60V or 72V setup with 36V 500W motor?

[Dolfino]

Firstly, if you're afraid that you might put too much voltage into the motor, then why don't you just get a bigger motor. you could buy a 48V motor and then overvolt that.

Running a 36v motor at 60v (66% overvolted) should produce more power and a higher rpm than running a 48v motor at 60v (25% overvolted) as long as the windings can cope with the extra heat generated.

Quote
Secondly, If possible, you could increase the wheel size, larger circumference= more distance rolled per revolution.

By increasing the wheel size you also increase the gearing, making it harder for the motor to turn the wheel under load.
This would also mean less torque would be available at the wheel.

Ok, so I understand the firs case, that was my bad, and I also understand the second case, but unless you're climbing lots of hills, or even one steep one, I didn't think that torque would be an issue. Is it? I mean would you really lose that much torque? If you would, then don't mind me, but I would like to find that out. would it be like you couldn't even move your bike from a stop?

[Gregte]

ps. Efficiency is output/input

Yes, I had the input-output exactly backwards for efficiency.

I don't know where you found the dyno specs for the Golden Motor so I will not comment. If they are correct then you appear to be correct to me. They just don't seem correct to me. Where can I find those specs? Thanks.

[Bikemad]

Firstly, if you're afraid that you might put too much voltage into the motor, then why don't you just get a bigger motor. you could buy a 48V motor and then overvolt that.

Running a 36v motor at 60v (66% overvolted) should produce more power and a higher rpm than running a 48v motor at 60v (25% overvolted) as long as the windings can cope with the extra heat generated.

Quote
Secondly, If possible, you could increase the wheel size, larger circumference= more distance rolled per revolution.

By increasing the wheel size you also increase the gearing, making it harder for the motor to turn the wheel under load.
This would also mean less torque would be available at the wheel.

Ok, so I understand the first case, that was my bad, and I also understand the second case, but unless you're climbing lots of hills, or even one steep one, I didn't think that torque would be an issue. Is it? I mean would you really lose that much torque? If you would, then don't mind me, but I would like to find that out. would it be like you couldn't even move your bike from a stop?

Dolfino

I'll try an explain:

A hub motor will develop a limited amount of torque.
(Torque is a force that turns, twist or rotates and is defined as force multiplied by distance.)

By increasing the wheel size you actually reduce the amount of force physically pushing the vehicle forwards.

A smaller wheel will give greater acceleration and be able to climb steeper hills than a larger wheel fitted with the same motor.
This is because the smaller wheel provides a greater forward force. (As it is effectively lower geared.)

However, if the wheel is too small it will run out of revs before it reaches the optimum speed where the wind resistance and frictional losses directly oppose the forward force of the bike.

If the wheel is too large, the maximum speed will be reduced because there is less forward force acting against the wind resistance and frictional losses.

Power and Gearing will both have an affect on maximum speed.

Power = Torque x Revs
Gearing = wheel size (With a gear less hub motor)

You're more likely to increase your maximum speed by increasing the power (supplying more volts/current) than increasing the gearing. (unless it is under-geared in the first place)

I hope some of the above makes sense to you.

Alan
 

[Bikemad]

ps. Efficiency is output/input

Yes, I had the input-output exactly backwards for efficiency.

Greg,

This should make it more clear for everyone:

Efficiency Formula



Where:
Efficiency = motor efficiency
Useful power output = measured hub power output (Watts)
Total power input = electric power supplied to the motor (Watts)

I don't know where you found the dyno specs for the Golden Motor so I will not comment. If they are correct then you appear to be correct to me. They just don't seem correct to me. Where can I find those specs? Thanks.

Dynomometer results for the GoldenMotor 36v 500w hubmotor can be found here.

 I  = Current draw (Amps)
P1 = Power In (Watts)
P2 = Power Output Reading on Dynomometer (Watts)


Alan
 

[Dolfino]

You're more likely to increase your maximum speed by increasing the power (supplying more volts/current) than increasing the gearing. (unless it is under-geared in the first place)

Ok, sorry then, I was under the impression that the extra voltage to the motor had increased the torque to the point where the motor could be geared up without sacrificing performance. Sorry for the misinformation.

