2000W Inverter

[Lazyboy]

Following on from my previous question about wire diameter, does any one know why an inverter would be supplied with two negative and two positive leads as opposed to just one of each. Is there any advantage or more importantly disadvantage?

 

[autorouter]

The current-carrying capacity (amps) of a cable depends on its cross-sectional area (CSA), usually measured in square millimetres (mm2). It's the total CSA that matters. Two 16mm2 wires is just as good as one 32mm2 wire.

A further reason might be, one wire is sufficient for safety purposes, but two wires will reduce the voltage drop in the wires to an acceptable level. There are cable area calculators on many websites, such as this one (scroll down a bit). Longer cables require thicker cross-section to keep the voltage drop down.

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[John H.]

If you have two leisure batteries (connected in parallel) then one set of leads to each battery would be good.

 

[Tombola]

mine is plumbed in with 2 pos and 2 neg. No problem.
Actually easier to manouver the cables too.

 

[Derbyshire wanderer]

2 smaller cables are easier to form into shape and the termination fixings will be smaller too. Also thick cables tend to be expensive compared to smaller sizes that have more sales

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[Lazyboy]

So on a 2000W inverter, say 1 metre from the battery, what should the cable thickness be if two cables are used?

 

[autorouter]

So on a 2000W inverter, say 1 metre from the battery, what should the cable thickness be if two cables are used?

The minimum CSA would be 16mm2, which would give a voltage drop of 3% for a 1 metre positive and negative path (ie 2 metres of wiring). So you could use 2 x 8mm2, but 2 x 10mm2 might be more easily available and give less than 3% voltage drop.

 

[Raul]

For full use of a 2kw inverter, you should have 70mm2 cable or two 35mm2 if more practical to install, and a 250-300A fuse. The maxi fuse is a good match with a enclosed holder. Personally I would get the cables ready terminated if you haven’t got a hydraulic crimper. DIY crimps without proper tools are a waste of copper wire and a hazard.

 

[cmcardle75]

So on a 2000W inverter, say 1 metre from the battery, what should the cable thickness be if two cables are used?

50mm2 total minimum, with about 0.3V voltage drop (2.5%).

So 2 x 25mm2, which is a common size for meter tails. This is assuming you are actually running 4 cables, 2 positive, 2 negative.

If you go for bigger cable, you'll get less voltage drop and, thus, higher electrical efficiency (and more of a workout bending the things!)

 

[Raul]

The minimum CSA would be 16mm2, which would give a voltage drop of 3% for a 1 metre positive and negative path (ie 2 metres of wiring). So you could use 2 x 8mm2, but 2 x 10mm2 might be more easily available and give less than 3% voltage drop.

Have a look at a victron manual for a similar inverter, and see what cable is recommended and why.

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[autorouter]

​

For full use of a 2kw inverter, you should have 70mm2 cable or two 35mm2 if more practical to install, and a 250-300A fuse.

When I had a 12V 2kW inverter, that's exactly what I used. I was thinking it was a bit OTT, but maybe if you want to minimise voltage drop it's a good choice.

 

[Raul]

I had a 1600va inverter with 50mm2 cable about 0,8-1m long. From buss bar to inverter. Worked excellent. Later I have upgraded the inverter to a 2kva, and left that cable in. It proved insufficient at 3/4 to full load. It was safe but to much voltage drop and high DC ripple. Any inverter gets some, but, to much is not good. The worst DC Ripley you can see it with a oscilloscope, puts massive microcycles on battery. The primary cause is high resistance from source(battery) to inverter DC bus. I changed the cable AFTER I have seen the recommendation in the manual, 70mm2. Voltage loss under load is under 0,1v now with all the connections hydraulically crimped by me. I have re done couple of them that came with the battery cables, all covered up with heat shrink. In my opinion if economically viable, it’s best to keep voltage loss up to 1% max at 12v systems. At 3% is a massive loss and big discrepancy voltage when we count 0,1-0,15v, added to the battery voltage sag, then battery SOC will throw of any settings we rely on. One thing we notice on battery monitors with shunt, when things don’t add up, or drift. It all depends on voltage loss, sag under load, you will never recoup that back, is lost in efficiency.
Usually I allow 2-3% loss for 48v systems.

 

[Lazyboy]

Thanks for that Raul. I don't profess to understand DC ripple etc. but I am concerned about the size of cable to fit to be safe and efficient. The inverter comes with two negative and two positive cables and as best I can measure the overall diameter with a vernier is 7mm2 inc insulation. Based on information supplied via this forum this would appear to be totally inadequate leading to high temperature in the cables and also inefficiency with power supply. Why would the supplier include such inadequate cabling knowing that it leads to voltage drop and heat build up in the cables?

 

[Raul]

I would hazard a guess the two cables to be 16mm2, making 32mm2 for each leg. This is safe to operate but with the caveats mentioned above, and lower efficiency. Any heat, is lost power, and faster equipment/ components degradation. The DC ripple is the voltage fluctuation under load, like voltage sag but much faster 1-2 kHz. This is smoothed out by the capacitors in the inverter to a degree. High resistance makes high voltage drop and high ripple. You strive to reduce voltage loss to minimum as reasonably possible. This will result in good efficiency of the system, better life and less strain.

I have a inverter with 35mm2 cable, at 1,5m long. Max draw 100amp. I still get voltage drop, but acceptable and dc ripple up to 0,8vdc. At 1,5vdc ripple the inverter will shut down, despite the battery being almost full. This only happens on high loads close to max, and I don’t go there often. Some inverters do not have ripple protection, they just run till pop. Studer is one make with the most intrusive ripple protection I know of; even with the right cable size, one bad connection or loose and you know it.

 

[autorouter]

I don't profess to understand DC ripple etc. but I am concerned about the size of cable to fit to be safe and efficient. The inverter comes with two negative and two positive cables and as best I can measure the overall diameter with a vernier is 7mm2 inc insulation.

Cable size can be overall diameter including insulation, or cross-sectional area of the copper conductor, ignoring insulation. There are tables to convert between them - obviously only approximate because insulation thickness can vary.

According to this table, an overall diameter of 7.3mm corresponds to 16 square millimetres of copper conductor, ie 16mm2.
For comparison, a solid copper rod of diameter 4.5mm has a cross-sectional area of 16mm2.

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