# AC motor 12v (test) drive question



## toddshotrods (Feb 10, 2009)

We test DC motors by simply hooking a 12v battery to them, which controls the speed and is actually strong enough to move a vehicle around in the shop/garage/driveway. I rode Scrape (my electric motorycle) around, in the shop, with a simple momentary ICE starter button as my "contactor/controller", with the 12v motorcycle starter battery - worked perfect, and gave us some fun video, me the info I needed to move forward with the bike, and was surprisingly _peppy_.


The question is can I hook one of those little cheap inverters you buy, that run off the car's 12v battery/alternator, to an AC motor to test it? I have a little 5hp AC (industrial) motor that I would like to use, that will need to be rewound. This would allow me to play with it until I get around to rewinding it; and figure out what I want to do for an inverter.

My motor:


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## major (Apr 4, 2008)

toddshotrods said:


> We test DC motors by simply hooking a 12v battery to them, which controls the speed and is actually strong enough to move a vehicle around in the shop/garage/driveway. I rode Scrape (my electric motorycle) around, in the shop, with a simple momentary ICE starter button as my "contactor/controller", with the 12v motorcycle starter battery - worked perfect, and gave us some fun video, me the info I needed to move forward with the bike, and was surprisingly _peppy_.
> 
> 
> The question is can I hook one of those little cheap inverters you buy, that run off the car's 12v battery/alternator, to an AC motor to test it? I have a little 5hp AC (industrial) motor that I would like to use, that will need to be rewound. This would allow me to play with it until I get around to rewinding it; and figure out what I want to do for an inverter.
> ...


Simple answer is no. The motor is 3 phase 208 volt. A 12 VDC to AC inverter is going to be 110 VAC single phase. A 3 phase motor won't run (or at least won't start) on single phase. While it might run at 110VAC, 60 Hz, the reduced voltage would produce little torque. And then without a V/f ramp or soft starter, the inrush or starting surge would fault out any inverter you could run from 12V.

It is not quite the same as 3 phase but for example: I have a 3/4 hp, 110V single phase induction motor on my well pump at home. A 3.1 KVA inverter would not start it. A 4.3 KVA inverter would. For starting induction motors at line frequency, you need about 5 times the rated power from the inverter.


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## JRoque (Mar 9, 2010)

Hi. What Major said plus you can use one of these cheap ones to spin it (some): http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313.TR0.TRC0&_nkw=110V+VFD&_sacat=0&_from=R40

JR


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## PStechPaul (May 1, 2012)

You can run most 3 phase VFDs on single phase at reduced power, but you do need at least 180 VAC. Some of the 110V inverters in the eBay link are 3 phase out, but still 110V, so you can't run the motor at full rated voltage. But certainly they would be OK with full torque at half-speed or even above nameplate rated RPM with field weakening and reduced torque. These 110V VFDs seem to be Chinese, and I have no experience with them. I was lucky to purchase a new Fuji/GE 2HP VFD for about $65. Similar bargains are usually available. Make sure that the drive is still capable of being serviced.

Something else you can do is get an automotive inverter like this:
http://www.ebay.com/itm/181102816053

It is 24 VDC in and 220 VAC out, with a continuous power of 1200W and peak power of 2400W. It might be able to run a single phase induction motor directly, but probably not a three-phase unless you spin it manually up to near running speed.

But you can open the inverter and access the internal 270 VDC supply, and connect that to the DC link bus of a 220 VAC VFD (you may need a precharge resistor), and then you can control the motor with the VFD. I have done this with my own 2HP 3-phase electric riding mower, but I have not tried it under much load. The inverter I have is 12V input so even at 1 HP it will draw at least 62 amps from the battery. But I was able to ride the machine (using a different 24V-320VDC converter), at 15-20 amps, or about 1/2-3/4 HP.


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## toddshotrods (Feb 10, 2009)

major said:


> Simple answer is no...





JRoque said:


> Hi. What Major said plus you can use one of these cheap ones to spin it (some): http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313.TR0.TRC0&_nkw=110V+VFD&_sacat=0&_from=R40
> JR





PStechPaul said:


> You can run most 3 phase VFDs on single phase at reduced power...


