I have a Black&Decker electric hedge trimmer - you know the kind, with the thumb safety, the index finger trigger, and the 2-3 ft long shears, which operates on electrical power from a cord plugged into an outlet.
All of a sudden the unit keeps cutting off even with the trigger held. The cord is firmly seated for electrical continuity. At one point I had severed the power cord, repaired it, so was thinking it was the cord, but even with a new replacement cord the symptom persists, and I do get the intermittent brief "on" with the original cord. The original cord does provide power for other things, so it is not the cord, but perhaps the severing shorted something in the trimmer?
Here's the peculiarity: If I rotate the unit so that it is upside down, it runs. As soon as I rotate it rightside up, it conks out again.
Any ideas as to what this is, and if it is easily repairable, or do I just need to buy a new one?
My guess is that the brushes are worn down and the commutator is worn to a slightly smaller diameter where they have been riding on it. When you flip the unit over the armature may slide slightly endways within the limits of the bearing spacing and bring the unworn portion of the commutator into contact with the brushes, so it starts.
Brushes are easy and cheap to replace yourself. Check it out.
No, the way it works when you put a piece of metal through the electric cord is that either it touches both wires at the same time or it doesn't.
If it doesn't it still might cut one of the wires, so the cord doesn't work again, and that wire has to be repaired.
If it does touch both wires at the same time, you are likely to blow a fuse in your basement, and you may also cause a pop or a burn where the blade cuts the wires, and you may even find copper balls at the end of the wires where the copper melted and then hardened again. But all the current that is going through this "short circuit" is power that is NOT going through the trimmer itself. So the trimmer is getting less current through it at that time, none or almost none at all, because the current takes the shorter, easier, path.
It's also possible if the blade touches both wires at the same time that it won't make good contact with one or both, and only some current will flow through. It may not melt either of the wires in two, and it may not even trip the circuit breaker or blow the fuse. But again, this won't cause more current to flow through the trimmer. The electrical resistance of the trimmer determines the maximum amount of current that flows through it. Even a bad-contact short circuit might lower the amount available from the wall to the trimmer, but it won't increase it.
So all this had no effect on the trimmer.
Both of the other answers seem to figure it's not the switch. They probably have more experience on this problem than I and might well be right. But I'm thinking maybe your hand on the switch changes in some way when you twist your arm, and then the swtich works. So I would try, with the trimmer unplugged, tying the swtich down with a string or a wire or plastic tie, plugging it in and seeing it not run, then turning it over without touching the switch.
I have about 4 B&D trimmers in the basement that I got at yard sales or out of the trash, and I haven't had trouble with either the switch or the brushes. I think the case has to be opened to replace either, so just be careful to note, or to make a sketch, which holes have the short screws and which have the long ones, and just after the case is opened gently, how the wire is routed through the handle, where it bends around the plastic ribs, where/how the switch is held in place.
The case determines all this, but it can be hard to tell after the wire is out of place.
I would attempt to repair it myself if it is otherwise in good shape and there is meat left on the cutters-but it is a cheaply made unit and I would only do so for the challange. These things can be a real pain in the ass to reassemble so sit down with it when you are fairly calm and unhurried and split the case following the wiring in and checking each connection as well as the brushes. An ohmeter with alligator type probes will allow you to wiggle wires and find an intermittant.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.