# Volts and amp question again



## frodus (Apr 12, 2008)

Batterypoweredtoad said:


> I frequently see people mentioning that higher volts mean you have to use less amps. Is that true without changing motors? Amps determine torque, and voltage determines rpm. More voltage will drive the motor to create more torque at the same rpm, or more rpms at the same torque, but I dont see how it will allow you to use less amps at the same rpm.


well, thats KIND of true...

if you overvoltage a motor, it speeds up, and as RPM's increase, the torque drops off and the motor uses less amps. torque and RPM are not constant with eachother, torque drops off as RPM goes up.

Here's an illustration (note, the efficiency calc is wrong, but its a good curve to look at.


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## Batterypoweredtoad (Feb 5, 2008)

Torque and rpm are not constant, but torque to maintain a certain rpm under a set load is. So how can you increase the voltage and decrease amps to maintain the same rpm without changing to a different motor?


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## major (Apr 4, 2008)

Batterypoweredtoad said:


> Torque and rpm are not constant, but torque to maintain a certain rpm under a set load is. So how can you increase the voltage and decrease amps to maintain the same rpm without changing to a different motor?


Hey toad,

You change the gear ratio. The motor RPM will change, but you can get the same vehicle speed with the same motor using a higher voltage and lower current. Power will be the same.

Regards,

major


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## ww321q (Mar 28, 2008)

I'm not sure but I was thinking that torque is equal to watts . So a certain torque can be obtained by higher volts and lower amps . Someone knows a better answer I'm sure J.W.


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## 3dplane (Feb 27, 2008)

Batterypoweredtoad!
Your question on how is it possible to keep same rpm,same load,lower amps more volts?:I do believe that is only true when the motor is "fed" thru a PWM controller.The duty cycle (motor on time) will decrease,because now the higher voltage can achieve the same power (required to maintain the same rpm at a set load) at lower amps.When talking about "balls to the walls" no controller just direct battery to motor, then yes you can not maintain the same rpm at a set load at higher voltage.(either amps going to rise at rpm held constant or rpm has to rise for same amps. More power.)
That is just how I see it anyway.
Barna


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## LithiumaniacsEVRacing (Oct 9, 2010)

Wow, you post crap around this forum like your Mr. Know it all, and now I find this question. You really have no clue. 



Batterypoweredtoad said:


> Torque and rpm are not constant, but torque to maintain a certain rpm under a set load is. So how can you increase the voltage and decrease amps to maintain the same rpm without changing to a different motor?


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## kek_63 (Apr 20, 2008)

Thread's 3 years old - maybe he's learned something since then.


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## major (Apr 4, 2008)

LithiumaniacsEVRacing said:


> Batterypoweredtoad said:
> 
> 
> > I frequently see people mentioning that higher volts mean you have to use less amps. Is that true without changing motors? Amps determine torque, and voltage determines rpm. More voltage will drive the motor to create more torque at the same rpm, or more rpms at the same torque, but I dont see how it will allow you to use less amps at the same rpm.
> ...


Toad's question was legitimate and an intelligent query. I've seen a lot, lot worse from you in the clueless department


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## EVfun (Mar 14, 2010)

Batterypoweredtoad said:


> I frequently see people mentioning that higher volts mean you have to use less amps. Is that true without changing motors? Amps determine torque, and voltage determines rpm. More voltage will drive the motor to create more torque at the same rpm, or more rpms at the same torque, but I dont see how it will allow you to use less amps at the same rpm.


There are 2 different things that can happen.

1. You can stay in a lower gear to a higher speed because the extra voltage allows the motor to take the needed amps up to a higher rpm. The needed amps (torque) is lower because you have more torque multiplication in the lower gear. This means the motor amps can be often be kept lower if you have more voltage. 

2. Your motor controller acts a lot like a variac, only for DC. Going down the road you may see 120 battery volts at 100 battery amps (12 kW.) The motor may be seeing 100 volts at 120 amps (still 12 kW) because the controller can step down the motor voltage and step up the current (power is conserved.) If you raise the pack voltage to 150 volts the motor will still need 100 volts at 120 amps to go the same speed in the same gear, however, it will get that needed power from the pack at 150 volts at 80 amps. This shows how your battery amps will be lower if you increase the pack voltage.


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## Batterypoweredtoad (Feb 5, 2008)

LithiumaniacsEVRacing said:


> Wow, you post crap around this forum like your Mr. Know it all, and now I find this question. You really have no clue.


BTW-If you actually read the thread, I wasn't wrong when you are talking about motor amps. 

Love you too Ron. 

aaaaaaaaaaaaand just because it drives you so nuts: Boogity boogity, NEDRAs gonna get you!


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## LithiumaniacsEVRacing (Oct 9, 2010)

LMFAO! Just felt like throwing a couple of jabs your way! No hard feelings.


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## LithiumaniacsEVRacing (Oct 9, 2010)

Thanks Major, your my hero! 



major said:


> Toad's question was legitimate and an intelligent query. I've seen a lot, lot worse from you in the clueless department


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## gor (Nov 25, 2009)

Batterypoweredtoad said:


> I frequently see people mentioning that higher volts mean you have to use less amps. Is that true without changing motors? Amps determine torque, and voltage determines rpm. More voltage will drive the motor to create more torque at the same rpm, or more rpms at the same torque, but I dont see how it will allow you to use less amps at the same rpm.


maybe like this?


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## Batterypoweredtoad (Feb 5, 2008)

gor said:


> maybe like this?


Gor-would you mind clarifying that graph? It's probably due to my ignorance, but I don't understand what I am looking at. 
Thanks.


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## gor (Nov 25, 2009)

Batterypoweredtoad said:


> Gor-would you mind clarifying that graph? It's probably due to my ignorance, but I don't understand what I am looking at.
> Thanks.


this should be better : )
p.s. numbers - just to show v2>v1 and a2<a1


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## Batterypoweredtoad (Feb 5, 2008)

gor said:


> this should be better : )
> p.s. numbers - just to show v2>v1 and a2<a1


I bet where those lines cross they are at the same motor voltage, amps and RPM.


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## gor (Nov 25, 2009)

here with torks, amps and volts


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