Thanks guys. I was hoping to find a simple way to spin it like DC, but AC always has to be difficult. 





PStechPaul said:


> ...But you can open the inverter and access the internal 270 VDC supply, and connect that to the DC link bus of a 220 VAC VFD (you may need a precharge resistor), and then you can control the motor with the VFD. I have done this with my own 2HP 3-phase electric riding mower, but I have not tried it under much load. The inverter I have is 12V input so even at 1 HP it will draw at least 62 amps from the battery. But I was able to ride the machine (using a different 24V-320VDC converter), at 15-20 amps, or about 1/2-3/4 HP.


That is a very interesting idea. Looks like a couple hundred bucks worth of parts. At that price wouldn't I be better off buying a small Kelly AC inverter? I know their reputation proceeds them, but compared to a bunch of cobbled Chinese parts doing something they weren't meant to do...


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## major (Apr 4, 2008)

toddshotrods said:


> .....wouldn't I be better off buying a small Kelly AC inverter? ...


You'll be sorry


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## toddshotrods (Feb 10, 2009)

major said:


> You'll be sorry


I was expecting that reply. 

...wonder if this is going to turn into a good Kelly/bad Kelly thread now. 

I know they're the polar opposite of say a Soliton, but just for making an AC motor function, equivalent to hooking a 12v battery to a DC motor? Still that bad Major?


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## major (Apr 4, 2008)

toddshotrods said:


> I was expecting that reply.
> 
> ...wonder if this is going to turn into a good Kelly/bad Kelly thread now.
> 
> I know they're the polar opposite of say a Soliton, but just for making an AC motor function, equivalent to hooking a 12v battery to a DC motor? Still that bad Major?


I was unaware they made a controller they claim will function with an induction motor for vehicle propulsion. So I read over the manual. I don't want to waste the time explaining why I think they fall short of having a suitable product, but, let's say, I don't like what I see there, and throw that in with what we have seen in the past from them; need I say more?

In short, I think you'll waste the $250 plus whatever it cost you to get it here from China. In some ways, I'd like to see you buy it and try to use it, and I won't even say I told ya so  Go ahead; make my day; prove me wrong


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## toddshotrods (Feb 10, 2009)

major said:


> ...In some ways, I'd like to see you buy it and try to use it, and I won't even say I told ya so  Go ahead; make my day; prove me wrong


I doubt that I'll be doing that.  In the end, spending >$200 to make an AC motor do what my DC motors do with a starter battery hooked to them doesn't make a lot of sense. I was curious is there was even a way, but it seems not...

I could just buy another forklift motor with that money, hook the cables up, flip the switch, and spin my way into bliss!


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## PStechPaul (May 1, 2012)

That Kelly inverter is only rated for 48VDC and their other product is 72VDC. That might work for a specially wound AC motor like the Azure Dynamics and AC20-50 motors, but will only spin a 220V ACIM at 20% of rated speed with full torque.

If you can find a cheap industrial VFD and a 12V or 24V to 120 or 240 VAC inverter, you will at least be able to get used to AC motors and drives, which will most likely become ubiquitous in the DIY EV community. If you can put enough batteries together for the 200-240 VDC minimum bus voltage, you won't need the 12V/24V inverter, and you will gain the benefit of regen with an AC induction motor. 

I will probably be using 20 x 12V 8Ah SLAs for my larger tractor project, and I'll have 1.9 kWh for about $350 and I should be able to do normal mowing with about 2 HP (1.5 kW) for at least 1/2 hour. I may even upgrade to 40 batteries so I can use my 7.5 HP 460V VFD which I got for about $80. I already have a 5 HP 4 pole motor which I may be able to overclock for 10 HP at 3600 RPM and 20 HP at 2x torque (with a bigger inverter of course). But I don't need that much power for a tractor which originally had just an 8HP ICE! 

For the smaller riding mower toy I will probably use the 12V to 220V inverter and maybe rig up a charger from the 270VDC bus to the battery for regen. I could get a 105 Ah 12V deep cycle battery for $90 or so, which should let me run around at 500W for up to 1.5 hours.


