OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions on Other Engines Burn't out electric motor

Hello everyone

I'm a frustrated English guy who brought a great bargain !! (Scott Bonnar cylinder mower)

And the story goes like this " purchased this mower from a police officer who advertised it through Gumtree, great, went and had a look all looked fantastic old mower but in good working order, had to get the cylinder sharpened as it pulled at the grass, sharpened it even better cut the grass really well. Then being a family man i neglected the lawns for a couple of weeks and it was a couple of inches long by now and this put additional load on my poor old electric motor and now I've burnt something out inside."

The motor will start but hums only whilst it tries to turn.

So i took it to Statewide motors in adelaide for a service! sorry sir this needs to have a rewind..... $ 350 + GST after i picked myself up of the floor, the kind gentleman said we have a new similar one for $295 Inc but it has a capacitor housing and is not the same physical size so the cover will not go back on.

So you see my dilemma....

If anyone can advise me the best place to purchase a refurbished motor i would be grateful.

The Mower as mentioned is a Scott Bonnar. Mower Number 45 21418

The motor is a Crompton Parkinson 1/2 HP 3.3 Amp single phase motor

Many thanks
Tony

Is the motor stiff to turn? Are the windings burnt? How to the capacitors? Lots of things can make a motor hum but if the magic smoke has been let out of the windings then I would look for a good second hand unit.

The most common reason for an old or badly made single phase electric motor to hum but not start, is that the centrifugal switch that operates the starting winding is not making contact. Your motor could be burned out, but it is not the most likely explanation unless it had water enter its windings or was held in a grossly overloaded condition for a time.

You can see a rudimentary circuit diagram for a typical old-style single phase capacitor-start motor here:
http://mcmullanzu.livejournal.com/4538.html

In my experience a motor of the vintage of yours is very likely to be designed as in that diagram, but of course you can easily trace the internal wiring and see. The motor is reversed just by reversing the connections to the starting winding (the one with the capacitor and centrifugal switch in series with it).

You can very easily tell whether your motor has a starting circuit problem. Just disconnect the drive from the motor to the mower (it will be a V belt or a chain: just remove whichever it is), power up the motor so it is humming, and twist the motor's output shaft once fairly briskly. It doesn't matter which direction you twist it in: single phase motors run in either direction with equally poor efficiency. If the motor starts running smoothly and stops humming, it is just a starting circuit problem, not a burned out motor. If it makes you feel any better, I've had single phase motors that I've always started by hand for years, because it was too much trouble to fix the centrifugal switch: no harm was done.

I have never much cared for Crompton Parkinson motors, and would certainly not spend that kind of money to have one repaired. When I need an electric motor I customarily go to the flea market and buy a second-hand one. The usual price for a half horsepower single phase motor seems to be $25-50 depending on luck. The most I've ever paid was $70, but that was a 1.5 hp low speed three phase of advanced design, and I resented paying so much even then.

It might be unlawful for me to tell you how to fix your motor if the starting circuit has stopped working, so I won't, but if you have a resistance meter and about ten minutes to spare you should be able to track it down. Hint: it is usually the centrifugal switch not closing properly when the motor is stopped (it makes a quite audible click just before stopping) but occasionally the starting capacitor has failed, and rarely the starting winding has lost continuity - I've never even had one of those happen to me.

Hi TonyF, and a warm welcome to the forum. Its great to have another Scott Bonnar owner on board.

I have a Scott Bonnar Model 17 electric as well as my Scotty 45 (petrol) and I notice that the Model 17 Supercut has a 3 HP single phase motor....a half horse power unit may, I feel, struggle in fairly long grass, especially if it is a 17" cutting width machine. It's a bit of a pain, but you may have to raise the cutting height in future, if you find your grass has grown to such an extent again, this will take the strain off the motor a little.

Deejay, I wonder if that mower has no drive to the rear drum? I agree with you that propulsion plus grass-cutting from a half hp motor over a 17" width sounds a lot to ask. I suspect the propulsion takes more power than the cutting wtih a reel mower, so if a previous owner put that little motor on it but also removed the drum drive, it might be a more or less workable tenant's improvement situation.

What we really need is a picture or two, so you can compare the mower with yours.

Hi Joe

The motor still turns very slowly, and agreed once the smoke is out hard to put back in.

Would you have anyone in mind that may have a second hand or re-conditioned one for sale in the Adelaide area?

regards

Tony

Hi Grumpy

I believe in the most part what your saying is correct, I have removed the motor from the mower itself and rewired to a plug top and tried to hand start it. The shaft would spin at a snails pace and no faster when encouraged by hand.

