I just bought a new 14ah 48v li-ion pack from an ebay seller that I've used before (with good feedback). My prior two purchases were for 10ah 48v packs, which work as they should. The new 14ah pack only charges to 51v. I only used it for one ride, taking it down maybe 25% before recharging. It still shows 51v. I used three different 2A chargers and all work the same with this pack. I contacted the seller and he sent me info and a few charts showing how this pack is different from my last purchases, and how this pack has a different charge/discharge curve. I'm trying to figure out if I should return this while I can, or just use it as-is. I don't have a device to discharge it at home, so I can compare to my other packs, seeing if I'm getting the extra 4ah compared to my other 10ah packs. Any ideas?
New 48v pack only charging to 51v
- Thread starter dannytroy
- Start date
ZeroEm
1 MW
I maybe in the dark about something. If it is the same chemistry it is not even charging up to 80% (52.6V). I would guess the BMS is cutting it off early. Just my option.
raylo32
100 kW
Many battery sellers offer the option of different types of cells, such as high power (max current) and high energy (more watt hours) to meet different user needs. These will have somewhat different charge and discharge profiles, but for the same series number of cells they should still charge to the same max voltage. I agree, it sounds like the the BMS is malfunctioning or set up wrong.
The seller sent a very detailed explanation, but I'm not yet convinced. I'll test it against my 10ah pack and see if it does better. To me, it looks like the LVC will be sooner than the 10ah pack, but I don't have a way to test it accurately. The attached photos might help understand the pack, or possibly were created to get buyers to accept a lower quality pack.
Attachments
Wouldn't touch it with a 10' pole as they say, but if you're skeptical why not compare its performance with one of your other batteries by charging both to max, then measuring the voltage after the same ride distance. I realize there are variables in any ride, so not perfect but may help.
raylo32
100 kW
I would ask the seller exactly which brand and series cells make up the pack. Then independently look up their profiles.
dannytroy said:
docw009
10 MW
Let's make sure your meter is calibrated. Your 51 volts is measured with a meter that will show 54.6V on the other two batteries?
It could be that the seller has set up his battery to charge to 80%, or about 3.96V per cell, which gives you 51V on a 13S battery. No one is going to do that and be competitive. It's stupid, giving away 20% on the top end, especially on an ebay pack. I can't believe anyone does that.
AT the same time, I'm trying to think of a defect scenario where you can have a 13S 48V battery stop charging at 51V and still put out a reasonable capacity. I cannot. Not unless the BMS is set up like that or is defective.
You should know how long you can ride on a 10AH pack. You'll have to ride this one til it runs out and compare the miles. If you get the same, and I think you might, is that what you paid for? Also provide the ebay listing. What did he promise as far as AH and voltage. You only have a limited time to get paypal to step in, so don't delay.
It could be that the seller has set up his battery to charge to 80%, or about 3.96V per cell, which gives you 51V on a 13S battery. No one is going to do that and be competitive. It's stupid, giving away 20% on the top end, especially on an ebay pack. I can't believe anyone does that.
AT the same time, I'm trying to think of a defect scenario where you can have a 13S 48V battery stop charging at 51V and still put out a reasonable capacity. I cannot. Not unless the BMS is set up like that or is defective.
You should know how long you can ride on a 10AH pack. You'll have to ride this one til it runs out and compare the miles. If you get the same, and I think you might, is that what you paid for? Also provide the ebay listing. What did he promise as far as AH and voltage. You only have a limited time to get paypal to step in, so don't delay.
The seller seems to me legitimate and has great feedback on ebay. Also, he ships from the USA. I believe the two prior 10ah packs I bought were from a sister company, but it may all be the same owner. Here's the listing: https://www.ebay.com/itm/293213345157
As far as voltmeter, I used two different meters and they read the same lower voltage, as compared to my other packs. I don't get on the bike everyday, so putting enough mileage on two batteries to compare might take some time. The seller seems helpful and probably wants to avoid negative feedback, so I' pretty sure a return would be fine. As a matter of fact, I already printed a return label, but that was before he sent the tech info on the pack.
