Chargers and battery technology

[Geoff Sleath]

I'm fairly new to eBikes but a fairly experienced cyclist and adequate mechanic. My professional background is as an electronics design engineer though long retired so quite out of touch. My other pastime is aeromodelling with an interest in electric flight and I've converted several models designed for liquid fuelled (methanol/oil/nitro mix) engines to Lithium Poly (LiPo) energy sources. These are lower voltage (3S to 6S - nominally 11.1 to 22.2v) but much higher currents than is common on eBikes (maxima are 40 to 70 amps - 400 to 1,400 watts) but much shorter durations.; I aim for around 10 minutes flights for a scale model weighing from 2 to 4 kgs.

Now to my problem. I've mislaid the charger for my Cyclotricity 36v battery on a front wheel conversion kit I've fitted to my bike. One from the supplier seems to be very expensive for what appears to be a fairly rough 36v 2 amp (nominal) DC source. Having damaged a radio control transmitter by trying to recharge it with my 'intelligent' LiPo/NiMH charger rather than the wall wart charger supplied because there is a controlled charger built-in rather than a direct connection to the battery as used to be common, I'm wary of using a different source.

What I'm wondering is if there is a built in charge control circuit in ebike batteries that simply needs a rough DC source as a supply or is the supplied charger more than simply a transformer and rectifier? I do have a charger for my wife's bike so I'm not totally stuck and I also have a charger for an electrified Airnimal Rhino which has a Panda bottom bracket motor but that gives a specification of 42v even though it's for a 36v battery. I'd normally be happy to experiment but the cost of damaging the battery is too high.

Incidentally I'm very impressed with the Cycotricity supplied conversion kits (I've done my own, my wife's and a couple of club mates) less so with the Panda bottom bracket set up.

Geoff

 

[Andy-Mat]

I'm fairly new to eBikes but a fairly experienced cyclist and adequate mechanic. My professional background is as an electronics design engineer though long retired so quite out of touch. My other pastime is aeromodelling with an interest in electric flight and I've converted several models designed for liquid fuelled (methanol/oil/nitro mix) engines to Lithium Poly (LiPo) energy sources. These are lower voltage (3S to 6S - nominally 11.1 to 22.2v) but much higher currents than is common on eBikes (maxima are 40 to 70 amps - 400 to 1,400 watts) but much shorter durations.; I aim for around 10 minutes flights for a scale model weighing from 2 to 4 kgs.

Now to my problem. I've mislaid the charger for my Cyclotricity 36v battery on a front wheel conversion kit I've fitted to my bike. One from the supplier seems to be very expensive for what appears to be a fairly rough 36v 2 amp (nominal) DC source. Having damaged a radio control transmitter by trying to recharge it with my 'intelligent' LiPo/NiMH charger rather than the wall wart charger supplied because there is a controlled charger built-in rather than a direct connection to the battery as used to be common, I'm wary of using a different source.

What I'm wondering is if there is a built in charge control circuit in ebike batteries that simply needs a rough DC source as a supply or is the supplied charger more than simply a transformer and rectifier? I do have a charger for my wife's bike so I'm not totally stuck and I also have a charger for an electrified Airnimal Rhino which has a Panda bottom bracket motor but that gives a specification of 42v even though it's for a 36v battery. I'd normally be happy to experiment but the cost of damaging the battery is too high.

Incidentally I'm very impressed with the Cycotricity supplied conversion kits (I've done my own, my wife's and a couple of club mates) less so with the Panda bottom bracket set up.

Geoff

The charger must stop charging at the correct maximum voltage for your battery, for example 42 volts for a 36 volt battery. Not a milli volt more.
Chargers are cheap on ebay, though you must be careful that the right adapter and polarity are either ordered, or you change it yourself.
https://www.ebay.co.uk/itm/Li-ion-lithium-Battery-Charger-for-electric-bicycle-e-bike-36V-36-volt-42v/273504086555?epid=18022932801&hash=item3fae1d2a1b:g:2wIAAOSwO1pbQ44O:rk:1:pf:0
Best of luck.
Andy

 

[vfr400]

You can use any standard 36v lithium battery charger that has a charge current around 2A and a charging voltage of 42v. The only thing to watch out for is that the polarity on the connector is the right way round. It would be very unusual to have a reversed charger connector these days, and I've never seen or heard of one on a 5.5mm jack like you have, but for peace of mind, it's only a 2 second check.

 

[Geoff Sleath]

Thanks, Andy

I know the Lithium Poly (and presumably Lithium Ion) charge regime is a constant current voltage limited one and on the LiPos I use a lot of (I'm charging a load right now for my model aeroplanes) the fully charged voltage is 4.2v. I guess the voltage for Lithium Ion is similar even though their nominal voltage is 3.6v/cell rather than the 3.7v/cell with which I'm more familiar.

That one you pointed to on eBay looks OK and really similar to the Panda one I already have. I'll check the polarity, of course. However I would still like to know if there is a charge control circuit inside the battery shell (it's a rear pannier rack mounting version). What does concern me a little is the lack of a balance feature. I have some very exotic chargers for my LiPos which ensure each cell is charged to the same level and also measures the Effective Series Resistance (ESR) of each cell (a good one is around 5 milliohms and higher than 10 milliohms means they're almost scrap). Of course my aircraft draw a lot more current than the measly 8 amps my 250 watt bike motor does.

Geoff

 

[Geoff Sleath]

Thanks vfr400, that's reassuring. I've not checked the polarity but centre positive and outer shell negative is the most likely.

Geoff

 

[Laser Man]

What does concern me a little is the lack of a balance feature.

With bike batteries, the electronics for cell balancing is normally fitted inside the battery pack - not part of the external charger itself.

 

[wheeliepete]

Your Panda charger will be fine to charge your Cyclotricity battery, just make up an adapter lead to convert from 5.5 mm jack to whatever connector your Cyclotricity battery has, observing polarity, then you can use it for both. You may need to open the battery to check this.

 

[Andy-Mat]

With bike batteries, the electronics for cell balancing is normally fitted inside the battery pack - not part of the external charger itself.

 

[Geoff Sleath]

Great, that's what I was suspecting but it's good to get confirmation. My fancy LiPo etc chargers are only rated for 8S packs anyway so wouldn't be much use with the 10S (or 12S) used on eBikes. Though I do charge at 1C which can be up to 6amps on my bigger packs. Some people charge faster but I prefer caution.

I actually tried the Panda charger earlier this evening and it topped up the battery on my bike OK. So I'm happy that I'm in no danger of doing harm. Thank you all.

Geoff