Problem charging Panasonic EKE007 NiMH battery for Lafree Twist

[brianandsusan]

Hi, new on the site although I have read lots of threads in the last year as I researched electric bikes. Finally two weeks ago bought a Lafree Twist on ebay (2002 vintage). Bike is great - took it out yesterday and got 35miles on full pedal assist which is brilliant. Battery was showing all five charge bars full but I put it on charge anyway for 2 hours to ensure it was fully charged before going out. Both the charger (SP1 type from METCO) and the battery felt fairly warm towards the end. On the ride ran the battery down until the power assist was auto turned off. The battery is now on single bar and blinks.

Now the problem. When the charger is plugged in, it flashes 3 times (which I think means it is on standby getting ready to charge) and then nothing else happens. The charger stays at ambient temp and no charge is getting through to the battery. There is about 30v on the lead to the battery and I can measure the same voltage on the supply line within the battery compartment. There is about 28v between the positive supply and a lead to the thermister (?) (orange wire in the SP1 charger lead). The battery discharge terminals read 23.5v.

The battery is a Panasonic EKE007 20 cell 6.5Ah pack. Looks like it dates from May 2010 (05/10 written on the pack). The battery was on the bike before charging so would have been at 2 or 3 degC so have wondered whether this is the problem. Also whether somehow in the initial top-up charge the thermistor overtemp protection failed.

I have tried to use another battery charger for a 24v power tool but the output voltage doesn't exceed 22.5v so no sucess there.

Has anyone suggestions for what to do next ? Assuming it is the batteries I have damaged I am happy to start dismantling the battery pack.

Thanks
Brian

 

[shemozzle999]

Hi, new on the site although I have read lots of threads in the last year as I researched electric bikes. Finally two weeks ago bought a Lafree Twist on ebay (2002 vintage). Bike is great - took it out yesterday and got 35miles on full pedal assist which is brilliant. Battery was showing all five charge bars full but I put it on charge anyway for 2 hours to ensure it was fully charged before going out. Both the charger (SP1 type from METCO) and the battery felt fairly warm towards the end. On the ride ran the battery down until the power assist was auto turned off. The battery is now on single bar and blinks.

Now the problem. When the charger is plugged in, it flashes 3 times (which I think means it is on standby getting ready to charge) and then nothing else happens. The charger stays at ambient temp and no charge is getting through to the battery. There is about 30v on the lead to the battery and I can measure the same voltage on the supply line within the battery compartment. There is about 28v between the positive supply and a lead to the thermister (?) (orange wire in the SP1 charger lead). The battery discharge terminals read 23.5v.

The battery is a Panasonic EKE007 20 cell 6.5Ah pack. Looks like it dates from May 2010 (05/10 written on the pack). The battery was on the bike before charging so would have been at 2 or 3 degC so have wondered whether this is the problem. Also whether somehow in the initial top-up charge the thermistor overtemp protection failed.

I have tried to use another battery charger for a 24v power tool but the output voltage doesn't exceed 22.5v so no sucess there.

Has anyone suggestions for what to do next ? Assuming it is the batteries I have damaged I am happy to start dismantling the battery pack.

Thanks
Brian

Welcome to Pedelecs.

A quick search threw up this site - I have no idea how good they are though:

http://www.batteryfix.co.uk/contactme.htm

You could see if they could help solve your battery problems although they look as if they are overloaded with work at present.

 

[flecc]

I'm familiar with the Metco charger which was supplied with the Lafree during 2003 after the original Panasonic charger for the unit was found to be failing prematurely. However, I don't recognise the three flashes you are getting on plugging in to charge.

These problems on the Lafree are usually due to an open NTC thermistor circuit or a faulty charger. The 2 volt difference you've measured is rather low and probably wouldn't permit charging since it indicates the thermistor sensing the end of charge temperature of the battery.

One thing you can do to check if the thermistor is at fault is to wire a 10k resistor in place of the thermistor which should then allow charging if the charger and battery are otherwise ok. If that doesn't allow charging to start the problem is probably elsewhere. A suitable replacement for the NTC thermistor in the Lafree series NiMh battery is Radiospares RS 151-237. The characteristics are R = 10k, B = 3914.

