Battery Cutting Out

[Eglwyseg]

My battery is 36v and have run it for about 20 times a year [ Summer Months] over 6 years now. The problem is, that although the indicator lights show the battery is fully charged, after about a hundred yards of gentle riding the battery cuts out completely. With the switch to off then back to on, the battery comes to life again.

It could well be I need a new battery but I have a feeling there is a faulty cut-out circuit somewhere but haven't a clue where to find it let alone attempt a repair.

Does anyone know whether these Lithium batteries can be serviced somehow to make them good again? Or perhaps someone can offer advice to do a D-I-Y to fix it.

 

[Deleted member 4366]

It would help if you told us exactly which bike it is.

 

[Eglwyseg]

The bike is a Marin so that is irrelevant as I bought a Chinese made, Electric kit for it and fitted it successfully myself. The motor is an "8 FUN" brushless motor.

The battery as I said is lithium and has a capacity of 9,000 m/a. hour.

It has been a really great piece of kit till now.

 

[Nealh]

The cutting out is due to voltage sag and the lvc cutting in as it should do, it is possible you have a low cell group that is out of balance or just had it. If you are up for it you could open the pack and check for your self with multi meter.
Being 6 years old it probably could do with a look at but most will just recommend a re - celling old for new with better cells or just get another ready made battery.

 

[Deleted member 4366]

The bike is a Marin so that is irrelevant as I bought a Chinese made, Electric kit for it and fitted it successfully myself. The motor is an "8 FUN" brushless motor.

The battery as I said is lithium and has a capacity of 9,000 m/a. hour.

It has been a really great piece of kit till now.

That's good background info but doesn't help us with the diagnosis. What sort of controls do you have: Throttle only, LED display, LCD display or something else.

 

[Eglwyseg]

The cutting out is due to voltage sag and the lvc cutting in as it should do, it is possible you have a low cell group that is out of balance or just had it. If you are up for it you could open the pack and check for your self with multi meter.
Being 6 years old it probably could do with a look at but most will just recommend a re - celling old for new with better cells or just get another ready made battery.

I think that makes sense so have gone for it and opened the case up to discover an inner case held together by triangular slotted screw heads at the bottom of steep sided tubes, These manufacturers definitely don't like us to look into these things do they.
Not a lot I can do until I can get a tool to open this inner box so can we consider my post closed for the time being. I will of course, open another post if I can make some progress with this issue and thank you all for your replies.

 

[Nealh]

Keep the thread going and just add to it as you go along, that way it all stays in one place rather then peeps going to another thread later.

 

[Eglwyseg]

Thanks, Okay, I'll do that. Been looking at triangular screwdrivers and most describe them as "security drivers" and used also on mobile phones and play things and some sources charging a fortune for them. My problem as you can imagine, I need a single size but unfamiliar with the new " security drive" thingy I should really order a set. I'll take your suggestion but holiday weekend, it may be time, when I get back, but I will post.

I suspect, when I, 'back engineer, this inner black box', I find a few wires, bus bar things and a small stack of torch batteries, perhaps, need replacing.

Be patient, I'll get back.

Thanks

 

[Eglwyseg]

Here we are again NeilH and d8veh.

I must relate this incredible tale first. I have looked all over for triangular screwdrivers but haven't been too impressed with the prices, some of them you'd need a mortgage. However, I finally got around to Amazon and found a set of four for about £11 plus some postage. I was very busy at home so put off the ordering. Today, in town, I wandered into Poundland to discover a set of 30 screwdriver bits with a driver, two of the bits were triangular and yes, one fitted my battery screws. They're actually a fairly robust set and took out the eight screws without bother, whatsoever.

Okay, back to the battery. There were 40, CGR18650CG, cells in all and all reasonably accessible to check the voltage. 36 cells measured 4.1 volts while 4 cells came out at 3.9 volts. Now this leaves my more baffled than when I started as I can't believe so less a value for just 4 cells would cause my problem, battery power dropping out after a hundred yards of very gradual acceleration?

The measured output voltage from the battery was 41 volts which I assume would be normal for a rated battery of 36 volts not under load.

There is a small circuit board inside the inner case, it is very well made and no obvious signs of poor soldering or broken components.

I would love to find a way to sort this bothersome problem but getting myself psyched more and more for a new battery.

If anyone has more ideas to explore then do shout.

Thank you again.

