Wire Size for 200A BMS

[keithd]

I posted this on the BMS page as well, but this could be more battery than BMS. Sorry for the duplication!

Need some guidance for my battery build. I have a 4S 12V LiFePo4 battery and installing the JBD 4S 200A BMS. The battery is 280ah cells. My question is what size wire should I attach too the tabs on the BMS that connect to the battery for B- and to the battery box connector for the load on C-? The distance is about 8” from the BMS tab to the battery connection and about the same from the other BMS tab to the battery box connection. I have been looking at wire size charts to get the answer and saw everything from 2 AWG to 2/0 AWG.
I am building 2 batteries that I will connect in parallel and the heaviest load in the RV is the 2000 PSW inverter.
Thanks in advance for the advice.

 

[mdatot]

2000W at 12V nominal is about 167A. At these high amp ratings you need to consider both voltage drop over distance and heat losses in the cabling. If you take a look at e.g. this page you get an idea of where the limits are. 2 AWG can handle 170A (just about, with the insulation becoming pretty toasty), but the JBD has double terminals doesn't it? I'd use two 4 AWG connectors, that's the same total cable area as 0 AWG so voltage drop should be under control over that distance. Just make sure they're the exact same length. If you want to be safe you can use 2x2AWG, that's about the same area as 2/0 AWG (which is the minimum recommended for 200A in marine installations, for example).

 

[keithd]

2000W at 12V nominal is about 167A. At these high amp ratings you need to consider both voltage drop over distance and heat losses in the cabling. If you take a look at e.g. this page you get an idea of where the limits are. 2 AWG can handle 170A (just about, with the insulation becoming pretty toasty), but the JBD has double terminals doesn't it? I'd use two 4 AWG connectors, that's the same total cable area as 0 AWG so voltage drop should be under control over that distance. Just make sure they're the exact same length. If you want to be safe you can use 2x2AWG, that's about the same area as 2/0 AWG (which is the minimum recommended for 200A in marine installations, for example).

Thanks Mdatot. The 200A JBD BMS has only one connection for each of the C- and B- taps. It is a larger copper bus connection. I looking at the chart you referenced, it appears that the PTFE insulation can support more amperage with 2 AWG - supporting up to 240 Amps if I am reading this correctly. Perhaps 1AWG or even 1/0 AWG would be more than enough, correct?

 

[DJSmiley]

What is your continues max load? You're probably good with 2AWG if you're only occasionally pulling 200A.

You also can consider building an Y-cable using 2 4AWG cables.
1 site: fit both 4AWG cables into a 1AWG lug
Other side: 2 lugs, 1 on each cable.

On the BMS you can use both lugs to 'sandwitch' the busbar between both lugs for maximum connection.

 

[newbostonconst]

What is your continues max load? You're probably good with 2AWG if you're only occasionally pulling 200A.

You also can consider building an Y-cable using 2 4AWG cables.
1 site: fit both 4AWG cables into a 1AWG lug
Other side: 2 lugs, 1 on each cable.

On the BMS you can use both lugs to 'sandwitch' the busbar between both lugs for maximum connection.

FYI, not technically legal in US for per NEC, but do what you want....

 

[Quattrohead]

NEC does not care about 12v

 

[keithd]

What is your continues max load? You're probably good with 2AWG if you're only occasionally pulling 200A.

You also can consider building an Y-cable using 2 4AWG cables.
1 site: fit both 4AWG cables into a 1AWG lug
Other side: 2 lugs, 1 on each cable.

On the BMS you can use both lugs to 'sandwitch' the busbar between both lugs for maximum connection.

Thanks. The largest potential load in the system is the 2000 watt inverter. I will be wiring two of these 12v 280ah batteries in parallel to support the needs in the RV. I would expect the load of the inverter to be shared across both batteries in this configuration. I chose the 200A BMS for overkill, but do not expect to get anywhere near that rate. But, I also want to make sure this is installed safely as I do not know what the future requirements might be. I also have limited space and want to find the cables that will support the rated capacity yet be the minimum size needed. Thinking that 1 AWG would be the minimum and 1/0 AWG would be ideal. Thoughts?

 

[mdatot]

Thanks. The largest potential load in the system is the 2000 watt inverter. I will be wiring two of these 12v 280ah batteries in parallel to support the needs in the RV. I would expect the load of the inverter to be shared across both batteries in this configuration. I chose the 200A BMS for overkill, but do not expect to get anywhere near that rate. But, I also want to make sure this is installed safely as I do not know what the future requirements might be. I also have limited space and want to find the cables that will support the rated capacity yet be the minimum size needed. Thinking that 1 AWG would be the minimum and 1/0 AWG would be ideal. Thoughts?

That sounds reasonable to me; I missed that there are two batteries in parallel earlier. I assume each of them have its own BMS with its own connection to the load bus? In that case you're right, only half the current will be supplied by each battery, so you can technically get away with even thinner wires. Do keep in mind however that if one of the BMS's disconnects for whatever reason, then the remaining battery will be handling all of the current on its own, so I'd still feel safer if the wiring for each battery could safely handle the full current.

 

[shadowsteve]

I have 4x 280Ah but with a 150A JBD BMS and I'm using #2 for the pos & 2x #4 for the neg. The board is the long style with the copper bus strips with more than one hole to bolt a lug into

I have two battery units and the largest load is a 3000w inverter but I don't ever get to the full 300A draw

 

[kshopper2084]

I'm actually in the identical situation, though I'm only using a single 280Ah 4S 12v battery with 200A JBD bms for my rig. It also has a maximum load of 2000w inverter.

