# Possible lead on a used motor



## Jamie EV (Oct 3, 2012)

I'm going to pick up a used 24 volt DC motor tomorrow. Apparently it was used by some sort of heavy equipment (don't know what. Owner does not know. Found it in a garage). It looks pretty large in the photo.

He wants 40 bucks. Hopefully it will be something I can overvoltage to get higher HP. If it's ideal, it might be the steal of the century.

Is anyone else here running an original 24 volt motor for their EV? (car I mean)

I'll keep you posted on the motor...I'm all excited...I hope it's good.


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## Jamie EV (Oct 3, 2012)

Never mind. It was a tiny motor used to raise and lower the arm on a construction machine. POWERFUL BUT SLOW RPM...sigh....my search continues...


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## PStechPaul (May 1, 2012)

You should check eBay and craigslist in your area. I found this 25 HP motor for $250:
http://annapolis.craigslist.org/grd/3311080873.html


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## Jamie EV (Oct 3, 2012)

Actually, I did see some on eBay for 200-300 bucks. Rebuilt Crown forklift motors 36-48 volts. hink they would be able to handle my 2635 lbs initial curb weight Elantra?


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## PStechPaul (May 1, 2012)

I realize that you are looking for a DC motor, and although they seem to be much simpler and easier to use, there are some distinct problems that would steer me away from that route even before I tried it. So I don't have experience with series wound DC motors and I only know what I have read on-line and here on the forum. 

Today I connected a 12V to 220V automotive inverter to a 17 Ah SLA and the output to a 2 HP VF drive and I was able to run a 2 HP three phase motor on my little tractor. The inverter is rated 1000W peak but only 400W continuous, so it won't really provide the full power I need to be practical. But I think I might be able to use two more inverters, each with their own battery, connected to the three phase inputs, and that should be enough for 1200W or 1.5 HP which will be enough. And here is the total cost:

Batteries (12V 12 Ah) 3 at $24 each: $72
Motor (2HP 3 phase 2 pole): $50
Inverter (12V-220V 400/1000W) 3 at $43 (including shipping): $129
VF Drive (2 HP): $65
Riding mower: $40
Total: $356

It's not a car, of course, but I've learned a lot. The tractor will run with about 300 watts, so the batteries (432 Wh) will probably give me about 1/2 to 3/4 hour run time on flat terrain. Maybe a mile or so. But I want to use a data logger to learn more about the overall efficiency, and I might upgrade to larger batteries. Maybe floodies (weight is good for a tractor), or maybe Lithium.

But with standard inexpensive components there is little chance of catastrophic failure. AC motors and controllers and inverters are essentially fail-safe because the high voltage will turn off if there is an overload and the motor cannot run unless the controller is producing an AC signal. Series wound DC motors need safety interlocks and speed sensors to avoid possible dangerous overspeed if unloaded, and destructive high currents if the there is a locked rotor condition or shorted IGBT in the controller.


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## Jamie EV (Oct 3, 2012)

PStechPaul said:


> I realize that you are looking for a DC motor, and although they seem to be much simpler and easier to use, there are some distinct problems that would steer me away from that route even before I tried it. So I don't have experience with series wound DC motors and I only know what I have read on-line and here on the forum.
> 
> Today I connected a 12V to 220V automotive inverter to a 17 Ah SLA and the output to a 2 HP VF drive and I was able to run a 2 HP three phase motor on my little tractor. The inverter is rated 1000W peak but only 400W continuous, so it won't really provide the full power I need to be practical. But I think I might be able to use two more inverters, each with their own battery, connected to the three phase inputs, and that should be enough for 1200W or 1.5 HP which will be enough. And here is the total cost:
> 
> ...



It's true, there are loads of AC motors out there that are a lot cheaper than the equivalent DCs....but I'm so unsure of controlling the speed on an AC motor, it frightens me. Yes I agree that this is the way the industry is going (AC)....but from what I gather AC controls are difficult. I like the idea of using inverters....but hey'd have to be purpose built on an EV unlike your tractor.


