Battery balancing problem

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
Read through everything. Not SURE I'm following it all, but I think my focus would be on the fact the charger is shutting down at 50v or so, when it shouldn't shut down until 54 and change. Is that true? If so, and that could be verified with a voltmeter, that would have me looking to replace the charger....
 

Carlosebermudez

New Member
I'm already talking to the provider in aliexpress, they asked for multimeter tests, etc. Waiting for the answer. The problem is the language barrier is very high and they take forever to answer.
 

Gionnirocket

Well-Known Member
Read through everything. Not SURE I'm following it all, but I think my focus would be on the fact the charger is shutting down at 50v or so, when it shouldn't shut down until 54 and change. Is that true? If so, and that could be verified with a voltmeter, that would have me looking to replace the charger....

The charger is shutting down at 54v.. Acceptable.
The battery is shutting down at 50v during use. Problem
 

Gionnirocket

Well-Known Member
I'm already talking to the provider in aliexpress, they asked for multimeter tests, etc. Waiting for the answer. The problem is the language barrier is very high and they take forever to answer.

Who did you buy from?
I got mine from Greenergy and though I haven't had any real problems they come across as helpful and trustworthy. Had a missing tool and they sent it out really fast shipping. Answered all my questions before and after sales.
I found when communicating with Aliexpress it's best to use simple English and keep your messages as short and to the point as possible.
If I were you... duplicate the problem and make a video showing it cutting off at 50V on the display and also measuring the battery with a multimeter. This should help expedite things.
 

harryS

Well-Known Member

Gionnirocket

Well-Known Member
There are a few sellers, Greenergy being one that have service in the USA.
My battery shipped from the USA and was one of the reasons I chose to buy from them.
 

harryS

Well-Known Member
One thought. What's happening when the battery resets? Are you pulling throttle up a hill, or using heavy acceleration? Your typical display voltage readings might catch a voltage sag, but isn't fast enough to capture the actual dip that triggers the BMS to reset the battery.

In fact, many displays filter the voltage so it appears more stable. Otherwise customers get confused and complain about something that is normal,

I think you have a weak cell in your battery. Tom J. and I would simply pop in a known good spare battery and confirm that. So would a decent e-bike shop, One could also put in a $15 RC wattmeter, which will log the minimum voltage.

How do you prove it to aliexpress. Get their OK to open the pack. Check all 13 individual group cell voltages,
 

Gionnirocket

Well-Known Member
One thought. What's happening when the battery resets? Are you pulling throttle up a hill, or using heavy acceleration? Your typical display voltage readings might catch a voltage sag, but isn't fast enough to capture the actual dip that triggers the BMS to reset the battery.

In fact, many displays filter the voltage so it appears more stable. Otherwise customers get confused and complain about something that is normal,

I think you have a weak cell in your battery. Tom J. and I would simply pop in a known good spare battery and confirm that. So would a decent e-bike shop, One could also put in a $15 RC wattmeter, which will log the minimum voltage.

How do you prove it to aliexpress. Get their OK to open the pack. Check all 13 individual group cell voltages,

The BMS shouldn't be resetting anywhere near 50v, especially with the large capacity he purchased.
So yes bad cell, bad BMS?
I don't think you need to be specific about the problem, just show that there is a problem. Hence the suggestion to make a video.
 

Carlosebermudez

New Member
Quick note.

Today I changes a few things, I lowered the speed limit to 25kmph (too low), and instead of using 9 levels of pedal assist, I set 5 to be the max. I did a similar run of 10km (6 miles) and the power dropped to 52. I was using the bike at a max of PAS 3 and on a straight road I throttle it to the max and for a brief second doing 45 kmph (27mph) The voltage dropped to 48v and it didn't shut off. I'm waiting for the rain to pass so I can take it out for a spin once again. Will check the voltage as soon as it dies.
 

Gionnirocket

Well-Known Member
Setting it to 5 PAS isn't much different. I believe that the 5 is equal to 1,3, 5, 7, 9 in the 9 setting.
What you should be watching as well is the current draw, the bottom half of your screen. You don't want to see a full scale for more than a burst and try and keep it under 50% for extended periods. You have to remember it is Pedal Assist, not a motorcycle.
 

