brainwagon

As part of my attempt to become slightly more virtuous, I’ve been trying to do four hours of work cleaning and organizing my garage workshop every weekend.  Last weekend, I got to the point where I was forced to address my cordless lawnmower.

My mower is a fairly old Black and Decker model CMM1000, which uses a 24V lead acid battery.  I hadn’t used it in several years.  I had bought a gas-powered Toro lawnmower because the B&D was occasionally underpowered, particularly when the lawn got tall.  It was also a mulching lawnmower, and over the years a thick layer of thatch had formed in the lawn, and it didn’t really look very good.  I tried shifting to use the side outlet to bag the clippings, but that never seemed to work very well either.

But in any case, I had thought the B&D should be in good working order: it certainly was when I had left it a few years ago.  I plugged it in to recharge it, and… well, nothing good happened.  12 hours later and the mower still wouldn’t start.  It’s not shocking really: I had probably left the battery in a discharged state for a very long time, and it was probably dead.

Sunday I decided to try to extract the battery and put it on the bench, and see what I could figure out.  Sadly, Black and Decker doesn’t seem to have the manual for this mower on their website any longers.  Boo!  A bit of Internet searching found lots of websites that would install various bits of crap on my machine or exchange a new account for a download of the manual, but all that was irritating.  I decided to turn to YouTube to determine if someone had done this.   And, of course they had.

This didn’t look too hard, so I dug out a Phillips screw driver, and my socket set, and started to work.   Removing the throttle control and the two rear screws on the main housing wasn’t difficult.   I then moved to the front screws, which lie in the bottom of a hole (maybe two inches deep) in the front housing.   These holes were chock full of grass and dirt (naturally) but luckily I have an aircompressor and a blow gun, which made short work of the dirt.   I blew them all out, and then took my handy Phillips to it.

Hmmm.  No dice!  I couldn’t get a grip on it.   I changed bits to a smaller one.  Still no dice.  Finally, on a hunch I got a small flashlight so I could peer down into it.  And… it was a Torx screwhead.   Grumble!

Luckily, I have a pretty good supply of (very seldom used) Torx drivers, and a few minutes later I got the silly thing out.   What was kind of annoying was that the video didn’t mention them being Torx screws, and the fact that the other two bolts on the same part were both Phillips.   Grrr.

But it was pretty easy going from there.  I took off the cover housing, and revealed the foam encasing the battery.   Pulling the front piece did snap part of it off, but a little glue will restore it to good condition, and I got the battery out.

I say “battery” but it is in fact two 12V batteries mounted back to back and jumped in series to form one 24V pack.  I got out my trusty multimeter, and found that the total voltage was around 12.5V for both cells, or about 6.5V each.   I removed the strap that connected the two batteries so that I had them separated, and used my little 12V charger on one half.  I also wired in a small LED voltmeter across them.  It read about 11.2V.

Twelve hours later, it was about 11.3V.  I took off the charger, and the voltage immediately sagged and the LED volt meter went out.  Using my multimeter, it showed about 5v.

I proclaimed the batteries dead, and went inside to find out how much it would cost to replace them.    Our local Batteries+Bulbs seemed like they stocked a Duracell Ultra replacement, but they were $80 for each, resulting in a replacement cost north of $150, which seemed like a lot.  Amazon would ship me a pair of MightyMax batteries that would serve as a replacement for just $75.  I’ve been using a Mighty Max as the power source for my solar energy project, and they seemed to work just fine.  So, I placed my order and am awaiting the shipment.

So, while I’m waiting, I went back to thinking about Torx screws.   I stripped one of the heads pretty well trying to motor it out with the Phillips, so I thought I should replace it.  The question is should I replace it with Torx or Phillips?

See, while I grumble at Torx screws, I do basically admit to their fundamental superiority.    Let’s face it, Phillips heads suck.  They are actually designed to cam out as part of a crude form of torque limiting.  This wouldn’t be bad if either the screws or the screw drivers you used were tough enough to handle this ill-treatment without mangling themselves.  This is simply not the case with crappy zinc-pot-metal-lowest-bidder fasteners.  They are really easy to mangle, and if you think that you might have to undo and redo them, it’s possible for you to end up with a bout of swearing.   I hate regular hex key screws (such as seem prevalent in 3D printers) for much the same reason: in small sizes they simply are too easy to strip.

Torx screws are simply engineered better.   They are designed not
to cam out, and thus are much harder to strip.   That alone means I should like them.

But I hate that the mower uses a mix of the two.  So, the question of the day is: Should I replace all the screws I took out with Torx, replace them all with Phillips, or leave them with the odd mix that I found?

Feel free to leave your comments in, well, the comments.