GGoodrum
1 MW
In the seemingly endless series of BMS testing I've been doing of late, one thing I've noticed is that these Turnigy and Zippy 6s-5000 packs I'm using, just don't get out of balance very easy, without forcing them out-of-balance. This has made me re-think how to manage these packs. What I really need to do is monitor each cell during charging, but not worry about balancing every time. What I've now done is use combo LVC/HVC-only boards in the pack, in conjunction with the new charge control board. What this does is use the throttling logic to hold each cell from exceeding the set point, which is about 4.16V, in my current setups. The current will drop all the way down to essentially zero, as the high cell gets full. With the cells fairly well balanced, they will all get full.
With all the BMS weirdness we were seeing, the problems were causing the cells to get as much as 100mV delta between the lowest and highest cells. What I used to re-balance the cells was my trusty Hobby City Battery Medics. These units work amazingly well, and will balance the cells to within about 5mV, but it can take quite awhile. They have 10 ohm shunts, so they should be capable of at least 300mA of balance current, but there's no fans inside, so it would be hard to believe they'd really shunt that much. As it turns out, the unit pulses the current, so that all the channels aren't all on at the same time. The duty cycle is roughly 2 seconds on and 1 second off.
I then decided that maybe it was easy enough to come up with a way to boost the shunt current, so that the balance time would be reduced. As it turns out, this was actually pretty simple. What I did was tap into the collector of the shunt transistors, and use this to drive the same KSA473 power transistors and 3.1 ohm shunt resistors we use on the full BMS. I finally am able to make use of some of the earlier version shunt boards, that have been accumulating in a big pile at an alarming rate.
It took some experimenting to get the values right, and Richard made some circuit "adjustments", but this works amazingly well. There's just under 3.0V across the shunt resistors, so just about 1A of "boost" current. Here's what the schematic looks like:
View attachment Battery Medic Booster v1 0b.png
Pretty simple, really. The BM has a PNP transistor that drives a bank of ten 100 ohm resistors in parallel. This is similar to what we do on the BMS shunt boards. Anyway, a tap from the collector is inverted, and this is used to turn on the KSA473 shunt transistor. The LEDs are not necessary, but it is nice to have a visual indication of when each channel is actually on.
Next, I took the booster board, and stuck it in one of my favorite boxes. Here's what it looks like:
View attachment 3
View attachment 1
View attachment Battery Medic Booster-03.jpg
Anyway, I'll give this a good workout, and see how much time is cut out of the balance process.Later, I'll also post some pics of the new LVC/HVC boards, and the special version of the BMS control board I'm doing for this application. The board fits in one of the smaller versions of the boxes.
-- Gary
With all the BMS weirdness we were seeing, the problems were causing the cells to get as much as 100mV delta between the lowest and highest cells. What I used to re-balance the cells was my trusty Hobby City Battery Medics. These units work amazingly well, and will balance the cells to within about 5mV, but it can take quite awhile. They have 10 ohm shunts, so they should be capable of at least 300mA of balance current, but there's no fans inside, so it would be hard to believe they'd really shunt that much. As it turns out, the unit pulses the current, so that all the channels aren't all on at the same time. The duty cycle is roughly 2 seconds on and 1 second off.
I then decided that maybe it was easy enough to come up with a way to boost the shunt current, so that the balance time would be reduced. As it turns out, this was actually pretty simple. What I did was tap into the collector of the shunt transistors, and use this to drive the same KSA473 power transistors and 3.1 ohm shunt resistors we use on the full BMS. I finally am able to make use of some of the earlier version shunt boards, that have been accumulating in a big pile at an alarming rate.
It took some experimenting to get the values right, and Richard made some circuit "adjustments", but this works amazingly well. There's just under 3.0V across the shunt resistors, so just about 1A of "boost" current. Here's what the schematic looks like:View attachment Battery Medic Booster v1 0b.png
Pretty simple, really. The BM has a PNP transistor that drives a bank of ten 100 ohm resistors in parallel. This is similar to what we do on the BMS shunt boards. Anyway, a tap from the collector is inverted, and this is used to turn on the KSA473 shunt transistor. The LEDs are not necessary, but it is nice to have a visual indication of when each channel is actually on.
Next, I took the booster board, and stuck it in one of my favorite boxes. Here's what it looks like:
View attachment 3
View attachment 1
View attachment Battery Medic Booster-03.jpg
Anyway, I'll give this a good workout, and see how much time is cut out of the balance process.Later, I'll also post some pics of the new LVC/HVC boards, and the special version of the BMS control board I'm doing for this application. The board fits in one of the smaller versions of the boxes.
-- Gary
What I will do is only use the balance mode if I happen to be using these while charging the pack. Otherwise, I'll use the discharge mode, set to something like 4.10V.
