Strange battery issues on powerbyke

[mutmost]

Hi all,
after a while of lurking and learning I have a problem with my 24 speed powerbyke battery.

The bike itself is about 8 years old and is a bit tired looking, lots of duct tape on the battery case and plastic parts. It has covvered about 3000 miles a year for the last couple of years and probably a couple of thousand in the previous years.

Issues which I have had have been the interrmitent power so improved the battery wiring to controller. I have also rewired the control board loom as the conntector was arching (soldered the loom directly to the board) I have also stripped the motor and given it a service.

But the issue which has me stumped is the current battery issue. I am on my 4th set of cells, the first (which came with the bike) were neglected and when i finally got round to using it for work they did not last long. The next set came direct from powerbyke and did 279 charges and covered about 5500 miles which I was happy with, the next set came from someone else who deals with powerbyke parts (and as the current set is back with him for testing and he seems like a good bloke I would rather not name at this stage). This set only covered 90 charges and 1800 miles but at about 40 charges one of the cells collapsed internally and the charger would not attempt to charge. The symptoms were no power (as if a connection was broken) and then power would be back as it nothing had happened then it would do this over a couple of days increasing on each ride 1-2, then 3-4, then 5 times plus and then it would not charge. One of the cells was replaced and up until the 90 charge total until it happened again everything was fine.

As this set had been split up and were diferent ages we came to an arrangement over a total new set. But at 20 charges in the same thing happened. i visited the supplier as he had never seen this before and thought I was making it up/ done something silly/ wanted to see for himself but on inspection he found nothing wrong and replaced the cell and charger. 25 charges further on it has just done the same and is going back for further testing.

basically has anyone got any suggestions of what could be causing this?

To give an idea the cells post ride when it happened this last time were 12.65 volts for two of them and the thrid cell (same one as last time) was 12.4 and will not hold a charge, if this cell is charged on its own it will get to 12.65 volts but will not charge with the powerbyke charge as a set and if you put a 12v bulb on it it will not light it. Left on charge overnight it was 12.04volts in the morning!

The cell that this has happened to is the last one (vertical one) in the powerbyke pack.

hopefully that makes sense and i look forward to any pointers anyone can give, i know i would like a new bike but not just yet or like this!

Thanks All

Mutmost.

 

[rog_london]

Hi there and welcome

From what you say I'm assuming that your elderly Powabyke (I think that's what you meant) is fitted with three SLA (sealed lead acid) batteries. Just to avoid a little confusion, these aren't 'cells' - each of them contains six cells which each accounts for 2 volts of the total 36. The cell is the basic unit of a battery, which is the assembly containing several cells, and that's what you're referring to.

Having got that out of the way, it sounds as though your problem is more likely to be mechanical than electrical. Your symptoms indicate that one particular battery (the one mounted vertically) fails, and if this keeps happening I'd be inclined to say it is not putting up with the battering it will inevitably get when the bike is being ridden. As you will no doubt know, an SLA is pretty damn heavy due to the lead it contains, and if it's not been manufactured to withstand a fair bit of vibration/bouncing about it may well fail, and the fact that it's been the same battery points towards this too.

Perhaps the 'genuine' Powabyke batteries were manufactured with this in mind. Alternatively, since you have replaced them, are they perhaps not too well packed in the case? This might allow some movement within the case while you're riding. The intermittent power does point to a mechanical fault within the battery - perhaps the electrode frame in one of the cells has broken free and sometimes you get a connection, sometimes not.

Moving on from that into the electrical considerations, you would not get away with replacing a single duff battery and keeping the others, even though they appear to be working fine. What happens is that the capacity of any battery (and especially an SLA) will fall away with use, even more so if you discharge it fully before recharging.

If you have a new battery with two old ones their charge state gets out of synchronisation. When you discharge to cut-off the old ones give out first and because the new one maintains its voltage as it's not yet flat, you tend to over-discharge the old ones before cut off occurs. This reduces their capacity even further. Then when you recharge, the old ones will top out before the new one does (maybe long before) but the charger won't know as the overall battery voltage will be low because the new one isn't yet fully charged. The older ones get hammered again with over-charge this time.

To sum up, it sounds as though mechanical failure within one battery is the source of your problem, and if that happens you MUST replace the complete set, and pack them out within the case so NO movement is possible.

I've mentioned this before in another thread so I won't labour the point, but the life of SLAs is much improved if you don't fully discharge them and you re-charge as soon as possible - immediately after riding if possible. Much better to take the charger to work with you (unless by now you've acquired a spare) and recharge there as well as when you get back home.

Rog.

 

[mutmost]

Rog,
Thank you for your reply. I awaited a response form the guy who is testing them before replying.

He has basically said the same thing and is replacing the batteries.

I am looking to build my own case with the plan for the batteries to all be horizontal this time and housed within a corrugated plastic case (think old estate agent sign). I am not sure what to sit the batteries on though so any suggestions would be welcome. I am thinking of the dense packing type foam and then to use the top two parallel bars to compress them onto the foam with maybe some small tie down straps (webing with a ratchet).

Thanks again.

 

[rog_london]

I am not sure what to sit the batteries on though so any suggestions would be welcome. I am thinking of the dense packing type foam and then to use the top two parallel bars to compress them onto the foam with maybe some small tie down straps (webing with a ratchet).

Thanks again.

I can recommend a computer mouse mat. I mean those thickish ones, obviously. They can usually be cut easily with scissors and they're dense enough not to squash down to nothing beneath the weight. Foam rubber, foam plastic or anything like that is not usually robust enough.

Rog.