Battery or charger problem - advice please

[Bikerbob]

Hi. When it reached about 14 months old my Giant Suede started only doing about half the mileage it used to on one charge. Now I can't get the battery to charge at all. The charger is supposed to go into standby mode for a few seconds and then when it gets the message that all is well it should start charging. Mine just stays in standby. The manual suggests a blown fuse in the battery but this has been checked and is OK. Can't find any loose wires etc.

I'm wondering if anyone with more knowledge than me can suggest whether I should be going for a replacement battery or charger. I tend to suspect the battery - and if I guess wrong at least there would be some sense in having two batteries - but I would be gratefull for any (polite!) suggestions.

 

[flecc]

Hello Bikerbob

With Giant's Twist series bikes using Panasonic units and batteries, they've had persistent trouble with two generations of charger, and the characteristics have been like those you describe in every way, only part charging and this diminishing to almost unusable. It's quite rare for a battery to suddenly fail in this way, usually they almost imperceptibly very gradually lose their capacity and range, though it's not impossible for a cell to fail and render the battery useless.

Very difficult for you to faultfind for which though, but if you could locate another Suede owner you may be able to check if their charger starts to charge your battery. Could your dealer help you here in contacting another Suede owner, or even momentarily try your battery on a stock bike charger to see if charging starts? We do have a couple of Suede owners as members so with luck one of them might be within reach and see this thread.

If not, as you say, another battery could be useful anyway, and your present battery will be around halfway or so through it's life anyway and be quite a bit down on range.
.

 

[flecc]

P.S.

Do you have a multimeter and have an idea on how to use it, or know anyone who does?

 

[Bikerbob]

Hello Flecc, thanks for the very quick reply. I live in the Isle of Man and my friendly local Giant dealer hasn't sold a bike with a similar battery or charger to anyone else on the Island, so you can see the problem! He has been trying for a month to get Giant to send over a 'test' battery or charger so we can try it with mine. They keep promising to do so but nothing ever arrives, so I thought I'd seek advice on the forum. I'll give Giant a bit longer before tossing a coin. I'd read of the charger problems in AtoB mag and it could well be the charger as you suggest. Not much point in being left with two chargers and one battery though if I get it wrong. I'll let you know the outcome.

P.S. Just read your last post. No I don't have one but I know an auto electrical workshop that should. What should we look for? My own battery is flat and they don't have a suitable charger.

 

[flecc]

If you can take the charger and battery down to the auto electrical outlet, there are a couple of checks you can do. Hopefully it will be a simple three connector socket on it. The thing to do first is plug the charger in to the mains, than do these checks:

Check between the three connector pins for voltage. Across two of them there should be a charge voltage of around 39 to 44 volts roughly. Across the remaining connector pin and one of the first pins there should be a much smaller voltage of probably about 5 volts or less. The pin that was common to both readings is the ground connection. Carefully note which two pins carry that small voltage.

Now go to the battery and connect the meter to check for resistance across the corresponding connector pins you noted. It should give a resistance reading of anything from about 4 kOhms to 40 kOhms. This is the thermistor resistance.

If either of the charger voltages is missing, it's probably a faulty charger, though very occasionally they won't work without the battery's thermistor connected.

If there is an open circuit on those thermistor connections, the thermistor within the battery is open circuit and has failed. In that case, it's possible to either replace the thermistor if it's type can be identified, or it can be replaced in circuit with a resistor, usually a 10 kOhm will do, and future charging being done on a time basis to avoid overcharging.

Try those and let me know how you get on, so I can help further if necessary.
.

 

[Bikerbob]

flecc. Thanks again for your time and trouble. I bought an inexpensive multimeter as it is something I should have anyway. The charger does have three pins. Accross two sets I got about 56V and accross the other set 2.3V. I checked for resistance accross the two sockets on the battery which corresponded to the low voltage pins. As I put the probes in I got a fluctuating reading but when they settled I got a zero ohm reading. From what you said I think it seems that my charger is probably ok (thought whether it gives a full charge is another matter) but that the thermistor has probably failed. If you agree with that diagnosis I will probably buy a new battery but will think about fitting a resistor to my existing battery so I can use it to extend my range. I can't actually see anything that might be a thermistor. Apart from the socket there is a 5amp fuse on the in side and a 40amp one on the power out side. There is a plastic connector box on the out side but anything else must be buried inside the cell wrapping.

 

[Bikerbob]

Hello flecc.
This is my second post of the day - please see the above. After I had done all that - and taken your time - the bike shop phoned this afternoon and said that, after over a month of trying, a loan battery and charger had arrived from Giant. (Very good of Giant, just a shame about the delay). The upshot is that neither charger will charge my battery but both will charge the loan one, which more or less confirms the conclusion in my previous post. I'll charge the loan battery with each charger over the weekend and compare the mileages. Our efforts have not been wasted. At least I know that it is worth trying to put a 10 kOhm resistor in my old battery circuit in the hope of getting some more use out of it,though I'll buy a new one anyway. Thanks for your expertise. I'm pleased to know a lot more about the subject now!

 

[flecc]

A pleasure Bob. I'm pleased the Giant stuff turned up.

The thermistor is indeed buried inside the cellpack and is held in close contact with a cell somewhere near the centre of the pack. It consists of a tiny bead with two thin wires coming from it for the connections. Once you've seen it it might just have an ID marking. It's an NTC thermistor, which stands for Negative Temperature Coefficient Thermal Resistor.

In simple words, it's a resistor which loses resistance as temperature rises.

The reason it's used is for accuracy of charge cutoff. The voltage rise towards the end of cell charge isn't very sharp so it's difficult for the charger to read that and know exactly when to terminate the charge and avoid damaging the cells. In contrast, as the cell reaches maximum capacity, it's temperature rises sharply, the thermistor resistance drops just as sharply and that small signal voltage is let through to tell the charger to terminate. That's why your short circuit one is keeping the charger shut off.

Now you know the full picture of how it works and you can explain it to your dealer.
.

 

[Bikerbob]

Just in case anyone with a similar problem reads this thread I can report that I fitted a thermistor from Radiospares, part number 188-5256, and it works well.

 

[Carl]

I may as well add here, as it may be useful to others - it is highly unusual (apart from known problems as above) for a charger to be faulty.
If you get any sort of display (lights) on the charger, then you can 99% eliminate that as the cause of the problem.
Nearly all charging problems are down the the battery. Sometimes fuses blown, but the big majority because of bad cells/end of life.

 

[flecc]

My experience has been the same, the only charger problems I've ever known have been in the two Panasonic types that Giant used on the original Twist crank drive series.
.