Single phase induction motor wiring help needed

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Today, apart from cutting up shockers, I also salvaged an induction motor from an old Karcher pressure washer. The years had not been kind as it had been sitting outside for about 5 years. I really had no idea what to use it for until the scraping class and the tool grinders we were using. I figured I could make use of it by attaching a diamond cup wheel for shapening TC inserts.

Anyway, after disassembling the motor it became apparent that it really was in bad condition. I'm not sure if it will still work but I can't even test it because I have no idea what wires to connect. The motor has 4 wires coming out, I assume 2 are the starting coil used in series with the missing starting cap and the other two are for running.

Is there a DC continuity test I can do to work this out? Are the start windings typically of a lower DC resistance to the run windings?

I think the motor is rated at approx 2Kw

I could have a crack and stand back to see what happens but it would be a shame to destroy an otherwise still good motor by releasing the magic smoke!

Cheers,

Simon

what color are the wires.
is there any continuity between any of the wires?
what about a continuity test to the body of the motor to each of the wire?
got a photo.
be careful dont work on it with it plunged into any power source
aaron.

Quote:

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Originally Posted by azzrock

what color are the wires.
is there any continuity between any of the wires?
what about a continuity test to the body of the motor to each of the wire?
got a photo.
be careful dont work on it with it plunged into any power source
aaron.

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Hi Aaron,

There were two purple wires, a blue and a white. A continuity test revealed that each wire had between 7 - 10 ohms between each other wire. This has confused me as I thought that the start windings would be completely separate to the run windings. I also thought that the DC resistance was rather low, although I'm aware that the impedance from an AC source will be different.

Before the pressure washer was scrapped, the motor was working fine, only the pressure washer pump was a little worn out.

I don't care how good the RCD is on my power circuit, I'm not plugging it in and touching it during any test! :no:

Forgot to add, the resistance between the wires and the body was in the Mega ohm range. There maybe some leakage from the residual cleaning fluid I used when cleaning it up. Not sure.

Cheers

Simon

Hi Simon,

A picture would help, also any motor nameplate? Single phase motors come in all kinds of flavours, and the first thing would be to figure out exactly what it is that you've got, how many capacitors are there (if any)..

Sometimes there is a wiring diagram printed and stuck on the inside of the plastic covering, also if it's a current model you might be lucky and find a service manual on line with a wiring diagram.

Regards
Ray

Hi Ray,

here's a picture. No nameplate on the actual motor. I think from memory it was a Karcher KM520. I assume it had a cap but to be honest I can't be sure. I assume all single phase induction motors must have a starting cap, unless like my drill press they have an internal centrifugal switch for the start windings?

Cheers,

Simon

Yep, just found the parts list online. It's definitely a KM520 and it needs a start capacitor. Now, just need to work out the windings and i'll have a kick #### diamond cup grinder!

Hi Simon,

I think it will be a 64uF cap according to this pdf at least, I was hoping for a circuit diagram, but no such luck...

Write out the resistances between the windings, and maybe it will be possible to figure out the connections.

Regards
Ray

Hi Ray,

A 64uF sounds like a plan. I managed to get the motor running, so it's game on with the project! I discovered that the two purple wires are connected together internally, which leaves the blue and the white. So, I assumed (yea yea I know) that purple and white is one pair and purple and blue another pair. One being the starting and the other the run.

Measuring the DC resistance, one was higher than the other. So, I made another assumption that the start windings would most likely be lower than the run windings and wired the thing up accordingly.

So the pair being purple and white are for start and pair being purple and blue are for run?

I don't have a cap at this stage, will buy one now I know it works but I got around it by wiring in a momentary switch to simulate the start pulse. Anyway I got it to work.

Out of interest, does anyone know the consequences of connecting the cap to the run windings instead and having the start windings on the AC power? Would it start? Would it instantly overheat and smoke/destroy the motor?

Cheers,

Simon

Hi Simon,

Ok, that all makes sense..

Follow this diagram. ( note that the colours are different to yours )

http://backsaw.net/pics/motorcct2.jpg
2x purple == red/white
white == violet
blue == blue

So, connect the 2x purple to Active. the white wire to cap and then to neutral, and blue is connected to neutral.

I'm assuming that there isn't an internal centrifugal switch is there?

All the start cap does is give it a kick on power on.

Regards
Ray

If you connected the start and run windings the wrong way around, the start winding would be drawing excessive current, and probably damage the motor if left long enough.. :)

Quote:

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Originally Posted by RayG

Hi Simon,

Ok, that all makes sense..

Follow this diagram. ( note that the colours are different to yours )

http://backsaw.net/pics/motorcct2.jpg
2x purple == red/white
white == violet
blue == blue

So, connect the 2x purple to Active. the white wire to cap and then to neutral, and blue is connected to neutral.

I'm assuming that there isn't an internal centrifugal switch is there?

All the start cap does is give it a kick on power on.

Regards
Ray

If you connected the start and run windings the wrong way around, the start winding would be drawing excessive current, and probably damage the motor if left long enough.. :)

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Thanks ray. You have confirmed what I thought!

Cheers,

Simon