Hole in PCB for BMS not Big Enough for Current

[YoshiMoshi]

I'm building a power tool battery pack. The BMS allows for a maximum continuous discharge current of 35 A. However I can only get about 8 pieces of 10 mm wide by 0.1 mm thick pieces of nickel strips on the holes for the B+ and B- connections in the PCB. I cannot get pieces any more wider in the hole, or stack any more pieces.

Per Metador ampacity tables that are cited on here frequently, 13 pieces of 10 mm wide by 0.1 mm thick has the current carry capacity of over 36 A.

So what is a guy supposed to do? The holes in the PCB are not big enough to carry the rated maximum continuous discharge carrying capacity. Is there some single wire surface mounted connector or something I could use that can withstand 35 A?

Looking online, OEM battery packs usually are 0.3 mm thick for like Kobalt. Interesting.

 

[fechter]

A picture might be useful.

If the strips neck down right before they attach to the board, the length of undersized strip will be short enough to not cause a problem. 35A isn't that much. Otherwise use a piece of copper and solder the strips to the copper, then to the board. I've made short strips of copper by using tin snips on a copper pipe coupling and pounding it flat.

 

[Comrade]

So what is a guy supposed to do?

Study Ohm's law? Seriously. You are doing this blindly.

 

[YoshiMoshi]

Study Ohm's law? Seriously. You are doing this blindly.

Thanks for the input. How would ohms law be helpful here? I can calculate the resistance of the small section of nickel strip that is 0.8 mm thick over 1.3 mm thick, and I know the maximum current of 35 A, I can determine the voltage drop across it. But how do I determine how much the portion of nickel at 8 mm thick would heat up from this and determine if that is acceptable from this information?

 

[Comrade]

But how do I determine how much the portion of nickel at 8 mm thick would heat up from this and determine if that is acceptable from this information?

Using the green 'Power' section of Ohm's law.

 

[YoshiMoshi]

Using the green 'Power' section of Ohm's law.

View attachment 363549

So your saying to calculate how much power is lost by the 8 mm section? But how do I know if that will result in overheating?

 

[Comrade]

So your saying to calculate how much power is lost by the 8 mm section?

More or less, yes. It's how much energy will be dissipated.

But how do I know if that will result in overheating?

You can do math that's more complex than Ohm's law. But most people can just estimate it in a split second just using experience. It doesn't need to be exact.

 

[YoshiMoshi]

More or less, yes. It's how much energy will be dissipated.



You can do math that's more complex than Ohm's law. But most people can just estimate it in a split second just using experience. It doesn't need to be exact.

Thank you, so how many watts is considered overheated?

 

[Comrade]

so how many watts is considered overheated?

That question makes no sense as temperature rise depends on what is radiating it.

100W can make a light bulb filament glow at several thousand degrees. The same 100W roughly keeps a human body at 98F degrees.

 

[YoshiMoshi]

That question makes no sense as temperature rise depends on what is radiating it.

100W can make a light bulb filament glow at several thousand degrees. The same 100W roughly keeps a human body at 98F degrees.

I understand that is a good point. How many watts for Nickel strip?

Power of DC current from battery is current squared times resistance. So power is directly proportional resistance.

Also as you add more nickel strips, wouldn't the resistance increase, and therefore the power it consumes? But more nickel is safer to carry larger current.

But if I have to little nickel strips resistance goes down, power is less.

But to little nickel is dangerous.

Thanks for help in understanding things.

 

[docw009]

"Also as you add more nickel strips, wouldn't the resistance increase, and therefore the power it consumes?"

You should know parallel vs series.,

R = 1/(1/R1+1/R2+....+1/Rn)

 

[amberwolf]

Both of them say the same thing except for the blue text that has been added to them, so I don't understand your question "Which of these is the AI lying to me?".

AFAICT the statements in them are correct.

The blue text does not appear to have anything to do meaningwise with the black text that is underlaying it. If it's supposed to, you'll need to explain it.

Resistance question. Which of these is the AI lying to me?

 

[iampaulpease1]

You are correct after looking at the screenshot...even the correct screenshot which I didn't post. The AI was right and I read it wrong. I will delete that post if I'm allowed to