£20 Ebike Battery

[jerrysimon]

Why don't you get a lipo setup? It would be lighter and because you won't use a lot of amps you should have several hundred of cycles out of it.

Although I have used lipos extensively in my RC hobby, for safety reasons I would not be happy leaving them unattended whilst charging at work or having them lying around in my house.

I know they are fine if treated with respect, but that's me.

My larger 3000 mile/two year old pack has over 750 cycles on it already. Technically these will out perform lipos cycle wise.

Regards

Jerry

 

[Geebee]

I must admit that crossed my mind as well, more capacity at lower weight and good c ratings,pre built, and not a lot different in price.

 

[cwah]

but you can have much more cycles if you use low C rate isn't it? I've heard up to 1000 cycles

 

[shemozzle999]

I don't know if your a BMFA member Jerry but in the latest news mag there is a reference to calculating true "C" ratings and a link to RCGroups, they are attempting to create a battery database, apparently this applies to A123 cells as well.

A simple LiPo performance tool - RC Groups

 

[smudger1956]

I am a prolific Lipo user, as outlined they do require some attention and respect, I have some RC packs I have been using in RC models purchased 2005,still working and balancing well, the next pack for my bike will be made from 5s or 6s1p 5000 mah packs.

As for Jerry's £20 battery....top marks for that.

 

[jerrysimon]

Thinking about it I forget that these cells were amazing when they came out in 2006/7 or earlier I can't remember. 30C then was amazing but I guess things have moved on and modern lipos would probably match/out perform them both C wise and power to weight.

For me still though its about knowing I can do what ever I want with them (within reason) without fear. If I was charging lipos at work and they caught fire (ok I know its unlikely) I would be devastated. Then again maybe lipos are also safer these days.

All I know is that they work for me and I am happy to use and abuse them

PS shemozzle999 use to be a BMFA member but I rarely fly RC any more. Thanks for the link I will read it through.

Regards

Jerry

 

[daniel.weck]

Great idea, especially with the smaller controller. Keep up the good work! (and continue to keep us posted )

 

[jerrysimon]

Daniel how are your A123 packs doing ?

Regards

Jerry

 

[Scottyf]

Great post as ever Jerry, Good to see some useful information.
Least with the cylindrical cells and Lifepo4 chemistry Even if you run them low or overcharge them all they do is heat up and you have some saftey margin even if you abuse them a bit.

Lipo isn't as kind. There alot better. I've had one of my packs hit 2.7v and its recovered fine. But it did puff and heat up considerably. I got rid of that cell.

Lipo can take some abuse but the chances of the cell being usable ever again is very slim.

 

[Cyclezee]

Absolutely brilliant thread Jerry, you are one talented ebiker

 

[jerrysimon]

Thanks John,

I have only been in this game just over two years and to give credit where it is due everything I have learnt has come from this and other ebike forums. I have made some great contacts on here from which I have learnt almost everything, the most enjoyable being wheel building

I do also have quite a few years in the aero modelling game, which has helped with battery pack constrution/choice I guess. These days though all my tinkering is with electric bikes.

Regards

Jerry

 

[neptune]

It would seem that there are financial savings to be made in building your own battery. Even if the initial investment turned out to be the same, there are long term advantages. There is a learning curve involved, but knowledge is never wasted. To the average consumer, a battery is a black box. If the BMS fails, or more likely a cell fails, then the whole thing is scrap. In a home made system, the BMS is built into the charger, and is less likely to be damaged, as it lives in a kinder environment. But if it fails, it can be replaced without buying new cells. Likewise, individual cells can be replaced. You can also build the size and shape of the battery you want.I shall be looking into this more closely.

 

[jerrysimon]

Agreed the big advantage in a DIY battery is you know how it was built and therefore as you say it becomes serviceable.

Obviously not for the average consumer but a big advantage if you are doing conversions yourself for family and friends.

I still wonder how many people are carrying larger expensive batteries than they need for most their trips.

Obviously there is a balance to having enough capacity so you don't exhaust your battery every trip and reduce its life span. But I would rather have two or three 2.3Ah batteries which I choose from depending on how long I expect my trip to be.

Adding 0.5kg or 5kg to the weight to a light weight bike makes a big difference. Fine if you have a big robust electric bike which you never expect to have to pedal under your own power, but putting a 5kg battery on a light weight bike seems like a waste.

Regards

Jerry