A DC motor question.

[Dave Plowman (News)]

I bought a new car wiper motor from Ebay for a project. When sorting out what does what with the connections to it, I accidently reversed it.

It is a fairly standard permanent magnet type with three brushes - the extra one for the second speed.

When I first powered it up it made a few strange noises then settled down to running ok. When I reversed it, it ran a few revolutions then locked solid. Applying the current the correct way didn't shift it.

Investigation showed the ferrite magnets to be cracked in several places with some smallish bits broken off completely and jamming the armature. Removed those bits and it ran again.

Can I just confirm this was likely caused by it being dropped at some time and not by reversing it?

[Ian Jackson]

In message , "Dave Plowman (News)" writes

I can't see how reversing the supply could possibly have broken the magnets.

[fred]

In article , Dave Plowman (News) writes

Does the park function still work?

My thought is that if the park switch mechanism was incredibly badly designed it could rely on one way operation and by reversing it, the mech could have been damaged causing something to break off and damage the magnets.

If the sole cause of the reverse stall was the magnet fragments then it should now operate continuously in reverse. I can understand of course if you prefer not to risk it in reverse again to find out.

[Dave Plowman (News)]

It's a simple common micro-switch driven off a cam on the main gear wheel. And all the gearbox part is just fine.

The motor is quite separate from the gearbox - only the worm drive pokes through into the gearbox housing.

I'm not inclined to risk using it at all - as other fragments of the magnet might break off through normal vibration etc.

[fred]

In article , Dave Plowman (News) writes

Ah well, it was just a thought. Given that it does point to some kind of physical abuse such as dropping as you suggest.

[Dave Plowman (News)]

Guess so - I was really just making conversation on a quiet day. ;-)

I bought it from an Ebay seller who didn't usually sell this sort of thing. He also cancelled the transaction after I'd bought and received it

- which I thought strange. However, I got it cheaply - about 10% of the retail price. I've bid on another secondhand one - swapping the cover containing the magnets should give me a good as new one.

[Tabby]

I wonder what the life expectancy of Brits would be if we drove cars with all parts bought from ebay

NT

[Dave Plowman (News)]

I've bought lots of stuff from Ebay and been generally satisfied. Just as likely to get faulty parts elsewhere, IMHO.

[Steve Firth]

Longer, if my recent experience is anything to go by.

I bought rear self levelling shocks (£25 a pair, UK dealer price £500), four brake disks, four hub bearings, four sets of pads, two handbrake shoes (£300 the lot, UK dealer price about £2000) and fitted them over a weekend. The ride and handling of the car was greatly improved, stopping distance shortened significantly, brake fade when descending mountains eliminated.

"I'd say it's a major contribution to road safety."

[The Natural Philosopher]

Little different to what it is today.