Gas station without pumps

2021 March 28

Electric lawnmower repaired yet again

Filed under: Uncategorized — gasstationwithoutpumps @ 19:55
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In Vaccine vested! I reported

I also took apart the lawn mower to see it if is fixable.  As always, it took me a long time to clear out the grass packed into the recessed screw holes to get the cover off, and a long time to vacuum all the grass out of the interior of the mower.  When I did finally get access to the motor and electronics, I determined that the bridge rectifier had failed again—this time with a short circuit instead of an open circuit.  I’ll buy another GBPC5010-G‎ 50-Amp bridge rectifier, and see if this one lasts a little longer.

There is one mistake in the quoted section—the first failure of the lawnmower (back in 2017) was also a short circuit.  The new behavior was identical to the old.

When I got back from Berkeley today (where my wife and I were visiting our son), I found the rectifier and a couple of other packages that had been delivered on Friday sitting on our porch.  I took apart the lawnmower and replaced the bridge rectifier.  I verified that the old rectifier really had shorted out two of its diodes, so I was pretty confident that I had fixed the problem and I put the mower back together.

It still didn’t work.

There was no longer a short circuit that blew fuses, but the mower just ran for a few seconds and died, as if the blade were blocked.  With the mower unplugged, I could turn the blade by hand, but took the opportunity to chip some of the dried-on grass from the bottom of the mower anyway.

After removing the cover again, I inspected the motor more closely, and I decided to take off the top plate of the motor (which holds the brushes), to see if there was anything wrong with the rotor or commutator.  The commutator looked very dirty, and it looked like the carbon from the brushes (or perhaps some carbonized grass) had gotten stuck between adjacent plates of the commutator, so I scrubbed the commutator with an old toothbrush.

After I reassembled the motor I tested the mower without replacing the cover—it seemed to work ok.  I replaced the cover, and lawn mower worked just fine.  I was too tired to mow the lawn (very little sleep last night, and the trip back from Berkeley had taken 6 hours, rather than 3 hours, because of BART delays, the BART train we were on going out of service, and missed connections), but I should be able to mow the lawn sometime in the next week.

Incidentally there was another error in Vaccine vested!: the 500 is a “Rapid bus”, not light rail.  It does provide a pretty quick connection between Diridon station and the new end of the BART line at Berryessa. It was also free, because VTA is not charging for transit until April 1.  I could have ridden the Highway 17 Express for free also (because I’m old), but I just took their half-price offer for regular passengers.  I did use my new senior Clipper Card on BART for the first time, though only on one leg of the trip, as I had some money on my old regular Clipper Card to use up.  The whole round-trip to Berkeley cost only about $17, which is about what it would cost me with all the senior discounts.  I don’t plan to take senior discounts on the local buses (SCMTD really needs the money), but I will take them on BART and VTA, which have a much bigger and wealthier tax base.

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