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## PStechPaul (May 1, 2012)

For an EV you should put together a battery pack with enough voltage to run the motor controller without an inverter. You can get 40 Ah 3.3V LiFePO4 cells for about $50 each. You need about 100 of them for a practical vehicle, so $5000 for a 12 kWh pack which will give you about 30 mile range. You will need to be careful with up to 350 VDC, but it's really no more dangerous than 120/240 VAC house wiring, if you have the proper safety components installed. 

There is also danger from low voltage DC motors. You will need at least 48 VDC for a car and more likely about 100 volts. That's still "potentially" lethal. And you need very heavy wires to carry the current, and you need a motor controller with safety features as explained on this forum to prevent overspeed explosion and brush/commutator damage. 

With a standard AC motor and VF control, you can get "up and running" pretty quickly, and the wiring will be much like house wiring, probably #10 or #8 which is easily handled and inexpensive. You can even get started by using three car batteries and inverters to run a 25 HP motor at about 20% rating (about 5 HP or 4 kW) which will allow you to drive the car for testing, before you invest in a proper Lithium battery pack. Others may disagree, and they have more experience, but I contend that a standard industrial VF drive can be configured for torque control which is suitable for EV use. And the total investment can be under $1000 for a first run prototype and then upgraded with a battery pack and better controls.


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## Jamie EV (Oct 3, 2012)

PStechPaul said:


> For an EV you should put together a battery pack with enough voltage to run the motor controller without an inverter. You can get 40 Ah 3.3V LiFePO4 cells for about $50 each. You need about 100 of them for a practical vehicle, so $5000 for a 12 kWh pack which will give you about 30 mile range. You will need to be careful with up to 350 VDC, but it's really no more dangerous than 120/240 VAC house wiring, if you have the proper safety components installed.
> 
> There is also danger from low voltage DC motors. You will need at least 48 VDC for a car and more likely about 100 volts. That's still "potentially" lethal. And you need very heavy wires to carry the current, and you need a motor controller with safety features as explained on this forum to prevent overspeed explosion and brush/commutator damage.
> 
> With a standard AC motor and VF control, you can get "up and running" pretty quickly, and the wiring will be much like house wiring, probably #10 or #8 which is easily handled and inexpensive. You can even get started by using three car batteries and inverters to run a 25 HP motor at about 20% rating (about 5 HP or 4 kW) which will allow you to drive the car for testing, before you invest in a proper Lithium battery pack. Others may disagree, and they have more experience, but I contend that a standard industrial VF drive can be configured for torque control which is suitable for EV use. And the total investment can be under $1000 for a first run prototype and then upgraded with a battery pack and better controls.


That is a very compelling argument for going AC! What precisely does VF control entail? Is it something where rpms can be easily adjusted?


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## Jamie EV (Oct 3, 2012)

30 hp VF controllers cost as much as a DC motor and controller combined. Not sure if that's a solution for me. If you're comfortable with AC then that's pretty neat though.


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## PStechPaul (May 1, 2012)

If you watch my videos you will see my VFD controller. There is some programming involved to match it to the motor, but then all you need to do is connect an AC or DC supply to it, and connect the three motor leads to the output. The control panel shows the RPM (or optionally the voltage, current, frequency, or torque), and you can control the motor by using the start/stop buttons and up/down buttons to adjust speed. You can program the ramp-up and ramp-down so it changes speed and starts and stops smoothly. 

I connected a potentiomenter and an SPDT center off switch to the control inputs, so the motor can be started and stopped and speed adjusted from a remote hand-held box. It could also be connected to a foot operated pedal. And I also built an interface that allows control with a joystick. I have not tried direct torque control (DTC), but you can program the VFD so that it produces an analog signal indicating torque. So you can use an op-amp or a microcontroller to read the throttle position and the torque, and apply a control signal proportional to the difference between throttle position and actual torque. You can also add a little bit of delay to make it smoother. The controller will automatically protect the motor against overload with a built-in time delay overcurrent shutdown, and an instant shut-down if a short is detected or if bus voltage exceeds the limits. 

