Hello, I’m seeing ERR(16): OV on my pack while charging. I assume this is overvoltage? It seems to work fine, but I’m not sure how best to safely clear the error. Is there any way to restart it, or to figure out what’s wrong exactly? The charge is at 44%, but I’m seeing 4/4 green lights, even while charging, thought sometimes it goes to 2/4 green lights. For now I’m not going to charge it anymore, but I’d appreciate any advise.
Hello Sean,
yes OV is overvoltage.
This error occurs when you charge a pack and that one group of cells reaches the 4,2V faster than the other. With this error, the pack should still be able to discharge and to be used and the BMS will do some balancing to try to remove this unbalance but if it is more than a few mV it can take days even weeks.
There are two possible way to understand an solve this problem faster:
If you used refurbished cells
This may come from the fact that all cells were not perfectly matched in voltage when you assembled them. You can disassemble the pack (thank you modularity) and then use a cell charger to charge all cells to 4,2V. Once charged, check that they all have the same voltage (around 4,1V) and that you don’t have cells that have a high self discharge. Then you can reassemble the pack and it should solve the problem. By doing this you just balanced the pack externally.
If you used new cells
If the cells are new, this almost certainly means that one row (row 10 in the example beneath), one cell isn’t making good contact (not tight enough contacts, or dirt on the contact ball) and so there are only 3 cells active on that row – so they charged faster than those on other rows.
What to do:
- Dismantle the battery but leave all the cells in place.
- Only remove the cells from row 10 (these are numbered 10-1, 10-2, 10-3, 10-4 on the contact plates).
- Measure the voltages; one of them should have a voltage lower than the other three (confirming the problem).
- Clean the cell contacts and lightly scrape the surface of the 8 contact balls with a screwdriver (just a tiny scratch, like scoring the surface).
- Don’t put the cell back in if the voltage gap is significant, as this would cause a strong current between them to rebalance.
- To charge the cell with lower voltage, two options:
- If you have an individual lithium cell charger, you can charge the cell so its voltage is close to the other three – within 0.05V.
- If not, only put the cell that needs charging back into the cell holder, fully reassemble the battery, check on the app to make sure everything is connected (you should see row 10 with just the single cell voltage).
- Using the charger, begin charging; the single cell in row 10 should charge faster than the others and quickly catch up (this assumes you’re using a 2A charger or less – definitely not more – and that you’re using Samsung35E cells, which should accept a 2A charge).
- Once all the cells are approximately at the same voltage, put the remaining three back in and close everything up.
- It’s possible the battery will remain slightly unbalanced in voltage but the BMS will work to reduce this difference, which may take a few days.
Thank you Alex, this is helpful!
I’d like to offer an unrelated suggestion: the tolerances in the cell holder should probably be quite a bit tighter. I noticed a few times during assembly that the positive ends of adjacent cells can touch each other, leading to sparks. Not an issue once assembled, but it can be a bit scary while putting the pack together.
Thanks again for all that you do!
hello Sean,
humm never seen this ! do you use cell without shrink wrap around ? this is the only explanation I see. In this case, this is a good remark that I will add to the doc. If you have a picture on hand it could be helpful
thanks
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Ah that’s totally it! One of the recommended suppliers sends them unwrapped, ha I just assumed that’s how they were meant to go in. I’ll buy some wraps!
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On all 18650 cells I have seen so far, only the tab in the middle is positive, while the ring around the top edge is negative. I do not understand how you were able to short your cells while they are in the cell holder. Can you explain in more detail how that happened?
It’s because the ones I ordered were unwrapped, with no protection; totally my fault. I’ve since wrapped them and they’re safe now. For reference, these are the ones I ordered:
As I explained in my previous message, only the tab in the middle of the top is positive. Therefore, having unwrapped cells should not be an issue.
The only way you could get a spark is if the cells are already fully in the cell holder, such that the positive terminal of one cell is already in contact with the negative terminal of the next cell in the series chain, and then bend the cells together such that their other ends touch. That means it’s not the positive ends that touch each other. Only the negative casing of the cells can touch each other when the cells are parallel in the cell holder.
The issue is that when unwrapped, the clearances in the cell holder are such that the cells are able to touch each other during assembly; like, even when they’re all the way in the cell holder, they can easily lean over and touch each other. If you’re careful it’s not too bad, but it can be a bit scary during disassembly. There’s also the issue that they are able to move around, even once assembled, which probably doesn’t help with longevity.
hello Anton,
you are right that only the center terminal is positive while all the rest is the negative pole. So unconnected cells should make no spark when you touch the outer parts of the cells together. However, during the assembly, I suspect that in a group where you have 4 cells connected by the positive terminal and 4 cells connected by the negative terminal, you can have sparks because you create a loop
Mine gives the OV warning but doesn’t show any cells in red. Charge is indicated at 95% of capacity and the max voltage difference is 0.019v. The BMS seems to be doing it’s job very well as the voltage difference lowered to 0.015. However none of the cells reached full charge 4.2v even after a second charge which again showed OCV(16) with no red cells marked. The voltage difference again dropped to 0.015 as the BMS got work and the warning disappeared . Charge indicated again was 95%. The cells are brand new Samsung 35E from a reputable supplier. Not charging to 100% doesn’t me in the slightest, in fact it will likely prolong battery life, but I am interested to know if it will eventually charge all the cells to 4.2v which they capable of reaching as I charged them in groups of 4 in a charger before assembly.
"and that you don’t have cells that have a high self discharge”
How could that be measured for refurb cells?
Charge them to 4.2, let thm sit for how long .. and measure voltage again?
Is there a correlation between self discharge and internal resistance?
Update…..the charge at 95% in my case should have been a big red flag. It was two cells in Bank 7 not making a satisfactory contact which resulted in arcing during my first ride and shocking bad battery drain. It was caused by the type of finish on the Samsung battery terminals. I have posted the solution in another post. Just be aware that if your battery doesn’t reach full charge you may have a battery contact issue (no matter the brand);which won’t fully show itself until you ride a reasonable distance.