[Gregte]

I've used actual dynomometer information for the Golden Motor 36v 500w motor in this example:

• A single motor drawing a current of 17.8 Amps has an output of 451.5 Watts and is only 70.7% efficient.
   
• A single motor drawing half this current (8.9 Amps) has an output of 260 Watts and is 81.1% efficient.
   
• Therefore two motors drawing a combined current of 17.8 Amps would produce 520 Watts of power. (Also 81.1% efficient)
   

I looked at the pdf  you listed, with the graph and table, but I cannot find any numbers that correspond with the above. For instance, the table shows that a current of 15.99 amps would produce 447 watts output rather than "17.8 Amps has an output of 451.5 Watts". The watts of output power are similar but the amps, and thus efficiencies are not very close.

Maybe I am still misunderstanding something?

[Bikemad]

I've used actual dynomometer information for the Golden Motor 36v 500w motor in this example:

• A single motor drawing a current of 17.8 Amps has an output of 451.5 Watts and is only 70.7% efficient.
   
• A single motor drawing half this current (8.9 Amps) has an output of 260 Watts and is 81.1% efficient.
   
• Therefore two motors drawing a combined current of 17.8 Amps would produce 520 Watts of power. (Also 81.1% efficient)
   

I looked at the pdf  you listed, with the graph and table, but I cannot find any numbers that correspond with the above. For instance, the table shows that a current of 15.99 amps would produce 447 watts output rather than "17.8 Amps has an output of 451.5 Watts". The watts of output power are similar but the amps, and thus efficiencies are not very close.

Maybe I am still misunderstanding something?

Sorry Greg,

I used a printout for my figures and posted a link to what I thought was to the same sheet, but it appears to be a different one.
(I'll try to double check next time before I post)

Here is the correct link to the information that I used:

Golden Motor 36v 500w Dynomometer results

Hopefully the numbers will correspond now.
(I used rows 24 and 35 to make my comparisons)

Alan

[muzza.au]

First I have to say I only have the old GM 36v 10ah Lifepo4 battery with an Infineon 36v 18a controller and GL-1 400w motor. But hearing that the new GM controller can be overvolted I did some research and found out that the infineon controller can be overvolted too, that the 36v controller can work with 48v. So I gave it a try. I have a few 14ah sla's to I put one in series with the lifepo4 to make 48v. I did fear that I would burn out my controller and/or motor but I gave it a try because I have a spare motor and controller, but it actually worked. It went a lot faster. Feeling a bit daring I put another sla in series making 60v and it worked as well, the bike now flew, too fast for me to peddle. One thing I did notice was that while the top speed was much greater, the torque seemed to be mostly the same maybe a little bit more. From dead stop on a slite slope it still stuggled a little bit to get going so I think to get greater torque you need more current or amps, but I think that your wiring must be able to handle the extra current as well. Maybe one day I'll try that too when I upgrade my controller.

Muzza.

[Bikemad]

I put another sla in series making 60v

Muzza

Don't forget that 60v is the nominal rating of the batteries.

Fully charged they would be nearer 70v, which might be a little too much for the controller.

Alan
 

[muzza.au]

Fully charged they would be nearer 70v, which might be a little too much for the controller.

They werent at their max charge. I measured the voltage of the sla's and each were at about 12.95v. The 36v GM lifepo4 pack was not full, but had only 5km on it since last charge. I went around the block a couple of times with no problem at all. I felt the controller and motor afterwards. The controller was normal, felt the same as ambient temperature. The motor was a little warm to touch, but not hot all.

I guess infineon controllers are built to take it. (Which reminds me; my other controller I accidently connected with reverse voltage at one stage when I was testing it and I thought I had surely toasted it, but it continued to work fine after that).

Muzza.