Voltage going down while NOT in use
- Thread starter Joey11
- Start date
Chalo
100 TW
Yes, it's normal. The term is "self discharge", and batteries vary widely in their tendency to do it. In your case, the voltage between 77.0V and 76.75V probably doesn't represent very much energy in the pack.
Back when some of us used NiCd batteries in e-bikes, self discharge rates were about 10% of the remaining capacity per day.
Back when some of us used NiCd batteries in e-bikes, self discharge rates were about 10% of the remaining capacity per day.
izeman
1 GW
losing 12mV PER cell in 3 days seems too much for me. lithium keeps it's voltage for a very long time w/o losing a bit.
if you charge it to 4.2V per cell and voltage falls a bit this is normal as at the very low and high end there is only very little capacity.
i would check the voltage of every one cell in the 20s string. it looks to me as i ONE battery maybe dropped, and the others remained the same.
if you charge it to 4.2V per cell and voltage falls a bit this is normal as at the very low and high end there is only very little capacity.
i would check the voltage of every one cell in the 20s string. it looks to me as i ONE battery maybe dropped, and the others remained the same.
Ykick
1 GW
It is something to be concerned about on the cell level. The term is called “leaker” and while healthy RC Lipo cells “leak” a small amount of voltage from the top charge it should slow down if not completely stop within a day or two.
For example, some of my cells sit @ 4.2V/cell after charge. By the next day I expect them to be between 4.18-4.19V/cell. Maybe 4.17V/cell but the point is that it should remain around those voltages after a week of sitting with nothing draining the cells.
after a few days or week, if you’ve got one which is now down to 4.10-4.05V, there’s definitely a “Leaker” and my rule is to remove those from service.
Some sort of defect or contamination is shorting internally and that’s a recipe for disaster.
You need a CellLog or some form of multi-channel volt meter for quick reliable measurements of cell voltages.
For example, some of my cells sit @ 4.2V/cell after charge. By the next day I expect them to be between 4.18-4.19V/cell. Maybe 4.17V/cell but the point is that it should remain around those voltages after a week of sitting with nothing draining the cells.
after a few days or week, if you’ve got one which is now down to 4.10-4.05V, there’s definitely a “Leaker” and my rule is to remove those from service.
Some sort of defect or contamination is shorting internally and that’s a recipe for disaster.
You need a CellLog or some form of multi-channel volt meter for quick reliable measurements of cell voltages.
Thanks for you reply.
My bad, battery is sitting for 5 days (since Friday noon). As I said, 5 days ago, voltage was about 77v, now (5days later) voltage is about 76.7v(losing 0.015v per cell) with controller and BMS connected..
Cells voltage different are 0.01v.
I know my bms "Static power" consumption is less than 200uA.
My bad, battery is sitting for 5 days (since Friday noon). As I said, 5 days ago, voltage was about 77v, now (5days later) voltage is about 76.7v(losing 0.015v per cell) with controller and BMS connected..
Cells voltage different are 0.01v.
I know my bms "Static power" consumption is less than 200uA.
izeman
1 GW
you say "controller connected" - do you mean connected and turned-on? or just connected? i don't know how much the big input caps draw over time. i always disconnect the controller.Joey11 said:
i wouldn't worry much as long as all cells have the same voltage. just check voltag from time to time, charge to storage voltage before riding season ends and totally disconnect from the controller.
jimw1960
10 kW
Dumb question, but is your controller turned off with a key switch? One time, I accidentally left my controller turned on while the bike sat idle for several months and the battery drained slowly like that. I caught it before it hit the LVC but it had drained several volts over a three or four month period.
dogman dan
1 PW
Holy cow! That's all they lost after taking them off the charger? That's doing great!
But yeah, a bms or anything else connected to your battery will gradually draw them down some in a week. But your "problem" is no problem. Just don't put your battery into winter storage connected to stuff.
But yeah, a bms or anything else connected to your battery will gradually draw them down some in a week. But your "problem" is no problem. Just don't put your battery into winter storage connected to stuff.
dogman dan
1 PW
Ok, so it's not just that vanishing charge when you unplug the charger.
Nevertheless, it's not going to be any problem, unless you park the bike for a week or two while it's empty. Definitely get some charge back into it if you drain it all the way, as soon as you can. 77v is fairly close to empty I'm thinking. So get a bit more in there next time you park a week.
I see no problem with parking the bike a week half empty. you are only losing a volt a week, or less.
Nevertheless, it's not going to be any problem, unless you park the bike for a week or two while it's empty. Definitely get some charge back into it if you drain it all the way, as soon as you can. 77v is fairly close to empty I'm thinking. So get a bit more in there next time you park a week.
I see no problem with parking the bike a week half empty. you are only losing a volt a week, or less.
