Cable size for inverter

[Odd-no-more]

Having now bought the inverter I have looked into the cable and fuse size, a 2000w load at 12 volts is approx 166 amps so I have ordered a 200 amp circuit breaker and 6mm cable to connect it.
People who know, is this right please?

 

[Bolti]

When I was looking for cables I found this he does them in different thicknesses.

https://www.ebay.co.uk/itm/240-Amp-35mm-Battery-Power-Cable-Starter-Earth-Custom-Made-Car-Auto-Connection/402794700240?mkcid=1&mkrid=710-53481-19255-0&siteid=0&customid=link&campid=5338547443&toolid=20001&mkevt=1

 

[Hoovie]

Having now bought the inverter I have looked into the cable and fuse size, a 2000w load at 12 volts is approx 166 amps so I have ordered a 200 amp circuit breaker and 6mm cable to connect it.
People who know, is this right please?

6mm? if you are meaning 6mm2 (I think you are), then that is way way too small! I would also forget the circuit breaker and use a proper fuse (circuit breakers are notoriously poor unless you spent proper money on decent ones)

The right size cable is a combination of the current being drawn and the length of cable. Without knowing both, impossible to say appropriate size cable needed.

 

[Odd-no-more]

6mm? if you are meaning 6mm2 (I think you are), then that is way way too small! I would also forget the circuit breaker and use a proper fuse (circuit breakers are notoriously poor unless you spent proper money on decent ones)

The right size cable is a combination of the current being drawn and the length of cable. Without knowing both, impossible to say appropriate size cable needed.

Sorry I'm a bit confused, it's 16mm² I should also say it will never run at 2000w nearer 500w and only for a minute or 2.

 

[Hoovie]

Sorry I'm a bit confused, it's 16mm²

What is the distance from inverter to battery? PS. Whatever it is, 16mm2 will still be too small.

 

[Odd-no-more]

What is the distance from inverter to battery? PS. Whatever it is, 16mm2 will still be too small.

I haven't worked it out yet but as close as possible, I should think about 300mm

 

[funflair]

Sorry I'm a bit confused, it's 16mm² I should also say it will never run at 2000w nearer 500w and only for a minute or 2.

My guess would be still no where near enough, our last van was 80 mm sg I think and this one must be over 100.

There is a good calculator on 12 volt planets web site.

Voltage Drop Calculator | 12 Volt Planet Cable Calculator

Use our Voltage Drop Calculator to select the correct Cable for your campervan, motorhome or boat wiring application. Cable Calculator for Auto and Marine Electrical Components from 12 Volt Planet - Cable Size Calculator

www.12voltplanet.co.uk

 

[Odd-no-more]

My guess would be still no where near enough, our last van was 80 mm sg I think and this one must be over 100.

There is a good calculator on 12 volt planets web site.

Voltage Drop Calculator | 12 Volt Planet Cable Calculator

Use our Voltage Drop Calculator to select the correct Cable for your campervan, motorhome or boat wiring application. Cable Calculator for Auto and Marine Electrical Components from 12 Volt Planet - Cable Size Calculator

www.12voltplanet.co.uk

I'm well out I did check online and it gave me the numbers, I may have inputted it wrong or it was a dodgy site. Thanks I will get new cable

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[Lizbiebrowne]

I've recently fitted a 1500 W inverter and used 25 mm2 cable with a run length of 0.5 m and 150 amp fuse. If you're going to use a 200 amp fuse you should use cable that can carry that load without melting or catching fire so that would be at least 35 mm2 in my opinion. 12 V Planet sell this: https://www.12voltplanet.co.uk/extra-flexible-pvc-battery-welding-cable-35mm-240a-metre.html.

 

[Mike001]

My 2000watt invertor is around 600mm from battery.
200amp mega fuse plus isolating switch. I use 35mm x2 cable so 70mm sq for each. Pos and neg

 

[Howard B]

I've recently fitted a 1500 W inverter and used 25 mm2 cable with a run length of 0.5 m and 150 amp fuse. If you're going to use a 200 amp fuse you should use cable that can carry that load without melting or catching fire so that would be at least 35 mm2 in my opinion. 12 V Planet sell this: https://www.12voltplanet.co.uk/extra-flexible-pvc-battery-welding-cable-35mm-240a-metre.html.

Same as i fitted to my 1500w inverter.