I have not yet checked the windings with a meter yet, but have instead tried to take the motor apart and try some self diagnostics coming across my first hurdle how to remove the motor from the case, bearings in the way... help needed.

There seems no visible signs a capacitor on the motor

I am a sparky by trade but am at a loss when it comes to motors as i mainly get involved with BMS ( building Management Systems)

I guess same question to you grumpy would you know of a flea market in the Adelaide CBD area??

Regards

Tony

Deejay

I also thought that for it to labour whilst cutting longish grass would indicate a motor a little on the small size

Thanks

Tony

Tony, not all single phase motors are capacitor start. Some are shaded pole, for example, but I've never worked on one of those. However if the motor runs, but slowly, and yet its bearings are free, I'd say it's a goner: the motor guy's diagnosis of shorted winding sounds correct. If you are interested by all means take it apart, but I think it is unlikely any positive outcome can occur. How it comes apart depends on the idiosyncrasies of the design engineer, but most likely the tight fit of the bearing inner rings on the rotor axle is the problem. If you have removed the longitudinal screws that hold the ends on, and proved this by moving the two end plates about, you should be able to support the outer casing and press or drive the rotor axle out of the upper bearing. The lower end plate will come out with the rotor. Just be careful that it doesn't have wiring attached to one of the end plates though: if it does, that one has to stay in the casing, with the field winding.

To find an Adelaide flea market, unless a local Outdoorking member can help us I'd begin with a google search of "trash and treasure adelaide", and look for an entry that is long on "second hand" and light on "collectables", "craft", and kitsch generally. I suggest you get details from Deejay of his electric SB mower, including a photo of the motor manufacturer's identification plate. It seems pointless to put an unsuitable motor on the machine just because that is what the previous owner did. It is not only a matter of horsepower; you also have to pay attention to the speed. Many large (over 1.5 hp) single phase motors are 2 pole (3,000 rpm), not 4 pole (1,500 rpm), because the torque required is then only half as much and the motor can be smaller. The usual way to get a good-quality 3,000 rpm 2 hp single phase motor at a good price is find an old swimming pool pump motor, because many of them are of that type. Alternatively there is a large range of new motors on ebay for about half what your local supplier quoted. Remember, though, you should use the same speed (3,000 or 1,500 rpm) that Scott Bonner did originally, so you can use the same pulley or sprocket size they used.

Hi grumpy, the electric motor on my Supercut (Model 17) would not be suitable to fit onto a Model 45. Completely different drive layout and uses a counter-shaft and dual pulleys. I am not familiar with the drive set-up on the electric Scotty 45's.

However, I believe Tony should contact Keith on (03) 5339 9385 or his mobile 0438 357 100. He has a lot of second hand Model 45 parts and very handy with his knowledge of all things Scott Bonnar.

Thanks Deejay. My solution to the problem runs to the simple, bordering on brutal: see if I can find a disused swimming pool pump in some junk area or whatever, and focus on how to mount it on the mower. I wouldn't do that on a collectable mower, but I have difficulty taking electric lawnmowers seriously as collector's pieces. However your contact would obviously know exactly what the original motor would have been, and that is useful information.

I wonder if it is possible that the whole thing is an engine-driven SB that someone converted to electric?

Hi Grumpy, without a photo it's hard to tell, but I doubt it, as the electric 45's don't have a cutter clutch. The motor is directly connected to a shaft through the chain set-up to the reel....switch on, reel rotates...squeeze the rear roller clutch lever...away you go!
BTW, I do think the RPM of the motor would also be significant to a degree.

Is it possible to make changes to convert an electric to petrol?

Like Grumpy, I'm not able to really see electrics as long term members of my collection, so if my electric 45 were to be able to be converted, it might have a brighter futre with me.

Guys

Many thanks for your responses to my dilemma, i will contact Keith on the above number to see if maybe able to help.

The motor itself is connected directly to the shaft then straight to the chain linkage. So is that correct that i only need the keep the RPM to the same as before?

Many thanks once again i will keep you up to date on how i go.

Also i have looked on ebay to no avail but i'll keep looking

Hi Ty, the answer is yes mate, you could convert it, (electric to petrol) but you would need the following:
(1) new engine shaft
(2) Cutter clutch assembly complete
(3) new chassis with the clutch lever assembly complete
(4) suitable horizontal shaft petrol engine with throttle control.
The best method would be to grab a second hand petrol machine and christmas tree the bits you need to make one good petrol machine!

Sounds like a mighty fine garden ornament.


Prop up a stuffed up Santa suit behind it, Replace the slow turning worn out motor with an angle grinder, and its instantly and interactive display.



Sorry not real helpful. Id look for a petrol or another one that uses the same reel and bed knife.