Using 7.2V RC packs, to make a bike battery.

[newbike]

Hi, I have ordered a bike which is NIMH (i know everyone has Li-ion but I am familiar with working with NIMH, and dont trust Li-ion to last that long EG could be done in 200 charges).
I have ordered a spare battery but thinking way in to the future.

Could I connect 5X 7.2V race packs in series (serial) to make a 36V bike battery?
I have seen 6800mah in ebay, which is not huge but you could make a 2KG batter for around £70-80. Also all you would have to do is solder the odd cable + to - and your battery would be done and still shrink wrapped.

Would it be possible or have I missed something? is there any overheating cutoffs etc in an assembled bike battery?

 

[NRG]

Hi, I have ordered a bike which is NIMH (i know everyone has Li-ion but I am familiar with working with NIMH, and dont trust Li-ion to last that long EG could be done in 200 charges).
I have ordered a spare battery but thinking way in to the future.

Could I connect 5X 7.2V race packs in series (serial) to make a 36V bike battery?
I have seen 6800mah in ebay, which is not huge but you could make a 2KG batter for around £70-80. Also all you would have to do is solder the odd cable + to - and your battery would be done and still shrink wrapped.

Would it be possible or have I missed something? is there any overheating cutoffs etc in an assembled bike battery?

Yes you can. I use RC packs from hobbycity.com to power my Peugeot DIY conversion. However you must be aware of the pitfalls to this. RC packs can be leathal if abused, overdischarge a cell and you damage it, upon charging they can explode and burn with an intense heat. Modern RC packs from Turnigy are very resistant to abuse but they still have the potential to 'let go'.

You will also need to controll very carefully maximum and minimum cell voltage so some form of cell level based LVC will be needed and a compatible charger required to ensure max cell voltage is not exceeded.

Cell balancing will also need attention and whilst these newer RC packs hold balance exceptionall well they will require balancing at some point.

It may be better to simply get a Ping battery and charger and be done with it.

However RC batteries do offere great power and the highest density available.

 

[newbike]

I may look at Lifepo4 in the future then. Just try to manage the current ones well I suppose until I get to that bridge.

 

[NRG]

Alternatively, take a look at the A123 cells. Dan uses these as do others on here, they don't have the same power density ratio but they are very robust, can take the abuse and won't explode when things go wrong. I think Dan bought some recently in packs from Ebay....

 

[daniel.weck]

Alternatively, take a look at the A123 cells. Dan uses these as do others on here, they don't have the same power density ratio but they are very robust, can take the abuse and won't explode when things go wrong. I think Dan bought some recently in packs from Ebay....

I opted for the easy way:

http://www.pedelecs.co.uk/forum/electric-bicycles/6956-diy-stage-9-a123-nano-battery-pack-photos.html#post88165

Jerry Simon built his 36V packs from scratch (well, A123 cells already with tabs, I think...but that's all). Having spoken to him, he agrees that the solution above (6S packs already assembled) is more time and cost effective.

http://www.pedelecs.co.uk/forum/electric-bicycles/5098-building-small-a123-battery-pack.html#post64491