 

[Deleted member 4366]

I would love to find a way to sort this bothersome problem but getting myself psyched more and more for a new battery.

If anyone has more ideas to explore then do shout.

Thank you again.

You could start by answering questions instead of wasting your time making wild unsubstantiated guesses.

 

[Eglwyseg]

You could start by answering questions instead of wasting your time making wild unsubstantiated guesses.

"Wild unsubstantiated guesses" ... 'It would help if you told us exactly which bike it is'. Pot, kettle?

Okay, then let's give it a try. The control box is wired for pedal assist but I chose not to fit it as it would have meant my getting a longer bottom bracket to fit the sensors. Omission of this part, has never had adverse influence on the running of the bike for the last six years.

The bike can be considered as throttle only with three LEDs on the static part of the throttle grip, green, full battery then orange then red only, battery near exhaustion.

The LEDs have all shown, i.e. battery fully charged, when my cut out problem occurs.

The cut out has only ever operated when the battery was at the end of its charge.

The cut out is now operating on a fully charged battery.

Hope that might help.

Thank you

 

[Deleted member 4366]

Your battery didn't cut out if the indicator LEDs stayed on. They get their power from the battery!

 

[Eglwyseg]

Your battery didn't cut out if the indicator LEDs stayed on. They get their power from the battery!

I've put that badly. The three LEDs are present *until* the battery cuts out, then all three disappear on the cut out.

Battery power resumes and the three LEDs light up again when I throw the power switch to 'out' and then 'in' again.

 

[Danidl]

"Wild unsubstantiated guesses" ... 'It would help if you told us exactly which bike it is'. Pot, kettle?

Okay, then let's give it a try. The control box is wired for pedal assist but I chose not to fit it as it would have meant my getting a longer bottom bracket to fit the sensors. Omission of this part, has never had adverse influence on the running of the bike for the last six years.

The bike can be considered as throttle only with three LEDs on the static part of the throttle grip, green, full battery then orange then red only, battery near exhaustion.

The LEDs have all shown, i.e. battery fully charged, when my cut out problem occurs.

The cut out has only ever operated when the battery was at the end of its charge.

The cut out is now operating on a fully charged battery.

Hope that might help.

Thank you

.. with the additional information you now have re read Neath s post.
Your battery pack has 40 cells, in 4 parallel rows each of 10 cells in series.
Note that even when fully charged one of the paralleled groups is charging to a lower level than the rest. .. if might only be 0.2v but that is significant. If this set is below, it could well be that they are defective and will have only accepted a very small amount of charge before exhibiting full voltage. This would mean that in use they will deplete very rapidly, and their internal resistance will rise rapidly this triggering the lb control

Your battery is 6 years old, even if the number of charging events was limited to as you suggest about 120, age matters and also the nature of these charging cycles .. was the battery left in a depleted state over winters , ? Was the battery usually allowed to empty before recharging? Each of these will affect lifetime.
Why not reassemble the battery , charge it , measure the voltage run it until it cuts out and immediately or constantly measure the battery voltage. That will provide proof of the voltage sag.

 

[Eglwyseg]

.. with the additional information you now have re read Neath s post.
Your battery pack has 40 cells, in 4 parallel rows each of 10 cells in series.
Note that even when fully charged one of the paralleled groups is charging to a lower level than the rest. .. if might only be 0.2v but that is significant. If this set is below, it could well be that they are defective and will have only accepted a very small amount of charge before exhibiting full voltage. This would mean that in use they will deplete very rapidly, and their internal resistance will rise rapidly this triggering the lb control

Your battery is 6 years old, even if the number of charging events was limited to as you suggest about 120, age matters and also the nature of these charging cycles .. was the battery left in a depleted state over winters , ? Was the battery usually allowed to empty before recharging? Each of these will affect lifetime.
Why not reassemble the battery , charge it , measure the voltage run it until it cuts out and immediately or constantly measure the battery voltage. That will provide proof of the voltage sag.

.. with the additional information you now have re read Neath s post.
Your battery pack has 40 cells, in 4 parallel rows each of 10 cells in series.
Note that even when fully charged one of the paralleled groups is charging to a lower level than the rest. .. if might only be 0.2v but that is significant. If this set is below, it could well be that they are defective and will have only accepted a very small amount of charge before exhibiting full voltage. This would mean that in use they will deplete very rapidly, and their internal resistance will rise rapidly this triggering the lb control

Your battery is 6 years old, even if the number of charging events was limited to as you suggest about 120, age matters and also the nature of these charging cycles .. was the battery left in a depleted state over winters , ? Was the battery usually allowed to empty before recharging? Each of these will affect lifetime.
Why not reassemble the battery , charge it , measure the voltage run it until it cuts out and immediately or constantly measure the battery voltage. That will provide proof of the voltage sag.

