Luna ga 14 ah shark pack

[Alan B]

+1 Fechter, this is why Luna's claim of 14Ah@20A, etc. are nothing but smoke and mirrors.

Alan, solid info ofc, but I think you missed that the 46V is OCV taken after the cells have cut off and had time to bounce back. He ought to be actually hitting 38V LVC accordingly.

"The already weak cell group is being repeatedly rammed to LVC, which is likely to cause further reduction in capacity."

is spot on in describing the recent sudden loss he mentioned at 11.x Ah. Thanks for describing that in detail.

I would not expect a bounce back that deep, and we don't have data to support that. Taking a voltage reading immediately at cutoff via the charging connector would be very useful to help understand what is going on. Individual cell group voltages would really be useful, if we could get those.

The data supports a deteriorating pack scenario, with increasingly reduced capacity, which is not the behavior of a healthy 4P GA cell pack (irrespective of any particular claims or expectations about pack capacity). Deterioration would most likely be a single cell group rather than the whole pack synchronously behaving this way.

It is true at higher currents that the capacity is reduced, but one of the reasons we like lithium is that it suffers from this effect very little with the varying loads of ebike use, which don't draw peak currents all the time. I often see essentially full (low current rated) capacity from a pack in ebike use, so I don't expect that is the issue here with these high quality cells. It also doesn't fit with the rapidly declining capacity data. It could be something like a marginal weld on one cell, or physical damage to one cell, or even just a problem with the BMS (which is actually more likely than a bad cell), the cells may be just fine, but an increasing imbalance could cause these results and a broken BMS may be unable to restore balance.

 

[liveforphysics]

Something interesting with the LG MJ1s and the GA cells was getting more capacity discharged in my cycle testing at 10A discharge than at 1A discharge.

That small amount of added heating bumps both those room temp 3.3-3.4Ah cells to >3.5Ah.

Likewise, when you cool the cells a bit it decreases notably (as is common with many types of cells).

 

[Alan B]

Something interesting with the LG MJ1s and the GA cells was getting more capacity discharged in my cycle testing at 10A discharge than at 1A discharge.

That small amount of added heating bumps both those room temp 3.3-3.4Ah cells to >3.5Ah.

Likewise, when you cool the cells a bit it decreases notably (as is common with many types of cells).

That makes sense, one time I fully discharged an 18650 triangle pack clear to LVC and got full capacity (and maybe a little more) from it, the pack was very warm - almost hot.

That was the result of not having good instrumentation, I rarely go that low normally. It is not consistent with getting long pack life to draw it so low and hit LVC. If the pack gets down to 10% it is time to shut down the motor and pedal.

 

[Alan B]

Hot cells have high output voltages as well.

 

[999zip999]

All it takes is one bad cell in parallel group or weld ? Your whole pack is only as good as your weakest cell. So to speak.

 

[Hillhater]

Either the LCV is set wrong ( can we confirm this is not a controller setting confusing things ?)..or the OP is hitting the pack too hard near the end of discharge.(yes, controller LVC was adjusted to 38V, and he tried using the lowest level of assist on his bafang unit)

Effectively these are 2C discharge rated cells with heavy voltage sag.
Either way, I will say this again ..GA cells are the wrong choice for the OPs stated riding style!< +1, despite what Luna suggests

Hi, I'm not sure where you're getting 3.18 (perhaps you meant 3.28V) or your discharge numbers, but you're not far off from what I gather. Rebounding to 46V OCV is quite near empty fwiw.

Yes, that was a typo..should have been 3.28..corrected now..thanks.
but the 3.0Ahr is the important point, that is much the same as the 12Ahr OP is from the pack.
sure 46v is quite near empty, but its not full capacity drained, there is still another 15% , 0.4Ahr in each cell , or 2Ahr in the pack.....if its well balanced !
..you can get the full 13-14 Ahr,.... just not at high loads.

 

[Hillhater]

Broke,..in amongst all those Ebikes and experience you have, do you not have a MMeter with max/min memory, ?
or a cheap wattmeter that does all that and more ?
or even a cellloger ?
any one of these cheap instruments could answer a few questions very easily.

FYI
with 11-12 Ahr used. that pack will be at about 48v resting
if you then try to pull 30A from it you will see 6-7 v sag..and unless that is a very smooth load, it can spike much lower.

 

[broke]

I gave away all that stuff with my LiPo batts. And charger

 

[broke]

Oops

 

[fechter]

What are you using to measure the pack capacity?

 

[broke]

Multimeter and satiator

 

[spinningmagnets]

So I think I have a dead cell

Thank you for being honest about this, and posting this info. It could happen to any vendor. I am sure Luna will swap out your battery pack, or provide a store credit if you prefer...

