gdinim wrote: ↑
Aug 22 2018 2:10pm
Thank you I am just converting to electric propulsion so I have no experience I am reading as fast as I can.
I was under the assumption that the 300 Samsung would give me a 36V 75Ah S10P30 battery, are you saying that no matter what I am limited to the 20Ah discharge rate of each cell.
In your experience 2 x 500 watt motors would be inadequate for my purpose?
are you saying that no matter what I am limited to the 20Ah discharge rate of each cell.
Yes, the cell discharge value does not change, but as one adds capacity(paralleling), there is less demand on each cell.
And I didn't pay enough attention to your battery spec.s(I'm not a round cell guy). A string of 10 cells in series (10S) would be almost 40 Volts.
And then if you parallel 10 of those strings(10P), you will have a capacity of 25,000 mAh or 25 Ah. More than enough battery, in fact, any more cells than that and I think the bike would be getting really heavy(I sometimes carry 25 Ah's of battery on my 2WD mountain bike and it weighs over 70 lb.s w/out any trailer).
So let's say battery power is not a problem except I don't know how much would be the acceptable safe dis-charge rate for the pack(Maybe teklektik or another expert will chime back in).
So let's say you can pull 40 Amps(2 20 Amp controllers) from your pack and look at motor performance alone.
For that we need to go to the sim. @ Ebike CA. I used the two system feature and guessed that your total rig weighs 300 lb.s(and gave each system a weight of 150 lb.s)
The rest of the spec.s as follows;
36V/12.5Ah battery(half capacity)
20 Amp controller(for ea. system)
26 " wheels
one MAC 12T motor for each system(these are low-speed 201 rpm rated @ 36 V which would be about the same as a BPM "201")
On a 10% grade(about what a really fit cyclist would be able to do, but he would be on the biggest gears)we get;
An "able to maintain" speed of 14 mph and no "overheat". But interesting enough, that big battery would run "dry" in 9 miles(if there was a hill that long). To get an idea of how much power hills consume, a 25 Ah battery would go at least 40 miles in the flat.
Now if we make that hill an impossible to cycle up 15% grade, we get;
A very low "maintain" speed of 10 mph and overheat in 15 min.s and a crazy low range of less than 7 miles.
So, on paper, it looks doable, but there are some things in the nature of electric motors doing hills that makes it an "iffy" proposition.
The first and most important "rule of thumb" concerning hub motors and hills is;
At approx. half the top rpm/speed of the motor, more energy starts to be converted to heat rather than forward motion.
The motor(s) can never be allowed to start lugging and asolutely never let chug to a stop. Something will start melting.
Last month, here in Mex. where I'm spending the summer, I didn't follow my own advice.
The hill was long(several miles) and not so terribly steep, but the road was so bad, I had to slow down to a crawl several times to cross washed-out gullies. Once the momentum is lost, it's really hard to get going again and on my last leg I melted the wires going to the rear motor.
If you want to stay w/ the 500 Watt motors(and there are several reasons you want to, bigger motor require bigger everything, torque arm, wiring gauge connectors, etc), use the lowest speed rated ones available, which I believe is the "201" versions. The trade off is top speed and the sim shows that on your imaginary bike(12T in a 26: wheel on a 36V Battery), the top speed is only 17.5 mph. But, if the pack is 48 Volts, a more fum top speed bumps up to 22.5 mph.
There really is no advantage to using 36 Volts over 48 V. No bigger wires are needed(you probably want to use 12 AWG silicone) and 48 V controller are as avail. as 36 V ones.
And one last thing, if your total system weight is going to be more than 300 Lb.s, the critical numbers will "tank" real fast as the weight goes up. You will need to "run" the numbers on the sim real carefully.
Hope this helps a bit.
PS-I'm sure you know doing actual work would be much easier if you just bought a gas rig and built the ebike for fun/touring. But I guess there wouldn't be much challenge to that.