per connection, rather than one very thick one. But the combined surface area of both cables has to be equal to the recommended surface area. For example, 2 x 35 mm 2 cables equals a 70mm 2 cable. Our bigger inverter/chargers have 2 connections for positive and negative in our larger units. It is okay to double up cable
Use as short as possible cable lengths Avoid these mistakes:
• Don’t use cable with course strands • Don’t use non-flexible cable • Don’t use AC cable • For marine use marine rated cable. This is cable with tin coated copper strands
Marine cable
Calculating cable thickness, yourself is hard, so we help you with selecting the correct cable thickness. There are several options: • Look in the product manual • The Victron toolkit app • The rule of thumb • Recommended battery cables document
Product manuals All our manuals recommend the battery cable size (and fuse size) that needs to be used for the product.
Victron toolkit app This App helps you calculate cable size and voltage drop. You can select: • voltage • cable length • current • cable cross section • And the app will calculate the voltage drop over both cables. The app can be downloads from here.
Recommended battery cables document This document contains a table that shows the maximum current for a number of standard cable where the voltage drop is 0.259 Volt. The document can found here.
Rule of thumb For a quick and general calculation for cables up to 5 meters use this formula:
Current / 3 = cable size in mm 2
Example: Current is 200A Then the cable needs to be: 200/3 = 66mm 2
4.2 Busbars Busbars are like cables only the are rigid copper bars. They are used in large systems where larger currents flow. They are used as a common positive and common negative point between the batteries and multiple inverters. But busbars are also used in smaller systems, especially when there are a lot of DC equipment. A busbar in this case provides a nice location to connect all the various DC cables to. To calculate busbar thickness, simply use the recommended cable surface area and apply that to the bus bar cross section area.
surface area = with x depth
For example: A busbar of 10mm x 5mm The surface area cross section is 5 X 10 = 50 mm 2
When wiring the system please make sure that the cross-section of the connection between the batteries and the DC distribution point equals the sum of the required cross-sections of the connections between the distribution point and the DC equipment
We also have a product range that can be used as a bus-bar. This is the Lynx range. The lynx consists out of 3 products that can be connected to each other to form a bus-bar. It is rated up to 1000A.
• Lynx Power in - to connect batteries • Lynx shunt - This unit houses the main fuse, the shunt and battery monitor electronics. (CCGX needed to read out the battery monitor) • Lynx distributor – to connect the DC loads and their fuses and indication light per fuse.
For more info on the Lynx see here.
4.3 Cable connections There are several ways to connect cables to batteries or to Victron products. Connections are made is a variety of ways:
Nuts and bolts • These usually come in M5, M6, M8 or M10. • To fit a cable onto a bolt, the cable needs to have an eye cable lug. • The cable lug needs to match the cable thickness.
• A special crimping tool is needed to attach a cable lug onto a cable. • If the cable lug does not have insulation you will need to add this. • When connting the cable eye to the bolt, place a washer and spring ring and then the nut. • Use insulated tools when tightening the nut. An acidental battery short curcuit can be very dangerous and the currents can melt your unisualetd spanner, or the spark can cause a battery explosion.
Screw connectors • These come in all sizes, for thick or thin wires. • When inserting a wire, the insulation needs to be stripped. Make sure to strip the cable correctly. • Avoid cable insulation enter the connector. This can lead to too much resistance and the connector will heat up and potentially melt. • Avoid insolated cable to be visible outside the connector. This is dangerous. Electrocution or short circuit risk.
Push connectors • Push down the orange part with a flat screwdriver.
• Insert the stripped wire. • Release the orange part. • The cable is now locked in place. Give the cable a small tug to check if the cable is securely fastened. Ferules • These are sleeves that slide over a stripped cable end. • A special crimping tool is needed.
• They are used to align the stripped cable strands and to prevent them splaying when inserting a cable into a screw or push connector. • Use these if you are after a tidy wiring job. Spade connectors • A spade crimp terminal needs to be crimped to the cable • A special crimping tool is needed.
