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Old 10-29-2008, 03:42 PM
deadtoaster2 deadtoaster2 is offline
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Default Question on controller amperage

So here is a question that I have searched for but couldn't find. It is probably a simple answer but I cant seem to find it.

Say you have a medium sized motor (8" or whatever) and a 400A peak (200 amp continuous) controller. You are cruising along using about 175amps and you get to a huge hill. Your gonna need to accelerate a little to keep your speed, but you watch as the ammeter goes up into the 400's...

What will happen once it reaches 400? Does the controller cut back on the juice? Will the car completely stall? Will it deliver MORE than 400A for a short period? Will it catch fire?

Probably a simple answer, but Its stumping me.

Thanks!
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Old 10-29-2008, 04:20 PM
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TX_Dj TX_Dj is offline
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Default Re: Question on controller amperage

The answer to some of those questions (i.e. catch fire) is "yes" depending on who made it. I don't think I'd ask a Kelly controller to climb a hill unless the fire brigade was behind me.

The current number that controllers are rated at is the amount of motor current they can deliver. Part of the PWM cycle is to "current limit". This is why Curtis switches PWM from 15 kHz to 1.5 kHz at slow speed (because the motor looks like a short at low speed, and it's easier to limit current with longer pulse-width).

You should be able to deliver *motor amps* up to the max current limit for the amount of time that it's rated for duty cycle at that amount. If that's 10 seconds, you have a problem for a hill. Most numbers I've seen have been 5 minutes. If it takes you more time to climb the hill than that, you'll either be forced to slow down (thermal limits reached, controller will go into "limp mode" or shut down), or you will need to take your foot out of it to get back to the "continuous" rated current.
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Old 10-29-2008, 04:33 PM
vgslimo vgslimo is offline
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Default Re: Question on controller amperage

Quote:
Originally Posted by TX_Dj View Post
You should be able to deliver *motor amps* up to the max current limit for the amount of time that it's rated for duty cycle at that amount. If that's 10 seconds, you have a problem for a hill. Most numbers I've seen have been 5 minutes. If it takes you more time to climb the hill than that, you'll either be forced to slow down (thermal limits reached, controller will go into "limp mode" or shut down), or you will need to take your foot out of it to get back to the "continuous" rated current..
sorry 4 quick hijack but doesn't a higher voltage system generaly mean lower amps so will this help a vehicle go up a long mountain?
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Old 10-29-2008, 04:56 PM
deadtoaster2 deadtoaster2 is offline
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Default Re: Question on controller amperage

So basically what you are saying is that when you begin to go up the hill it would go up to the max current rating of the motor. Once that was reached the motor would begin to overheat and if the motor had a thermal sensor it would set off the little light? However this could be fixed simply by slowing down and trying to get the amps down much lower? By slowing down the rpm's would drop and you would get more torque which would push you up the hill no problem but at a much slower speed?

In an ICE you would downshift to get more torque at a higher RPM, could you do the opposite and up-shift with an electric motor to get lower RPM's, more torque and less amperage draw?

Thanks for answering.
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Old 10-29-2008, 05:31 PM
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Default Re: Question on controller amperage

Quote:
Originally Posted by deadtoaster2 View Post
So basically what you are saying is that when you begin to go up the hill it would go up to the max current rating of the motor. Once that was reached the motor would begin to overheat and if the motor had a thermal sensor it would set off the little light? However this could be fixed simply by slowing down and trying to get the amps down much lower? By slowing down the rpm's would drop and you would get more torque which would push you up the hill no problem but at a much slower speed?

In an ICE you would downshift to get more torque at a higher RPM, could you do the opposite and up-shift with an electric motor to get lower RPM's, more torque and less amperage draw?

Thanks for answering.
thats not really what he's saying. Just because you're going up a hill doesn't mean you'll automatically max out the controller amps. It all depends on how much current the motor wants per RPM (see the motor torque curve). If you need xxxftlbs of torque to go up a hill, it will correlate to a given xxxAmps.

If 400A is what the motor "wants", and the controller is a good controller, it'l throttle back so that it stays ONLY at 400A and doesn't go past that. If the motor is rated for LESS than 400A, it might start to heat up and smoke. Its best to match the two together, or at least have the motor handle everything the controller can throw at it.

Slowing down RPM's make the torque increase, but higher torque = higher amps. It would push you up the hill at slower speed, but at a higher current. Amps is torque, volts is RPM.

You still downshift with an EV. Upshifting would cause you to lose almost all your generated torque. Best thing to do is to use the transmission to keep the motor in a good spot so that the Amp draw at low vehicle speed is lower.
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Last edited by frodus; 10-29-2008 at 05:35 PM.
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Old 10-29-2008, 05:33 PM
deadtoaster2 deadtoaster2 is offline
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Default Re: Question on controller amperage

alright thanks. I think I get it now.
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