Hooking up a BMS and wire guage

[mark_s]

Hi. I have a Daly 200A 12 volt, BMS. It has two 8" +/-6 guage leads one to negative battery terminal and one to negative loads. I have a 3000w inverter utilizing a 4/0 cable, 60-60 dc battery charger using a 4 guage wire, and 1200 watt solar energy panels to connect to the 6 guage BMS load lead. Can the 6 guage BMS leads handle this? Thanks in advance.

 

[John Frum]

Probably not.
Is there any writing on the wire that indicates the temperature rating of the insulation?
Most inverters can be driven by a solid state relay to work around the limitations of the bms.
I can explain if you are interested.

 

[John Frum]

3000 ac watts / .85 conversion factor / 12 volts = ~294 dc amps.
Even if the wires in and out of your bms were up to snuff the bms itself is under spec.

 

[mark_s]

Thank you for your responses.
The two cables are 6awg, 200C or, i figure 392 F.
Assuming the inverter problem is solved as noted below, will this BMS and its cables handle the energy input sources as noted in my initial question? I also have a 55A RV charger/converter.
It looks like I have a few choices:
1. Take your suggestion and consider a relay if it compensates for the 200A (vs. 294A that is suggested above) and if the wire gauge/temp. is high enough.
2. Downgrade the inverter to a 2000 watt inverter which would meet the requirements of the presently owned 200A BMS (utilizing the calculations as noted above) and if the wire gauge/temp. is high enough to handle the input energy sources.
3. Upgrade to a Daly 300A BMS.

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Buy DALY BMS 4S 12V 300A LiFePO4 Battery Protection Module PCB Protection Board with Balance Leads Wires BMS for 18650 Battery Pack 12V with Cooling Fan: Power Converters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

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The battery specs are:
12v, 360A, 2p4s or 8 3.2v 180A cells
constant current 180A (1c)E
End of discharge voltage: 2.5v
Recommended constant current 90a (.5C)
Maximum pulse discharging current: 360A 3min.
maximum pulse discharging current: 540A 30s
Max continuous discharge current 200A (1c)

I'm not sure about the BMS protection numbers, they seem too high:
stop charging when instantaneous current over 800A(AMP) and will stop discharging when instantaneous current over 1000A(AMP).

I can answer any questions to the best of my ability. Any help would be greatly appreciated. thank you.

 

[ereams65]

Won't the charge controller specs say how many amps are flowing for wire sizing? I'm new to this whole world, so forgive if that's a dumb question.

 

[John Frum]

Assuming the inverter problem is solved as noted below, will this BMS and its cables handle the energy input sources as noted in my initial question?

I'm struggling to follow you.
You have selected a new bms that is rated for 300 amps.
I don't really trust that company's ratings so I would de-rate it by .66
The picture doesn't show the p- and b- leads so I can't answer your initial question.
300 amps * .66 de-rate factor = 198 amps.
294 amps is substantially greater than 198 amps.

 

[mark_s]

How about if I use the 200A with a 2000 watt inverter? Still derate it by .66?
what other company can i use for BMS. Any BMS that I can by in USA? for say, a good 200A or a 300 A.?

 

[John Frum]

How about if I use the 200A with a 2000 watt inverter? Still derate it by .66?

2000 ac watts / .85 conversion factor / 12 volts low cutoff = 196 dc amps
200 amps * .66 de-rate = 132 bms amps

what other company can i use for BMS. Any BMS that I can by in USA? for say, a good 200A or a 300 A.?

The only bms that I can recommend is 120amps at 12 volts.
I really like the product and the distributor but it won't handle a 2000 watt inverter without the help a solid state relay or contactor.

Contactors are expensive.
solid state relays are cheap.

 

[mark_s]

Ok so how about a 2000 w inverter, 2000/.85/12=196..... with a 300a daly, 300*.66=198?
But, I'm not sure if the bms (link above) is compatible with the batteries as listed above. What do you think?

 

[John Frum]

Ok so how about a 2000 w inverter, 2000/.85/12=196..... with a 300a daly, 300*.66=198?
But, I'm not sure if the bms (link above) is compatible with the batteries as listed above. What do you think?

The math works.
They make 4s lifepo4 versions at 300amps.
Make sure the one you get is smart because the default config sucks.

 

[brb58]

Ok so how about a 2000 w inverter, 2000/.85/12=196..... with a 300a daly, 300*.66=198?
But, I'm not sure if the bms (link above) is compatible with the batteries as listed above. What do you think?

How short are your 6 AWG wires going to be? If you were actually flowing 200A through one 6AWG wire that was 6" long, it would only drop 0.0125V. Not a lot really. Since there are two(one going in and one going out, it will be 0.025 which is not much.

 

[mark_s]

Thank you Joey for your support. I'll order a 300A BMS. And, Tahnk you Bruce for your information. i assumed that a short distance of smaller gauge wire would be OK. But I was not sure. Now I know it is OK.
Regards and thanks.!