BMS Balancing "optional"

[WheezyRider]

Have you noticed how a lot of BMS devices these days are not even offering a balance option? You have to ask for it as an extra it seems

 

[Nealh]

One has to pick the brand as there are many sellers, I think typically the Be Much Safer brand of BMS is one that typically offers the smaller footprint BMS for small batteries where size of BMS is important.

If one doesn't mess about with charge voltages and simy charges to the required full charge voltage of the battery series then there isn't much need for the balance , good quality cells should keep balance .

 

[saneagle]

Have you noticed how a lot of BMS devices these days are not even offering a balance option? You have to ask for it as an extra it seems

View attachment 55518

It's getting complicated because some say they have it, but don't have any bleed resistors. I was wondering if they found another way to balance, though I don't think they have.

 

[Woosh]

some have active balancing. You don't need to do anything.

 

[saneagle]

some have active balancing. You don't need to do anything.

How do they dissipate the charge without bleed resistors?

 

[Woosh]

They switch small amounts of charge to those less full cells, a bit like a waterwheel, instead of wasting the excess through bleeding resistors. As it's done automatically at any depth of charge, the mechanism is not limited to the CV charging time. The mechanism is faster and wastes less energy.

 

[saneagle]

They switch small amounts of charge to those less full cells, a bit like a waterwheel, instead of wasting the excess through bleeding resistors. As it's done automatically at any depth of charge, the mechanism is not limited to the CV charging time. The mechanism is faster and wastes less energy.

Is that a wind up?

 

[Sturmey]

Different ways to activately balance a battery without load resistors. One way is for the BMS to charge a capacitor with the high cell and discharge it back into low cell. etc.



Exemplary passive (left) and active (right) balancing circuit topologies

 

[saneagle]

Different ways to activately balance a battery without load resistors. One way is for the BMS to charge a capacitor with the high cell and discharge it back into low cell. etc.
View attachment 55543

View attachment 55544
Exemplary passive (left) and active (right) balancing circuit topologies

Those BMSs don't have any capacitors!

 

[Woosh]

Is that a wind up?

not really. Although I don't know the details, I have read some articles about active balancing. You can figure out how that works from reading. I have noticed that bleed resistors disappeared, the BMSes get smaller and smaller, now no bigger than a couple of square inches at most. The balancing wires also get smaller, connectors are now spaced at a millimeter pitch. The Chinese rub off the markings on the main chip making following up nigh impossible. The main thing is I used to get a couple of calls a months telling me that they lost some range. I told them usually to leave the charger on for a couple of hours after the LED on the charger turning green to rebalance the battery. For the last 4-5 years, nobody calls about this anymore.

 

[saneagle]

not really. Although I don't know the details, I have read some articles about active balancing. You can figure out how that works from reading. I have noticed that bleed resistors disappeared, the BMSes get smaller and smaller, now no bigger than a couple of square inches at most. The balancing wires also get smaller, connectors are now spaced at a millimeter pitch. The main thing is I used to get a couple of calls a months telling me that they lost some range. I told them usually to leave the charger on for a couple of hours after the LED on the charger turning green to rebalance the battery. For the last 4-5 years, nobody calls about this anymore.

You're not going to get active balancing in a £15 BMS.

 

[Woosh]

You're not going to get active balancing in a £15 BMS.

why? you can get a whole micro computer with wifi and BT for $5.

 

[saneagle]

why? you can get a whole micro computer with wifi and BT for $5.

You tell me. Why don't you have active balancing in the batteries in your bikes? Next time you see your battery supplier, see if you can arrange it, then all those guys that want to extend the life of their batteries by a few days by 20% -80% charging can buy a Woosh bike. Sales will go through the roof.

 

[Woosh]

I am in France at the moment. I'll ask them to confirm what is in their BMS when I get back to work.

 

[Woosh]

this is a typical BMS:
you can see the thermistor, the soft switch wires

The old bleed resistors disappeared, in their place, a dozen small plastic thingies in plastic cases:

The heatsink is riveted. The whole thing is supposed to be replaced, not repaired.

 

[saneagle]

The old bleed resistors disappeared, in their place, a dozen small plastic thingies in plastic cases:

I can't see any plastic things, nor a plastic case.

 

[Woosh]

I can't see any plastic things, nor a plastic case.

look between the heastsink and the PCB. There are about a dozen of them, about the size of a TO220 but without individual heatsinks. I don't know what they are without drilling off the rivets and remove the heatsink.

 

[saneagle]

look between the heastsink and the PCB. There are about a dozen of them, about the size of a TO220 but without individual heatsinks. I don't know what they are without drilling off the rivets and remove the heatsink.

Do you mean the MOSFETs?

 

[Woosh]

Yes, they can be mosfets. It's difficult to see.

 

[guerney]

Yes, they can be mosfets. It's difficult to see.

Are they raised bleed resistors bonded to/held tightly against the heatsink? Can your supplier provide you with schematics? Drill off the rivets.