John in CR
100 TW
Some controllers have drain down resistor which can kill batteries when left unattended for long periods (a month or more). At that pack voltage you shouldn't see that much self discharge in a week, so my guess is that the controller is doing it.
dogman dan
1 PW
YES charge it before you ride it. I'm assuming 72v is empty?
Good idea to park it a week half full, but not if it's too close to empty. Storing the battery less than fully charged for a week should help it last longer. But you want to fill it just before you ride again. You don't "save a cycle" by running it empty before you recharge. Forget any of the old NiCad myths you may have learned for your drill battery. They were bull even back then.
Park it at least half charged if it will sit a week, and always top up before any ride however short.
Good idea to park it a week half full, but not if it's too close to empty. Storing the battery less than fully charged for a week should help it last longer. But you want to fill it just before you ride again. You don't "save a cycle" by running it empty before you recharge. Forget any of the old NiCad myths you may have learned for your drill battery. They were bull even back then.
Park it at least half charged if it will sit a week, and always top up before any ride however short.
dogman dan
1 PW
Reading back, 20s lipo. Ideally don't let it go below 73v, 3.65v per cell. Sure, if you need to to get home, lower. But don't park it below 73v ever, with that drain going on.
Right now you are at about 3.8v per cell, which could be anything from 1/4 full to close to half. It's Wednesday, it should not drain itself past 73 by the weekend.
But I'd be happier to park it a week myself, if it was more like 78 volts. Something that is for sure half full.
Right now you are at about 3.8v per cell, which could be anything from 1/4 full to close to half. It's Wednesday, it should not drain itself past 73 by the weekend.
But I'd be happier to park it a week myself, if it was more like 78 volts. Something that is for sure half full.
dogman dan
1 PW
Yes, especially since voltage will drop faster at the tail end of a charge. If above 50% charged, you might lose those watt hours with almost no change in voltage.
But if its easy, is there a reason you don't unplug the controller? I'd just unplug. I just set up all my bikes like that. the off switch is unplug it completely.
This is because I never charge on the bike. I don't like to set my bike, garage, or house on fire.
But if its easy, is there a reason you don't unplug the controller? I'd just unplug. I just set up all my bikes like that. the off switch is unplug it completely.
This is because I never charge on the bike. I don't like to set my bike, garage, or house on fire.
dogman dan said:
It is technically easy but the access to the connector is challenging...
Be sure I will do it next time....
I didn't wire the switch to completely cut off controller input because I didn't found a witch that can handle the amps going in there..
So as I asked, is lost of 0.7v (I road from full charge (83.7v) to 77v, then bike was parked and today the voltage is about 76.3) in 6 days is a normal thing when battery connected to BMS& controller?
Thanks again
Ykick
1 GW
Most BMS have tiny idle current 20-50uA but over several months that can significantly deplete 5-10Ah cell groups. That’s why any commercial eBike battery pack should always be partially charged once per month.
IIRC my controllers when switched OFF using the ignition switch wire continue to draw around 10mA? Can anybody confirm or refute that for the basic Infineon controller?
But for estimating purposes let’s use that 10mA. In 1 hour we would burn 10mAh, over 10 hours we’ve burned 100mAh. 4 days (100 hours) sitting with that seemingly small drain would be about 1Ah burned up in the ignition OFF position.
Even if my estimate’s off and it’s only 20-50uA give it enough time you can see how controller/BMS circuits will eventually discharge packs.
This is different from what I was describing earlier about “Leaker” cells. They drop voltage merely sitting not connected to anything. Definitely something you want to avoid in your life.
IIRC my controllers when switched OFF using the ignition switch wire continue to draw around 10mA? Can anybody confirm or refute that for the basic Infineon controller?
But for estimating purposes let’s use that 10mA. In 1 hour we would burn 10mAh, over 10 hours we’ve burned 100mAh. 4 days (100 hours) sitting with that seemingly small drain would be about 1Ah burned up in the ignition OFF position.
Even if my estimate’s off and it’s only 20-50uA give it enough time you can see how controller/BMS circuits will eventually discharge packs.
This is different from what I was describing earlier about “Leaker” cells. They drop voltage merely sitting not connected to anything. Definitely something you want to avoid in your life.
izeman
1 GW
yes
izeman
1 GW
drop from what voltage to 56V?
have you disconnected bms and controller as we suggested to see if that would change??
you need to sort out one possible error source after the other.
i din't know why you don't do so and just wait ....
56V is dead empty for 20s lipo. voltage will go down to zero within hours now. you need to charge to 3.8V per cell immediately and start testing as we told you.
have you disconnected bms and controller as we suggested to see if that would change??
you need to sort out one possible error source after the other.
i din't know why you don't do so and just wait ....
56V is dead empty for 20s lipo. voltage will go down to zero within hours now. you need to charge to 3.8V per cell immediately and start testing as we told you.