See http://www.youtube.com/PaulAndMuttley for my videos.


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## PStechPaul (May 1, 2012)

If you search diligently you can probably find a good used 20-30 HP drive for under $1000, and 5-10 HP for under $500, and 2-5 HP for under $100. You could get a small drive and motor to use for a while to get familiar with them, and maybe make an electric tractor or go-cart. Here's a new 20 HP 208-240V drive for about $1200:
http://www.ebay.com/itm/20-HP-Varia...986?pt=LH_DefaultDomain_0&hash=item3f16818a72

And a new 3 HP VFD for $120 including shipping:
http://www.ebay.com/itm/PROFESSIONA...751?pt=LH_DefaultDomain_0&hash=item46004efadf


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## Coulomb (Apr 22, 2009)

PStechPaul said:


> But I think I might be able to use two more inverters, each with their own battery, connected to the three phase inputs, and that should be enough for 1200W...


Err, you'd have to synchronise the three inverters, and arrange for a 120 degree phase shift... it doesn't sound easy to me. With three unsynchronised 60 Hz rough sine waves, I'd hate to think what would happen. Remember, you need a rotating magnetic field to drag the rotor around.

You could use a 3-phase inverter, but I doubt that you'd get one for near $43, including shipping or not


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## PStechPaul (May 1, 2012)

You are correct, and I made some false assumptions. I ran an LTSpice simulation and you can connect three single phase inverters in a star configuration or two in a delta, but depending on the relative phase, the DC link through the three phase bridge can vary from about 300V to 600V:










A better way may be to connect a full wave bridge to the output of each inverter, and then you can connect the DC outputs to the DC bus input. You can connect any number in parallel, although the one with highest output will take most of the load. This is self-regulating, however, especially if the battery has significant sag.

The best way may be to modify the inverter. Internally the 12 VDC is first converted to about 160 or 320 VDC, and then is switched by a low frequency (50/60 Hz) full bridge. These DC supplies may be fed through diodes to the DC link, and the internal diodes of the VFD may be used for this purpose.


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## Coulomb (Apr 22, 2009)

PStechPaul said:


> You are correct, and I made some false assumptions. I ran an LTSpice simulation and you can connect three single phase inverters in a star configuration or two in a delta, but depending on the relative phase, the DC link through the three phase bridge can vary from about 300V to 600V:


Sorry, I had also made some incorrect assumptions. I thought you were driving the motor directly from the output of the three inverters, and that's why you wanted three of them. But you are rectifying the outputs and using that for the DC bus for the real inverter.

So three in star would be better, I think, but really the two in delta isn't delta, it's just three in star with one always zero volts. So it would be better because it reduces the chances that none are opposing at any one time.

But they could all be synchronised in the same direction for some time, halving the voltage. Having the voltage varying at a very low frequency (the difference between two inverter's frequency) could be very disconcerting. Much better to just use two of them, and force anti-synchronisation somehow (so the outputs are always opposite, so the output voltages will always add when in series). The obvious way to force anti-synchronisation is to force exact synchronisation and swap the outputs on one.

Then again, if you have to open them up to modify them, why not just discard the output stage (DC-AC) and hook up the two DC buses from the two inverters in series. There is still the problem that they won't be rated for double bus voltage isolation to chassis. I would think that a cheap inverter would not last long with ~680 V DC stressing the insulation all the time.


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## mizlplix (May 1, 2011)

Not to rain on your parade, But ask on this forum:

Has anyone successfully converted an industrial inverter and have used it to power a surplus 3 phase motor in a car, driven daily on the road?


It is one thing to make a motor turn over sitting on a table. It is another to drive it in a car a while without any problems.


Miz


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