A friend gave me her Kenwood Chefette 2000 to repair. Making a stink and lots of sparking.
I opened it up and one of the motor brushed was stuck in its holder so I cleaned it up and freed it off. Alas, no better after the clean up so I suspect the capacitors are kaput. (Picture below).
Tim
1nF or 1000pF, the code is 1 0 *10^2 in pF.
It's probably an 'across the mains' capacitor, it's possible that's what the Y or Y2 signifies but it's not absolutely clear from the markings.
However, having said all that, given that the capacitor is almost certainly ain interference suppression device I don't think its failure would cause the symptoms you're describing.
that's just a 1nF suppression cap, nothing to do with the motor running.
Is the commutator surface smooth?
NT
The capacitor is a mains rated, 1kV actually 1nF device. It is extremely unlikely to be faulty.
The commutator will have been damaged and must be cleaned and inspected for uniformity. You should change the brushes and carefully inspect the guides they are in.
Look at the windings to see if there are signs of overheating.
If you want to check the motor off load, it will work on a low voltage DC supply, so a laptop adaptor should easily drive it for a test. A fully functional universal motor with good bearings and brushes will work from a 12V supply if you have one.
Don't check it on mains if there is no mechanical load connected.
Malc
Agreed. Also, are you sure that the brushes are not significantly worn down? Your symptom is often the sign that they need replacing.
Class Y caps go from mains to case. It can only be an interference suppressor.
NT
Sounds more like a shorted armature winding... probably runs rough and slower than expected as well.
Its a suppression cap - for the purposes of testing you could simply disconnect it. I suspect it won't make any difference.
Really? What do you think will happen?
Thanks. A bit more info.
On the slowest (of three speeds) it runs without any significant arcing. It doesn?t always start when powered up though. Turning the armature slightly gets it going. On either of the higher speed it starts arcing a *lot*.
I don?t think the brushes are too worn. Put it this way, they have to pushed a long way back into their holders to reinsert the armature/commutator. There are moving freely now. One was sticking before I stripped it down.
Perhaps the commutator just needs a better clean or could it be something else? The commutator is smooth although a bit blackened.
Tim
There are a few possibles.
NT
If the motor is out of its containment and there is a mechanical imbalance, the vibration is truly something to behold.
A vigorously vibrating motor with no restraint isn't fun to share space with. Easier and safer to use DC low volts for testing, but be aware that the field coils produce quite a back EMF on disconnection.
Malc
Okay, I put the armature in my drill and gave the commutator a good polish with some very fine Emery cloth that I have. Looked lovely and smooth and there was nothing bridging any of the segments. Cleaned it with a bit of lighter fluid and reassembled it again.
This time, on slow speed, no hesitancy about starting and it ran beautifully smoothly with minimal visible sparking at the commutator. As soon as I turned the speed up though there was a *lot* of angry/scary sparking and even though it was only run for a second or two at speed, the commutator is significantly blackened again.
I guess new brushes are the next thing to try although as I say, there seems to be a good bit of carbon left. Unlike most on sale, they don?t have a ?pigtail? running up through the spring, the brush is ?free? and the only conductor to is is via the spring (and maybe the brush holder body itself).
Haven?t seen any quite like them yet on eBay.
Tim
Why would there be any imbalance unless the armature is damaged? It?s only a food mixer. A motor with any serious internal imbalance would soon destroy its bearings surely?
Tim
Carbon or ash? If there has been serious sparks/arcing perhaps the ends of the brushes are no longer solid carbon, but burnt carbon. Perhaps before replacing the brushes re-face them on a bit of emery cloth.
Shiny graphite is what they look like. Not burnt.
Tim
You may have a shorted turn or o/c segment.
I've never had much luck in repairing universal motors.
Correct! "only a food mixer".
Take the motor out and run it at mains Volts and it becomes a different ball game. The speed it pretty impressive and with nothing to impede it, even a gram or two out of kilter will turn it into a nightmare akin to a jumping jack firework.
It may be o/k, but as you obviously do not deal with the things on a regular basis, it is simpler and safer to use DC Low Voltage for testing.
You can of course reassemble it all and switch on, but you will be no better off if you open it again to find a repeat of the damage.
Malc
OK then what about the commutator. It will probably also be black and shiny. If that is *just* graphite then there won't be much resistance. But, if it is a "lacquer" caused by overheating of organics in the atmosphere (e.g. oil or grease escaped from the bearings) then it will be resistive. Polish the commutator down to nice fresh copper with fine abrasive paper. Clean out the segment gaps (the classic tool for that was a bit of hacksaw blade, with the tooth kerf ground down to the correct width, but even scratching it out with the tip of a stanley knife or a jewellers' screwdriver will remove the worst). Then see how it runs.
Um no. If it was in balance before why would it suddenly be out of balance? I?ve already run it on mains.
A motor 1 or 2 grams out of balance would hopefully never leave the factory. I simply don?t understand where all this imbalance is supposedly suddenly coming from.
Tim
Been there, done that.
I didn?t scrape it out as visually it looked clean. I think it may just be down to the brushes.
Tim
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