Mark42

I keep the battery inside during the winter and charge it periodically. This would be the third season it will be used. Battery is a Chinese 48v 20Mah Li no name. After charging battery, it was connected to bike and console won't come on and bike does not work. Tester showed 37v on battery. Hooked charger to battery and it indicates its fully charged. Hooked charger directly to bike and console came on normal, and twist of throttle made bike lurch. So put battery back on charger. Still not charging.

I know if the voltage is too low, the bike will not come on. I also read if the battery voltage has dropped too low, the charging circuit in the battery may not allow it to charge. I am confused that the tester shows 37 volts on battery, but when connected to a 36v lamp, it will not light.

Don't feel like dropping $300 on another battery. So I'm ready to tear into this one and start some diagnostics on the charging circuit. Any suggestions on where to start or what the solution is are greatly appreciated. I have the tools and ability to do soldering so that is not a problem.

Thanks!

prathmann

Can you take the battery apart and test individual cells? You may have one (or a few) cells that have failed and are keeping the battery from accepting a charge.

Nelson37

Describe the last charge before your last ride. Describe your last ride. Describe the vary last charge before storage. Describe how long ago, in days, weeks, or months, this was.

DETAIL ANY EVENT, ANYTHING AT ALL, THAT WAS IN ANY WAY UNUSUAL IN THE SLIGHTEST, THAT HAPPENED DURING THIS SEQUENCE.

Stop, think, read that again, think hard. With EXTREME frequency, this information points to the solution to the problem. Not always, but very often. If many posts from now you suddenly remember that your fat aunt Sally rode it uphill all day until battery shutdown, I am going to be exceptionally unkind.

If at any time you saw smoke, sparks, and possibly actual flame erupting from the main components, that would be important to mention. His name was Blinky88 and he waited until three pages in to make that statement.

SFAIK, the BMS can stop any charging when battery drops too low, it can also show an output voltage with no load present but cut power quickly once a load is applied.

Also it sounds like you have no seperate charging connector and charge through the output leads? This can have an effect on how the BMS operates under these conditions, so it is important to know this accurately.

Test charger for proper output voltage.

Next, CAREFULLY examine, use strong light and magnifying glass, ALL wires and connections from battery to BMS, both connections at each end, and wire length in between. Loose sense wire or connector is common cause of this issue. Look for any crimps or kinks in all wires. Continuity check might be useful.

Next is test individual cell strings and individual cells. This is way out of my comfort zone and beyond my skillset so I have no clue on specifics, but I know it can be done fairly easily.

Mark42

Yes, I can take it apart. That is my next step, just need to get some detail on how to test. I do have a multi meter.

Mark42

Last time the bike was used was last fall. Battery had been charged about 50 or 60 times by then over a two year period. Never ran the battery down to the point the console shut off. Battery was performing very well. I often made the same ride to the food store and back about twice a week and the battery performed consistently.

Battery was stored indoors and charged periodically.

No smoke, shorts, melting wires, etc. The motor controller is housed in a hard case saddle bag with air vents. When the bike is moving, air is forced over the heat sink of the controller and out the back vent in the saddle bag. It does get warm, but no much more so than when I rode with the saddle bag lid off. I also disassembled the motor controller after the first few rides to inspect the heat transfer paste between the transistors (I think thats what they are) and the aluminum housing that acts as heat sink. There was very little, so old was removed and new paste was applied (same stuff used on cpu to heatsink in laptops and desktop PC's.). This made the motor controller noticeably hotter to the touch, which is a good thing because the heat is being pulled out of the controller better than before.

On hills, I would peddle along with it to save power and reduce stress on the battery and controller.

Generally I kept speeds to 13 mph or less. Could easily go 50 miles round trip at 10mph, and 20 miles round trip at 15 to 18 mph. That performance did not change that I could tell over 2 years.

So now its time to cut into the shrink wrap that holds this block of cells together. Been looking at youtube videos, but not getting a lot of detail on this style battery.

This is the battery, assuming the BMS is on the end where the wires exit the block. Is that the typical location?

