Testing a motor...

[dishman]

Hello,

I am repairing a faulty flymo lawnmower. Ground to a halt one day without warning.

I have checked the cable and microswitch (although not internally yet) and both seem fine. You hear a specific click if the switch engages properly and I can hear that.

The motor is the next thing to check. I have removed it and physically it seems fine. It had a bit of grass mess on it. However it spins fine. The carbon brushes look good (hardly worn). The commutator is in good condition. There is no burning smell or anything to indicate a burn out.

My question:

I assume I can do a direct mains connection to the motor for a short blast bypassing the switch and capacitor to see if it actually fires up. I should not do any damage without the capacitor for a short burst should I?

If it works, the issue may come back to checking the switch internals.

 

[flameport]

If you bypass the capacitor, it won't work.
The capacitor may be the faulty component.

 

[dishman]

Ahh, I thought the capacitor just regulated it somehow as it looks like it is connected in parallel within the switch, so I did not think it could prevent the motor from powering up. Please excuse my ignorance. I am, as a the website suggests, a diy repairer. I refuse to throw something that stops working away. You should see the number of flymos at the local tip. They all probably work too. Very sad....

I have a spare switch (retrived from a skip) from an old flymo (still works) with the same rating - should make for an easy test.

 

[eveares]

It may not fire up without the capacitor as the capacitor may be a start capacitor to start the motor. Start capacitors often fail and can be picked up quite easily online.

The capacitor may also be a power factor correction capacitor, in which case it is fine to run the motor without it. Lastly if the motor has got multiple windings and is a induction motor, it could be a motor run capacitor to create the necessary phase difference between the secondary and primary windings.

Can you tell the capacitance and voltage value of the capacitor and how it is wired in regards to the motor.

I would also recommend you test the micro switch with a multi meter on the continuity mode to see if it is OK or if it is faulty. You can tell if it is bad as you won't get any continuity in either of the micro switches states (on vs off).

Reagrds: Elliott.

 

[dishman]

See above... the capacitor is wired in parallel (which is what made me think it was ok to bypass). Does that mean it is a power factor corrector capacitor, I thought it was that type of capacitor without knowing specifically what it was.

I have actually opened up these microswitches are repaired them before, so I can always do the same again. However, I hear the distinctive click when you press the saftey switch, which suggests it is connecting correctly. I can always open it up though.

 

[Adam_151]

A motor with brushes will be of the universal / DC type (very common on power tools, vacuum cleaners, etc) and will not have a capacitor to start it

Any capacitor is likely to be small in value and for EMC or PF reasons

 

[Echo the husky]

The capacitor is for interference suppression. Universal motors do not have start/run capacitors. Faulty wiring or switch is the place to check first.

Edit: Beaten to it again!

 

[eveares]

The motor is the next thing to check. I have removed it and physically it seems fine. It had a bit of grass mess on it. However it spins fine. The carbon brushes look good (hardly worn). The commutator is in good condition. There is no burning smell or anything to indicate a burn out.

My bad, I missed that part. As Adam said, the capacitor is for minor reasons like EMC or PF correction. First check the motors winding is not in a open circuit or short circuit state, then try to run the motor directly on the mains.

That should hopefully tell you if it is the motor or something else of which is at fault.

 

[Mikefromlondon]

Yup that cap is for EMC and switching noise suppression, it won't have anything to do with your motor not working, so check continuity all the way from fuse to two final leads that end up at the motor terminals, including any switches, Do not Bypass any capacitor (as I understand bypassing means shorting it out) if you did that you would short out live and neutral and so as soon as you press the on leaver it will go bang! (the fuse would blow as well as it may damage your switch contacts.

Just check the motor continuity, most lawnmowers are now manufactured (obviously in China) and use cheapest aluminium enamelled windings, they look very similar to copper due to enamel coating and since aluminium soldering is very expensive, they are usually crimped to the terminal tabs, and vibrations can break the aluminium wire just where it is crimped, I have had my lawn mover (flmo) suffer from broken connection, and sadly I could not re-crimp it or solder it to metal tab, so I stripped back the enamel and pulled enough slack in it to enable it to wrap around the terminal post about 1 turn, then I wrapped over it some thin tinned copper wire of 24swg, so as to secure it tightly and I got it going, in many cases you could also wrap ordinary copper wire (solid 24 swg) around the aluminium conductor tightly, (after stripping enamel coating) and then terminate that wire to the post by soldering or wrapping it tightly, etc, I had this happen to my flymo once on each terminal at two different times. It also happened within its guarantee period but when I took it back to B&Q, they asked me to take it to their repair place at an address that would have been more hassle for to drive to and then to go back to collect it, so I chose to fix it myself. It is still going ok and I have used it for 2 years now since its failure.

 

[dishman]

Thanks - and just to claify I ment bypass as in to avoid, as in taking the switch and capacitor out of the equation and just going from mains to motor.

Thr motor itself looks sound, terminals (If i understand where you mean) all look fine. The cables are all connected correctly, and tight. Cannot see any issues with the motor. So a test should rule it out.

 

[endecotp]

Do you have a multimeter?

 

[dishman]

No - unfortunately -

However after you mentioning the connections I had a much closer look at the motor and found the fault.

It appears the conection from the coil side (feild windings? or whatever the proper terminology is) of the terminal has failed. Now there is slight char markings around the terminal where it detached. It may be that this is a result of it coming off rather than the cause. There was a lot of dirt around the motor (dead grass etc.) so another possibility is that it over heated around the connection causing it to fail. Although the motor cut out straight away, rather than after prolonged use, so, maybe not an over heating issue.

The coil was soldiered on through the base of the terminal, this has melted/snapped off somehow. Problem now is that the coil is a tiny bit too short to easily reach the terminal now as there is no slack....bugger.

Option....extend the coil?

 

[Mikefromlondon]

Option extend the coil, Yes indeed.

That is exactly what i had on mine, the coil wire where it just terminates to the connection post, it can be a bugger but if you can get to the rest of the coil wire and remove the insulating enamel, you may then see what exactly is the make up of the wire i.e. copper or aluminium, if it is copper you could solder another wire to it, but if it is aluminium, then you can forget about it, as aluminium soldering is not only expensive but difficult as well, so get some ordinary solid copper wire of roughly 24 swg (approx 0.8 mm diameter) and if you can wrap this wire around your aluminium coil wire and then solder it to the terminal post, and squeese the joint with a pair of pliers where you wrapped copper over the aluminium coil wire, that would do you. Mine has lasted two years, more than its failure within 6 months as mine was still under warranty.

Aluminium wire are more brittle than copper so they snap right near their final termination due to small vibrations from the motor as well as larger vibration as the mover blades get knocked about with stones and get out of balance.

Thanks also for clarifying about your "bypassing of a capacitor"

 

[dishman]

What about taking apart the motor and unraveling one "wind/wrap" of the coil?

 

[Mikefromlondon]

It wouldn't be easy on some motors, but if you can do it, you can always unwrap one turn if you are lucky if it is the finishing side of the windings, but if it was the starting side of the windings, you wouldn't be able to pull out one turn as it would be buried beneath other turns on top of it.