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The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

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  #1  
Old 05-11-2012, 11:20 PM
karlis123 karlis123 is offline
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Default 3 phase ac motor speed control from battery

hello!
i got a 5kw 3phase AC motor I want to use it for a small cart but the problem is that i cant find a system that regulates voltage before the inverter, is that even necessary? i was thinking of using the adjustable frequency inverter alone hooked to the battery which means that i can only change the frequency but not the voltage. I've read something about flux increasing and making the motor heat up when the frequency is really low at lowspeeds if you dont lower the voltage.
or should i go from dc to ac then to a controlable rectifier back to dc(to contral voltage) and then to the inverter(to control frequency) then to the motor? :S
any suggestions would be apritiated
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Old 05-11-2012, 11:26 PM
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strantor strantor is offline
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hello!
i got a 5kw 3phase AC motor
what motor?
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i was thinking of using the adjustable frequency inverter
What inverter?

If your motor is inverter duty rated then you should not have any problems there.

If your inverter has the capability to accept HV DC on the DC common bus (some do, some don't) then you shouldn't have any trouble there.

Your battery voltage needs to be 1.41X the voltage of your motor. If your motor is 480V then you need a 680V battery. Do you have one of those laying around?
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Old 05-12-2012, 06:45 AM
karlis123 karlis123 is offline
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What motor?

What inverter?


If your inverter has the capability to accept HV DC on the DC common bus (some do, some don't) then you shouldn't have any trouble there.
110v 3phase AC and I want to hook 3 - 50v batteries in series

how do I know if the motor is inverter duty rated? and how to find the correct inverter?
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Old 05-12-2012, 08:25 AM
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strantor strantor is offline
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110v 3phase AC
110vac 3 phase? what motor do you know of that runs on 110VAC 3 phase? Model #? Link?
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Originally Posted by karlis123 View Post
I want to hook 3 - 50v batteries in series
What 50V batteries? model #? amps? link?
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how do I know if the motor is inverter duty rated?
You could look at the nameplate, get the model number, and post it here and I'll tell you if it is or isn't.
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and how to find the correct inverter?
We've got a long way to go before I'll even touch that question

You are not giving enough information for anyone to help you. Every once in a while I deal with someone on this forum who makes me ask 1000 questions; I'm done with that. If I have to post another reply full of questions, I'll simply walk away from this thread. Start volunteering information.
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Old 05-12-2012, 03:37 PM
Experimentonomen Experimentonomen is offline
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I suggest a 48-100V battery, a 5-10kW inverter that turns 48-100V into 300-600VDC which then connects to the DC bus of a Variable Frwquency Drive rated drive your size motor.

Something better than this would be a Brushless DC motor rated to around 5kW as these can run directly from the battery voltage through a BLDC controller/drive without having to step up the voltage to 500+ volts.
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Old 05-12-2012, 04:53 PM
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strantor strantor is offline
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I suggest a 48-100V battery, a 5-10kW inverter that turns 48-100V into 300-600VDC which then connects to the DC bus of a Variable Frwquency Drive rated drive your size motor.
This is terribly inefficient IMO. If you're going to do it this way, why not use an inverter that turns 12V into 600V? The step-up inverter is an unneeded conversion. It would be far simpler, cheaper, and energy efficient to put enough batteries in series to achieve 600 (680V)
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Old 05-12-2012, 09:14 PM
Experimentonomen Experimentonomen is offline
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at 12V you would have several hundred Amps at 5kW, hence why i suggested 48-100V battery voltage.
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