# Determine DC motor specs from measurements?



## major (Apr 4, 2008)

thingstodo said:


> The motor is claimed to be a surplus brushed DC aircraft motor, 21 HP, rated 120 VDC, separately excited, about 7.5 inches in diameter. There is no nameplate and no serial numbers/part numbers.
> <snip>
> Any suggestions would be appreciated.


Sounds like an aircraft starter/generator. Post photos and see if you can get member onegreenev aka Pete to tell you about it. There is info out there, I just don't recall where.


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## thingstodo (Jul 16, 2010)

major said:


> Sounds like an aircraft starter/generator. Post photos and see if you can get member onegreenev aka Pete to tell you about it. There is info out there, I just don't recall where.


I did some video of the motor with a not-so-good video camera ... but I didn't get still pictures before I put it into the car for testing.

I guess it was too much to hope that the specs could be determined from measurements.

Do you think that pictures 'inside the car' (engine compartment) would show well enough? Or do I need to remove the motor from the engine compartment?


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## major (Apr 4, 2008)

thingstodo said:


> IDo you think that pictures 'inside the car' (engine compartment) would show well enough?


Give that a try first


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## thingstodo (Jul 16, 2010)

I had time this evening, so I yanked the electric motor out.

I verified that the motor has no markings (nothing stamped or embossed, anyway) - but the motor has been painted black, same as the new motor mount.

If I missed anything that will help in identification, please point it out.


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## major (Apr 4, 2008)

thingstodo said:


> I had time this evening, so I yanked the electric motor out.
> 
> I verified that the motor has no markings (nothing stamped or embossed, anyway) - but the motor has been painted black, same as the new motor mount.
> 
> If I missed anything that will help in identification, please point it out.


Punch in "jack & heinz #g23 aircraft generator" to google.


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## onegreenev (May 18, 2012)

Yup, it's a Starter/Generator motor. Mostly used with contactor speed controllers. Old Skool. Many of these have one of the field windings internally connected to the armature so there are usually only three terminals usable. The other one is usually marked D and is used in the aircraft to measure voltage and not used for actually powering the vehicle. I am not sure about the Jack Heinz motors but the GE Starter/Generators have only three terminals to use. You can actually use a regular series motor controller to power these. What I did was do a cross over for the field to armature and then just connect the two big terminals like you would a normal series motor. You get pretty high current in the field but it does work. These are usually run with 72 volts or less. With the controller setup you can use it but do not let it sit without running it while turned on because you will be pumping in current through the fields and heat the motor up. These are best used in old VW buggies and light vehicles like that. Don't expect very high performance but they are built well. 

I plan on using one for a generator to charge my vehicle. It will be a project for the future but hopefully not too far away. 

I have a video using mine with a normal series controller. It does work. Just don't use too high of voltage. 

You might want to see if the two small terminals are not connected internally. If they are not connected internally you can connect a small controller to the field and a larger one to the armature and control the motor with two series controllers. One small one and one large one. Be sure again to turn off the field if your motor is sitting at a stop. 

I recommend you use a larger normal series motor for your ride. If you use them be sure you cool the motor. A good cooling fan is a MUST. 

Pete 

PM me if you want more information.


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## onegreenev (May 18, 2012)

Forgot to mention they are interpole motors. Good thing.


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## thingstodo (Jul 16, 2010)

I labeled the terminals so I could keep them straight.

On the first picture, the connections are frame ground on the left (F2), 12V from aux battery on the right (F1). +12V from the traction battery on top (A2) and 0V from the traction battery on the bottom (A1). This wiring is as the car was purchased ... and does not appear to be an optimal solution.

Measurements show A2 (Top) connected to F1 (Right) as 0.0 ohms. 

A2 (Top) to A1 (Bottom) is 0.7 ohms

A2 (Top) to F2 (Left) is 2.4 ohms

A1 (Bottom) to F2 (Left) is 2.9 ohms

A1 (Bottom) to F1 (Right) is 0.5 Ohms

A1 (Bottom) to A2 (Top) is 0.7 Ohms (not a bad idea to check ...)

F1 (Right) to F2 (Left) is 2.4 ohms (not a bad idea to check ..)

So it appears that A2 and F1 are the same terminal, connected by a jumper. A1 to F1 + A2 to F2 = A1 to F2. It confuses me a bit that each terminal appears to be internally connected to EVERY other terminal through a jumper or a coil. I guess one of those would be the interpole?

I'll get the motor connected tomorrow and see if the peak current goes down, and if it still turns the same direction. Hopefully not. It sounds very difficult (way past my mechanical ability) to reverse the direction of rotation.

It should be more reliable to have the field internally connected. I was a bit worried about verifying the field current before allowing the armature contactor to engage. It appears that I only need two connections ... A1 and A2 ... perhaps I'll start with three terminals - A1+, A2-, F2+ and add a decade resistor in series with F2 so I can vary the resistance to see what effect it has on the current or the speed (or both).

The specs from the internet search are not an exact match (at least the ones that I found). 5,000 - 10,000 rpm sounds the most likely. I would not expect to run the motor above 4000.

