Question about my system

[Rednecktek]

I have another question: Is it true that both the positive and negative wires going from the inverter to the battery must be exactly the same length?

Common misconception. It's for hooking batteries up to bus bars or terminals, each side needs to be the same length. I.E. if the positive wire of your furthest battery is 22" from the connection point, then all the positive wires should be 22". If the negative is 30" away then all the negative wires should be 30". Your positives don't have to be 30" just because the negatives are.

In practice it usually ends up that all your wires are the same length just because of where the battery terminals are physically in relation and if you're cutting a bunch of wires it's easy to just cut them all to the same length at the same time.

 

[houseofancients]

I have another question: Is it true that both the positive and negative wires going from the inverter to the battery must be exactly the same length?

no not persé ..
equal cable lengths are required if using multiple inverters connecting to the same battery....
equal in this case means equal size paths ( so total distance path pos to neg to each inverter)

 

[Rednecktek]

no not persé ..
equal cable lengths are required if using multiple inverters connecting to the same battery....
equal in this case means equal size paths ( so total distance path pos to neg to each inverter)

That too, forgot about the top end.

 

[OffGridInTheCity]

My battery bank is so large that the + side is ~10ft of 4/0 AWG and the - side is ~15ft. I have 2 x inverters where one set of 2AWG +/- is about 6ft and the other is 4ft from the buss. So there's a little difference but I don't see any issues. The bank is 9 parallel batteries with main pos at 'top left' and main negative at 'bottom right' - e.g. encouraging current to flow from corner to corner.

On the battery bank - the relative amps flowing thru the battery bank make a difference. Lower amps / cell = less of an issue. Other than occasional periods the max current is around 15a/battery where each battery is 260ah@48v.

Note: I have a broken inverter at the moment that I'm working to fix/replace.

 

[sunshine_eggo]

delete

 

[Retired newbie]

2000w / 12v × 1.2 = 200a at least and 2/0 copper wire.

Sir,
I didn’t know that 2/0 and 2/0 AWG wire were different. I found some 2/0 AWG in red and black for a decent price. Do you think this would be enough to run my 1800W tabletop induction cooktop with my Renogy 2000 PSW inverter? With a 250A breaker? My local welding shop has 2/0 welding cable and it is quite a bit thicker! And more expensive.
I contacted Renogy and they say that #4 is enough. But It wasn’t.
Thank you for your help!

 

[sunshine_eggo]

Sir,
I didn’t know that 2/0 and 2/0 AWG wire were different. I found some 2/0 AWG in red and black for a decent price. Do you think this would be enough to run my 1800W tabletop induction cooktop with my Renogy 2000 PSW inverter? With a 250A breaker? My local welding shop has 2/0 welding cable and it is quite a bit thicker! And more expensive.
I contacted Renogy and they say that #4 is enough. But It wasn’t.
Thank you for your help!

2/0 is 2/0 awg (american wire gauge). Different 2/0 wire has different ratings because the insulation around the copper strands is made from different materials that can handle different temperatures. Example:



The copper wire itself can handle a huge amount of current (see the "fusing current" values above), but current generates heat, and the insulation can only handle so much. Don't want your wires catching fire.

 

[OffGridInTheCity]

As a practical example - I use this specific 2/0 AWG wire - https://www.wireandcableyourway.com/2-0-welding-cable-class-k - from my battery to my 12,000w inverters over ~8ft length. It's nice and flexible and has these key specs....
Jacket: Premium-grade 90ºC EPDM, black or red. Temperature range: -40ºC to +90ºC
Current Amps: 223 (For 600 Volt In-Line Applications)

My 12,000w Inverters / 48v = 250a and I use 250a circuit breakers. I routinely run 8,000w / 50v = 160a and the 2/0 AWG wires don't even get warm to the touch. The distance matters as well - e.g. 10ft will warm up more than 1ft.

I know you're probably looking for an exact answer but wire temp specs and distance (1ft, 3ft, 10ft) all play a roll in the absolute minimum you 'need'. From my experience, for a short distance (<10ft) of this 2/0 AWG welding wire would be OK for a 2000w @ 12v situation.

Whatever you go with, you can check your system once it's running to make sure the wire isn't too hot - just touch it. If it's cool or just warm to the touch - e.g. <50C/120F - then from my experience that's great. Also, bigger wire / cooler = better efficiency, so it's OK to oversize a bit if that helps you justify spending a bit more on thicker wire.

As a further example, I even have a set of 4AWG wires in conduit (charge controller -> battery) that occasionally reaches 80a over 20ft causing the wire to reach 60C/140F temps. This is flat out *warm* to the touch and bothers me - but it's in spec and I haven't noticed any degradation in the wire or covering over the last 5 years.

 

[Retired newbie]

Thank you! I have another solar system with 8-230a PV’s, 6-225AH sealed LA batteries, a 3000W PSW inverter and a Midnight Classic 150 charge controller. What size battery cable and what size breaker should I have between the inverter and the batteries?