 

[Odd-no-more]

I will never run the inverter at max, my battery would not be able, I have decided on 60mm² cable and a short run so should be ok

 

[RedFrame]

Sorry I'm a bit confused, it's 16mm² I should also say it will never run at 2000w nearer 500w and only for a minute or 2.

I'm well out I did check online and it gave me the numbers, I may have inputted it wrong or it was a dodgy site. Thanks I will get new cable

I will never run the inverter at max, my battery would not be able, I have decided on 60mm² cable and a short run so should be ok

YOU may not, but if you sell your van on...?

Do the job right..!

Cheers
Red.

 

[Hoovie]

I haven't worked it out yet but as close as possible, I should think about 300mm

a minimal distance there, which is always a good idea

For a 2000W inverter, I would go with 70mm2, but I wouldn't be overly concerned to see 50mm2 so your plan of 60mm2 will do the job fine.
(PS. I don't know if your 60mm2 come from a table that quotes the sizes in AWG and the 60mm2 was a metric conversion, but I am not aware 60mm2 is a buyable size. the sizes tend to go .... 16mm2 - 25mm2 - 35mm2 - 50mm2 - 70mm2 - 90mm2 - etc)

 

[funflair]

I will never run the inverter at max, my battery would not be able, I have decided on 60mm² cable and a short run so should be ok

I haven’t done the numbers but I would think that would be fine

 

[bigtwin]

Does the instructions for your inverter not define the size necessary? I know that Victron do.

I share other’s concerns regarding your plan and justification that you’ll never use full power. As an ex-gasman you should be familiar with accounting for inexperienced/foolish users and protecting them from themselves. Don’t be that person that‘s responsible for an accident ‘x’ years down the line when another user, not unreasonably, uses the full capability of the inverter.

Do it right, you know it makes sense.

Ian

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[funflair]

Sorry didn’t see your reply Hoovie as I am trying to multitask cook tea and post at the same time and I started about 10 minutes ago

 

[funflair]

I

Does the instructions for your inverter not define the size necessary? I know that Victron do.

I share other’s concerns regarding your plan and justification that you’ll never use full power. As an ex-gasman you should be familiar with accounting for inexperienced/foolish users and protecting them from themselves. Don’t be that person that‘s responsible for an accident ‘x’ years down the line when another user, not unreasonably, usescthe full capability of the inverter.

Do it right, you know it makes sense.

Ian

If it does it’s most likely way under what he is going with, when I have seen something pre attached to a 2kw inverter they are usually like a shoe lace.

 

[bigtwin]

I

If it does it’s most likely way under what he is going with, when I have seen something pre attached to a 2kw inverter they are usually like a shoe lace.

Eeek!

Ian

 

[Odd-no-more]

a minimal distance there, which is always a good idea

For a 2000W inverter, I would go with 70mm2, but I wouldn't be overly concerned to see 50mm2 so your plan of 60mm2 will do the job fine.
(PS. I don't know if your 60mm2 come from a table that quotes the sizes in AWG and the 60mm2 was a metric conversion, but I am not aware 60mm2 is a buyable size. the sizes tend to go .... 16mm2 - 25mm2 - 35mm2 - 50mm2 - 70mm2 - 90mm2 - etc)

I got it on Amazon

 

[Odd-no-more]

Does the instructions for your inverter not define the size necessary? I know that Victron do.

I share other’s concerns regarding your plan and justification that you’ll never use full power. As an ex-gasman you should be familiar with accounting for inexperienced/foolish users and protecting them from themselves. Don’t be that person that‘s responsible for an accident ‘x’ years down the line when another user, not unreasonably, uses the full capability of the inverter.

Do it right, you know it makes sense.

Ian

If we sell the van with what it's cost I'm taking the inverter out
I only have a lead acid 95 amp hour battery, the inverter is to power a milk frother 480w so Mrs. Ex can have a cappuccino coffee off grid. We have a coffee machine but that is for EHU it draws 1470w and would kill my battery

 

[funflair]

If we sell the van with what it's cost I'm taking the inverter out
I only have a lead acid 95 amp hour battery, the inverter is to power a milk frother 480w so Mrs. Ex can have a cappuccino coffee off grid. We have a coffee machine but that is for EHU it draws 1470w and would kill my battery

Sounds like Lithium next

 

[Howard B]

I

If it does it’s most likely way under what he is going with, when I have seen something pre attached to a 2kw inverter they are usually like a shoe lace.

