Inverter cable and fuse (1 Viewer)

bigtwin

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Oct 29, 2009
5,298
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In order to ascertain the size (mm2) of the cable it is necessary to know not only the current to be carried but also the length of the cable run.

Does the inverter manual not define the requirements? Edit: I see that itā€™s a potential purchase!

Edit: A 2500W inverter will pull around 250A and, at 5000W will pull around 500A. On that basis a 250A fuse (and similarly rated cable) would be too low.

There are various online cable sizing calculators available such as this one.

Ian
 
Last edited:
OP
OP
S
Mar 1, 2022
48
9
Funster No
87,175
MH
Burstner
Hi,
Thank you for the reply, maybe if I outline what we want to use it for it might help. I have chosen the 2500W version too allow a bit of wiggle room in usage, however I don't think we will be using high wattage items. We really want it to charge up our EcoFlows as we drive between locations. We have tried charging them on the 12v but it is a slow process. We will then use the EcoFlows for our cooking and anything where we might need a higher wattage. I may use it to run our small TV or for a laptop
I chose the 2500W over the next one down because there was not a great deal of difference in the price, also the plug sockets are on the front rather than the side. Where I am planning to put the inverter it would be easier to access the plugs
The distance from the batteries is between 2 to 3 metres.
Ian
 

pappajohn

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Aug 26, 2007
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70mmsq cable for just over 3% volt drop in that situation.
90mmsq will bring it below 3%

Screenshot_20230404-112554.png
 
OP
OP
S
Mar 1, 2022
48
9
Funster No
87,175
MH
Burstner
Hi,
I have had a go with the calculator and checked the data on the eco flow website
Screenshot 2023-04-04 at 11.46.52.png


Charging from an AC socket has a maximum 1800W. So I make that 150A.

Using the calculator
Screenshot 2023-04-04 at 11.45.23.png

So that would bring me in at the 3%
If I go 70mm2 it would give me a safety buffer.
Should I go with a 250amp fuse or should I go higher?

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Apr 27, 2016
6,955
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Since the 80s
3 metres is a very long way for a 2500W inverter and 12V batteries. Is there any way you can make it nearer to the batteries? Longer cables on the 230V output would be no problem. If not, then you just have to shell out for thicker cables. That's why truck and house installations are 24V or 48V, and house wiring is 240V. If you already have the cable, you could double it up - all that matters is the total cross-sectional area of the combined cable.
 
OP
OP
S
Mar 1, 2022
48
9
Funster No
87,175
MH
Burstner
We are tight for available space, our battery compartment is under a single seat, that is behind the drivers seat. So no more room in there, there is a small cupboard above this at around 1800mm distance between. The other available space is in a cupboard on the opposite side of the van behind the drivers seat. This is the 3m approx distance
When I watch YouTube videos and people have large battery compartments under a double seat I get very jealous.
Whatever happens I will go for a thick cable, minimum 70mm2. From what I can tell this has an amp rating of 485 amps which if my maths is correct is 5820 Watts.
If that is correct and for what I need it for a 250amp fuse?
 
Apr 27, 2016
6,955
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Manchester
Funster No
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MH
A class Hymer
Exp
Since the 80s
Whatever happens I will go for a thick cable, minimum 70mm2. From what I can tell this has an amp rating of 485 amps which if my maths is correct is 5820 Watts.
If that is correct and for what I need it for a 250amp fuse?
The amps rating, while obviously important for safety, is not really the problem. It's the voltage drop along the wires. If you size the wire to keep the voltage drop to about 3% then the amps rating will be well within the spec. As for fuse size, in theory that's to protect the wires in case of a short-circuit, so as long as it's less than 485A it will be ok. 250A sounds about right.
 
OP
OP
S
Mar 1, 2022
48
9
Funster No
87,175
MH
Burstner
Thank you everyone, you have put my mind at ease. It always sounds straightforward "I will just buy an inverter and fit it at the weekend"
It's only afterwards you realise there are a few other things to consider. But that is why I am on this forum, to get good advice and fill in the many blanks I have.(y)šŸš

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bigtwin

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Oct 29, 2009
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From what I can tell this has an amp rating of 485 amps which if my maths is correct is 5820 Watts.

The amp rating isnā€™t the issue, itā€™s the voltage drop that you need to address otherwise the voltage at the inverter input is too low. And what happens when the voltage drops, the current increases!

Iā€˜m not to sure about your logic of using your leisure battery to power an onboard inverter to power a dc charger (integral to your ecoflow) to charge your ecoflow dc battery to power your ecoflow inverter to power your MH ac loads. Youā€™re building in loads of inefficiencies. Why not just use your planned inverter install to power your MH ac loads? Much simpler and more efficient.

Ian
 

stevewagner

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May 14, 2013
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I would recommend the Renogy inverters. Mine works very well and has a built in automatic changeover switch.
 
OP
OP
S
Mar 1, 2022
48
9
Funster No
87,175
MH
Burstner
Iā€˜m not to sure about your logic of using your leisure battery to power an onboard inverter to power a dc charger (integral to your ecoflow) to charge your ecoflow dc battery to power your ecoflow inverter to power your MH ac loads. Youā€™re building in loads of inefficiencies. Why not just use your planned inverter install to power your MH ac loads? Much simpler and more efficient.

Ian
My thinking on this, is firstly we have the eco flows so we might as well use them. They are very useful for most things including anything that might have a large load. We use a Ninja 8 in 1 mini oven for some of our cooking this has a 2400W load, so far we have only used this on EHU or the Ecoflows. The inverter is a new addition. We are doing a short European break and expect to do a few overnights without EHU. We have 3 X 125ah AGM batteries as well as 3 X 175w solar panels, so on a good day we have plenty of power.
However this is a first venture with an inverter as well as our first European motorhome trip, so I don't want to put all my eggs in one basket and just rely on it for our AC power and find it wipes our batteries out.
I would rather charge the Ecoflows as we drive using the inverter. It should only take a couple of hours. Then wherever we end up with have enough of everything.
Some might say I am being overcautious, but we will be trying a few experiments on the journey and you may be right, may be we can just go with the inverter and leave the eco flows at home the next time. But we will find that out.
Ian
 

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