Sense check - Wire sizing / layout

jdzl

The system (first system, working on the learning curve as fast as I can)

8 x 6v 225AH GC2 Batteries (Costco) for 24v/450ah bank
1 x Honda EU2000i
1 x Mean Well PB-1000-24 battery charger
1 x Pure sine inverter w or w/o transfer switch (Tentatively looking at Samlex ST-1500-CT - Auto transfer)

Panels are to coming soonish / later

Battery interconnects are going to be 12-16" long, 4awg [0.5% voltage drop at 24v/125a (calculated for 2ft interconnect)]
Battery bank to inverter is 4 awg, 3 feet [0.79% voltage drop at 24v/125a] with 200 amp t-fuse inline
Battery bank to battery charger is 4 awg, 6 feet [0.75% voltage drop at 24v/60a] *should this also be fused inline?

As far as actually wiring the bank goes - you want to take positive and negative from opposite ends of the bank on opposite strings? Is that right? So in example below, I would take negative off 1, and positive off 8, with series interconnects between 4/8+ and 1/5- or am I looking at that wrong?

1___4
++++
- - - -

5___8
++++
- - - -

Thanks all!

Cariboocoot

Re: Sense check - Wire sizing / layout

I'm pretty sure there's a diagram for parallel battery wiring on here somewhere ...
Instead of two in each series string you'd have four.

jdzl

Re: Sense check - Wire sizing / layout

So much for my ASCII diagram... :P That's exactly what I was looking for - makes sense now.

Is it ok to stack connections on the positive and negative terminals? I.e. As in the diagram above; inverter, charge and battery sense appear to begin at the +/- terminal and run to each device. Is that ok, or do you need a bus bar? Or is a bus bar purely for convenience / when you run out of space to add wires to the terminals themselves?

NorthGuy

Re: Sense check - Wire sizing / layout

#4 AWG wire between inverter and battery bank seems small for 200A breaker.

Cariboocoot

Re: Sense check - Wire sizing / layout

Wire sizing/fusing is going to depend on exactly what inverter you buy and how close to its maximum power it will be run. They usually have recommended sizing in the instructions, but it's based one maximum power out divided by minimum Voltage in equals greatest current draw: the wiring has to be able to handle that over the length with minimal Voltage drop.

So 1500 Watts on 24 Volts is about 62.5 Amps (remember some additional current will go to powering the inverter). In that case 4 AWG might be a bit light, as it is meant for 60 Amps in transmission but at short distances can take about 90 (you will see many charts giving many different ratings for the same size wire; much depends on how it is used).

In any case, the 200 Amp fuse is wrong because the wire will not take 200 Amps. 100 Amps would be the largest you should have on 4 AWG.

If the battery charger does not have internal circuit protection on its output you should also put a fuse/breaker on that sized according to its maximum output capacity.

jdzl

Re: Sense check - Wire sizing / layout

That makes sense...

In the end the local shop here cut me a deal and I got [I think] way oversized wire...

Battery interconnects are 2/0 and 12"
Series interconnects are 2/0 and 18"
Inverter cables are 2/0 and 5 feet with a 125 amp fuse (Unfortunately that's all the had for now)

Cariboocoot

Re: Sense check - Wire sizing / layout

No worries: 2/0 will handle 190 Amps without problem, and you want the fuse to be the weakest part of the circuit. 125 mps on 24 Volts is around 3kW.

NorthGuy

Re: Sense check - Wire sizing / layout

jdzl wrote: »

In the end the local shop here cut me a deal and I got [I think] way oversized wire...

The inverter measures voltages at its DC terminals. If there are high currents and the wire is not thick, these voltages may be significantly different from the voltage measuread at battery terminal. Since inverter uses its voltage measurements to control charging process, these difference may distort your charging set points. Therefore, you want really thick cables between inverter and batteries. 2/0 is not oversized.