 

[Jon NCal]

Ok guys my pack is 55.6 I opened the pack and all banks are 3.7 except bank one that is 3.6
So I think I have a dead cell weAK bank I'm going to drain the pack to lvc and recheck my guess bank 1 will be way low. I hope they can send me a new bank of cells and I will just sodor it up

This doesn't add up, ie if your total voltage is 55.6 and then the individual cell groups are 3.7 x 13 groups + 3.6 = 51.7v?

 

[spinningmagnets]

Hey eTrike, if you look at my posting history, I've said a lot of positive things about several vendors around here who have proven to provide quality products and good customer service, based on what ES members have posted. So...if a friend of yours wanted to buy a battery pack, who are your top three vendors to recommend?

 

[Hillhater]

Ok guys my pack is 55.6 I opened the pack and all banks are 3.7 except bank one that is 3.6
So I think I have a dead cell weAK bank I'm going to drain the pack to lvc and recheck my guess bank 1 will be way low. I hope they can send me a new bank of cells and I will just sodor it up

Jumping to conclusions there i fear !
How do you know its not a bad bms channel that is not maintaining that cell group correctly ?
You could replace a cell group with new cells ( if the soldering doesnt damage them ?) and the bad bms would put you right back where you started !.
No, more checks are needed before you know what the solution might be.
First answer the question Jon Ncal asked, then check the accuracy of your measurements as SM suggested, then test the shit out of that bms !
Pesonally, i dont think there is anything abnormal with your pack ...i just think you are expecting it to perform like lipo !

 

[Green Machine]

Does it bother anyone else that etrikes (an obvious crooked ebike dealer) quotes endless sphere users and puts his comments in blue.....

I have never seen this done and seems like obvious abuse.

how is anyone suppose to know that the quote has been altered?

If you are going to quote a user you should not be allowed to interject your own comments inside the quote.

It appears to a first time user that the quoted user are saying etrikes comments.

 

[broke]

Oops

 

[Alan B]

If you charge for awhile you should be able to see if the BMS is working. 2.8V is about right for cell group level LVC.

If, after charging overnight, the cell groups are balanced, or close to balance then the BMS is doing its job.

If the low cell group shoots up to a higher voltage than the rest early in the charge cycle, it has reduced capacity.

If the low group has normal capacity it will follow the other groups up but stay behind them. Then near the top of charge the BMS should start balancing all the high groups and letting the low group catch up. If you map out the voltages at a few time intervals we may be able to see if the BMS is doing its thing. The balancing resistors should be getting warm when it is balancing.

 

[Alan B]

Yes.

As far as I know the Satiator keeps outputting the finishing voltage to allow the BMS to work.

There are so many "cases" that it becomes a bit hard to predict the possibilities, but if data is collected periodically we can learn something from it.

If this were my pack I would probably use a BC168 to balance it, 6S at a time, if the BMS has trouble. Though only the low cell group is likely to need individual charging. But let's wait and see what the data looks like.

 

[999zip999]

I would charge then check voltages. One low cell I would put a single cell charger on it as I was sitting there watching . I would fill that group up. Button up and get back on the road. Having an electrical ghost is no fun. Been there had it done with me. Hang in their.

 

[RickM39]

The Satiator shuts off when the "complete amps" are reached.

The charger outputs the set amps until the set voltage is reached, then reduces the output to hold the set voltage.

It then shuts off the charger when the complete amps are reached. The default is .15 amps.

If you want to hold the pack at the finishing voltage longer you can change the complete amps to a lower value.

 

[Alan B]

My experience with the Satiator is that it continues to put out voltage, while indicating "Charge Complete" (at least in a Lithium chemistry profile). The amp-hour display will very slowly climb due to the small charging current as balancing takes place.

From the Satiator Manual:

 

[RickM39]

Interesting, I missed that part of the instructions.

I'll have to experiment a bit to see how far the voltage has to sag before the charge is resumed.

 

[Alan B]

The indicated voltage of the Satiator doesn't change, so I don't think the output voltage changes.

The "charge resumption" they are talking about is the BMS cycling, when a cell group exceeds the maximum allowed voltage (typically 4.25 to 4.3V), the BMS will interrupt the charging. It will then bleed off the high cell groups to bring their voltages down. At some point it will reconnect to the charger to continue the charge which is not complete until the low cell group(s) are brought up to full charge and all cells are at the same voltage. Thus the BMS controls the charging cycle during the balancing.

If the charger shuts off at the first BMS disconnect then the BMS will not be able to complete balancing if more than one cycle is required. Balancing will then require many discharge/charge cycles.

Thus the Satiator is designed to facilitate the BMS balancing and allow multiple BMS cycles within one charge cycle, so it will be more effective at obtaining a balanced battery when combined with a properly functioning BMS.

 

[fechter]

The BMS will take forever to balance that much difference. Like days. And you'd need to make sure the charging voltage was set high enough so all the rest of the cells are shunting, which may be higher than the normal setting. It would be a lot faster if you could charge the low cell individually to try bringing it up to the same as the others. I'd do this after charging the whole pack. All the cells should be around 4.2V at full charge.