Can (4) 12 gauge wires in parallel handle 320A at 48 volts on a BMS?

bhoth

New Member
Hi All, I just bought 2 of these 320A 16S BMS on eBay. I just received them and wow, how can (4) 12 gauge wires in parallel handle 320A at 48 volts?

Also what I received is not the same as what is shown in the picture. The picture shows 2 wires coming out of each side (that are bigger than 12 gauge) . The two that I purchased have 4 12 gauge wires.

 

MisterSandals

Participation Medalist
Looking at the wire sizes:
12awg = 0.0808 sqin.
0.0808 x 4 = .3232 sqin

0awg (1/0) is .325 sqin

According to voltage drop calculator, it should work for 350a at 48v, what looks like 12" wires.
Screen Shot 2021-02-19 at 10.48.55 AM.png
 

bhoth

New Member
Looking at the wire sizes:
12awg = 0.0808 sqin.
0.0808 x 4 = .3232 sqin

0awg (1/0) is .325 sqin

According to voltage drop calculator, it should work for 350a at 48v, what looks like 12" wires.
View attachment 37675
Ok and I just measured the wires on each side of the BMS are aprox 5 inches long. Do I count the length of both the in and the out from the BMS?

Also I have ordered 32 Lishen 3.2 volt 280ah cells to make (2) 16s 48 Volt banks. My plan is to use one BMS per 48 volt bank. (yes I know I could have done a 2p 16s bank but I was worried about putting that much current through one of these BMS's) These battery banks will be driving a Growatt 12000T.
 

codfish

Solar Enthusiast
Ok and I just measured the wires on each side of the BMS are aprox 5 inches long. Do I count the length of both the in and the out from the BMS?

Also I have ordered 32 Lishen 3.2 volt 280ah cells to make (2) 16s 48 Volt banks. My plan is to use one BMS per 48 volt bank. (yes I know I could have done a 2p 16s bank but I was worried about putting that much current through one of these BMS's) These battery banks will be driving a Growatt 12000T.
12 awg has a diameter of 0.0808 in and a cross sectional area of 3.31 mm
4x the cross sectional area is 13.24 mm

This corresponds to approximately AWG 6 at 13.3 mm.

AWG 6 has a maximum current of 75 amps if you are using 90C wire.
These wires cannot feed a high power inverter.
 

Rider

Photon Sorcerer
Not sure why all the conversions to a different wire size. A 12g wire by itself can carry about 20A. 4 of them in parallel is 80A, each wire carrying a max of 20A.
 

codfish

Solar Enthusiast
Not sure why all the conversions to a different wire size. A 12g wire by itself can carry about 20A. 4 of them in parallel is 80A, each wire carrying a max of 20A.
The previous one was wrong, I thought it best to correct it rather than just state the answer.
 

bhoth

New Member
Well it looks like I need to solder onto the board some additional wire, what do you all recommend?
 

Rider

Photon Sorcerer
I don't know anything about that BMS, but from the wires provided, I'd question whether it can actually handle over 100A. Not saying it won't, just that I'd have questions.
 

bhoth

New Member
Not sure why all the conversions to a different wire size. A 12g wire by itself can carry about 20A. 4 of them in parallel is 80A, each wire carrying a max of 20A.
Is this at 12 volts? Isn't the capacity different the higher the voltage?
 

Rider

Photon Sorcerer
Is this at 12 volts? Isn't the capacity different the higher the voltage?
Check the chart in this link. There is no column for voltage, only amps over wire size. You can play with the loss calculator to see there is not much difference between 12 and 48VDC as far as wire loss.

BTW... that calculator will blindly accept anything you plug in and not validate it. It will happily let you put in 12V at 350A over 14AWG wire and give you a voltage drop. It won't tell you about the resounding flash and fire if you actually did it.
 
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MisterSandals

Participation Medalist
Check the chart in this link.
So the pic in my post #2 shows my results from this Voltage Drop Calculator.
Was there a problem with how I calculated the cross section of the wire, 4x 12awg to get to a 0awg
equivalent? Or a problem with how I used the calculator?
Note that I used 1ft for the run which was my assumption from the OP's pic.
 

Maast

Compulsive Tinkerer
According to powerstream.com wire size chart the maximum amps a single insulated 12 awg wire in free air (chassis wiring) can handle is 41 amps. When bundled in thhn with another layer of insulation it get heavily derated. NEC then heavily derates it again in code as a safety factor. I have no idea how they expect 4 wires to handle 320A. If you go up to 10awg a single wire can handle 55A. I would imagine even the powerstream chart is derated by a bit to reflect the wire insulation.
 

Rider

Photon Sorcerer
K.I.S.S Keep It simple.
One 12gauge wire can carry 20A (as noted above with insulation and etc degrading). Paralleling it with 3 more doesn't magically make it capable of carrying 80A (320A / 4) by itself. Each wire can still only carry 20A, no matter what calcs you throw at it.
 

Rider

Photon Sorcerer
If it were possible to make 4 #12 wires carry 320A, then all of our discussions on getting power from the solar panels to the SCC are rendered moot and if that simple, why didn't we do this before?
 

Gazoo

Dumb Dumb
Hi All, I just bought 2 of these 320A 16S BMS on eBay. I just received them and wow, how can (4) 12 gauge wires in parallel handle 320A at 48 volts?

Also what I received is not the same as what is shown in the picture. The picture shows 2 wires coming out of each side (that are bigger than 12 gauge) . The two that I purchased have 4 12 gauge wires.

There are four wires on the BMS, two for positive and two for negative. The combined effective AWG of each pair is 9 AWG.


According to the following calculator, a 9awg 1 foot wire will be able to handle 320 amps.


Of course you will want to use larger wire from the BMS depending on the length of the wire needed and the loads.
 
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codfish

Solar Enthusiast
So the pic in my post #2 shows my results from this Voltage Drop Calculator.
Was there a problem with how I calculated the cross section of the wire, 4x 12awg to get to a 0awg
equivalent? Or a problem with how I used the calculator?
Note that I used 1ft for the run which was my assumption from the OP's pic.
You used 4x the diameter, not 4x the cross section.
 

KenDan

Solar Enthusiast
Length matters (that's what she said) 👩🤣
Seriously, wire resistance and voltage drop increases linearly with length. It's not just about diameter and cross sectional area.
The only time wire cross sectional area alone matters is when you are concerned about wire heating. This is why wire gauge vs. current (actually power) is an important safety consideration. A short wire will see the exact same temperature rise per foot as a longer wire of the same gauge carrying the same current. However, the longer wire will have that heating spread out across it's longer length. But being longer, the total voltage drop and power loss will be directly proportional to the increased wire length. Wire resistance is always so many milliohms per foot.
So, if those 4 - 12 gauge wires are kept very short, you will have very little voltage drop and very little power loss.

I have one of the "320 amp" Ant BMS's. I cut the wires off much shorter than it came (to about 2 inches). I then crimped each group of 4 wires into a large circular lug which was then connected to a #6 gauge cable going into my LV5048. That cable was also cut to the minimum needed length needed (less than 3 feet). I'm pretty sure that the voltage drop across the internal FET's, the PCB foil, and the shunt is significantly higher than the drop across the wires.
I don't believe for a second that this $72 320amp Ant BMS can handle anywhere near that much current - but I'm certain that the wires are not the limiting factor (especially if you cut them to the minimum length needed).
 
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