Mystery power cuts

[tomtag]

After nearly 1000 trouble free miles I have just hit an issue that I can't explain & was hoping some of the vast experience here may be able to help me.
I have a MXUS XF08C rear wheel motor with KT controller & KT LCD5 display. Last night when riding home, about 5 miles in, the whole system suddenly shut down. I was using assist level 3 of 5. I then turned the battery off & on again & the system restarted. But only ran (at level 3) for around 30 secs, then shut off again. I then reset again & turned on, but went down to asssist 1, it then lasted 2-3 minutes before shutting down. It seems to be a load related issue, but neither the controller or motor were hot to touch, there were no mystery noises, or error messages or burning smells etc. No obvious damage to cables, connectors etc.
I did have a fall a few weeks back which tore the cable out of the throttle, but it has been working fine since that, so I don't think that is contributing.
I wondered if anyone had any ideas as to what may be happening or has seen similar before?

Many thanks in advance for any input.

 

[sjpt]

It sounds a bit like a failing battery, but I would expect that to degrade slowly rather than sudden failure. Also, it certainly shouldn't happen after just 1000 miles.

 

[matthewslack]

After nearly 1000 trouble free miles I have just hit an issue that I can't explain & was hoping some of the vast experience here may be able to help me.
I have a MXUS XF08C rear wheel motor with KT controller & KT LCD5 display. Last night when riding home, about 5 miles in, the whole system suddenly shut down. I was using assist level 3 of 5. I then turned the battery off & on again & the system restarted. But only ran (at level 3) for around 30 secs, then shut off again. I then reset again & turned on, but went down to asssist 1, it then lasted 2-3 minutes before shutting down. It seems to be a load related issue, but neither the controller or motor were hot to touch, there were no mystery noises, or error messages or burning smells etc. No obvious damage to cables, connectors etc.
I did have a fall a few weeks back which tore the cable out of the throttle, but it has been working fine since that, so I don't think that is contributing.
I wondered if anyone had any ideas as to what may be happening or has seen similar before?

Many thanks in advance for any input.

Matches failing battery. If you can manage to read the voltage whilst it is working, you will see if there is significant reduction as it fails.

Is there a spare battery you could try?

 

[Nealh]

Usually indicative of battery voltage sagging/collapsing under load usually age related or knackered cells with high resistance. If you have voltage readout on the lcd5 use it and watch the voltage to see what occurs.
The fact it is happening in PAS 3 one understands but also in PAS 1 isn't good.

 

[Nealh]

What battery type ?

 

[tomtag]

Thanks for the replies. The battery is a 36v 11.6Ah with Samsung cells. (I am just trying to remember which cells they were). I would be surprised if /disappointed if the battery is on the way out, as it has only done <1000 miles in 2 years. So not too many charge cycles, I haven't been overly cautious in looking after it, but haven't left it fully charged or fully empty for long periods. However it has had the odd month or two without being used. Would anyone expect that to be enough for it to be on the way out? I will try and watch the voltage and see what is happening. The day this happened, the battery did seem to run out a bit quicker than previously. If it is battery related, is there any way to try and bring it back to life, or is it past help?

 

[tomtag]

It looks like the lcd5 does allow a real time voltage display so will have a look at that too. Would it be that the BMS cuts all power when it sees the voltage drop, or would the controller be doing it?

 

[GLJoe]

I would be surprised if /disappointed if the battery is on the way out
...
However it has had the odd month or two without being used. Would anyone expect that to be enough for it to be on the way out?

I'm afraid what you have described is a VERY common problem. A thread like yours pops up pretty much every month here.
Note - its often seems to happen more in cold weather.
Also, it might (MIGHT) be a balancing issue, so running the battery down, then FULLY charging it up (and leaving the charger on for a good few hours after 'full' just to be sure), rinse and repeat a good few times, and you MIGHT be lucky and get it re-balanced that way. That's the first thing I would try before proceeding to open the battery up and measure voltages etc.

 

[matthewslack]

It looks like the lcd5 does allow a real time voltage display so will have a look at that too. Would it be that the BMS cuts all power when it sees the voltage drop, or would the controller be doing it?

A hub motor can potentially give a battery a harder time than a mid-drive because every start from rest, especially if in a high gear with not much help from pedals, is asking for max torque at min rpm, which means high current.

