Shopping list for battery install

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Pwood811

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Hi all,

I’m looking for a bit of help with what to buy for my electrical install. I already have an AGM battery fed by a victron dc-dc with a 25mm cable which I’m swapping for lithium.

I have 2x 100ah renogy batteries to install. One under each seat. I’m thinking I need 35mm2 cable to link them, 2m of each and some 8mm cable lugs. Should I get a bus bar or come straight off battery to fuses?

I’m also fitting a 3000w renogy inverter. Again with 35mm cable? Am I best using Anderson plug I’ve seen some people use?

What’s the best option for fusing everything?
Is 35mm cable the correct size?
How about battery monitoring or low battery cut off?

Many thanks in advance
 
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The current from running a 3000w inverter is beyond the limit of 35mm^2 cable.
At full load, taking into account of losses, and you will be pulling more than 250A: look at the cable rating and it’ll be rated for less than that. You’ll need higher current rated cable. 35mm^2 will be ok for linking the batteries as they will be sharing the current between them. The link cable will need fusing at both ends, then fuse the larger cable (50mm^2 min) to the inverter. I’d personally use the bigger cable even between batteries if it was my install.
Anderson plugs come in different current ratings. The typical ones are SB50 and rated at 50A, which is below your requirements.
You’d need to use SB350s (350A) operating at such high currents (those connectors are massive) if you want a connector (why?) and using 50mm^2 cable is the absolute minimum size for them: Depending upon distance to inverter you’d probably want larger still to compensate for voltage drops from the cable resistance.
Fuses also don’t blow at the currents they are rated for and will allow significantly more current to flow for quite a significant time dependant on fuse type and amount of overcurrent, so take that into account too when selecting your cable and the fuses to protect them. I’d never choose a cable to run near to its rating personally for that reason.
There’s also a further potential problem with the max fault current from your lithium battery and whether the fuse type can actually break it before the fuse stops being a fuse and becomes a conductor.
 
EAN said:
The current from running a 3000w inverter is beyond the limit of 35mm^2 cable.
At full load, taking into account of losses, and you will be pulling more than 250A: look at the cable rating and it’ll be rated for less than that. You’ll need higher current rated cable. 35mm^2 will be ok for linking the batteries as they will be sharing the current between them. The link cable will need fusing at both ends, then fuse the larger cable (50mm^2 min) to the inverter. I’d personally use the bigger cable even between batteries if it was my install.
Anderson plugs come in different current ratings. The typical ones are SB50 and rated at 50A, which is below your requirements.
You’d need to use SB350s (350A) operating at such high currents (those connectors are massive) if you want a connector (why?) and using 50mm^2 cable is the absolute minimum size for them: Depending upon distance to inverter you’d probably want larger still to compensate for voltage drops from the cable resistance.
Fuses also don’t blow at the currents they are rated for and will allow significantly more current to flow for quite a significant time dependant on fuse type and amount of overcurrent, so take that into account too when selecting your cable and the fuses to protect them. I’d never choose a cable to run near to its rating personally for that reason.
There’s also a further potential problem with the max fault current from your lithium battery and whether the fuse type can actually break it before the fuse stops being a fuse and becomes a conductor.
Click to expand...
Many thanks for your in depth reply.

So I’ll order 50mm2 cable to link them batteries and also for the inverter. Link pos to pos fused at both batteries (what type of fuse?) pos to dc-dc, neg to neg and one neg to ground

Inverter- one 50mm2 cable from battery positive (fused at 250/300amp?) to inverter. One 50mm cable from ground to inverter.

Have I missed anything or got it completely wrong?
 
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Do you really need a 3kw inverter? What are you running off it? You might be spending a lot of cash and jumping through hoops for something you don’t need.
 
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Salty Spuds said:
Do you really need a 3kw inverter? What are you running off it? You might be spending a lot of cash and jumping through hoops for something you don’t need.
Click to expand...
i don’t really need a 3kw inverter but it was cheaper than a 2kw at the time. I paid £193 for 3kw. 2kw is £210 1kw is £120. It seemed a good deal at the time…
 
Pwood811 said:
i don’t really need a 3kw inverter but it was cheaper than a 2kw at the time. I paid £193 for 3kw. 2kw is £210 1kw is £120. It seemed a good deal at the time…
Click to expand...
For comparison, we have a 1600W inverter (because I thought we’d need one) and have used it a couple of times in 7 years of ownership. I probably won’t bother in the next van.
 
Salty Spuds said:
For comparison, we have a 1600W inverter (because I thought we’d need one) and have used it a couple of times in 7 years of ownership. I probably won’t bother in the next van.
Click to expand...
I did wonder. My thoughts are for boiling a kettle or induction hob for a one pan wonder. Maybe I should send it back and not bother or get a smaller one. I’m new to this and doing it as I. Go along.
 
The more power you consume the more complicated and expensive it gets. I use a 1000W inverter and select my appliances to be compatible with that consumption. I don’t use gas (have it as a back up) and use a kettle, single hob, Remoska (not together) to stay at 1000W or below. It can be a bit more challenging on the cooking front using only one hob but it works for me. A 230Ah Roamer seatbase battery and I’m fine for 3 days off grid.
Work out your use first: Decide what appliances you want to run, then see what wattage versions are available and how long will you be off grid before committing yourself to a 3000W inverter.
Once you’ve decided on that then we can help more as your plan matures.
 
The Bear78 said:
What's the maximum output of those batteries?
I have a Renogy Core Mini 200 ah and the max continous output is only 200 amps! Not enough for a 3000w inverter (at maximum output).
Click to expand...
If they’re in parallel you have 400A theoretically
 
Reply #10 is in response to the OP who said they have two 100 ah batteries. I mention my 200 ah as an example.

Renogy quote the maximum continous output of the 100 ah Mini Core battery as 100 amps. Two in parallel would be 200 amps

They appear to make three different 100 ah batteries with maximum continous outputs ranging from 100 to 150 amps, hence my question about the OPs batteries.
 
If you’re running batteries in parallel, check whether the cabling needs to be identical to each battery at the point where the circuit joins because this would be tricky with massive cables and a battery under each seat.

Running a single (maybe slightly larger if you need it) battery would be a lot easier.
 
Yes they have a continuous max output of 100a each. So in parallel, 200ah capacity with a 200a continuous output. Not enough for the 3kw inverter.
It seemed a good idea at the time. I think I will return it and thin about a smaller one.

In terms of load from the batteries can I take power from either of the positive terminals and the negative to any ground? Also a battery monitor/shunt do I need one on each battery or just one on one terminal.

Thank you.
 
Generally when connecting 2 batteries in parallel you would run a positive link cable between the 2 positives and run a negative link cable between the 2 negatives, keeping both the positive and negative link cables the same length (as best you can anyway as the positive link cable should be fused at each positive terminal due to the distance between them and risk of cable damage). You’d then take the negative of one battery through your single shunt to chassis GND and the positive of the other battery to your loads (inverter positive) via appropriate rated fuses. You can connect the negative of the inverter to chassis GND.
A single battery solution is simpler: Have you worked out what capacity (Ah) you actually need for your usage requirements?
 
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