litespeed said:
I’m stuffing 17kw into a QS 205 3.5T motor and it’s a wonderful experience that continually puts a smile on my face every time I ride the bike. All I was going to add is if you want to “continue” to pump your 16kw into your 4T motor you will need ferro fluid and Hubsinks. You will also need a good controller and I can not recommend the Nucular 24F enough. It’s tiny and keeps the motor running the most efficient and coolest…..ask me how I know!
I would recommend NOT using regen in any way on a bicycle frame. Years ago I did what you are doing with a Giant DH Team bike frame. I straight cut the axle holes out the back (like a motorcycle!) and used “Doc’s” epoxy on drop outs. Worked great but not being clamping drop outs regen would allow the axle slightly move/rock and rounded the axle. I quit using regen all together. You’ll never recoup enough to make a difference on a bicycle unless you have thousands of feet in elevation change.
As far as the “battery in a backpack” I understand why you have to and that is a bummer. Since your using a low turn motor I don’t believe there is a reason to go 22s since you won’t/don’t need the speed. I like that it would lower the amperage but with 4 gauge cables coming from the back pack I think your overkill already. Not to mention the 5 lbs in 4 gauge cables from backpack to controller. As someone else has already recommended, I’d recommend you go to a 21700 Samsung 4000 35 amp or Molicel 4000 45 amp cell. 22s5p or 20s6p would be a bad ass pack.
Hope the bike turns out for you.
Good luck and be safe.
Tom
Thanks for an informative an well thought out answer!
I will get a motor with a temp sensor so I can keep an eye on temperature. I will most likely have to install ferrofluid and hubsinks down the line, but I am planning to start out without it.
I would consider that controller, but not for that price. $1650 will almost be the cost of my whole build! I have heard good things about the sabvotons you can buy directly from qs motors, and the 72150 (unlocked to 200A) and 72200 have really good price. They are sinewave and very customizable as far as I know. As I will buy my motor from qs, getting the controller at the same time is convinient.
At first, I planned to build my own 20s battery pack using molicel p26a or the molicel 21700's you recommend, and that would have costed me right around $1000 to build where I am (including making/buying a spot welder), but then I found a way to get my hands on a few eig c020 cells. They are 3.65v nominal 20Ah cells rated at 100A continous and 200A peak, building a 22s1p pack of these (80.3v nom, 20Ah) will only cost me about $700, and I don't have to do a lot of work building the pack as they are big cells. The reason for going 22s is that the limit of the sabvoton 72150 and the 72200 is 95v, making 22s the highest I can run while charging the cells to 4.2v. 20s would be enough speed wise, but I like the little extra capacity 22s gives me, as well as the slightly improved torque higher voltage gives (the extra 2 cells will probably provide more than enough extra voltage to cancel out the voltage sag from drawing 200A from a 20s pack).
Not using regen without clamping dropouts seems wise, I have read of others rounding axles or dropouts from it as well. The kona bear dee lux seems to have removable (thru-axle) dropouts, so I would ideally be able to make my own clamping dropouts (maybe supported on the chainstay) to put on the bike, and in that case, I would use regen, otherwise it seems to be a dumb idea.
What gauge cable do you use? What gauge do you think would be optimal for about 60A continous, 200A max?
Thank you!
