Garden chipper blowing fuses?

How about you whip the capacitor out of circuit, switch on and flick the motor over manually to get it running? Seems the obvious thing to do if you're concerned about a dodgy cap, but if it's reading its proper value it can't be shorted internally AFAICS.

Hmm, not tried that, however, if it's a run capacitor (rather than start) won't I need it in there for the motor to run at all?

No, that's what I was thinking. I tested it with the DMM for short and open circuit (reversing the meter leads on M ohms and watching it charge) and on my component tester and I can't *see* anything wrong with it?

The motor is pretty clean so I don't think it's burnt out or even overheated (not that that counts for much etc).

(That was just how I found it after taking the output end casing off to check the brake clutch).

The left two connections you see on the picture are the main stator windings and the pair on the right are for the capacitor and the lighter windings you can see in the picture (run windings)?

It's a Black and Decker motor apparently (I don't think it's a good thing), even thought the Shredder is marked 'Lynx GS2200'

Should you just be able to connect up the stator and have it sitting there (even if only briefly) or would not having the rotor in place have a negative impact (on it tripping the power I mean)?

It's a Black and Decker motor (I don't think that's a good thing particularly), even thought the Shredder is marked 'Lynx GS2200' and looks like this:

Apparently, when it worked it worked pretty well. ;-(

Cheers, T i m

If there is no functioning RCD in the circuit (which would trip) it might be a fault to earth.

Earth faults are far more common than partial short circuits in motor windings.

So check RCD is functional first. (Press test button) If none existent or faulty, the MCB may trip insteadd.

BTW The stator can't be "powered on it's own" this will definitely overload, the motor must be assembled.

Perhaps run it with a series resistor, i.e. put a hefty (conventional) light bulb in series with the motor, or even a heftier load, such as an iron or kettle.

The current may not be enough to run the motor, but may be enough to heat up the fault. Also, any flickering of the bulb when prodding about is an indication of a bad or intermittent connection.

Thomas Prufer

I believe there is Harry and it didn't trip in this instance.

Understood. FWIW (and I know it's not a lot in many cases) I checked for continuity between all the windings and earth and there were none.

They have an RCD in the main CU in the house and (apparently) that has tripped when running iffy stuff in the workshop in the past (where we were testing this shredder yesterday). I might suggest he gets a plug-in one for the workshop.

Thanks for the thoughts but if it's not an earth fault (and I don't think it is as it tripped the workshop MCB even with the earth wire disconnected from the motor assembly) what else could it be do you think please? Whist this shredder may be old, apparently it's only been used now and again and wasn't being worked 'hard' when it failed.

Cheers, T i m

Funnily I thought of that previously Thomas, using a light bulb, but didn't think even a 100W one would be 'heavy' enough to allow the motor to start.

Ah, good point. The only thing we might have to be careful with is the automatic brake. If there isn't enough magnetic flux in the rotor the brake won't pull off and rotor will still be mechanically 'stalled'.

Another good point, thanks. More stuff to try now. ;-)

Cheers, T i m

That's what I thought / feared so thanks for the confirmation Harry. ;-)

Cheers, T i m

No, only to get full power under load. You will need to fick the motor into motion almost the same instant you apply power, as it will likely blow the fuse in a second or so if you apply power without it turning. Obviously, this is dangerous, particularly if you have the cutter attached, and from the starting torque kick-back.

If you can find a 100W (or higher) filament lamp, connect it in series with the capacitor. It should come on dimmer than normal. If it's either full brighness or doesn't light, then the capacitor is dead.

Alternatively, if you have a plug-in power meter, connecting the capacitor directly across the mains should draw abut 400VA (but very few watts). Beware that if the capacitor is faulty, there is a chance it might explode when connected across the mains - use a

It will draw much more current without the stator fitted.

Other thing to check are the wires on the armature. These may not be obvious, but if you look closely, there will be a set of single thick wires running along the surface from end-to-end (usually in a slight spiral), and a conductor on each end connecting all the wire ends together. (The pattern of wires is like a cylindical cage, hence the name "squirrel cage motor".) Sometimes, these can break, usually at the ends where the joins are. If they break, the motor won't start, and will draw the locked rotor current which will probably blow a fuse after a few seconds. Armature expanding when overheated can break the conductors. These conductors carry a high current and the connections need to be very good - tiny fractures will wreck them.

Having looked through the other replies and your responses Tim, I think that you are looking at a motor with some shorted turns or a problem in the starter winding (the one with the capacitor). For the machine to have run for 30mins trouble free and then have a hard repeatable fault looks like something has changed. If the 22uf capacitor is sound - do the series light bulb test, then that can be discounted.

Try and get hold of a 110v transformer. for your testing, a 240v motor will still run ok on 110v but the reduced power draw should stop the

Repeat the test with only the 22uf and the other winding powered. If all seems well proceed to connect both windings as normal, omit the rope starter and see if it will start by itself. If it does, then measure the run current which I'd expect to only be a couple of amps on 110v and no appreciable load.

