26s BMS for 600A max?

Batteries, Chargers, and Battery Management Systems.
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BenjAZ   100 mW

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26s BMS for 600A max?

Post by BenjAZ » Mar 20 2019 4:58am

Hi
I didn't find any topic with similar information, so I hope you could help me.
I'm working on a 26s50p battery pack for an electric motorcycle. I need a BMS capable of dealing with up to 600A max peak current.
Could you recommend any good product or manufacturer, please?

Thanks

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Sunder   1 GW

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Re: 26s BMS for 600A max?

Post by Sunder » Mar 20 2019 6:37am

You don't. You use a relay/voltage sensing contactor instead.

So you have a relay between your battery and your load, without the BMS between it. Then, the signal for the relay is the BMS. If any conditions would normally trip your BMS, the voltage to the relay will vanish, closing the relay, and achieving the same thing with only a small millisecond delay.

The Mosfets to handle 600A would just be incredibly expensive, and the board would get less reliable from the parts in parallel.
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Philaphlous   1 kW

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Re: 26s BMS for 600A max?

Post by Philaphlous » Mar 20 2019 6:50am

Shoot...for 50A that I'm pulling im even bypassing my bms. For me personally, if there's the offhand chance that I can eliminate anything between the battery to the load, I will eliminate it! So essentially I only use the bms for my charge port which is fine considering I don't over discharge my battery...thats really the only risk I currently run. But yes, that could be fixed with a relay as discussed earlier.

I honestly don't trust bms's for anything other than balancing and overcharging cutoff...the traces are just too small on a lot of the lower voltage bms boards I've seen. 600A is like crazy current...like Tesla model S ludicrous current...

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fechter   100 GW

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Re: 26s BMS for 600A max?

Post by fechter » Mar 20 2019 9:47am

One approach is to find a 26s BMS with a much lower current ranting and use the output of that to power the coil on a big contactor. If the BMS trips due to voltage being out of range, the contactor will open. The contactor would bypass the BMS and go straight to the cells.
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liveforphysics   100 GW

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Re: 26s BMS for 600A max?

Post by liveforphysics » Mar 20 2019 12:57pm

What controller would 26s make sense for?

If you're already eating the penalty of 150V mosfets, you want to run 28s.

BenjAZ wrote:
Mar 20 2019 4:58am
Hi
I didn't find any topic with similar information, so I hope you could help me.
I'm working on a 26s50p battery pack for an electric motorcycle. I need a BMS capable of dealing with up to 600A max peak current.
Could you recommend any good product or manufacturer, please?

Thanks
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john61ct   100 GW

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Re: 26s BMS for 600A max?

Post by john61ct » Mar 20 2019 2:56pm

Would that approach still allow using the BMS for "live balancing" ?

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fechter   100 GW

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Re: 26s BMS for 600A max?

Post by fechter » Mar 20 2019 11:16pm

john61ct wrote:
Mar 20 2019 2:56pm
Would that approach still allow using the BMS for "live balancing" ?
Yes. The only thing you would lose is over current protection. Use a really big fuse.
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amberwolf   100 GW

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Re: 26s BMS for 600A max?

Post by amberwolf » Mar 20 2019 11:35pm

If the BMS has overcurrent sensing, it doesn't even lose that, becuase it would still trip the contactor off.

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fechter   100 GW

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Re: 26s BMS for 600A max?

Post by fechter » Mar 21 2019 8:05am

amberwolf wrote:
Mar 20 2019 11:35pm
If the BMS has overcurrent sensing, it doesn't even lose that, becuase it would still trip the contactor off.
If your are bypassing the BMS with the contactor, the circuit will only be sensing the current in the contactor coil.
It may be possible to use a humongous shunt in the main line and wire it to the BMS board to retain that feature. It would require some board hacking.

The under and over voltage triggers and balancing functions would work without sensing the current.
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Re: 26s BMS for 600A max?

Post by amberwolf » Mar 21 2019 7:40pm

Ah, yeah, I assumed that one would wire "around" the FETs, but still use the shunt in the BMS.

I guess an external shunt would be used for that, too (or even cut the shunt portion of the PCB off the BMS and use that).

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fechter   100 GW

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Re: 26s BMS for 600A max?

Post by fechter » Mar 21 2019 8:03pm

A typical small BMS won’t have a shunt rated for 600A. Otherwise you are correct.
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BenjAZ   100 mW

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Re: 26s BMS for 600A max?

Post by BenjAZ » Mar 23 2019 2:41am

Thanks for the relay/contactor idea, I'll give it a go!

If I understand,
1) Positive wire: battery(+)->600A fuse->controller
2) Negative 1 wire: battery(-)->contactor->controller
3) Negative 2 wire: battery(-)->BMS->contactor signal (to open and close the contactor)

So, there is no actual current going through the BMS and could use any 26s bms. 20A, 30A, 50A...

Am I right?

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fechter   100 GW

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Re: 26s BMS for 600A max?

Post by fechter » Mar 23 2019 11:49am

Right. Just the contactor coil is powered by the BMS so even a really low current rated one would work. Be sure to put a diode (reverse biased) across the contactor coil to catch the turn off spike. Some contactors have this built in.
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BenjAZ   100 mW

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Re: 26s BMS for 600A max?

Post by BenjAZ » Mar 24 2019 1:08am

fechter wrote:
Mar 23 2019 11:49am
Right. Just the contactor coil is powered by the BMS so even a really low current rated one would work. Be sure to put a diode (reverse biased) across the contactor coil to catch the turn off spike. Some contactors have this built in.
Great stuff!

Thank you very much

monette999   10 mW

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Re: 26s BMS for 600A max?

Post by monette999 » Jan 22 2021 11:27pm

Hi why not using a 75mV shunt behind the contacter. Something bigger than attached and use a proportional DC-DC amplifier to feed the output of the BMS.

If the current goes above a certain level the BMS will release the contacter buy the overvoltage protection.

I don't know if this is possible???
You have to connect it to the shunt of the BMS???

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flippy   10 MW

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Re: 26s BMS for 600A max?

Post by flippy » Jan 23 2021 4:33pm

why would you? for a 600A rating you can just buy a 750A megafuse and holder for a couple of [insert local currency] at a marine shop. its a LOT cheaper, safer and just works.

ig you rely on the bms over overcurrent you have a problem further upstream. people tend to forget the bms is a failsafe, not a way of controlling stuff. even in extreme operation a bms should never trigger. a bms exists to protect the battery, not the rest of the system.
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