The battery was nearly always empty before recharging but was never left depleted over any winter but you have just prompted a thought. Last winter the battery was left on the live charger for about five months, perhaps I've over cooked it?

I have just tried your suggestion to measure the voltage at rest and that was 39.6 volts. After a very gentle run the battery cuts out but the voltage was the same when I switched back on. It's not possible for me to monitor the voltage while running under load, that is, me riding it and opening the throttle.

I did try running the throttle fully open, just the wheel, free wheeling after having lifted it from the ground and the voltage dropped to 39.2 volts.

It really does sound I need a new battery, doesn't it?

 

[Nealh]

The one string of 4 parallel cells are already only reading 3.9v when fully charged so they have had it by the sounds of it and are sagging quickly to the lvc when a load is applied. You can try charging that one string of 4 cells manually via the jst connector to see if they will except more charge to match the others but will proabably bleed back after a couple of hours or so, if they refuse to accept more v's then your battery is ailing.

 

[Danidl]

The battery was nearly always empty before recharging but was never left depleted over any winter but you have just prompted a thought. Last winter the battery was left on the live charger for about five months, perhaps I've over cooked it?

I have just tried your suggestion to measure the voltage at rest and that was 39.6 volts. After a very gentle run the battery cuts out but the voltage was the same when I switched back on. It's not possible for me to monitor the voltage while running under load, that is, me riding it and opening the throttle.

I did try running the throttle fully open, just the wheel, free wheeling after having lifted it from the ground and the voltage dropped to 39.2 volts.

It really does sound I need a new battery, doesn't it?

Yes see Neath s posting below. Actually the best way to have treated your lithium ion battery is not to let it discharge fully but to charge it up after each use. Leaving it all winter in a discharged state not good also. Whether leaving it charging for a winter is good or bad would have depended on the nature of the charger. Some simple ones would have left it charging all the time and therefore under stress. Some would have gone dormant after charging the battery so would have been ok.
A defective cell or cells will have lost chemical activity and this appears as an increased electrical resistance, so when current flows there is a larger than intended voltage drop across that cell. When no current is being drawn they may well have the same voltage as an ok cell. This is why an on load test would have been better.

 

[Eglwyseg]

Between you, you have convinced me I need a new battery.

I see there are some monsters out there, for example, I see on eBay, a 15 amp hour for about £230. I'll continue to look around for a day or two but that does look appealing despite the huge price tag. Are these things to be recommended?

One thing I won't do in future, run the battery till flat then charge it, I will stick it on the charger after each run out whatever the length of time out with the bike, if that is better for the health of the battery.

For me cycling is a hobby and don't need to depend on a bike for work etc. so replacing a battery once in a while goes with the the hobby I guess.

It be be few days before I get the new battery but will keep you informed when it happens.

Thanks for all you comments, it has been very useful.

 

[Deleted member 4366]

Leaving a battery on the charger too long can damage it. General advice is not to store a battery in a fully-charged state, but leaving one on a charger will cause it to be at an even higher voltage, which wouldn't be good for it. Normally, it's nothing to worry about leaving you battery on charge overnight, but leaving it on charge for weeks or months must be damaging.

 

[Eglwyseg]

Leaving a battery on the charger too long can damage it. General advice is not to store a battery in a fully-charged state, but leaving one on a charger will cause it to be at an even higher voltage, which wouldn't be good for it. Normally, it's nothing to worry about leaving you battery on charge overnight, but leaving it on charge for weeks or months must be damaging.

That's something else I definitely won't do in the future, once charged it will come off the charger.

It's amazing how new chemistry comes along and the rules change but never really widely expressed,at least to some of us. In the lead/acid days it was considered good to keep a battery on trickle charge for weeks at a time.

As it happens I have a DPI quad copter and the batteries have circuitry that partly discharge the lithium batteries automatically after a week or so to keep them healthy, correlating your point I guess. Which now makes me realise I have probably ruined my own bike battery or helped it go that way.

However, I have had six years out of it, so perhaps my next could last ten years.

Thank you for your useful comment.