If that seems all OK (I'd expected to have found a problem on one of the above stages) then maybe a re-test on 240 via 32amp breaker (In the kitchen maybe when the mrs is out?) with a reinforced fuse in the plug - solder some 30amp fuse wire across one of the dead ones (but throw it away after the testing).

Oh, ok. So even without the capacitor brining the other coil into play it will still run? I though the whole point of the capacitor was to create a phase difference between the two coils to give the motor direction (but obviously I'm wrong). ;-)

Ah, so you do need the capacitor to get the initial motion, and for full power?

Understood.

Understood (you are using the lamp as an indicator to the capacitors state, where 'dim' is the cap doing something, bright is a shorted cap and off is an open cct cap).

I do.

Oh, ok, again, I would have never thought to even try that, assuming it would effectively 'short' the mains.

Understood.

Depending where on the cycle it is disconnected etc.

Yes, I didn't really check any of that and so I thought the armature was just iron but of course it needs some conductors to generate the magnetic field for the stator to work against. ;-)

Ah, so could very well be the cause of what we are seeing?

And it was after about 30 minutes of running (so would probably have warmed up by then) that it stopped, so again, that seems to tie in.

Understood. It's nearly a shorted turn (or two).

So, so you think 1 ohm resistance (not inductance which is more relevant to AC of course) would be about right for a motor rated at

Cheers, T i m

p.s. I was thinking of a test jig along the lines of what you (and others) have suggested so far.

So, a small / garage CU on a short flying lead to a 13A plug fitted with a 13A (or modded higher) fuse. The CU could have an RCD (to show earth faults) and two or three 13A sockets hanging off 6 and 10A (+16A?) MCBs?

You could put a 13A socket in series on the input leg that could take whatever you want to use as a load (100W lamp to 3KW bar fire etc) and that could be switched out (L-N shorted on socket) if you don't need the load?

Ok.

Agreed.

I think I have one somewhere. Site transformer, heavy yellow box with a handle on the top?

Good idea. ;-)

Luckily you can do such tests with the motor bolted into it's chassis (blade removed) and you could probably flick the external motor fan with a stick?

Check.

Check.

Check.

She is generally the one flicking the switch on or on standby with the fire extinguisher. ;-)

Understood.

Loads of things to try. ;-)

I have a new cap on it's way just in case and it's a handy thing to have on hand in any case. I knew there was a reason I shouldn't have just let our daughter take away our old washing machine (nice caps, connectors and cables ... ). ;-(

Cheers, T i m

For now I would say flicking to start is not good enough. Proceed as per my instruction with strong string or light rope. You need to get is going at a reasonable speed. Yes bright yellow transformer is just the ticket.

Good luck

That's how I started my model planes all those years ago. ;-)

I mentioned the use of the fan because I'm not sure how or where I could actually attach a line to be able to start it that way. There is no gap between the back of the fan and the motor and even if you took the blade off the other end (it's direct drive), there isn't much in the way of a shaft above the surface to get anything around. I'll give it a try of course, just that I'm not that hopeful and I'm not sure how much time my mate would want me to waste on it for him (especially as I have a Bosch garden chipper that I'm no longer using that he can borrow indefinitely). If it were mine, if it was expensive and a good chance that my efforts would actually make it work (rather that just proving why it never will again) and I had little else to do, I'd be happy to do whatever it takes. ;-)

Understood.

(Mate popped in tonight and has requested I don't waste too much time on it ...) so, if I replace the cap (cheap / easy) and it doesn't work I think I can say it's dead and I can give him mine (giving me more space). ;-)

As I said, given it were mine and I'd got nothing more important or more interesting to do, I'd carry on to doing more of the experiments but ..

Cheers, I'll try the cap and whatever else gleaned from you and the other good folk here that I can do quickly, easily and safely, but if it doesn't work I know he would be quite happy to let it go. And at the end of the day, there is a good chance it's fate was already sealed when it stopped working a while back ... ;-(

Cheers, T i m

No you want nearer 3kW. With that in series it should run fine always - if you use halogen lamps it will run at nearly full speed too. With some load with less resistance change it would lose more speed & power.

NT

f you use halogen lamps it will run at nearly full speed too. With some loa d with less resistance change it would lose more speed & power.

Another effective bodge is to disconnect the motor chassis from anything me tal and from earth. Ensure it can't be touched though. That deals with arci ng to chassis. All tochable metal must still be earthed, and a suitable war nign sign posted to caution future repairers.

NT

I was thinking that say a 3kW kettle in series with the / any load would guarantee that all but the heaviest test loads would work and it would never blow the (13A) fuse.

Yup, already done that to test for an earth related problem. In any case it instantly throws the MCB but never the RCD so I was fairly sure that wasn't an issue in any case.

The problem with that is the cutter is directly mounted on the motor, not that you should be going anywhere near that either when it's plugged in! ;-)

A replacement cap has now come though and if it's not that then the shredder is probably going in the recycling. ;-(

Cheers, T i m