Sue, there are a couple of things that may be causing that. Motors have " brushes"(carbon fiber type material) on either side of the armature with springs that keep them pushed against it. Once those brushes wear down then they loose their contact with the armature causing heat build up. Once that happens the power can be intermittent and cause excessive power draw tripping the breaker(Residual Current Device). Another thing could be the magnet that is attached to inside of the motor housing could be cracked and causing friction, but less likely you will see any sparks from that. Usually it locks up soon after that happens. The other thing could be the seals and/or bearing that keep the armature centered are worn out causing it to wobble.
Here are a couple of pics of the inner parts of "one" electric motor to help you see.
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Thank you very very much, Roadyy, that was so helpful! And illustrated with photos too! ...I will keep you posted on the planer/thicknesser. I hope it can be repaired - over here something like that costs several thousand dollars, and it's actually a loan from a friendly neighbour (who said, "I bought this because I was going to do some woodwork but then didn't!).
By the way, the pole saw is exactly what we needed and working out very well, so thanks again for that tip a while back.
PS: I'm good at... chocolate cake. Ever get any Qs, just ask me. Here's my favourite recipe:
FRENCH PROVENCIAL CHOCOLATE CAKE
Melt a 250g block of excellent quality dark cooking chocolate (we use Plaistowe or equivalent), on very low on the microwave. Meanwhile, separate 4-5 eggs and beat the whites as if making pavlova or meringues. Set aside.
Add 100g of butter to the melted chocolate and briefly return to the microwave on low to get butter to soften/melt. Beat 100g of caster sugar through this mixture, adding 1tbsp of natural vanilla essence (not fake), and 1-2tbsp of brandy - this will help the sugar dissolve. At the same time, add a tbsp of good-quality instant coffee, which also has to dissolve unless you like crunchy coffee surprises in your cake. ;-) Then mix in the egg yolks, followed by 150g of almond and/or hazelnut meal (I grind the almonds myself in my food processor to get a slightly coarser meal than what comes in packets, plus I use skin-on almonds as they have extra flavour.) Gently fold through the eggwhites with a spatula, and transfer the mixture into a non-stick-paper-lined square cake tin. Bake at 170 degrees C on the middle shelf, preferably fan forced, for 35-40 min (usually) until a skewer comes out clean. Care - don't burn this cake. Cool the cake on a rack in its paper case (it's fragile). Put on a serving platter, cut into squares, dust with icing sugar, and enjoy. Fresh berries, with or without cream, go well with this cake.
I got this recipe over 20 years ago when reading a newspaper in a university library on a short break from a relatively pointless assignment. Man, looking back, how infinitely more valuable this was to my life and the lives of others I shared it with than if I'd spent another 15 minutes on that assignment instead! ...it was from an international "World's Best Chocolate Cake Competition" and I copied down eight recipes, but have never actually made any of the others... there was a chocolate cake with Guinness in it from Ireland and I still have the recipe if anyone wants it.
(I'd make this cake for all of you, but I don't have a TARDIS...)