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cell imbalance in new hobby king lipo pack

Posted: Feb 12, 2018 9:01 pm
by TimJ
I received my Multistar lipos from hobbyking the other day and had tested out all cells in each pack over the weekend. Out of the box, everything was at 3.75V +/- 0.05 except for one pack where one cell was at 3.6V. Based on what I read in Neptronix's Lipo tutorial, I felt like this is probably a bad sign for the pack. I filed for a return of this 4s pack with HK but they rejected the RMA request today. This was the response I received:
Hello, From the information you have provided, we cannot determine your battery as defective. Lipo batteries have a storage chemical in the cells when they are new. This chemical dissipates after the battery is used for 5 to 10 cycles of normal use. This is called the "break in period". This chemical can cause the battery to not balance well in the beginning. Therefore, I would respectfully ask you to cycle (actually use the battery then balance charge it , do not just discharge on the charger and then charge) the battery between 5-10 times and see what the individual cell voltage readings are then.
Does anyone know if this is accurate? It sounded to me like it could be a strategy to see if the customer can correct a manufacturing problem by doing repetitive balance charging, or to get them to give up on a return after an extended period of time.

I was wondering if I should even be using this pack when it will be connected with 5 other packs for a 14s2p configuration (20 Ah total capacity). Should I just buy a replacement and keep this one for powering accessories like lights, phone charger, etc.? I would appreciate any suggestions for how to deal with this. I'm glad I stayed with the 10Ah capacity instead of the more costly 16 or 20Ah. Something others may want to consider if this is normal for HK quality and customer service.

-Tim

Re: cell imbalance in new hobby king lipo pack

Posted: Feb 13, 2018 8:22 am
by dogman dan
I'd have replied the same if I was HK. You are asking for a refund way premature IMO.

Charge them, and see if they are balanced then. Only if one shows severe symptoms will you get relief. Puffed all to hell, demonstrated severe low capacity, or self discharging itself.

If you run them, and one is hitting lvc way before the other, that does indicate lower capacity. Sure, its a bad sign for it to arrive less than the others. It may have self discharged, and taken a year to do it. See if it self discharges much overnight before you freak out.

I think if you have a bad pack, it will puff by cycle 5 or so. Run it like normal, after a full charge and watching it a day or so to see if it does self discharge more than .05v.

Personally, the few times I got a bad pack, I just bought another. I DO like to buy in the spring, after china new years, when the stock is likely to be new. After most old stock is bought up. You might have gotten an early 2017 pack, and the rest from 2018 stock.

Re: cell imbalance in new hobby king lipo pack

Posted: Feb 13, 2018 12:48 pm
by motomech
Yeah, you worry too much.
Do what Dman said and if the brick puffs-up, take a pic and send it to HK.
the Multistars have a high turn-over rate and I suspect that one cell will fall in to line and everything will be ok.

Re: cell imbalance in new hobby king lipo pack

Posted: Feb 13, 2018 8:01 pm
by TimJ
Ok, good to hear that I am over-reacting. I had just read thru the Neptronix lipo tutorial (again) and it said early on that a difference over 0.10 volts was a bad sign, so I was feeling concerned. Whenever I buy something new, I want it to work perfectly at the start, so this is part of my reaction too... I'll do the initial balancing later this week, but it will be a while before I can get the bike together and be ready to go.

I ordered my Leaf motor on 2/5. They told me the next day that their shipping company took vacation for the Chinese New Year (2/16) and will not begin making any shipments again until 2/22! All shippers in the city are the same, so it'll be a couple weeks before I can put things together. I have a large report due at work anyways, so don't really have a lot of time to work on the bike right now.

Thanks, guys!

-Tim

Re: cell imbalance in new hobby king lipo pack

Posted: Feb 14, 2018 1:15 am
by 999zip999
I would like to know how things work out.

Re: cell imbalance in new hobby king lipo pack

Posted: Feb 15, 2018 7:32 am
by dogman dan
It is a bad sign, which is why you want to check it out with a cycle or two to get it fully full and balanced, then see how the cell behaves.

There will be inbalance of some degree, that shows when the pack is fully empty, at 3.5v or lower. At 3/6v and above, it should do better.

BTW,, I call anything up to .1v off balanced enough, though better is nice. So if its turns up .05 off, I call this perfectly normal.

If it continues more than .1v off, you do have a weak cell. Still usable, but the cell you want to watch when you check voltages.

Re: cell imbalance in new hobby king lipo pack

Posted: Feb 15, 2018 8:17 am
by TimJ
I'll post back when I have results. I will do a normal balance charge to full and then will be storing them for a little while before I am ready to use. Will monitor periodically. Without doing anything else, the one cell was down another few hundredths of a V, while the others remain strong, so I am expecting it may have a permanent issue, but I'll check it out thoroughly with actual use.

-Tim

Re: cell imbalance in new hobby king lipo pack

Posted: Feb 19, 2018 2:41 pm
by jordison
i have 14s pack made from 6s+6s+2s, the 6s they arrived betwen 3.78 and 3.8v, the 2s i bouth a couple months later and came with 3.9v, only after 600 cicles i had a problem with them, a bad cell in the 6s pack after not balancing or cheking them for several months of daily use . now has more than 800 cicles after replacing one of the 6s.

you should cicle them and not worry for now.

Re: cell imbalance in new hobby king lipo pack

Posted: Feb 20, 2018 8:21 am
by dogman dan
Again, only if you have self discharge that continues after the first 24 hours, do you have anything other than a normal, cheap ass hobby king cell.

Brand new, or after just a few cycles, holding at 4.18v overnight is a damn good cell!!!

My general experience is that a typical cell charges to 4.2v, then pretty quickly sloughs off surface charge to settle closer to 4.15-4.18v.

In year two, the worst ones might hold as low as 4.10v overnight, but most of them will still hang in there at 4.15 at least. By year two, you can balance out the whole pack at 4.2v, come back in the morning, and there it is, right where you found it before you balanced it. This is why I so seldom worry about anything less than .1v out of balance.


This is also part of why I generally test out new cells, then put them on a routine of charging only to 4.15v. It gives me .05v of wiggle room at top of the charge, and in general, results in little to no lost real world usable capacity.

Re: cell imbalance in new hobby king lipo pack

Posted: Mar 07, 2018 5:11 pm
by TimJ
I did several charge discharge cycles, with balance charging it and using about 4A discharge current using 6 halogen bulbs to provide the load. The bad cell was discharging below 3.4V when the others would only be down a couple tenths from wherever I started, and it was getting worse each time. I contacted Hobbyking again and sent some pictures showing the discharge voltage. They finally did warranty the battery, and should be sending a new one out. It was a hassle to get it taken care of with hobbyking: lots of emails back and forth, but all's well that ends well.

Now I just need to get my bike built! I have everything for the build now, except for a couple connectors that I have on order, and there may be something else that will pop up before I get it all together. Will post something once I have it built, hopefully it won't take me too long...

Tim