The car is not in good enough shape to pass an inspection, so I will not be taking it above 30 mph. I might take it out of first gear to check how the acceleration is in second. I'll be using it to test out some DC versus AC configurations. The tests should be short (30 seconds?) but I will add an external blower to try to avoid heating issues.

Thanks for the assistance!


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## major (Apr 4, 2008)

Hey thing,

I helped Michael out with his Mitsubishi years ago on the EVDL. http://www.flickr.com/photos/mbarkley/sets/72157603518876045/ You might try to find that in archives. It is a bit tricky to get it wired correctly and I don't remember anymore.

major


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## onegreenev (May 18, 2012)

That motor has the field in common with the armature from internal. Terminal D is not used. Terminal D is a small one and was used to measure voltages and has nothing to do with running the motor in either traction or generation. The small terminal A is jumpered to the armature so the field is given a low amperage current to allow the field to be energized. You no longer have the ability to use this as a generator if you jumper this and use a modern controller. But it does work as a motor. Keep lots of air on the motor as it will get hot.


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## thingstodo (Jul 16, 2010)

major said:


> Hey thing,
> 
> I helped Michael out with his Mitsubishi years ago on the EVDL. http://www.flickr.com/photos/mbarkley/sets/72157603518876045/ You might try to find that in archives. It is a bit tricky to get it wired correctly and I don't remember anymore.
> 
> major


Thanks for the link. I can see the pictures but no luck digging it out of the archives. I'm likely just not very good at it yet.


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## thingstodo (Jul 16, 2010)

onegreenev said:


> That motor has the field in common with the armature from internal. Terminal D is not used. Terminal D is a small one and was used to measure voltages and has nothing to do with running the motor in either traction or generation. The small terminal A is jumpered to the armature so the field is given a low amperage current to allow the field to be energized. You no longer have the ability to use this as a generator if you jumper this and use a modern controller. But it does work as a motor. Keep lots of air on the motor as it will get hot.


I did not connect the smaller terminal that appears to be connected to the A2 terminal (I had called it F1). There are no markings. I have not found a wiring diagram to match so far.


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## thingstodo (Jul 16, 2010)

Deep cycle battery used, just one, at 12V. The current is likely limited by this battery.

So the first test was wired + battery to A1, A2 to a contactor, contactor to - battery. Jumper, as suggested, from A1 to F2 for the field. That jumpers out the A1-F2 coil that shows as 0.7 ohms. 

The motor starts up with a peak of 120 amps instead of 200+. Progress. The speed is still about 770 rpm. It runs faster until it warms up (under a minute) and levels out at about 10 amps (like yesterday's test). 

UNLIKE yesterday's test, the rotation is CCW from the drive end, or CW if you are facing the brush end. This would be the correct direction to move the car forward in first gear, reverse in reverse gear. (Yay!)

Second test - putting a power resistor (8 ohms, 10W) as a jumper between A1 and F2. The rest of the circuit is the same. Result? Motor draws 180 amps when the contactor energizes but the motor DOES NOT SPIN. I guess the field is too weak to give the motor starting torque?

Third test - put a switch across the 8 ohm power resistor, so that I can start the motor with the switch closed (like the jumper in the first test) and then open the switch after to weaken the field, or that's my theory. Result is the normal 770 rpm running speed, same motor sounds, same 120 amps on start. After the current levels out at 10A, open the switch that jumpers the resistor. The motor speeds up slowly (higher pitched whine, maybe 30 seconds). Ends up at 2900 rpm. The current to the armature rises. Total current from the battery levels out at 13A

I think that the 8 ohm resistor I had on hand may be a bit large for this voltage. 

It will be a while before I get the motor back in. I need a controller - the Kelly that the car came with failed. I think it wanted a larger precharge resistor to limit the capacitor current on start. Do I need a way to verify field current, dropping out the armature if the field current is lost?

For a 24V or 36V pack, would replacing the A2-F1 jumper with an automotive relay (limit current, drop the voltage a bit) work? I could put the relay contacts of this new relay in the control circuit for the armature - so the contactor will not be ON unless the contacts are closed. Is this being too paranoid? The controller should deal with this (if it works with SEPEX) - right?

How much air pulled through the motor is 'lots'? 100 cfm? 200? 400? 

So far, the tests at 12V (maybe 10 minutes of running over an hour) did not bring the temperature measurably above ambient (cheap infra-red thermometer).


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## thingstodo (Jul 16, 2010)

Cross-post. kennybobby's response appears to me to be a very good method that can be used to determine several parameters of a DC motor given a set of measurements:

Start with claimed voltage and claimed HP, giving rated current for field
Measure no-load current at a lower voltage
Measure stalll current at a lower current

Do some calculations:

Scale things up to claimed rated voltage
Calculate output torque at stall (assuming that the motor does not melt)

Measure to confirm calculations at a higher voltage, and monitor the temperature of everything to make sure it won't melt.

Increment the voltage being used for testing until the motor begins to heat. Stop there.

http://ecomodder.com/forum/showthre...gure-out-dc-motor-specs-23654.html#post335292


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