MC4 connectors
• To connect solar panels to MPPTs. • Male or female connectors. • Special crimping tool is needed.
• Can be bought as pre-assembled cables. • MC4 Y-pieces (or Y cables) used to connect solar panels in parallel.
Anderson plugs • Often used in automotive or mobile applications. • Available in different current ratings and cable thicknesses. • Make sure the current rating matches the currents when your system is under load. • They will add to the cable resistance. • Limit or avoid their use.
Cigarette plugs • Used in low-end automotive applications. • Not capable of carrying large currents. • Consider that the circuit in the car might only have a low fuse rating • Take care to insert the plug correctly, and deep enough, if not inserted correctly. the connector can heat up and melt. • Limit or avoid their use. Battery clamps
• These are only meant for temporary connections. • They often do not have a high enough current rating. • Should never be used as a permeant connection in a system. • Limit or avoid their use.
Always make sure all connections are tight, but not too tight. Look in the product manuals for the recommended torque moments. Most electrical connections are tinned brass nuts bolts and screws and they can get damaged when applying too much pressure when tightening.
4.4 Fuses
Each product that connects to a battery always needs to be fused. No matter how big or small the load is. The reason behind this is because batteries can potentially produce very high currents capable of cause a fire.
The fuse needs to be situated in the positive battery cable.
Traditionally, a fuse contains a wire that melts as soon as an unacceptable high current passes through this wire. When the wire in the fuse has melted, the electrical circuit has been broken and no additional current will flow. The fuse protects against: • Severe overload - when more current runs in the system than normally expected. • Short circuit - when one conductor accidentally comes in contact with another conductor. For fuse ratings always see the product manual. Most DC fuses are suitable for 12 and 24V, but they are not necessarily suitable for 48V and higher. Current rating and voltage rating normally is displayed on the fuse, or alternatively look in the fuse datasheet. In multiple phase systems use one DC fuse per phase. If a big single fuse is not available, use one fuse per unit. Use the exact same fuse per unit.
Some fuse types:
For low currents
Glass fuse + holder
Blade fuse (car fuses) many types Blade fuse holder
For medium currents
MIDI fuse
MIDI fuse holder
DC MCB
For high currents
MEGA fuse + holder (Victron) CNN Lynx fuse ANL fuse + holder Blade fuse + holder
4.5 Battery isolation
The rules and guidelines for battery isolation vary in different countries, but, it is recommended, that if battery isolation is needed, to only isolate the positive battery cable. When a battery isolation switch is needed always make sure you use a quality battery isolation switch. A bad switch can cause a voltage drop. The battery switch must be rated to the currents that can be expected in the system under full load.
Type of battery isolator switches • Marine or automotive systems (usually 12 and 24V) use battery isolators • Land based systems (usually 48V) din mounted DC MCBs or blade fuses are used
Battery Isolator switch
high current DC MCB
Blade fuse and holder
Switching the negative in multiple unit systems Our inverter/chargers do not have galvanic isolation between the battery and VE-BUS. In a system with more than one inverter/charger it is extremely important to always follow below rules. Not following these rules can lead to damage to the communication chip.
• Each unit’s negative battery connection needs to be connected to the other unit’s negative connections. • Only when the common negative is in place, the RJ45 VE.Bus cables can be connected to the units. • When one unit is taken out of the system all the RJ45 cables needed to be disconnected before removing this unit.
4.6 Shunt
A shunt is needed in a system to measure battery state of charge The shunt is wired in the negative cable. The shunt measures all the current going in and out of the battery bank. Therefore, the shunt needs to be the last item before the battery bank or battery bank bus bar. All DC loads and DC sources need to be connected after the shunt. See on the right how to wire the shunt into a system: The shunt needs to be big enough and should be rated to the maximum DC current that potentially can occur in the system. The battery monitor comes with a 500A, 50mV shunt, but in case the shunt is not big enough you need to add a bigger shunt. Shunts are available in the following sizes: 500, 1000, 2000 and 6000A
When using a bigger shunt make sure that you change the shunt parameters in the battery monitor.
