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# how to measure the efficiency of bike motor???

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# how to measure the efficiency of bike motor???

07-22-09, 12:28 PM
#1
puddingbag
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how to measure the efficiency of bike motor???

Hi,

I have got, I think a 600watt electric bike which has four batteries which in total uses 50v
but i would like to test the efficiency of the motor.

I know its a 600watt motor and it uses 50v but i need to know what amps ie the current it is drawing from the battery.

I was thinking a multi-reader would be able to do this but it only goes up to 10 amps and i think my system would use a little bit more so would not work or would blow the reader ie

52v - 600watt = 11.5 amps

not sure if i used it at half speed ie 300watt or there is a better way to do this

many thanks

Tim
07-22-09, 07:32 PM
#2
similor
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Not as u think.

It's not as u think to measure.U must use the special machine.
07-23-09, 12:57 PM
#3
cerewa

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Yeah, it's pretty hard to measure.

If you don't mind a little bit of error, you can measure efficiency by going up a long hill. On uphills when there's not much wind, usually not much energy is lost to air resistance.

You can find out how many joules of energy went in to lifting the weight of your bike by calculating:

joules = (number of kilograms of mass, bike + rider) * (number of vertical meters you went up) * 10

you'd have to estimate the difference between the energy-output of the motor and the energy that went into lifting the bike+rider. If I were to guess I'd say the energy-output (joules) of the motor is about 1.03 * (energy that went into lifting the bike+rider vertically) - about 3% of the energy might be lost in ball bearings, tires, wind resistance, etc.

convert joules to watt hours. (try an online conversion web site)

figure out how many watt hours of actual energy-output you got from your battery by using an appropriate meter.

calculate:
(estimated number of watt hours energy-output from motor)
(divided by)
(watt hours you got from battery)

If you multiply by 100 you'll get the percentage efficiency of your motor+controller combination.

Note that if you run your motor on a steeper slope than it is intended for, your motor efficiency will be very low. But if you go fast (say, over 15mph) the energy lost to air resistance will be high, making it impossible to estimate efficiency without carefully measuring energy lost to air resistance.
07-23-09, 02:47 PM
#4
GTALuigi
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if you were to measure it without doing much match, and/or testers devices.

you can simply find a long straight flat path, or a school field/track and run loops on it, until the battery runs out of battery, on a fully charged battery.

to get a better measurement use pure electric power to go around the track field, until the battery gives up.

average school field tracks are either 200m per side, or 400~500m for the full loop.
pick a known track & field you know well, or you can measure the distance before hand, using a cycle computer or whatever.

so by using Time, distance, volt & watt from the batter/motor spec, then you can get a pretty good approximation.

for example my battery 36V (9.6 Ah) capacity and the motor is 350w, my average daily round trip distance is 90km, ride time is aprox 3.5hr to 4hr, on an average speed of 31km/h
so assuming we are running at maximum capacity 350W/36V=9.72A/s
9.6A * 3600s = 34560 As
34560As / 9.72As = 3555.5As provided in 1 hour
3555.5A * 4h = 14222.2Ah consumed after 4 hours
14222.2Ah / 90Km = 158Ah per Km
that gives me 158Ah/31Km/h= 5.1A/s average,
which is pretty close, as i don't always max out the motor/battery, i usually have 1~2 bars of battery left at the end of the trip.
07-24-09, 07:38 AM
#5
suncoast_dan
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Or, if you want to track this info over time AND know even more about your electric bike, you could pick up a Cycle Analyst. It will display, in real time, volts, watts, amps, amp-hours, watt-hours, speed, distance, time, regen, peak current, voltage sag, totally battery cycles & Ah. So, not only will it replace your standard bike computer, but it will give you a LOT of very useful info on your electric kit.

07-24-09, 10:58 AM
#6
GTALuigi
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Originally Posted by suncoast_dan
Or, if you want to track this info over time AND know even more about your electric bike, you could pick up a Cycle Analyst. It will display, in real time, volts, watts, amps, amp-hours, watt-hours, speed, distance, time, regen, peak current, voltage sag, totally battery cycles & Ah. So, not only will it replace your standard bike computer, but it will give you a LOT of very useful info on your electric kit.

got any link to the product?

i'll like to find out more about it

thx
07-27-09, 07:27 AM
#7
suncoast_dan
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PM me for info - I don't want to post inappropriate links.

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