Since I'm only assembling this one battery is there a good/cheap source for these cables where I wouldn't need to purchase an expensive giant crimper to make 2 cables?

 

[keithd]

I'm actually in the identical situation, though I'm only using a single 280Ah 4S 12v battery with 200A JBD bms for my rig. It also has a maximum load of 2000w inverter.

Since I'm only assembling this one battery is there a good/cheap source for these cables where I wouldn't need to purchase an expensive giant crimper to make 2 cables?

I bought my RV battery cables from Windy Nation. They are 2/0 cables as I had some longer runs. Make sure the cables are pure copper and not CCA (Copper clad aluminum) and you should be good. As far as crimping, I bought a hammer type crimper and it works really well. Makes a very solid crimp. https://www.amazon.com/TEMCo-Hammer-Crimper-Tool-Warranty/dp/B00E1UUVT0

 

[niccolosartor]

I use the manual Temco product (others sell a similar version). It works well. If you're close you can borrow it. I need to be somewhat portable for boat work but the hammer version would work for just a few crimps you could do on a bench.

https://www.amazon.com/TEMCo-Lug-Crimper-Tool-TH0012/dp/B00HJYVFSG?ref_=ast_sto_dp

 

[OTRwSolar]

Our 200a Daly BMS came from the manufacturer with approx. 8-10" long, 2 gauge silicone cables on the B- and P- terminals. We've run up to 150a continuously for 60-90 min. at a time and never felt these two cables project any noticeable heat. At 200a these cables should only introduce a .05v (.42%) voltage drop which is pretty minimal IMO.

 

[sunrise]

I posted this on the BMS page as well, but this could be more battery than BMS. Sorry for the duplication!

Need some guidance for my battery build. I have a 4S 12V LiFePo4 battery and installing the JBD 4S 200A BMS. The battery is 280ah cells. My question is what size wire should I attach too the tabs on the BMS that connect to the battery for B- and to the battery box connector for the load on C-? The distance is about 8” from the BMS tab to the battery connection and about the same from the other BMS tab to the battery box connection. I have been looking at wire size charts to get the answer and saw everything from 2 AWG to 2/0 AWG.
I am building 2 batteries that I will connect in parallel and the heaviest load in the RV is the 2000 PSW inverter.
Thanks in advance for the advice.

I built mine (12v 304ah, 4s, 200A JBD BMS) with TEMCo 1 awg wire, works great with 2000w Renogy inverter. I do run 2/0 awg from battery to inverter though.
I only run about 6" 1 awg wire total inside the battery, the JBD 200A layout makes wiring very easy. I think 1 awg actually gives pretty good safety margin, the section area of 1awg wire is larger than that of the BMS copper terminal. So it won't be the bottleneck. And the voltage drop for such short distance is very minimal.

 

[Solar123456]

I built mine (12v 304ah, 4s, 200A JBD BMS) with TEMCo 1 awg wire, works great with 2000w Renogy inverter. I do run 2/0 awg from battery to inverter though.
I only run about 6" 1 awg wire total inside the battery, the JBD 200A layout makes wiring very easy. I think 1 awg actually gives pretty good safety margin, the section area of 1awg wire is larger than that of the BMS copper terminal. So it won't be the bottleneck. And the voltage drop for such short distance is very minimal.

What is the max load you use? Do you notice any heat with the 1 awg wire?

 

[OTRwSolar]

What is the max load you use? Do you notice any heat with the 1 awg wire?

In addition to load and temperature, time is a factor, too. Whether you feel heat after 5 min., 30 min., or never, is an important indicator of how severe your voltage drop may be.

 

[Solar123456]

In addition to load and temperature, time is a factor, too. Whether you feel heat after 5 min., 60 min., or never, is an important indicator of how severe your voltage drop may be.

Good point. I was planning on using them as interconnects which I've already made for my 24v 8s 280ah battery with 150ah bms. My system will use a 3000 watt inverter which I will rarely max out. The battery interconnects (flexible bus bar) would be less than 5 inches each. I guess my main thing is to see how it performs so I know I should make new cables. But I might have to actually test them at max load in a realistic scenario to find out. Run water heater and small microwave and a few other things

 

[sunrise]

What is the max load you use? Do you notice any heat with the 1 awg wire?

I ran 2000w inverter with 13500btu AC unit, at 185a for about 15minutes, no heat at all, I used a temp gun to read every conductor inside and outside the battery. The only thing got fairly hot was a 250a breaker.

 

[ericfx1984]

I did a similar build(see signature below)

Basically wired the negative like this

Battery 1 >>> 1/0 >>> BMS >>> 1/0 >>> to 5/8 common lug >>> 4/0 >>> to inverter

Battery 2 >>> 1/0 >>> BMS >>> 1/0 >>> to 5/8 common lug >>> 4/0 >>> to inverter

The battery 1/0 cables are placed on the common lug sandwiching the 4/0 cable

The positive is like this

Battery 1 >>> 1/0 >>> 200amp ANL >>> 1/0 >>> blue sea 9003e lug 1 >>> 4/0 >>> 500 amp ANL >>> 4/0 to inverter

Battery 2 >>> 1/0 >>> 200amp ANL >>> 1/0 >>> blue sea 9003e lug 2 >>> 4/0 >>> 500 amp ANL >>> 4/0 to inverter

 

[ericfx1984]

Oooops double post