Please be aware that misplacement of the shunt can potentially cause a problem in a system depending how it is wired in. This is especially the case in large systems where there is be a long path between the battery and the inverter/chargers. When inverting, the inverter/charger near the shunt will “see” a lower DC input voltage than the units far away from the shunt When charging, the batteries near the shunt will “see” a lower DC input voltage. Than the batteries further away from the shunt. See below image:
To fix this, move the shunt away from the positive cable (not ideal). Or consider not using shunt at all but use smart batteries that generate their own sate of charge or use the VE.Bus battery monitor.
4.7 Parallel and/or 3 phase system DC wiring
In a system with more than one inverter/charger who are connected in a parallel and/or in 3-phase configuration it is essential that each unit has the same DC path from battery bank to each unit, or from the busbar to each unit. The reason why this is important is, that if there was a difference in cable thickness and length, the resistance between each unit will differ. The internal resistance of an inverter/charger is very low, so a difference in resistance will cause the DC path for one unit, to be much higher or lower than the path of the other unit. Different resistance means different voltages and currents for each unit in the system. Inverter/charger overload is directly related to current. The result will be that, the unit that has more current running through it than the other units, will go into overload before the other units do. The total inverter power of the system will be reduced. As soon as one unit goes into overload, the whole system stops working. The unit with the bad wiring will determine the performance of the whole system. To achieve a balanced system, you will need to use the same cable type, cross section and cable length to each unit from the battery bank or from the busbars. We highly recommend for you to consider using bus-bars or power-posts before and after the inverter/chargers. A parallel and/or in 3-phase system needs to connect to a single battery bank. It is not allowed to connect the individual units of a 3 phase and/or parallel system to individual batteries.
To check if a system is correctly wired or to trouble shoot wiring follow these steps: • Load the system to maximum load. • Current clamp the DC wires to each unit. • Compare the current readings, each unit should have similar DC currents. Alternatively, you can measure the voltage on the busbar or battery bank and compare this with the voltages you measure at each unit’s battery terminals. These voltages should all be the same.
4.8 Large system busbars In systems that contain inverter/chargers and MPPTs, that all connect to a busbar, it is important to alternately connect the inverter/chargers and MPPT to the busbars. This will reduce the current flowing through the busbars. And all MPPTs should have approximately the same cable length.
If the systems has only one battery bank you should connect the battery bank in the middle of the busbars. But in case of several parallel battery banks, they should also be distributed along the busbars.
4.9 Voltage sensing and compensation
Voltage sense is a feature that will compensate for cable losses during charging. This will ensure batteries are charged with the correct voltage. This feature generally will only compensate for voltage losses up to 1V. If the losses in the system are bigger than 1V (i.e. 1 V over the positive connection and 1 V over the negative connection), the charger or inverter/charger will reduce its charge voltage in such a way that the voltage drop remains limited to 1 V. The reason behind this is, that if the losses are bigger than 1 Volt, the battery cables are too thin and are unable to carry a large current and therefore the charge current needs to be reduced. Voltage sense also be used to compensate for voltage losses when diode splitters are used. A diode splitter has a 0.3 V voltage drop over the diode. Some products such as inverter/chargers or large chargers have voltage sense build in. For other products, such additional equipment might be needed such as the smart battery sense or the Smart VE.Bus dongle. • If the product has a voltage sense terminal two sense wires can be connected from the V-sense terminal directly on the battery positive and negative terminal or distribution. Use wire with a cross- section of 0,75mm². • In case of the MultiPlus II connect the VE.Bus smart dongle to the battery and connect the dongle via a RJ45 cable to the MultiPlus II.
• In case of a MPPT Connect a Smart battery sense to the battery and match it to a MPPT via the VictronConnect App.