I very much doubt you will have damaged the battery, so checking all the connections throughout is the next best move. You'll see some useful information on this recelling page of my Panasonic support site. The illustrated battery is an original with it's meter case mounted, but your 2010 one may be one made by a sub-contracted supplier and have the meter mounted on the battery pack. Otherwise there's no difference.

This other page gives some charger information and the User Instructions link at the foot gives useful information on the charge connector wiring.
.

 

[brianandsusan]

Flecc, Thanks for the advice.

The existing thermistor resistance at room temp, say 21 degC, is 7.5k. I put in a nominal 10k resistor (actually measured 7.5k) but charger did the same thing - 3 flashes and then nothing. Ditto with a thermistor (nominal 15k) which measured around 20k. On open circuit the same.

The thermistor circuit is entirely separate to the charging circuit, with a supply voltage about 3v. There are four wires in the charger supply line, 2 for 30v charging circuit, 2 for thermistor circuit. The voltage across the 20k resistor was about 3v, across the 7.5k resistor about 2.4v.

Visually all connections within the battery pack look fine although I have not stripped off the shrink wrapping yet. Next step I think is to open up the battery charger. I don't know much about battery chargers but I guess there is also a thermistor in this which protects the charger from overheating so I will look at this first.

Thanks

Brian

 

[flecc]

That battery thermistor at 7.5k at room temperature seems ok. Although these have always used the four connection system, you may find that one side of the thermistor circuit is commoned to earth somewhere. It was on my one that was supplied with the Panasonic charger in 2003 and you may have noticed I've advised using it as a three wire system when buying replacement chargers like the Powerstream one.

My Panasonic charger quickly failed like all of them and later in 2003 I was given a Metco SP1 to replace it and that worked fine as a three wire system. I have heard of some instances of the Metco charger also failing so that's certainly a known possibility. I never opened the Metco, but the Panasonic charger was typically for them fully encapsulated with no repairs possible.
.

 

[brianandsusan]

Flecc,
Having trawled the site I have found a similar problem in May 2009. aaannndddyyy reported the same three flashes on the charger and no charging.

Can't see how to send a question direct to a member on the site as I was wondering how he solved the problem. According to the METCO website they still make the SP1 charger - it is labelled as a SN20 producing 2A (whereas the SP1 I have says it does 3A) but I can't find a UK retailer. The US company Powerstream site says it is not stocked. They stock an alternative charger PST-N100-24V which looks suitable. They supply alot of interesting information with it including a good description of the requirement for a thermistor, which is a 10k, B=3950 type.

There are other chargers out there for 24v applications which look potentially suitable, e.g. a Panasonic EY0110B 31 7.2v-24v Universal Charger for Ni-MH which is available in the UK - can supply up to 32v. I think these chargers are intended for the power tool market, but unless there is an issue with the thermistor system it would appear one could used for the bike battery.

Also available are Mascot chargers which are sophisticated chargers but they don't appear to use the thermistor circuit in the battery. Logic to this is, I think, the voltage is monitored and controlled such that the battery pack cannot overheat.

I opened up the charger and I am impressed with the number of components within. All look in good condition and testing the board is beyond my abilities. Charger appears to be 2007 vintage. Reading up on chargers shows there is a wide range of chargers with different levels of sophistication, reflected in price level.

Do you know whether anyone has had success in using a general NiMH charger for these batteries ?

Thanks

Brian

 

[flecc]

Yes, the Powerstream PST-N100-24V is what I recommend on my Panasonic support site, and you'll see all the information on this webpage with connector information linked to there.

I've tried a number of different e-bike chargers and only the Powerstream one works off the shelf with the Lafree batteries. It has no refresh function but that isn't important. When buying watch out for the postal charges, it defaults to the very expensive UPS option. Scroll down in the buying process pages and on one you'll see the range of post options. USPS is cheap and ok, taking about 12 days to reach you in my experience

The Metco SP1 you've seen is not suitable, if you look beneath your one you'll see an overlaid paper label, it being a temporary modified SPI exclusively for the Lafree, pending Panasonic correcting their own design. Hence the current difference.

Incidentally, member aaannndddyyy had that problem with my ex Lafree that he bought from me. He doesn't currently come into this site so probably won't see a message. I can't remember offhand from that time but he probably also bought the Powerstream charger.
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