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## toddshotrods (Feb 10, 2009)

PStechPaul said:


> That Kelly inverter is only rated for 48VDC and their other product is 72VDC. That might work for a specially wound AC motor like the Azure Dynamics and AC20-50 motors, but will only spin a 220V ACIM at 20% of rated speed with full torque.
> 
> If you can find a cheap industrial VFD and a 12V or 24V to 120 or 240 VAC inverter, you will at least be able to get used to AC motors and drives...


You missed the point of the question/thread. Spinning at "20% of rated speed with full torque" would be ideal. That would, indeed, be the equivalent of hooking a 12v battery to a DC motor to test it; or move the vehicle around in the shop/garage/drive/parking lot. Actually, it would be a bit better because it would have a throttle instead of a on-off switch.

In the case of my bike, I was using the tiny little PM motor I had lying around, and wanted to verify that it would be strong enough to move the bike - before spending any more time and money on it. It worked really well, and allowed me to move forward to the next step. In some cases, it would permit testing a motor to see if it was okay, like we do on DC motors...

Major's point about the Kelly is well taken in this case, because I haven't seen any reports of anyone using one. For what I was interested in doing, I am not willing to roll the $250 dice on something that might not even work at all. I could just buy another DC motor and _know_ that it will work.


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## toddshotrods (Feb 10, 2009)

PStechPaul said:


> ...If you can find a cheap industrial VFD and a 12V or 24V to 120 or 240 VAC inverter, you will at least be able to get used to AC motors and drives, which will most likely become ubiquitous in the DIY EV community...


That is still an attractive/interesting/tempting idea, that I might explore someday.

What's the downside? Seems like that little 12 or 24v "battery pack" is doing a lot of work; can't be very efficient?


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## PStechPaul (May 1, 2012)

Automotive inverters are fairly efficient, at least according to their specs. Probably an honest 90%. They're probably even better at making the 270 VDC which is switched for the modified sine wave. For 1.5 HP the 1200W inverter will draw about 51 amps from a 24V battery. If you use 20 Ah or larger lithium cells they should be fine at 2C. For lead-acid batteries the typical 35-100 Ah types should be OK for testing, at least. For 50 amps, the usual leads supplied (about #12 AWG) will drop some voltage and run hot, so you will need to use larger leads unless you are only running for a few minutes.

I'm pretty much sold on three phase ACIMs, even for small projects like tractors and bikes. And I see no reason why standard industrial motors and VFDs can't be used, and that can bring the cost down to under $1000 for motor and controller for 10-20 HP projects and a few grand for bigger stuff. The main cost will be batteries, as always, and the BMS and charger which may be considerable for higher voltage packs.

I plan to complete one or both of my tractor projects this summer, and I'll have more data then. Good luck!


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## Siwastaja (Aug 1, 2012)

VFDs use IGBTs that have a voltage drop. Typical conduction loss of an industrial AC motor drive is 5 volts, so at 300V it's 98% efficient (not including switching losses), but at 12V it's only 58% efficient and you have only 7 volts left for the motor. In addition, the units will not work from low DC voltages without possibly heavy modification.

Then again, running a cheap 1-phase AC inverter to drive a VFD is overly complex, expensive and inefficient.

But if you are testing it in the garage, why not just plug in the VFD in the wall? Why use batteries? Just get an extension cord.


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## toddshotrods (Feb 10, 2009)

Siwastaja said:


> ...Typical conduction loss of an industrial AC motor... ...12V it's only 58% efficient and you have only 7 volts left for the motor. In addition, the units will not work from low DC voltages without possibly heavy modification...


Hooking 12v directly to an induction motor was never discussed? 





Siwastaja said:


> ...Then again, running a cheap 1-phase AC inverter to drive a VFD is overly complex, expensive and inefficient...


That's what I figure, because 24 measly volts is stepped up enough and converted to drive a 208v motor, but efficiency isn't a serious concern in this case.





Siwastaja said:


> ...But if you are testing it in the garage, why not just plug in the VFD in the wall? Why use batteries? Just get an extension cord.


