Puzzling battery issues with a Luna Wolf battery pack

[audacibus]

First of all, hi to everyone, I just registered here.

About myself I just clocked a year working for Vene Rides, a e-bike and e-kickscooter shop in Miami Beach and I was arguably the best Tech in the area because the others were very bad haha. Happy to help with issues to people around here and do some work if needed.

Having said that, there is a lot that I need to learn and this is one of the issues that I have at hand that puzzles me.

I have a Luna Banana with a Bafang BBSHD and ludicrous controller. This is fitted with a Wolf Pack V1.

I believe the battery to be a 52v, so the charger says.

Battery holds charge and charger, a 52v Luna mini charger works it magic and slowly but steadily charges the battery and it takes a few hours to do so.

Starting with an allegedly fully charged battery and showing this way on display, I can ride about 16 miles and then the display shuts off and is all pedal back home.

This is a too low range.

I have contacted Luna and although they reply pretty quickly, they do not provide much as in way of solutions.

Today I bench tested the Luna and monitored the info closely, as opposed to be on the road and looking at traffic, then bike shuts down and then pedal home which is not a great experience, although it is way better than on a super73.

Bench test shows that the battery goes from stated 100% charge to 76% charge and then dies and cannot be turned on. Motor temperature is reasonable, so this is not an issue of the system shutting itself down or so.

Voltage checked on battery immediately after system shuts down is 29.5v and oscillates a bit up and down.

I do not know how to interpret this apart from that the battery is dying, and if the only solution is to buy another one.

For anyone who knows more than me, please chip in.

Thanks!

 

[markz]

Even within the same shipment the bms's can be different. There is such a wide variety of BMS'es out there and how they work is all a bit different and most of all a variance in the amount of power the BMS always draws, 24 hrs a day, 7 days a week. So if you left your battery at low voltage cutoff and or half charged and left for a year or two

- If it was stored outside for a year, temperature changes

- Does your BMS balance only at the top voltage

 

[99t4]

Looking at your overall situation from a further perspective, ANY purchase of a used ebike MUST be done with the mindset that the battery is toast and WILL need to be replaced, UNLESS you can specifically and precisely prove otherwise (real measurements). It should figure into the purchase price. Otherwise you fall victim to your own wishful thinking, or rationalization, etc.

Why? Many commercially available ebikes (and most inexpensive replacement batteries*) have batteries of poor quality to begin with, with marginal or sub-optimal capacity for their application, their riders "abuse" them by using them in the way that "seems" safe and appropriate but really asks too much from the battery that cannot deliver as expected without shortening its life. Also, most consumer-owners (as opposed to enthusiast-owners) do not know, for example, that leaving the battery fully charged for extended periods reduces the life of the battery. Similarly, over discharging negatively affects the battery life. It's not really their fault. The bikes are marketed with these expectations. Ride the bike, then plug it in so it is fully charged and ready for the next time. There are other common "normal" behaviors that are similarly abusive to the battery health.

So it looks like you bought a used ebike that needs a new battery. So what else is new? :?

I like it that you are doing the right thing by wanting to verify that the battery is in fact bad before disposing of it. We are too much a disposable society, too wasteful.

You have gotten several answers already:
Do your measurements with a VOM (measure at the battery output connector, with the batt switch on if there is one) CANNOT trust the display!

Leave it on the charger for an extended period (12hr. to 3-4 days, depending on the battery's BMS). This allows the BMS to balance the cells (lower charge cells can be brought up to the same voltage as the rest-- an unbalanced battery cannot perform at its designed capacity).

Open the battery up and measure individual cells (your battery is fully potted so not going to happen given your skill set)(not a slight-- just trying to keep your safe and sane).

And... given your descriptions, someone stated sure looks like a textbook example of some bad cells.

Most here are hesitant to direct you to a good replacement battery because there are too many variables. Variables within the industry. Counterfeit cells abound. Makers cut corners, on design, materials, components, etc. What was good and reliable yesterday just got bought out and is crap today. Materials shortages, supply chain disruptions (some never caught up from the Suez Canal backup!). Then there are the variables you did not supply: Controller amperages (nominal & max.), your weight, bicycle weight, desired speed, desired range, hills? All this is needed to go into the calculation for an appropriate battery. THEN add another 50% to ensure the battery does not get overworked, to preserve its long life, your investment.


* Tell the truth here-- you want to ask where you can get a "good deal" on a replacement battery. Or a "good price." Or even a "cheap replacement." Just rechecked, you sort of already did: "Any recommendation as to a non-wolf batt that is cheaper in price and with similar quality?" We all want a good deal but that will almost always result in a sub-quality battery. So caveat emptor: you will need to spend some time and effort to educate yourself on how to perceive and verify a good quality battery, there is no other way.

 

[ZeroEm]

audacibus » Spend some time here and read up on past threads and you can be the best shop tech for a while longer. It's also fun.

 

[LewTwo]

Open the battery up and ....

Did you miss the bit about it being a "Fully Potted" battery (i.e. encased in a solid Polymer block).

 

[99t4]

Didn't miss it, LewTwo, I was just listing the numerous suggestions that other posters offered. In fact, I recommended the OP not attempt it because the battery is fully potted.

BTW, where is the OP?

 

[fechter]

Back to the original question, if the battery is cutting off when it shows around 76%, most likely there is one or more cell groups that is going low prematurely and triggering the low voltage cutoff. This can happen if there is a defective cell or if the welds are bad or if one cell group has a steady drain from the BMS and causes it to be lower than the others. Since the pack is fully potted, there isn't a practical way to repair it. The pack may still be useful as a door stop or counterweight.

While fully potting the pack makes repair impossible, it is supposed to reduce the chances of failure in the first place.

 

[john61ct]

It is also possible to pot the cells with a lower density material to allow the pack to be deconstructed without damaging the cells.

 

[justlooking808]

i think you guys scared the OP away

if he's still at least reading this can you do an experiment for me. always wondered if this would work.

1. charge battery and measure voltage
2. put battery in freezer for 24 hrs or more
3. take out battery and let thaw to room temperature
4. test battery voltage and see if voltage changes
5. if voltage changed, repeat steps 1-4 until no change

after all that and no change in voltage, test battery and see if battery is restored to life?

could never test something like this cause no battery to test it on. but always wonder to what degree this would or would not work :lol:

 

[john61ct]

What would be the objective of such a test, how would the result be useful? ?

What chemistry? What temperature?

Link to the datasheet, look at the min temp rating.

If not **used** while "frozen" like that, should have little impact.

But with a lithium pack, **charging** it that cold may render it instant scrap. Depends on the C-rate as well.

 

[justlooking808]

What would be the objective of such a test, how would the result be useful? ?

What chemistry? What temperature?

Link to the datasheet, look at the min temp rating.

If not **used** while "frozen" like that, should have little impact.

But with a lithium pack, **charging** it that cold may render it instant scrap. Depends on the C-rate as well.

almost everywhere on the net says this would work for bringing a dead battery back to life. so just wanted someone to try it out to "validate" the "net". :lol: if can, can, if no can, no worries. :thumb:

 

[john61ct]

waste of time