Why do we want more balancing current from a BMS?

[Battery_Mooch]

@Mr.Electronicist

The ideal BMS would shift the energy from the most charged cell to least charged, so the only losses are efficiency losses during transmission. It seems like it’s just the cheap BMS’s (like the ones we use in this hobby) that bleed the excess power via resistors to equalize pack voltage.

Agreed, but…
“Active” balancers, that shift charge instead of bleeding it off, are huge and expensive though. They’re typically best for verrrry large packs like in EVs.

[glyphiks]

Possibly, but i still think that the wires are undersized.

We are quickly derailing here though.

[mutantbass]

I think @Andy87 tried one of those active balancers from aliexpress. Wasn’t impressed.

heres the thread Active balancing boards

[glyphiks]

@Scepterr has a sweet external balancing setup, perhaps worth sharing here?

[Battery_Mooch]

@BenjaminF

That may have more to do with shitty soldering than the wire its self. A really poor solder joint can greatly increase the resistance of the wire+connector system.

A very good point and an under-appreciated aspect of DIY.
Though a lot of blame can be laid on the manufacturers who don’t offer a way to do a low resistance connection due to the way the connection point was designed or laid out.

[Battery_Mooch]

@glyphiks

We are quickly derailing here though.

A hallmark of my threads.

[glyphiks]

At least it brings about interesting and thoughtful discussion. Can easily spiral out of control here though

[mutantbass]

Dumb idea.

If there was a way to quickly turn series connections into parallel connections (turn a 12s2p battery into 1s24p), would the batteries balance within minutes?

[BenjaminF]

@Battery_Mooch

Though a lot of blame can be laid on the manufacturers who don’t offer a way to do a low resistance connection due to the way the connection point was designed or laid out.

I’ll gladly throw the Conflict Unity under the bus here:

This is what shitty QC on your solder joints looks like. The wire is not making sufficient electrical contact with the connector (therefore a ton of extra resistance), and there is vastly insufficient solder (so when it gets hot, it doesnt take much to de-solder).

[Battery_Mooch]

@mutantbass

If there was a way to quickly turn series connections into parallel connections (turn a 12s2p battery into 1s24p), would the batteries balance within minutes?

Roughly, yes.
Then the smaller and smaller voltage differences between the p-groups would result in smaller and smaller amounts of balancing current. Experiments would need to be done to know when to say “it’s good enough”.

[mutantbass]

I can imagine some kind of sliding rail on the side of the enclosure.

_  _  _  _  _  _  _  _  _  _ = series connections
 -   -  -  -  -  -  -  -  -  = parallel connection

But fuck me, if you bump into something mid ride. LMAO

[Battery_Mooch]

@mutantbass

I can imagine some kind of sliding rail on the side of the enclosure.

You just need a button…and lots and lots of MOSFETs.

[mutantbass]

Someone did this

Want to build a portable Charger

in my experience throwing a 3v and 4v 30Q cell together in parallel maybe increased the heat by 5 degrees F. MAYBE you could just throw the two in parallel when the one on the board is dying. [image] I did the math based on ohm’s law and assuming this 30Q resistance and 10s3p [image] here’s how MY math goes and maybe someone can correct it: first finding the resistance of the 3 cells in parallel would be 1/.034 + 1/.034 + 1/.034…and keeping it simple lets call it 1/.1, so answer being .01 f…

[Andy87]

I don’t think more balance current is the problem, the problem is that some of the old school bms just balance while charging.
This compared with the trend of bigger and bigger packs or higher charge currents on small packs just doesn’t work out.
We also tend to use charge only bms, which does have in average 40-50mA of balance current. That’s on a 1600Wh pack… hm, idk.
I think our answer to this is not higher balance currents, but smart bms with active balancing after the charger was disconnected.

[Battery_Mooch]

@Andy87

I think our answer to this is not higher balance currents, but smart bms with active balancing after the charger was disconnected.

Don’t some of the standard passive balancers also have the option to charge when not balancing? Hopefully only when above a certain voltage though.

[Andy87]

@Battery_Mooch

passive balancers also have the option to charge when not balancing

Hmm… I think there was something mixed up… or it’s too early for my brain to work. Need coffee

But yes you are right.
I think there are some different types out.
Some balance while charging over a specific voltage and some over charge and drain till a specific voltage which sometimes do need the charger to be plugged in to make it work.

[JoeyZ5]

@Battery_Mooch

You just need a button…and lots and lots of MOSFETs.

I figured this idea would never be used, as a small logic bug or some physical design error could lead to shorting the entire pack out at once pretty easily…

Like 1s24p and 12s2p mode get activated at the same time…

[taz]

We don’t.
A good battery should barely need any balancing to begin with.
Now I have a bad p group on one of my boards that gets out of balance a lot but faster balancing is just a bandaid for deeper problem in the battery.

I should probably get off my ass and change it …

[ENNOID]

Even cars & even expensive ones dont have this feature implemented. It is called active balancing. Such system tends to be large & expensive. Unless you want to pay several hundreds bucks for saving a few mW per use, it is not worth it. The energy payback would never be reached for the BMS higher price tag in most cases. Active balancing could be useful only for very special projects having a restriction on power where every mW count e.g. mars rover… I don’t think consumer electronics fits into this category.

[ENNOID]

I don’t think going above 100mA balancing is required in most cases even for quite large Ah packs for LEV. Heat dissipatiom becomes a problem & makes the BMS larger when going with higher balancing rate. Just use new & identical cells to build new packs. Use a good BMS to make sure you don’t kill the cells during normal use and the difference in balance will stay low until the cells have reached their end of life.