Carlosebermudez

New Member
Yes, I'm aware of how the 1-5 vs 1-9 works. I only used the throttle for those few seconds to stay with traffic. I'm monitoring the watts and it never went above 750 for a brief second. All the ride was done between 250w and 550w. Still raining.
 

Carlosebermudez

New Member
So I took it for a ride this morning. Didn't charge it last night so I started the ride at 52v. I rode a PAS 1 which gave me a max watt output of 350w. On a steep hill I switched to PAS 2 and the voltage dropped to around 49.5 for about a minute. It didn't shot off. On a straight at a constant 50v it shut off. Got it home, checked the voltage, it reads 51.1 on the voltmeter and the display. I'm charging it to full.
 

Gionnirocket

Well-Known Member
Did you video it?
The battery is the most expensive part of your system as you well know, It really is your best bet to get Aliexpress to help you.
Do you have a link to the seller?
When was the unit delivered to you?
 

Carlosebermudez

New Member
Since I don't have a GoPro it is very hard to video it. Sending it back it's too expensive from my country.
Do you think it's a faulty battery?
I'm riding in a very hilly area and roads suck. Does the road conditions affect the battery that bad? All I got out before shutdown was 17km out of the pack.

The bike I used is a very heavy Mongoose, plus the pack I think it weighs around 60lbs.

Here's an example of the ride.

Screen Shot 2020-09-10 at 8.17.12 AM.png
 
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Gionnirocket

Well-Known Member
You don't necessarily have to be moving.. maybe you can duplicate the problem with the bike on a stand or even a propped up on a bucket and use your phone.
Conditions drain the battery faster but you are experiencing premature shutdown which sounds like a faulty battery.
Once it shutsdown it will probably happen again very quickly if you toggle the power switch off/on and continue without charging the battery.
Then it will be easier to video and show the measurement with a multimeter.
I don't know the policy with your country and Aliexpress, but you may be able to get something from them.
If Aliexpress doesn't want to help you and you paid by credit card, your bank may be able to help. But this will depend again on their policy and how long you had it.
Repairing it yourself is harder than most people think and can be dangerous if not done properly.
 

Carlosebermudez

New Member
I'm waiting for a response from the manufacturer. I will do a bucket test tonight, but when I throttle it by itself it only shows 20W being used. So it will be a long night.

The problem with returning it is that Aliexpress only allows me to open a dispute 15 days after delivery. Thats how long it took to get the motor after a shipping delay. So, I'm screwed on that side.
 
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Gionnirocket

Well-Known Member
Well like I said...
Ride it first to make it happen and then do not charge the battery. Then do the bucket test. That should speed up the process.
Be careful with the bike on the bucket... That motor has a lot of power 💪
See if you can have a strong friend help you.
 

Carlosebermudez

New Member
Now, what if a cell group is heavily unbalanced. Let's say 1 whole volt. How can I balance it? Will switching to a smarter BMS do the trick? Something I can program? I've seen some that show each cell on a computer or Bluetooth app. I noticed that I got it to go below 49v after letting it sit with the Key ON. I've seen videos of people changing damaged BMSs and it doesn't look like a complicated process. I understand the dangers of dealing with high voltages and amps.
 
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Gionnirocket

Well-Known Member
That is beyond what I would give advice on.
In my opinion if a new battery is that far off it has a defect and probably can't be fixed by balancing. It can also be the BMS which is defective.
The battery seems to be cutting off way above the low voltage threshold and that would leave me to believe that a cell group, if that is the problem is off by more than 1v.
Curious.. What is the battery configuration #S#P?
If you think you can handle replacing the BMS... Be very careful.
I'm not a battery expert, but in order for a BMS to balance/read each cell I am assuming it would require a wire to each end of every cell. I don't believe BMS's for this application are capable of doing so

Maybe someone with more knowledge on the subject will help you further..
 

Carlosebermudez

New Member
The battery is a 13s9p. I've been looking at some smart BMSs, they're around $50. I would have to open it and test each cell group to see what's going on. Let's see what the manufacturer says tonight.