So giving it help to get started by pedalling in a low gear can help, as can setting a not too high maximum current in the controller if that is adjustable.

It only takes one bad cell to bring down a cell group, and one bad cell group so bring down the battery. So explore reputable repair routes. You might get quite a lot more life out of it for a manageable fee.

 

[matthewslack]

Thanks for the replies. The battery is a 36v 11.6Ah with Samsung cells. (I am just trying to remember which cells they were). I would be surprised if /disappointed if the battery is on the way out, as it has only done <1000 miles in 2 years. So not too many charge cycles, I haven't been overly cautious in looking after it, but haven't left it fully charged or fully empty for long periods. However it has had the odd month or two without being used. Would anyone expect that to be enough for it to be on the way out? I will try and watch the voltage and see what is happening. The day this happened, the battery did seem to run out a bit quicker than previously. If it is battery related, is there any way to try and bring it back to life, or is it past help?

To put a statistical spin on it:

Say 1 in a million cells fail early when used up to their maximum limits. Your battery is probably 10s4p, so 40 cells. So 1 in 25,000 batteries will have a 1 in a million cell. And if operating conditions go beyond manufacturer's limit, that 1 in million could come down quite a lot.

So there will be early failing batteries, just not so many that confidence in the product is dented.

Since it is only 2 years, even if out of warranty it might be worth asking questions of the supplier and manufacturer. I think I have read of positive outcomes in similar circumstances.

 

[Nealh]

As I mentioned we need a voltage reading from a meter when it is fully charged as that can give a idea if something may be amiss. Just because a charger light goes green or the battery says it is charged means little as neither give an actual reading.

 

[Nealh]

The cells are Sam 29e and 4 in parallel so a bit tight on higher current use in that config, 11a continuous is about there max draw before stressing them.
Which PAS mode is used the most and the controller max current rating ?

 

[donalexinder24]

hi

It sounds like a dying batteries, but I'd expect it to decay over time rather than fail suddenly. It shouldn't happen after only 1000 miles, either.

 

[tomtag]

Thanks all for the replies, been away the last couple of days so not managed to do any more investigations yet. Hope to later today or tomorrow. After reading all of the above though, I was also thinking that it doesn't seem to have been a gradual drop in performance, just suddenly one trip when it went wrong. So, it was the first longer trip since I had a fall, which although it didn't visibly damage the bike (except the throttle cable), it was a big impact. I was going around a corner fairly quickly and hit a wet manhole cover, my front wheel went out sideways from under me and I went down with a real bang. Could the above be explained by some kind of damage from the crash? If it could, could it be a connection between the battery & controller, or is it most likely to be something inside the controller?

 

[tomtag]

The cells are Sam 29e and 4 in parallel so a bit tight on higher current use in that config, 11a continuous is about there max draw before stressing them.
Which PAS mode is used the most and the controller max current rating ?

Hi NealH, I mostly use PAS2-3, sometimes 4 or 5 to get me home up a gradual hill if its been a long day, but rarely 5. I have never changed the setpoints of eash PAS level from the default. I think the controller is 7A/15A, but will open the box & check.

 

[Nealh]

The controller is 15a max draw in PAS 5 so PAS4 is 50%/7.5a and 3/33%4.95a and 2/20%/3a.
It is possible that the off if a hard off may have caused battery damage, one can only know by having the internal pack looked at. If a interconnector weld is sub standard then a shock could cause the weld to loose contact.

 

[Nealh]

Can you confirm the voltage reading of the battery fully charged ?

 

[tomtag]

Can you confirm the voltage reading of the battery fully charged ?

It is on charge now so will update as soon as charged. Its not been used since the problem happened & when I checked today just before charging, it was showing 2 (of 4) bars & 37.6V on the controller.

 

[tomtag]

Can you confirm the voltage reading of the battery fully charged ?

I have just checked after approx 6 hours charging and is showing 40.6v. Does this indicate anything? Thanks again.

 

[Nealh]

I have just checked after approx 6 hours charging and is showing 40.6v. Does this indicate anything? Thanks again.

Yes, it is a whole 1v short of being charged, if it doesn't reach at least 41.5/41.6v then it is out of balance or has a duff cell bank.
6hrs it should be nearly finished charging for a 11.6ah battery so looks like there may an issue.
Wait and see what the final voltage is once the charger goes green.