36v500w Questions 36

[Clemencello]

Hi

I've built a trailer to push a bike with a 36v500w motor and the 36v12ah hour battery with charger.

I'd like to find out what I can expect from day to day usage. I plan to travel about 7 miles a day on mild hills but would like to go on long distance trips if possible.

How long should the battery take to charge?

What distance/time should I expect for a full charge?

What total weight should a motor like this be able to cope with?

Thanks for any feedback.

Simon

Australia

[e-lmer]

500watts /36v is about 13 amps, or 12/13 hours.

Figure out your average speed, then multiply it by12/13 to
get miles per charge MAXIMUM.

Of course you won't run the battery dead, and you won't go
max speed all the time, but if you are honest in your testing
you can expect about 80% of your max on average.

[Clemencello]

500watts /36v is about 13 amps, or 12/13 hours.

Figure out your average speed, then multiply it by12/13 to
get miles per charge MAXIMUM.

Of course you won't run the battery dead, and you won't go
max speed all the time, but if you are honest in your testing
you can expect about 80% of your max on average.

That's great. Thanks for the quick response. So I should be able to run all day without too much concern by the looks of things. I've been reading your posts across the forum and they've been a been a big help. Have to get my head back to school as far as basic electrics is concerned. The bike+trailer+me tops out around 120Kilos or 260lbs. I realize motors are going to start to suffer under load. Am I being unrealistic to use this set up as it is? Can I "open the throttle" without concern? The motor so far has sounded fine.

Simon

[Bikemad]

500watts /36v is about 13 amps, or 12/13 hours.

Figure out your average speed, then multiply it by12/13 to
get miles per charge MAXIMUM.

That sounds reasonable to me, but you might also want to consider the inefficiencies of the hub motor.

To develop an output of 500watts, these hubs will consume 650watts of electrical energy, which at 36v equates to 18 Amps.

But, If it was ridden it at full power continually, the range would be approximately 2/3rds of the maximum speed.

eg. A range of 14 miles at 21mph on the level. (Without pedalling!)

The bike+trailer+me tops out around 120Kilos or 260lbs. I realize motors are going to start to suffer under load. Am I being unrealistic to use this set up as it is? Can I "open the throttle" without concern? The motor so far has sounded fine.

Simon,

By using the smaller wheel you have effectively lowered the gearing and increased the available torque, which to some extent will help to compensate for the additional load.

You should have no problems on the flat, but make sure that it doesn't get too hot under load on hills.

The biggest problem I can see is the 500watt motor..... It's 300watts too powerful to be legally used on Australian roads!

It looks good though.

Alan
 

[Clemencello]

The biggest problem I can see is the 500watt motor..... It's 300watts too powerful to be legally used on Australian roads!

It looks good though.

Alan
 

Seemed to have oversprayed with the paint job...can't seem to read the motor rating on the hub any more...must remember to clean it up!

[Gregte]

500watts /36v is about 13 amps, or 12/13 hours.

Figure out your average speed, then multiply it by12/13 to
get miles per charge MAXIMUM.

Of course you won't run the battery dead, and you won't go
max speed all the time, but if you are honest in your testing
you can expect about 80% of your max on average.

I do not understand your math. As I read it, you would get more miles per charge the faster you go, which cannot be right, so I must be missing something?

If I use your formula I get:
12/13 times 20mph equals 18.4 miles per charge.
12/13 times 10mph equals  9.2 miles per charge.

[Bikemad]

500watts /36v is about 13 amps, or 12/13 hours.

Figure out your average speed, then multiply it by12/13 to
get miles per charge MAXIMUM.

Of course you won't run the battery dead, and you won't go
max speed all the time, but if you are honest in your testing
you can expect about 80% of your max on average.

I do not understand your math. As I read it, you would get more miles per charge the faster you go, which cannot be right, so I must be missing something?

If I use your formula I get:
12/13 times 20mph equals 18.4 miles per charge.
12/13 times 10mph equals  9.2 miles per charge.

Greg,

Elmer was only trying to give Simon a rough indication of the distance he might travel on a fully charged battery.

You and I, might prefer a formula more like this:
Distance per charge = Average speed multiplied by 12 (Battery Ah rating)/Average current drawn by the motor (Amps) multiplied by 0.8 (Battery only discharged to 80%)
Other things to note:

• The result would be much lower for uphill use and headwinds. (And much higher for downhill use and tailwinds.)

• Constant stop/start braking and acceleration will also reduce your range considerably.

• The more you assist by pedalling, the further you will go.

Alan

 

[Gregte]

I see what was being said now. The fact is though that your current drawn (13 amps in the above example) varies immensely dependent upon your average speed. You cannot use the number 13 except for one particular average speed, not any speed that you want to plug into the formula. You can't have speed be a variable but yet have the current be fixed.

[e-lmer]

Those were simple back of the napkin calculations to get
a ballpark figure.

The point I was making is that you can approximate the
ideal distance per charge with simple math.

In real life you don't get the numbers you get from ideal
calculations, but should be within 20%.

If someone can check this for errors, thanks, but I think:

Power = Volts x Amps  therefore Amps = Power/Volts.

To simplify, just make that 500Watts/36V or 13.8A for my motor.
(Warning, that is the grossest oversimplification.)

The battery is rated in Amp Hours, so assuming constant Amps:
(Amp Hours in battery) / ( average current use in Amps ) = hours on a charge.

Distance is Rate time Time, so
( Miles Per hour) * (Hours per charge)  = (Miles per charge)

IF I use 500 watts on a 20AmpHour 36V battery and can ride 17mph on level ground with no wind,
THEN I get the following calculation:
(17MPH) * (20AH) / (500W/36V) 

Simplifying: 20 * 36 * 17 / 500 or about 24 miles on a charge.

That is about right.  I can more when I pedal, and less when I go uphill or upwind.