# What's most important? Volts, Watts, or Amps?



## notahybrid (Jan 14, 2009)

Ok, as I learned from my last post, I bought an AC motor. Now, as I'm shopping for an inverter, what is most important, volts, watts, or amps? In dealing with DC motors, if I want more power, I up the volts, but where do the other two come in, and what is different with an AC motor? Could an inverter meant to power power saws and TVs power an AC motor. It takes 24VDC and converts it to 240VAC. That's where I need to know where amps factors in. Also, every EV I've seen has more than 2 12v batteries feeding in. If this won't work, which I don't think it will, Where can I find an inverter?


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## Technologic (Jul 20, 2008)

notahybrid said:


> Ok, as I learned from my last post, I bought an AC motor. Now, as I'm shopping for an inverter, what is most important, volts, watts, or amps? In dealing with DC motors, if I want more power, I up the volts, but where do the other two come in, and what is different with an AC motor? Could an inverter meant to power power saws and TVs power an AC motor. It takes 24VDC and converts it to 240VAC. That's where I need to know where amps factors in. Also, every EV I've seen has more than 2 12v batteries feeding in. If this won't work, which I don't think it will, Where can I find an inverter?


 
I'm confused what you're asking.

I x V = W... amps x voltage = wattage (add a unit of time and it still works the same).

If you want more "power" you need to up amperage or voltage. Voltage tends to make the motor have more top end speed, amperage tends to make the motor have more torque.


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## mattW (Sep 14, 2007)

What are the specs on your motor? That will determine what inverter you need to buy.


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## notahybrid (Jan 14, 2009)

The whole measurement of electricity has always confused me. Mostly everything else can be measured with one unit, but current has 2 units that work in proportion of each other and multiplied give the third. Thing is is that I always forget which is which and what aspect of the current it measures. Anyway, after reading through an encyclopedia for an 1hr and 1/2, I think I'm getting it. The motor is a 30 horse 3 phase capable with a rated 2900rpm listed on the data plate. I think it says it is recomended for 415v at 39.5 amps, but that seems awfully high to me. Don't most homes run on less? This link will let you read the plate for yourself: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=310113998513. Thank you for clarifying the more amps and volts thing too. I wasn't sure what effect on the motor each would have. Now I can have a slightly better idea what converter to get.


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## Technologic (Jul 20, 2008)

notahybrid said:


> I think it says it is recomended for 415v at 39.5 amps, but that seems awfully high to me. Don't most homes run on less? This link will let you read the plate for yourself: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=310113998513. Thank you for clarifying the more amps and volts thing too. I wasn't sure what effect on the motor each would have. Now I can have a slightly better idea what converter to get.


Businesses often have 220, 440v, or sometimes even 550v directly sent from the power lines for industrial purpose.
Does that motor have a built in controller to take the AC and turn it into PWM for the motor?
Basically many industrial AC motors have a controller attached that can be calibrated to control power flow and convert the AC in, into the correct frequency (the low 60hz from your wall couldn't power a motor without either transforming to DC or increasing the frequency substainally).


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## notahybrid (Jan 14, 2009)

It may. There is a box attached to the side of it. I couldn't figure out what it was for, but that would probably be it.


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## CPLTECH (Sep 14, 2007)

The little box on the side is where the motor wires exit the frame and hook up to your wires. 
From the ebay description, it is a 3 phase, single voltage (415V) European industrial motor. Since that is the case it will not work on your single phase home power. To use in an EV, it will need a controller that will provide 3 phase output at variable voltage/frequency. AC EV’s use such a controller, hence the additional costs above a DC motor setup. Some here have tried to convert & modify an industrial VFD. Not sure of their success, but in my mind it should be possible IF the battery pack is high enough (Can you say 415V+?).
Not sure this is an ideal motor for EV use. I like the 30HP idea and an electric motor rebuilder may be able to rewind it to a lower voltage, but will leave that to someone else to address.


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## notahybrid (Jan 14, 2009)

CPLTECH said:


> The little box on the side is where the motor wires exit the frame and hook up to your wires.
> From the ebay description, it is a 3 phase, single voltage (415V) European industrial motor. Since that is the case it will not work on your single phase home power. To use in an EV, it will need a controller that will provide 3 phase output at variable voltage/frequency. AC EV’s use such a controller, hence the additional costs above a DC motor setup. Some here have tried to convert & modify an industrial VFD. Not sure of their success, but in my mind it should be possible IF the battery pack is high enough (Can you say 415V+?).
> Not sure this is an ideal motor for EV use. I like the 30HP idea and an electric motor rebuilder may be able to rewind it to a lower voltage, but will leave that to someone else to address.


If this motor were to be used, wouldn't it be easier to step up the voltage via a transformer? I think there would be a loss in amps, but it might be easier than 35 12v batteries. Although, the most practical solution might be just to find a different motor.


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## CPLTECH (Sep 14, 2007)

notahybrid said:


> If this motor were to be used, wouldn't it be easier to step up the voltage via a transformer? I think there would be a loss in amps, but it might be easier than 35 12v batteries. Although, the most practical solution might be just to find a different motor.


Transformers are only good for a max efficiency of 90% and only with Alternating Current (Not DC) and the frequency range they are designed for. The freq of VFD (Variable Freq Drive) changes, so a transformer is not recommended and I doubt that you could even lift a 15KVA transformer anyway. With all these issues, all the benefits of using a AC setup vanish. IMHO, its time to start looking in another direction. Sorry.


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## samborambo (Aug 27, 2008)

notahybrid, I see a lot of misinformation in this thread.

Congrats on your purchase. To use your motor is not impossible. You'll need the following:

- A battery pack of at least 600V (415V x waveform peak). You'll probably want it a little higher for better top end performance.

- The battery pack would be anything from 20Ah to 50Ah.

- An industrial VFD from europe or australia/NZ that can be set up to control torque instead of speed. I'd recommend something in the range of 70kVA. The battery pack becomes the DC "front end" to the inverter.

- An isolated rectifier / boost converter to charge the battery pack and a BMS depending on the battery chemistry.

- An excellent protection scheme to deal with the leathal voltage and fault current. Earth fault leakage for a DC system would be a must.

- Understanding of what you're doing.

Hope this helps.

Sam.


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