When I flew RC planes we used the discharge capability on the chargers to check for capacity. Unfortunately even though I have several RC chargers they don't handle anywhere near 48 volts.
As far as voltmeter, I used two different meters and they read the same lower voltage, as compared to my other packs. I don't get on the bike everyday, so putting enough mileage on two batteries to compare might take some time. The seller seems helpful and probably wants to avoid negative feedback, so I' pretty sure a return would be fine. As a matter of fact, I already printed a return label, but that was before he sent the tech info on the pack.
When I flew RC planes we used the discharge capability on the chargers to check for capacity. Unfortunately even though I have several RC chargers they don't handle anywhere near 48 volts.
The eBay ad says Cell Type : 18650 Cell Combination : 13 Series and 5 Parallel, although I didn't open the pack up to see what it really is. I hesitate to do that, since the return might get rejected. BTW, I tried 4 different chargers, all with the same results, and two different voltmeters. I have to do an endurance test to compare with my 10ah packs, and make a decision whether or not to return. Thanks for the advice everyone!
docw009
10 MW
I see a run-of-the-mill shrink wrap battery, 13S-5P. It should charge to the same as your other batteries, or about 54.6V. Clearly something wrong with it. It ships out of Texas. Ask for a replacement.
On further thought, It most likely has several cell groups unbalanced, enough cells involved to cost you 3 volts. Batteries like this don't have balance BMS. There's no way to unbalance it without opening it up, and manually charging the cell groups,
How do batteries get unbalanced? Defective BMS is likely answer. This one may have leaks in its monitor circuits and is draining the affected cells, or its monitor circuits are defective and stopping the charging early.
I would tell Paypal the battery only charges to 51V on three different chargers. It should charge to 54.6V. If you can ride the battery til it shuts down, that's more proof. It will shut down early.
On further thought, It most likely has several cell groups unbalanced, enough cells involved to cost you 3 volts. Batteries like this don't have balance BMS. There's no way to unbalance it without opening it up, and manually charging the cell groups,
How do batteries get unbalanced? Defective BMS is likely answer. This one may have leaks in its monitor circuits and is draining the affected cells, or its monitor circuits are defective and stopping the charging early.
I would tell Paypal the battery only charges to 51V on three different chargers. It should charge to 54.6V. If you can ride the battery til it shuts down, that's more proof. It will shut down early.
raylo32
100 kW
Exactly. Regardless of the profile it should still hit that 13S/54.6 voltage at full charge.
docw009 said:
I would guess it has a balance problem and one cell group is going high early and stopping the charge. Ideally, you'd want to measure the individual cell group voltages, but this usually means tearing into the pack. One way to restore balance, assuming the BMS is working properly, is to charge at a very low current and allow the BMS to do it's thing. Most cheap BMS units can only balance 50mA or less, so the idea is to limit the charging current to something less than this so it doesn't cut off when the first cell reaches full. This would require a bench power supply or placing a resistor in series with the charger to limit the current, then let it go for about a day.
I was planning on doing a trip today with both 10ah and the 14ah batteries. The same trip with each pack, weather permitting (and my lower back permitting). At this point I'm definitely leaning towards returning it. BTW....any idea on what value resister to use to bring down the charge current?fechter said:
I'd guess around 100 ohms. You can measure the voltage across the resistor when it's charging to calculate the actual current.
I once had a pack where one channel on the BMS shorted and completely drained the cell group. It would charge to a point and cut off. During discharge, the low group hit cutoff very early and left me pedaling home. If a cell group drops below about 2v, the cells can be damaged and become unsafe.
I once had a pack where one channel on the BMS shorted and completely drained the cell group. It would charge to a point and cut off. During discharge, the low group hit cutoff very early and left me pedaling home. If a cell group drops below about 2v, the cells can be damaged and become unsafe.
ZeroEm
1 MW
I would not take this pack off on a road trip until fixed or replaced.
Thanks for the replies..... I wound up returning it today. The seller asked me if I wanted a $15.00 compensation, if I wanted to keep it. No thanks. The last charge I did on it only went to 50.5v, so the pack looks like it's degrading. Not worth messing with.