Because that would suck, and I wouldn't be able to do this: 




The shop is 24,000 sq ft, so I have room to actually _go for a ride_, but it's a around corners, down aisles, around more corners, etc. I would have to buy a 500ft cord, and have someone literally run behind me to keep it flowing freely. 

I like experimenting and sometimes that involves seeing if some wacky idea I have will work before really investing into it. Just looking at it you would never think this little motor would be capable of doing what it is doing, but it actually has even more potential than I am using. that was discovered in the 12v DC tests, but I don't have an equivalent to that to allow me to play with AC.


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## PStechPaul (May 1, 2012)

It's good that you can ride with that little motor and 12VDC. Watch out for that kickstand, though! 

The motor is rated for 1.7 HP, with 605 oz-in (3.15 lb-ft) torque and 2840 RPM. That's also an intermittent rating. So it may be somewhat underpowered for a street machine, at least if you want reasonable life and reliability. It looks about twice the size of a series 12VDC motor I bought recently for $8, which is about 1/16 HP:
http://www.herbach.com/Merchant2/me...AR&Product_Code=TM01MTR4476&Category_Code=MTR

If you and the bike are 150kg (330lb), it will take about 1.7 HP to cruise at 50k/h (30MPH) on a 2% grade. Series wound motors can produce a lot of torque for short bursts, a lot more than their ACIMs of similar size, but at the cost of efficiency and longevity. That 5HP AC motor would make an awesome machine, but it may be rather heavy and bulky.

I searched for information on Protech, but their website is severely deficient for specs:
http://www.protech-inc.com/1.html

But it appears that this may be a brushed PM DC motor, so be careful about overheating and overcurrent which may destroy the magnets.


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## toddshotrods (Feb 10, 2009)

PStechPaul said:


> It's good that you can ride with that little motor and 12VDC. Watch out for that kickstand, though! ...


It's funny that people see the kickstand. It had no spring, and I was aware of what and how it could get caught on in the shop floor. The spring has been installed since then, so I lived to tell about it... 





PStechPaul said:


> ...The motor is rated for 1.7 HP, with 605 oz-in (3.15 lb-ft) torque and 2840 RPM. That's also an intermittent rating. So it may be somewhat underpowered for a street machine, at least if you want reasonable life and reliability...
> 
> If you and the bike are 150kg (330lb), it will take about 1.7 HP to cruise at 50k/h (30MPH) on a 2% grade...
> 
> ...


I'm not using that for the actual motor on the bike. The ultimate plan is for a Mars ME1003. The foam "case" around the ProTech motor is exactly the shape of a ME1003, so that I can just drop it in when I finally get one.

I was just trying to make sure an ME1003 would be enough for my intended purposes, and that I like PM motors - yes, on both counts. My 12v test gave me the necessary info, and was a blast to play with in the meantime. It was actually pretty peppy. I'm running at 48v now.




PStechPaul said:


> ...But it appears that this may be a brushed PM DC motor, so be careful about overheating and overcurrent which may destroy the magnets.


I only paid $80-90 bucks for it, with shipping, so it's kind of expendable, but I am trying to walk the tightrope between exploring its capability and wiping the magnets. So far, it has tolerated four times rated current, with no apparent (_seat of the pants_) signs of degradation. It feels as strong as it did the first time I used it. Initially, I had no control over how much current was going in it, with the on/off switch. Now that I have the Alltrax controller, I can try to take care of it. Current spikes at a little under 120 amps for _spirited_ acceleration, and it drops down to 30-40 amps pretty quickly. I don't have enough battery to push it long enough to even get it warm right now.





PStechPaul said:


> ...That 5HP AC motor would make an awesome machine, but it may be rather heavy and bulky...


It's about 7" diameter and 11-12" long (without the shaft), and maybe 30-40lbs, which is perfect for a bike, kart, etc.

As mentioned, I was hoping to find a cheap way to play with it to see how well it would do. I _might_ try the inverter-to-VFD idea... I think the info derived would also be helpful in figuring out how to rewind it for whatever type EV I decide to put it in.


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