volts/Amps...help with different efects.

[Addicted]

I have been thinking about the build I'm starting and am wondering the effects of raising volts and amps.specifically what would be the difference between raising the volts Vs amps.Say I'm running 48 volts and 40 amps vs 72 volts 20 amps.Mainly i am curious as to what diferent effects it has on a motor changing the two independantly.What has more of an effrect on the performance,volts or amps,and why,how.

Jason.

 

[Ypedal]

Volts = RPM = Speed
Amps = power = acceleration = drain rate..

V x A = Watts.

Up the voltage and the motor will want to spin faster, if up the amps at the same voltage, the motor will accelerate with more pull, with the same top speed, drawing more power from the battery as long as the battery can dish it out.

 

[Addicted]

Great simple explanation that answered my question fully,Thanks.BTW,V x A = Watts,That's the one thing i know from lurking around here for a while!

*EDIT* Now i may be satisfied with 48v,just mega amps!..That could change though,I'm a speed freak.

Thanks.
Jason.

 

[pwbset]

I was told by several and since felt first hand that upping volts makes for more efficient amp usage and "energizes" those same amps more... if that makes sense. In other words given the same motor 72v20a will "feel" more powerful than 48v40a and use less energy at a consistent throttle setting because of efficiencies (not counting wind resistance because of higher speeds etc. etc. in the end it just boils down to watt/hrs I believe). A lower wound motor will also pull more amps to get the same torque... like a low wound Clyte 406 will pull mad amps compared to a slower 4011 for the same torque etc. but clearly the 406 will go faster while the 4011 will pull more. Make sense?

Another rule of thumb seems to be that adding volts is fiscally cheaper than adding amps... especially in terms of controllers.

Okay... let's see if I've learned anything in the last 6 months... experts? Is any of that correct?

 

[Ypedal]

close..

one relates to the other in a way.

Say a 406 vs a 4011

406 will have a much higher rpm per volt. If you were to run both motors at the same voltage, at full throttle, the 406 will have to get up to a higher speed before settling down to it's running speed. The 4011 would reach it's speed much sooner at a lower rpm.

Now, throw in different wheel sizes, different amp limts, battery chemistries, etc and you have a 100 different ways to get the job done. 8)

IMO there is not a very big difference in pulling power from all the different models as long as you pick your rim size, wound model and voltage for the task at hand.

 

[billvon]

In other words given the same motor 72v20a will "feel" more powerful than 48v40a and use less energy at a consistent throttle setting because of efficiencies . . .

Yes and no.

On the battery side of things, yes. Higher voltages mean lower currents for a given power, and so you need less copper. With the same wiring, you get less voltage drop due to the lower current.

However, once it gets to the controller and motor it's pretty similar both ways. If you have a 72 volt system and you want 500 watts out of it, the controller will throttle back to get you the right amount of power to the motor. If you have a 36 volt system, the controller will give you twice the pulsewidth. You get best efficiency by operating the motor at its most efficient speed/power (see Justin's simulator for a graphical example of this.)

Another rule of thumb seems to be that adding volts is fiscally cheaper than adding amps... especially in terms of controllers.

Yep. More amps = more copper and silicon (expensive) whereas more volts = more insulation (and most wires already have enough to go pretty high.)

 

[dogman dan]

More amps from the same battery = harder use of that battery. It may or may not matter depending on what you are using.

 

[fechter]

If you keep the motor the same and just increase the voltage, the motor will be able to spin faster. This may put you into a situation where the motor wants to go faster than it can really go due to wind resistance. You might get full speed on a steep downhill, but on flat ground or uphill, performance could be much worse if the motor is outside of its efficient range.

It is important, therefore, to try and match the motor gearing and voltage so the top speed is still in the efficient range (unless you are racing).

In comparing 48v, 40 amps to 72v, 20 amps, if you are using the same motor, the 72v case may or may not be more efficient. At higher voltage, there will be less resistance losses in the battery wiring for a given power level, but that doesn't amount to much in the first place. In the 48v case, the controller losses will likely be less, which also should not be much.
Keeping the motor efficent is generally much more important than keeping the wiring or controller efficient.

 

[hippiehunter]

A fun thing to do with the hub motor simulator is to put in 48volts and 1000 amps on a 5303 only to notice that it actually levels out somewhere around 40amps. So my take home from this example is that Amps != acceleration. Amps == potential for acceleration and acceleration is actually caped by the amount of amps your motor is willing to pull at a given voltage. oh and the other thing is, I think higher volts leads to higher costs for controllers since you have to use higher rated fets and low quality higher voltage(read: same cost) fets have much more resistance and explode.