Beagle123 wrote:[size=18]Hey xter:
I wandered over here to your thread to check out your batteries, and I got caught-up reading about your bike. Its really awesome.
Thanks, Beagle. Hundreds of hours of work and experimentation went into it -- like I imagine is true of your present ebike project.
When I first encountered this site about 6 months ago, it was the first one I read, but I didn't know the meaning of all the info. Now that I understand it, I'm really impressed with your results. 10 amps to go 20mph is excellent.
Actually, 10 amps buys me 26mph now. 5 amps buys me 20mph. Of course extraneous wind and road conditions make a huge difference -- so that's just an average. Because the voltage is higher than yours' (84v fully charged), the amps needed to go X speed are proportionately fewer.
I think it was a huge gain switching to a 20 inch tire. I always favor smaller tires for all ebikes because we use motors that spin at 3000 rpms, so we're always gearing down. It seems like you ccan never gear down enough. In your case you really benifited.
This chart shows that you hit your max efficiency at 40mph (top speed) I think that's an indication that the smaller tire really helped. WIth your bigger tire, your bike must have been running at lower efficiency--perhaps 85% because that would coencide with about the 33mph level. In my estimation, an eve smaller tire could offer a little more power and efficiency (not that I'm suggesting you switch again).
Efficiency gain was part of the reason I switched. At the present voltage, the motor is about wound-out at 35mph, which is about the fastest I ever ride anyway. So gearing it faster with the previous 24" tire was a waste of power.
In one post you said that you were able to get about 30 amps from your packs, but I could swear that I saw a post of yours earlier saying you re-soldered your connections and you're now getting more amps. WHat is your battery power status now?
The difference in max amps turned out to be caused by the controller's current limit wandering with temperature. Cold day, cold controller limit is 31 amps. Warm day or warmed-up controller limit is 35 amps.
Rewiring and resoldering the pack, and switching to better connectors, cut voltage sag from 10 volts at 35 amps to 6 volts at 35 amps. That extra 4 volts is like getting an extra 15p1s pack for free!
The individual cells are rated 1.5c (49.5 amps for the 33ah pack). For reasons discussed in detail in other threads, I prefer not to push these cells much beyond 1C -- particularly as they drain beyond 50% SoC.
it seems like if you drew 2C (is that realistic?) you'd be getting 66amps! That's 4500 watts!
My next mini-project is to re-FET the controller for 60-80 max amps, and have installed an adjustable limit so I can limit it to 35-40 amps until I can build a 23s4p emoli "sport" pack that can handle 80 amps. I'll build this lightweight, short range, high power emoli pack to be snap-on/snap-off modular, like my presents packs are. Then, I'll switch between the packs for short-distance sport rides, and long-distance cruise rides.
I don't do much off-road riding right now because of the bike's one-hundred pound weight, 40lbs of that is the batteries and boxes. The back box is on a rather fragile seatpost rack. I'm thinking if I can cut the bike's weight down 20lbs by using 92 emoli cells, all mounted midframe, I can go off-roading more.
Does that thing go 50mph now?
No, 40mph is the absolute top speed with a fully charged pack. It should top out at 45mph with the future 92v60a pack. But I'm interested in increasing the power not to go faster, but to climb the steepest paved and unpaved hills around here better.