Wire Size for 200A BMS

[OTRwSolar]

Just replaced our Daly 200a BMS with a JBD 200a. The Daly had 2 gauge silicone pigtail cables preinstalled on the B- and P- terminals. Used 10-12" long 2/0 cables with the JBD. Almost .1v less voltage drop with a 150a load with the 2/0 (vs. 2 gauge).

Also replaced a generic, plastic 200a ANL fuse with a Bussmann Eaton 200a ANL fuse. With 120a of current, experienced a 55mv drop with the generic fuse. Only a 42mv drop with the Bussmann Eaton fuse.

It all adds up.

 

[RandyP]

NEC does not care about 12v

So untrue. Article 551 of the NEC is dedicated to RV and RV Parks. You should read it and learn much.
Here's a link to free view of 2020 NEC. You need to create an account and figure how to navigate. But it's free:

NFPA 70®: National Electrical Code®

<p>90.2(C) Installations Covered.<br /><br />This Code covers the installation and removal of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables for the following:<br /><br /> (1) Public and private...

www.nfpa.org

The NEC points you at the ANSI standard RVIA-LV for most of the DC stuff. Here's a link to a free download of that $75 standard:

ANSI RVIA LV

ANSI RVIA LV: Standard for Low Voltage Systems in Conversion and Recreational Vehicles Took me the better part of two years, but I finally found a free copy of the ANSI RVIA LV. RVIA LV ("LV" = "Low VOltage) is the American RV Industry's...

diysolarforum.com

 

[bgpeters]

I measured both the copper bars on my JBD 4S 200A BMS that the wire to B+ and B- will go to. It measures 2mmx14mm. If I convert that amount of copper to a round it would have a 0.235" diameter. 0.235" is a little less than the diameter of a 2 AWG copper cable (.2576" according to https://www.rapidtables.com/calc/wire/wire-gauge-chart.html). I suppose this is how some would simply extend the bar with 2 AWG to span from the BMS to supply the battery terminals.

I also see charts that limit 2 AWG to 181 Amps for Chassis Wiring, and 94 amps for Power Transmission. My situation fits the chassis spec since I'm not bundling the positive and negative in the same case... so it seems a good choice would be 1 AWG (rated for 211 Amps chassis wiring).

Still, how does JBD expect their 28 sq mm bar to sustain 200 Amps continuously with less copper than a 2 AWG wire? Is it because the copper bar has no insulator so it can cool easier?

 

[DJSmiley]

With 28mm2 (2x14) I don't see a problem in handling 200A. Yes, it will warm up slightly, but thats all. Its a short length, so voltage drop is also not that much

I do agree it's not sufficient for a wire run, but thats mainly because of voltage drop involved when run for 1m or so. It is bare copper, so any heat can dissipate easier as well.

And in reality, you won't be pushing 200A continously on a 200A rated BMS. It's more likely 100A.
On all BMSses its generally way better not to run it on max.

I recently charged a 280Ah set with 180A. The BMS got quite hot (54 celcius) after half an hour. The busbars between the cells (which are quite similar in area) were like 35 celcius or so, so they did warm up as well, but it was the actual BMS itself which had the most heat, not the busbars or cable.

 

[740GLE]

And in reality, you shouldn’t be pushing 200A continously on a 200A rated BMS. It's more likely 100A.
On all BMSses its generally way better not to run it on max.

I fixed that for you. It’s all about design and operational parameters. Having a 2000w inverter connected doesn’t mean you will have 2000w of load if you’re charging a laptop and running some lights and maybe a coffee maker.

 

[RandyP]

I fixed that for you. It’s all about design and operational parameters. Having a 2000w inverter connected doesn’t mean you will have 2000w of load if you’re charging a laptop and running some lights and maybe a coffee maker.

A Coffee maker can be a big load on a 2000w inverter.

 

[740GLE]

I’ve tested ours at 1000w, so yeah % wise a good chunk.

 

[RandyP]

I’ve tested ours at 1000w, so yeah % wise a good chunk.

There are some coffee makers that are well over 1KW load.

 

[740GLE]

And there are some under 1kw ?‍ as with everything verify your loads for your system.

 

[Alkaline]

I like using dual 6 awg, 2 awg is very expensive an hard to find but you can get 6 awg easily.

2 of them should be able to handle 200a.

 

[Grimmster]

I like using dual 6 awg, 2 awg is very expensive an hard to find but you can get 6 awg easily.

2 of them should be able to handle 200a.

No.

 

[740GLE]

No.

6awg is 13.3mm2

So dual 6awg is 26.6mm2 which is about 3awg, I’d have no issues running 200a through 3awg knowing my leads are short enough.