Doc_Wui

First, a disclaimer. If I can spend $300 to avoid it, I don't want a fire hazard inside my house. Poking around inside a lithium battery without expertise is dangerous. I've got some 12V lithium car starter batteries that failed. I took them apart and found water had corroded all the circuits, so they're stored in my outdoor barbecue grill til I get time to get rid of them safely.

It would be good to know exactly what kind of battery you have. I'll go out on a limb and assume you have a battery that uses LiFEPO4 pouch cells, because that 20AH is not a rating that is commonly available using the round 18650 cells. These pouch cells for a 48V battery would be arranged as a 16 groups of 2 cells per what these guys say.

37 volts is too low for LiFEPO4. That's an average of 2.3 volts per cell, which is under their safe value of 2.8 volts. When under the safe limit, the BMS won't let the battery work, either for charging or use.

So when you tear off the shrink wrap, see if you can determine the series groupings, Usually, they run wires from each group to a connector on the BMS circuit board, so that's a convenient place to measure voltages, if the wires and battery tabs are fully insulated,

You could have them all way too low, or most of the groups are OK and one or two groups are too low. They usually power the BMS circuit off two groups, and if left alone too long, those groups discharge below the safe limit. After you get the voltages, then you can decide on what to do next.

If any group is at 0, it's a fire hazard to recharge. if you discharge lithium too far, it forms metal deposits, and these later may short circuit, over heat and cause the dreaded lithium fires.

At some higher voltages, it may be safe to try to charge that group back above the minimum so the BMS will work again. I don't know what is a safe voltage. You want to check in on a battery forum for more expert advice. I have read that some users will put an individual charger on a group to recover it. This is something that has to be monitored full time. You can't fall asleep or walk away.

And be careful. Still enough power in that battery to burn down a house.

Nelson37

Reason I asked about the separate charging port is because that is often suggested as an alternate charging method which can bypass a disabled BMS, in some cases.

That does look like a pouch-style battery, charging it in the current state could be EXTREMELY DANGEROUS, this should be done outdoors in a grill or fireproof enclosure. Any fire must be smothered, sand recommended, do NOT use water or conventional extinguisher. If you haven't seen the videos, these are blowtorch-type fires, extremely hot, dangerous fumes, etc.

You are going to need to check each individual cell and likely replace some, or get a new battery. No storage, usage, or charge related issues indicated, so that leaves just failure of an individual cell or cells.

On the controller, most people use heatsink paste incorrectly. It conducts heat better than air, but NOT better than direct contact. The purpose of the paste is to fill any microscopic air pockets, the layer of paste should be extremely thin. You should be able to read through it. Heat retained on the components, most likely FETs, might actually be greater. Should be no effect on the battery issue, though.

Mark42

It's not a a lipo battery. Just lithium. Been busy, but hope to have time to cut into it next week.

Mark42

Heat paste should be applied paper thin. and that controller needed some. check your own controllers as this is a good way to extend its life.

01 CAt Man Do

First thing I'd do is take the battery out and take it to a battery store and have them test the battery. A battery store should be able to do this without charging you too much money. If the battery is fine then my next bet would be to consider buying a new charger. If none of that changes things then you have some other electrical problem, perhaps with the motor or the circuitry ( fuses or wiring ) that controls the motor.

All this said I'm thinking the first point of failure is usually something simple like the battery.

gsa103

How charged was the battery when you stored it?

Most likely the battery has self-discharged to below it's nominal threshold, and no longer safely charges. Self-discharge is a major problem especially for off-brand LiPo pouch cells. The devices are designed to be used regularly, so the manufacturer doesn't pay a lot of attention the self-discharge rate, which typically degrades over time.

Mark42

I think it is the battery too seeing as the bike runs directly off the charger.

Mark42

I believe at this point it is the battery BMS or a few bad cells.

But it is not a LiPo, it's a Li-ion.

LiPo is what I use in my RC airplanes. and yeah, they tend to burst into flames for no apparent reason.