Sabvoton controller not working! Help please!!!

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Ryanlaine
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Sabvoton controller not working! Help please!!!

Post by Ryanlaine » Thu Nov 09, 2017 2:19 pm

I recently installed a 80a sabvoton controller into my e-bike and it was working great untill today, i think it messed up because i accidently left the power on the controller when i unplugged it. Now i keep getting a low voltage error, but my battery is fully charged. Plz help

Ryanlaine
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Re: Sabvoton controller not working! Help please!!!

Post by Ryanlaine » Thu Nov 09, 2017 6:32 pm

So i think iv figured out it is not a problem with the controller but the battery/bms. battery led is on and measures 92v but when i turn on my ebike it only stays on for a fuw seconds then voltage drops to zero. after load is disconnected battery slowly rises back to 92v. any ideas?

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amberwolf
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Re: Sabvoton controller not working! Help please!!!

Post by amberwolf » Fri Nov 10, 2017 2:29 am

The battery is probably badly unbalanced. The first thing I'd recommend is leaving it connected to the charger for at least a few days (could take weeks if it's badly unbalanced), as this will at least temporarily fix it (until the next unbalancing event).

If the battery was left on the controller until it drained it completely (BMS shut off), cells could easily have ended up at different voltages; it's not uncommon for cells to not all actually have teh same capacity. So when they get drained past a certain point, then a single simple recharge doesn't bring them all up to the same point, so the BMS has to rebalance them.

Sometimes the voltage difference is very large, and a cell can even be damaged (or defective) and drain down so far it's far below the rest, and actually still so close to LVC that as soon as any load is placed on it, it drops in voltage below LVC so the BMS shuts down.

In those cases, it takes a very long time (weeks, probably) to rebalance a pack.

It can be faster to manually recharge individual cell groups, if you have a single-cell charger to do that with.

Note that when this kind of problem exists in a pack, it usually means those cells that are that low in voltage have a problem, and it will probably get worse with age--and the pack no longer has (or never had) it's full capacity, and is also likely to cut out under load when it gets closer to empty than full.

You can open the pack up and measure all the voltages between the balance wires at the BMS board, and post htem all up here, and we can help you find which groups are a problem so you can fix them.

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minde28383
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Re: Sabvoton controller not working! Help please!!!

Post by minde28383 » Tue Nov 14, 2017 7:58 pm

Ar you sure that keeping charger & BMS connected to even slightly unbalanced cells for a week might fix unbalance?
I got cells but keeping cells connected for days BMS does not balance them all equally - to 4.19v.

Battery pack 30Ah, 72v. Cells are in a good state but before stacking them to battery pack they were not charged up equally.
The BMS I'm using: https://goo.gl/cGZhWP
According to description BMS balance current is 50 mili amps.

The BMS does not balance cells even after a few days. After charger finishes charging, charger switches off / goes idle. Some LEDs stays for ten minutes or so, and then all LEDs one by one switch off. I doubt that BMS is doing anything to get cells equal charge ie discharge highest cells to be equal to lowest, and start whole battery pack charging again.

4,17
4,16
4,18
4,16
4,17
4,18
4,18
4,19
4,18
4,17
4,18
4,17
4,16
4,18
4,15
4,15
4,16
4,18
4,17
4,16

Later on these two cells with with 4.15v where charged up separately each; ~3Ah charged to each 4.15v till they
become 4.19v. After that regular 72v charger & BMS connected to the battery pack and it does not balance all 20 cells to 4.19v.
Will it be differently if I keep connected charger & BMS for weeks, I doubt.
I don't think that this BMS is faulty unless they are all faulty. I've tried few similar cheap BMS and they all do the same ie they do not balance.
At the beginning I was thinking that the BMS is discharging highest cells (when LEDs off) to be equal to lowest ones but after few days waiting I don't think so anymore.

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amberwolf
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Re: Sabvoton controller not working! Help please!!!

Post by amberwolf » Wed Nov 15, 2017 1:14 am

The typical resistive-drain BMS doesn't make the highest cells equal the lowest.

All it does is shut off charging input current once a cell reaches HVC, and then drain any cells taht are above it's balancing point down to equal that point.

Then it re-allows charging input current, and continues this cycle until all cells are at that point, so that any input current causes HVC to be triggered, and the input stays shut off.

(there are capacitive charge-transfer BMSs that *do* equal out all the cells directly, but they won't have a bunch of the same larger resistors on it).


If the charger doesn't kick back on after the balancing lights (which presumably mean cells above HVC) all go out, then either the BMS is not turning it's input back on, or the charger is not designed to turn back on by itself once voltage drops back below it's full-charge point.

Some chargers also keep allowing a small current when asked for it (to do balancing with) once they reach full charge, and don't actually shut off--only the BMS shuts off it's input as cells reach HVC, then as the balancing system drains the high cells the BMS turns it's input back on so the balancing can continue.


WIth systems like the above, you have to manually restart the charging process each time, which can be as simple as unplugging battery from charger and plugging it back in, or as complex as doing that *and* unplugging charger from wall, waiting a minute or two, then reconnecting them all up.


But eventually the balancing will work, as long as the systems support restarting teh cahrging on it's own, or you do it manually.

Note taht if the charger's voltage isn't high enough to cause current to keep flowing once the pack reaches the balancing voltage stage, then no balancing current will flow, and no balancing will occur.


The only time they won't balance cells is if the cells themselves have a problme that prevents them from reaching the balance voltage, or the internal resistance of some cells is so much higher than the others that even minimal charge current sends their voltage above HVC, triggering the BMS to shut off input, preventing the finishing charge / balancing from happening to the other cells.

Or if the BMS itself is either built or designed wrong, or defective. If the problem occurs with many types of BMS, used on teh same actual group of cells, then that's probably nto the issue--it's probably either the cells themselves, or the charger.

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minde28383
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Re: Sabvoton controller not working! Help please!!!

Post by minde28383 » Wed Nov 15, 2017 2:57 pm

Hi amberwolf, you wrote few scenarios. I really appreciate your advices.

My charger gives 83,7v but not 84v. I've measured this voltage without load, just plugged the charger into a wall socket and measured with a voltmeter. Maybe that the issue? Does it has to be 84v? Does measuring without load reveals anything as we don't know what voltage on the load but I assume (just assume) that voltage must stay the same because the charger is not some my DIY but bought from shop specifically for 84v batteries.

The battery pack is 20S, fully charged pack should be 84v.


You have written interesting points, one of which I had put some most thought:
"If the charger doesn't kick back on after the balancing lights (which presumably mean cells above HVC) all go out, then either the BMS is not turning it's input back on, or the charger is not designed to turn back on by itself once voltage drops back below it's full-charge point."

In my case, I think that few things happening. BMS does not drain highest cells with 4,19v but LED lights still go out and Charger does not go ON after LEDs go off becasue BMS does not ask for more current. Nevertheless, when I replug charger after waiting few minutes charging process initiates for few minutes. LEDs with highest voltages goes ON, stays for few or so minutes ON and then again goes Off and the cycle can be repeated with the same results.

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