Spring '10 Battery Build

[DerekG]

Pics to come in a bit but the rough idea is matching 9C's front and back... kinda like ??Methods?? dual burnout bike. Huffy frame solid as a rock after 850 miles... weighs almost 35 lbs without electronics but I'll trade weight for safety anyday

The rear wheel I grabbed used and worked on the dishing of it... got it to be really rideable which was a surprise as I never did anything more than truing before. (Linear pull brakes work great if that is a measure of how it is)

Anyways, tested around 6 miles with 2 controllers 2 throttles 2 batteries (36 volt sla and 36 volt LifePO4) and it was fun to ride, even at only 20 amps front and rear. Now here is what I want to do....

Build something using the existing motors and controllers (will switch out caps and fets on controllers if needed (22a ebikekit ones)) that will have a better top end and nice acceleration.

Top end around 35mph+ on flats would be needed (mainly to front for some of the really good road riders here)

Decent acceleration would be cool to have too obviously

Now the questions...

*Can I use one battery with common ground or will it have to be two independent ones? If they must be separate batteries then I may stick to just a rear hub and keep the front as a spare although I think Methods used really thick wire on the neg side between controllers and bat and didn't have trouble???

*I want to build / have built for me a battery which is still only 10-15aH for portability (need to take on and off bike so it doesn't get stolen/ take to class Would like it to be a max of 20 lbs for the sake of my rack too) but can put out more current. If we go dual setup then I have to figure I would want at least 30 amps or so at whatever voltage for each motor. If I stick to a single rear motor then 50 or so amps would be fine I'm sure (I don't want to have to get into replacing the phase wires as I'm generally easy on the throttle. I'm thinking either headways or A123's but you guys know a lot more than me. I prefer screw on connectors to solder only because I don't have a full workshop in my dorm and heading to the shop to make solder repairs is a pain. Having something really durable would be the big thing... don't want to tinker with it to make it work everyday.

According to ebikes.ca simulator I would need around 66v nominal which sounds like perhaps a cap upgrade but not a fet upgrade. Budget yet to be determined...

TLDR: Need a battery which will put out a good number of amps in a small package and will drive a 2807 9C (or two) around 35 mph on flats.

Thanks for all your help everyone on here... I think I converted a guy today Good to know what you are talking about when he starts asking questions

 

[Drunkskunk]

Sounds like a fun build

You can tie the batteries together. Infact I would recomend tieing them together to form one battery source from them. Or just using one battery. It would be better for the batteries and would be needed to use the same throttle.

You're going to need a bikker battery. LiCo would run the motors as 10amps, but only if you limited the motors to 20 amps each. A123s would too, but that battery would be expensive and heavy.
To run on LiFePO4 you needa minimum of a 66 volt, 20AH pack, and I would recomend a 40AH.

But I should also point out, a Single 9C with a 40AH controller would have the same output with more efficancy than two 9C's with 20AH controllers. There's not much point in 2 motors unless you're going for BIG power, beyond what 1 motor can do. So you likely need a 40AH battery as a minimum for LiFePO4, or 20AH of LiCo minimum.

As for controllers, go for 72 volt, 40AH controllers from the start. There's no point in modding a smaller controller when you can get right size just as easy.

 

[DerekG]

Yes it should be a very interesting build (Working with a local metal shop to custom engineer supports for the rear dropouts... even if they are stronger rear ones I don't want to be flying off

So yes, right now looks like I'll stick with one 9C in the back although I don't really like the way the weight is distributed. For this reason I liked how the front motor handled better even though they are otherwise identical

What if I went with something like Turnigy 4500mAh 6S2P 30C LiFePo4 Pack and got 8 of them to give me 79 volts nominal at 8ish aH. I never need more than 5 aH or so because everything is so short around here and 8aH at even 10C which is conservative for 30C cells would still be 80amps... more than I need. I could get everything plus a quality charger for under $750. Best part is that if I want 36 volts to go to class I just bring 4 packs for around 36 volts at 8aH... need a longer trip I configure to 36v 16aH

Anyone see anything wrong with this logic? I like the idea of a bag with several smaller packs vs one large one. This way if I have a pack which gives out down the road I can just replace it vs taking apart the entire pack and replacing cells.