# Testing Motor in Jet Electrica - Prestolite?



## major (Apr 4, 2008)

Revolting said:


> Hi I am new at EVs and am learning as I go. I got a Jet Electrica just before Thanksgiving. It's a project car and I am trying to test the motor. The motor didn't spin when I tried to test it. It looks like the Prestolite in the pictures and diagrams I can find.
> 
> I have seen mention of people testing motors by jumping 12vdc to them. The documentation I have leads me to believe that I should touch positive voltage to the terminal(S2) closest to the transmission and negative to the terminal(A2) further away from the transmission. There are two other terminals that are connected by a flat bar and I didn't use them, A1 and S1.
> 
> ...


Hi Rev,

Never use high voltage for a no load test on a series wound motor. 12 volts is as high as you can go. Higher voltage will cause overspeed and damage.

Did you have the A1 S1 jumper in place for the test? If so, and you got no rotation and no spark and 12V on A2 S2, it sounds like there is an open circuit in the motor. Possibly the brushes are hung up. Does the shaft rotate by hand?

Post up some photos and I'll help you.

major


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## Revolting (Nov 19, 2012)

Thanks for the reply.

The motor is mounted in the car. I have the car on jackstands with the front wheels off of the ground and I am testing with the car in first gear so I can see the wheels spin if the motor runs. The jumper is installed across A1 and S1.

Can I turn the shaft by hand with the motor installed?

I didn't put the meter on A1 or S1 with voltage applied, would that tell me anything about brush contact?

I have no idea how long it has been since this motor last ran or any problems it might have had. It is kinda rusty looking, not nice and clean.

Pictures coming...


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## mizlplix (May 1, 2011)

The first thing to do is to remove the motor band covering the brush area and let the crap fall out. Then you can see all. Let us know.

PS: You will have to cut the screw to remove it....LOL

Miz


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## Yabert (Feb 7, 2010)

Impressive performance of rust!...
Like Miz said, see inside the motor (brush area) will help to diagnostic.


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## Revolting (Nov 19, 2012)

How quickly should the motor get up to speed on 12VDC?

How many amps should it draw at 12V?

The motor runs. I turned the motor by hand, through the vents. It turned easily and smoothly. Then I tried again jumping 12VDC across S2 and A2 and it ran. It sounds kinda slow and took time to build speed. How quickly should it get up to speed? I think the book said 1700 some odd rpm on 12V. Battery voltage held at 12.26V or so while the motor was running.

I feel like a kid at Christmas time.

Edit: It goes up to about 32 amps and slowly drops off as the motor speeds up. I disconnected at about 26 amps. Battery maintained 12.28 VDC while running. I measured amps with a clamp meter, I think it is accurate.


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## major (Apr 4, 2008)

Revolting said:


> How quickly should the motor get up to speed on 12VDC?


1.47 seconds. Na, just kidding. But really fast if you have a good well charged battery. Like maybe even less than a second. That would be with an empty shaft. If you have a flywheel on it, it will take a little longer to accelerate that mass. But just a few seconds.




> How many amps should it draw at 12V?


Hard saying. If it was a good motor and stiff battery with large cables connecting it, maybe a 1000 Amps. But just for the first few microseconds  As it speeds up the current goes down. So typically it tries to draw a bunch of current at first and makes you twitch causing a spark between the jumper and motor terminal. Then as the connection is made the motor speeds up and the current goes down. So you get a spike of like a couple hundred amps for a fraction of a second and then it settles out to maybe 25 to 50 amps when it is running at speed a second or three later. No load on these series wound motors is such a steep curve it is really hard to pin down an exact RPM and Amps. 1700 RPM and 35A would sound O.K.

It sounds to me like you might have a high resistance in the motor. Judging from the terrible rust on the outside of the motor, I wouldn't be surprised if the brush springs are corroded and possible corrosion on the comm surface. Corroded terminals will also cause high resistance.

You need to get the coverband off the CE of the motor and post photos of the comm and brushes.

major


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## Revolting (Nov 19, 2012)

Hi, thanks for the reply.

I am going to have to pull the brush cover off. Maybe it isn't as difficult to get to as it looks but it looks like I might end up pulling the motor and transmission as a unit to get the cover off.

If I have to pull the motor and transaxle I will probably go ahead and have some refresh work done while I'm in there. The motor is directly under a battery box and it looks like maybe some acid leaked on the motor. The rest of the car looks much better, especially for its age, not rusty. 

I found the test info and attached pictures.


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## major (Apr 4, 2008)

Revolting said:


> Hi, thanks for the reply.
> 
> I am going to have to pull the brush cover off. Maybe it isn't as difficult to get to as it looks but it looks like I might end up pulling the motor and transmission as a unit to get the cover off.
> 
> ...


You should be able to get the coverband off. It is sheet metal and should pull off with a little flex (slight bending).

That's not to say I don't think the motor should come out for a good cleaning and inspection


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## Revolting (Nov 19, 2012)

Got the brush cover off, exactly as described. Cut the bolt, flex the sheetmetal cover.

Attached a couple pictures, it's kinda difficult to get good pictures up in there.

I'll have to get a battery box loose to get to the top brushes.

The brushes are as long as the guides around them. the springs are coated with rust but seem to have not deteriorated. I pulled on the springs and they feel firm, didn't try to measure pull. I can clearly see the lines between the bars in the commutator. There is a coating of residue on the commutator that doesn't look like copper, much darker, more grey than brown. The commutator bars look flat along their length, not worn concave or wavy.


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## major (Apr 4, 2008)

Revolting said:


> Got the brush cover off, exactly as described. Cut the bolt, flex the sheetmetal cover.
> 
> Attached a couple pictures, it's kinda difficult to get good pictures up in there.
> 
> I'll have to get a battery box loose to get to the top brushes.


Yep, very, very crappy  Springs are likely weakened and ready to break. Commutator is covered with crap. That all adds up to high resistance (poor electrical contact) and also bad abrasion on the mechanical side. It is possible with high voltage it could run but it'd get hot and likely do more damage. I suspect it is serviceable. Get it to a motor repair shop for a rebuild. New brushes and springs. Comm turned and undercut. Cleaned inside and out. New bearings. Insulation inspection and touch up. She'll be good as new......really


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## Revolting (Nov 19, 2012)

Thanks. That was my gut feeling, motor needs help.

What would you guess for the cost of servicing this motor vs buying another motor?

I know any kind of labor is high. What kind of money for a rusty motor service these days? Would another motor be a more reasonable consideration?

This motor doesn't look very worn to me. The car doesn't show much wear either. More exposure to the elements than wear.


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## major (Apr 4, 2008)

Revolting said:


> Thanks. That was my gut feeling, motor needs help.
> 
> What would you guess for the cost of servicing this motor vs buying another motor?
> 
> ...


It could go well and just a set of springs and cleaning for $100. But chances are it will take more. Bearings are sealed and may be good to go. But I bet it needs lathe time. Shouldn't take long. Try to find a shop that does forklift motor repair. The motor is Prestolite MTC-4001. Very similar to 7 inch pump motors used on 36/48 volt Clark, Allis Chalmers, Hyster trucks. Most parts like brushes and springs are the same. Difference was in the winding and shaft which look o.k. for you. 

You know? Rusty motors work just fine  Best way would be to disassemble it, sandblast and paint. But you risk snapping off screws and crap like that. So you can just wire brush it, clean it, mask it and rattle can paint it.


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