Looking for a decent LiFePO4 BMS (48V, 15-20A, 30-40A peak)

L

legend@gazeta.pl

1 mW
Joined
May 14, 2013
Messages
12
Could you suggest one?

I'm building a small battery for a lightweight bicycle and I'm looking for a small and reliable BMS (with LVC,LHC and balancing function).
Extra features (like diagnostic interface or temperature monitoring etc.) are welcomed.
I came across the "Zephyr" BMS but I didn't managed to find a retailer (neither for final product nor DIY kit).
There a couple of cheap and ready to pick Chinese boards but they don't seam reliable for me (at least if purchased directly from China).

Any suggestions?
What parameters should I focus on?

Thank you in advance.
Kamil
 
Pingbattery.com for a signalab lifepo4 bms. The thing I always liked about them was the row of led's that indicate when each cell reaches full charge. Lets you know when the bms has finished balancing the pack.

Since you are building your own, include a set of jst balance plugs spliced into the wires to the bms. It will allow quick and easy monitoring of individual cell levels, and or individual cell charging if you are in a hurry to balance the pack.

I'd love to see such plugs just built into the bms board.

I doubt you need to monitor temp of a lifepo4 pack very much.
 
Thank you for reply.

I'm considering this "Signalab BMS" (this one, 16S version of this one: http://endless-sphere.com/forums/viewtopic.php?f=14&t=49754).
Yes, I'm going to add JST plugs to the existing BMS wires.

I have a question concerning Signalab BMS - what happens when the battery is fully charged?
All diodes are up and what?
Are the cells being kept between overcharge protection voltage (3.9V) and Overcharge protection release voltage (3.8V) or the BCM ends the charging process and turns off (or switch to some kind of "micro-charging" mode)?
What happens when one cell is faulty? Does it influence charging process of the other cells? (probably yes - I can see the cells should be balanced before charging)
 
If you have a really wonky cell, it might get pretty high before the charger shuts off. Or it could cause the charger to run longer, tending to overcharge all the rest. One solution would be to set the charger itself to a lower voltage, so it will stop the charge before a cell drives all the way to 4v.

In the pingbattery setup using signalab, the charge is set to 60v.

When you see the led's lit on the signalab bms, it means that cell is being slowly discharged to the optimum level. All lit, means they all obviously got fully charged. So all lit means balanced. After you unplug, the lights all wink out as the cells draw down to the right level.

If you really really want to guarantee that no cell ever goes past a set voltage, then you might look at 12s charges that single cell charge each cell through the balance plugs.

That's overkill, I think you will be fine with the singnalab, and set the charger to 58v. Or any other BMS just recommended. Perhaps occasionally, set it higher to fully balance the pack. Or since you will have balance plugs, you can single cell charge to balance from time to time.
 
legend@gazeta.pl said:
Thank you for reply.

I'm considering this "Signalab BMS" (this one, 16S version of this one: http://endless-sphere.com/forums/viewtopic.php?f=14&t=49754).
Yes, I'm going to add JST plugs to the existing BMS wires.

I have a question concerning Signalab BMS - what happens when the battery is fully charged?
All diodes are up and what?
Are the cells being kept between overcharge protection voltage (3.9V) and Overcharge protection release voltage (3.8V) or the BCM ends the charging process and turns off (or switch to some kind of "micro-charging" mode)?
What happens when one cell is faulty? Does it influence charging process of the other cells? (probably yes - I can see the cells should be balanced before charging)
Click to expand...

when the battery is at final voltage then the charger continues to supply a small balancing current to the pack that is used to fill the last bits of the low cells as the hi cells bleed current through the shunt resistors to bypass the cells and prevent them from overcharging.

the 3.9V HVC is there to turn off the charger when one cell is too high and charges up ahead of the other cells. it usually only triggers when you have a new pack and it has not balanced. once you are able to charge the pack up to 59V or so and allow it to balance then when you charge it up the following times the cells all charge up together and the HVC never cuts off the charging again until one of the cells goes bad.

for a balanced pack the cells all charge up and reach full charge at essentially the same time so there is no voltage space left for one cell to climb to 3.9V.
 
dogman, how would you adjust the bms from 60v to 58v?

also, is it true their are chargers that balance all cells in bulk charging? If so,This would be good to make a dummy proof ebike
 
ftanka0 said:
but how are people without bms, balance charging their cells?
Click to expand...
Your problem for a 16S system is that there is only 1 external charger that balances 16S and it is about 600 Euro. You could use 2 8S chargers or othe combos of less costly balance chargers but you would have to split your battery every time you charged to get lower series batteries that you coul either parallel charge or seperately series charge. It is a nuisance at best and could be dangerous if you mess up the connections. Certainly a BMS for 16S makes more sense.
otherDoc
 
i have a balance charger for 16S lifepo4 that was on a 48V10Ah pouch pack. there was a BMS on the pcb that the tabs attached to and it monitored the pack for LVC so it could shut down when the pack was over discharged, or shorted/overcurrent.

the BMS was too much to figure out since it had two 64 pin processors but did nothing since it was dead so i bypassed it and used a ping signalab.

that pack had 4 pouches fail because the tabs were long and folded and the vibration of the pack caused the tabs to fatigue crack. it is currently a 14S 10Ah pouch pack that works under a v1 signalab BMS hacked from 16S down to 14S.

i have never used the 16S lifepo4 balancing charger itself.
 
Here is the commercial one I was thinking of. Big bucks!
otherDoc

http://www.pp-rc.de/SHOP/epulsar3.htm
 
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