Voltage sensing in an Energy Storage system with DC Solar In an ESS system with DC solar, the charger of the inverter/charger is disabled. Battery charging and feeding excess solar is taken care of by the MPPT solar charger. This controlled by the CCGX. It will set the MPPT at a higher voltage than the inverter/charger. This will result in a slightly higher DC voltage when the battery is (nearly) fully charged and the inverter/charger will attempt to reduce the “overvoltage” by feeding power back into the grid. In a 48 V system this overvoltage is set at 0.4 V and in a in a 24 V system it is 0.2 V But the DC cabling, fuses and connections will cause a voltage drop in the system. The voltage drop can reduce the “overvoltage” the inverter/charger needs before it can feed power into the grid. Example: In an ESS system with 100A MPPT with 2x 1m cable 35mm² and a 150A DC fuse the resistance is: Connections: 0.35 mΩ 150 A fuse 0.35 mΩ 2 m cable 1.08 mΩ The total resistance is 1.78 mΩ and the voltage drop at 100A is 178 mV The solution is to use an MPPT with automatic voltage drop compensation this will result in that the output voltage of the MPPT will slightly increase with increasing current. But if the MPPT does not have voltage sensing, then it is best to connect the MPPT directly to the MultiPlus.
4.10 Solar array design Multiple solar panels together are called a solar array. If you connect solar panels in series the voltage increases and when you connect them in parallel the current increases. The same as is the case when constructing a battery bank with individual batteries.
An example of panel in series: If you look at the specs of a 12V solar panel, you will find that the Voc is around 22Volt. For a 75/15 MPPT the solar voltage can be as high as 75V. This will allow you to connect up to 3 x 12V panels in series.
Note on charge current at different battery voltages : For a 75/15 MPPT the current rating is 15 A. This is the current going into the battery. This means that with a 12V battery you will get less power into the battery than with a 24V battery.
Solar array power To determine the total power of a solar array, you will have to add the power of each module no matter if they are connected in parallel or in series.
Both these arrays are 200W:
Series parallel arrays are possible as well this is a 400W array:
To help you deign a solar array and to match it to the correct solar charger see this calculation sheet here.
5. AC cabling
5.1 Power generation
The generator in a power station generates 3 phase electricity. Each of these 3 phases have an alternating voltage of 230 Volt (or a different voltage, depending on the country). The voltage alternates at a frequency of 50 (or 60) Hz. And because the coils in the generator are rotating, there is a 120°-degree phase shift between each phase.
The 3 coils are connected to each other and create a triple circuit, a so-called star configuration. A single coil (phase) has a potential of 230Vac. And a second potential level is created between two coils. Due to the 120° phase shift the potential is 400 Vac.
To be able to use the phases separately the common point (star point) is connected to a conductor called “Neutral”. Between the neutral and one of the phases a voltage of 230 Volt exists. The Neutral conductor is a conductor that can be used by all 3 phases and can be used in 3 separate electrical circuits. The star point acts as a neutral in electrical house installations. The function of the neutral conductor is to enable separate use of each phase and each phase can be used as an individual 230 Volt AC supply. The neutral is also connected to a metal spike driven into the ground, the so-called earth spike. In this way the potential of the earth equals 0 Volt. This connection is called earth. A 3-phase load, like a 3-phase electric motor, uses electricity from all 3 phases. The neutral does not have a function because the 3 electrical circuits will keep each other balanced. Only if one of the phases consumes more load than the others, the neutral will start to conduct current. This current is called the “compensating or equalizing current”.
When setting up 3 phase inverter/chargers they will need to be set up in a star configuration. They need to have a common Neutral. Delta is not allowed. The load they run can be a load in Delta configuration. Unequal loading is not an issue if the inverter/chargers run in inverting mode, but it might be an issue if they un in pass-through mode and they are connected to a generator that is unable to deal with an unbalanced load. 5.2 Distribution networks There are different ways in which power is distributed to the consumer. And different ways in how the consumer system is connected. All networks supply the 3 phases, but the way Neutral and Earth are bonded varies. TN-S network • The generator star point is connected to Neutral and to Earth. • The phases, Neutral and Earth are distributed. • The consumer uses the supplied phases Neutral and Earth. • Neutral and Earth are not connected to each other.
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