Cables that came with my inverter didn't look up to the job, hence i purchased another set from 12v Planet.

 

[Odd-no-more]

Sounds like Lithium next

Then I would need a new charger and solar control. If it gets to that she can have instant coffee

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[Lenny HB]

With only your 480 watt load you still need a second battery to cope with that load you should limit the maximum load to the C5 rate.
As Hoovie says forget about circuit breaker, you can get reliable DC ones but not at the sort of price you would want to pay.

 

[G7UXG]

I’m confused as to why you would use 70mm sq cable for a short cable run, running 200 amps maximum (because that’s what it will be fused at). The cable is rated at 485 amps according to 12 Volt Planet and their voltage drop calculator shows a drop of 0.9% for a 1 metre cable run.

35mm sq cable is rated at 240 amps and will result in a voltage drop of about 1.8%, or about 0.2 volts.

Would 35mm sq not be sufficient?

 

[funflair]

I’m confused as to why you would use 70mm sq cable for a short cable run, running 200 amps maximum (because that’s what it will be fused at). The cable is rated at 485 amps according to 12 Volt Planet and their voltage drop calculator shows a drop of 0.9% for a 1 metre cable run.

35mm sq cable is rated at 240 amps and will result in a voltage drop of about 1.8%, or about 0.2 volts.

Would 35mm sq not be sufficient?

Maybe it would be sufficient but 0.2 of a volt could be enough to make the difference between the inverter cutting out on low volts and it running, in this case less is more in my book.

 

[Raul]

I’m confused as to why you would use 70mm sq cable for a short cable run, running 200 amps maximum (because that’s what it will be fused at). The cable is rated at 485 amps according to 12 Volt Planet and their voltage drop calculator shows a drop of 0.9% for a 1 metre cable run.

35mm sq cable is rated at 240 amps and will result in a voltage drop of about 1.8%, or about 0.2 volts.

Would 35mm sq not be sufficient?

Because at 12v under load, battery will have a natural voltage sag by default, add a 1.8% loss on 12v is to big. You want as small as possible loss, under 1%, to avoid dc ripple. On 24 up to 2% and on 48v up to 3%. It’s all in the reputable inverters manual. The 12v planet calculator it’s just a indication for wiring, not necessarily accurate for sensitive equipment. A cable calculation takes many more factors in consideration, like method of installation, conduit/trunking or not, insulation rating, etc. Automotive wiring it has a very thin insulation, while welding or marine ratings are different.

 

[Hoovie]

Voltage drop is sometimes misunderstood I think (and hopefully what I am about to say doesn't demonstrate I've misunderstood it as well! )
1.8% sounds like a small amount on the face of it, but bear in mind if you take the "defaults" for a 12V Battery to be:
Fully Charged = 12.7V
50% Discharged = 12.0V (actually a little more at 12.04V but let's use round numbers).
The voltage difference between a 100% charged battery and a 50% charged battery is actually only 6%. Maybe a lot less than people realise initially?
As has been said, factor in voltage sag of a battery under high loads, then add in voltage loss on cables and the voltage at the inverter terminals is a lot less than you may think!

And there is a bit of a myth that only Lead Acid batteries suffer from voltage sag and it doesn't happen on Lithium? It would be true to say there is less of a sag, but it is sure still there. The chart below is from a few days ago and I think looking at the time is a 30 minute period where I was running the Truma water heater off the inverter while camped up off-grid.

The Voltage dropped by over 0.5V when the load hit nearly 100A. (note that this is the voltage reading at the battery, NOT the inverter).
If this was a smaller battery bank, the sag would be greater; If the current was higher, the sag would be greater; If it were a Lead Acid battery providing the power, the sag would be even greater.
Put all the above together and add in undersized (in actuality, not in tables) cables and you'd sometimes be hard-pressed to even have the inverter stay on for more than a minute or so!

 

[MisterB]

i have 35mm2 welding cable from my 300Ah lithium battery. its only around 150mm in length (cant remember exactly but certainly no longer than 300mm). i have had both my microwave and kettle on at the same time on testing after installation and there was no heating of the terminals or cable (touch test) that was noticeable after a few minutes - until 'full' kettle boiled. i did wrap the pos cable in red insulation tape but kept it to a minimum - i know i could have just done the ends on such a short run as its easy ti identify the pos cable from neg, but it makes me happy !