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On Thursday, May 26, 2011 3:07:57 AM UTC-4, Robert Green wrote:
"Bob F" > wrote in message
...
> Robert Green wrote:
> > "hr(bob) " > wrote in message
> > news:2b010cfe-1311-45ba-ab82-On May 22, 8:31 am, "Robert Green"
> > > wrote:
> >> "Michael B" > wrote in message
> >> On May 21, 8:29 pm, "Robert Green" >
> >> wrote:
> >>
> >>> I have a B&D cordless mulching mower that suddenly stopped running.
> >>> I've switched out the battery, but no joy. The motor turns freely,
> >>> so does the blade. The unit quit in tall, wet grass so I am
> >>> thinking some sort of overload kicked in. Unfortunately, I wasn't
> >>> mowing. The kid doing the mowing for me said it just stopped, but I
> >>> suspect he took too big a "bite" of the wet, tall grass and burned
> >>> up some protective element. The unit's simple: A motor, a
> >>> controller board with a relay, a handle switch and a wheelchair
> >>> sized 12V SLA battery. The motor shaft will, on occasion, turn a
> >>> few degrees with the pulse of the switch on the handle, but mostly
> >>> it just strains and whines slightly.
> >>
> >>> Any suggestions or clues welcomed. FWIW, the next step is to run
> >>> the motor directly off the battery without the intervening
> >>> controller board (not sure what it does, actually - it's got a
> >>> black plastic cover so solidly attached I can't remove it to trace
> >>> the circuit without seriously damaging it). What I can see of the
> >>> controller board is a heat sink about 1" by 5" by 1" that I assume
> >>> is a voltage regulator and a small black relay. Also, there used to
> >>> be a clicking sound when the unit engaged (the relay, I'm guessing)
> >>> that I no longer hear which leads me to believe that the relay has
> >>> failed or is not getting sufficient power.
>
> > Any ideas how to determine whether the relay has failed? Since it's a
> > mechanical part, I'd suspect it was the problem long before I'd
> > "indict" a passive component for the problem. I found my old
> > stethescope but the membrane is cracked. I'm going to convert it to
> > a solid bar head so that I can place the metal against the various
> > board parts to hear whether they're vibrating (or buy a solid head
> > 'scope from HF for $5 on my next visit).
> >
>
> Measure the voltage at the motor. What does it do as you turn it on? If
the
> motor is getting full voltage, then the motor is likely the problem.

I have not tried that yet. Got sidetracked by an ant invasion and an X-10
"jamming" problem that de-automated half my house (the RF controlled part)
for the last 5 days. As you might imagine, getting to the bare wires is not
terribly simple because they're (thankfully) well-sealed against moisture
(as well as servicing!).

> Check the voltage at the relay coil when you turn it on. Does the coil get
> voltage? If it does, and the relay doesn't click like it did before, the
realy
> contacts are probably welded together.

I did try this as the relay measured only 5.5 volts powering the coil.
That's when it started to rain so I had to put it back in the shed. Without
knowing anything about the controller card (so far no joy in finding a
schematic) and without even being able to see the component side without
cracking it open, I can't determine whether it should have more voltage than
that. IIRC, the lettering on the relay faced in. Tomorrow's the new day
set aside for lawn mower surgery and I'll be trying to document the
controller board as best I can, even if it means cutting it free from the
well-attached cables and cracking the cover. It could be worse - they could
have potted the whole thing.

> Many relays can be opened up. Then the contacts can be lightly filed,
restoring
> them to work fine.

IIRC, this has a black metal case and is about 1" by 2" by 3/4" tall. My
guess is a relay failure and it looks like it will be a bitch to desolder it
or even remove the casing. I haven't played with it since the original post
hoping that it was simply wet in the wrong spot and would dry out. What I
call the "minimum effort" fix.

> Chances are, the controller board may also work to short out the motor as
you
> stop it, to stop the blade FAST. I worked on an AC powered B&D recently
that had
> that. The motor brushes made quite an arc as it stopped with a thunk.. It
had a
> permanent magnet motor.

That's an interesting thought. None of the people who've used it can
remember whether the blade stopped instantly or not. Sounds like it would
be a good safety feature but hard on the parts. Would it short out the
motor or use the relay to briefly apply reverse polarity to the motor? This
relay looked like it had too many pins to be a simple On/Off control, but
then again, the might have already had thousands of that model around. Hard
to tell without cobbling together a schematic.

> Curiously, that mower had one brush that was broken.

Not so curious if it's spitting an arc like that!

> About the last 1/4 inch had cracked off. Carefully re-inserting the broken
end
> after I disassembled it, it worked fine anyway.

Visual inspection by my bud who grew up rebuilding motors in his dad's shop
said the motor looked remarkably unused (which it is for a 16 year old
mower). Spins freely and from what he could see of the brushes, they looked
fine. But he didn't have his reading glasses and he could have been looking
at a beached whale. (-: The motor does spin very freely along with the
blade. Tomorrow we'll try to isolate the source of the noise, which IMHO
*has* to be the relay. What else could buzz like that? If the contacts
were welded together, wouldn't the device be in an "always on" state? All I
get is the buzz and an occasional movement of a few degrees of the armature.

Thanks for your input, Bob!

--
Bobby G.

Sorry to Join this game so late, but I have a B&D cmm625 (working nicely with a 5 year old battery I just desulfated) and a CMM630 that I am fixing for a friend.

The CMM630 was shutting down after 5 min or so in tall grass (not even wet!) and we suspected a battery (only 1 year old, 35 AH). However, when it looks to be something along the lines of your struggle (above). We found the battery to be good (better than mine, when moved to my unit) and not dropping badly in voltage either during operation or immediately after the mower abruptly stops. We then suspected the motor or the control unit (there's not much else!)

It's not easy to swap motors/control units on these mowers, so I carefully swapped out the control unit and the brushes (crimped at to the controller).. In this way I was able to test that the motor ex brushes was fine with my good mower's controller.

Both motors with the known good controller were drawing about 20 Amps. Brushes on each looked identical as did the rest of the parts of the . The 'bad mower' was drawing 33 amps on start up from its controller, though. While we had both mowers open we lubed the top bearing (a felt hole at the top) and the bottom bearing (after SAFELY removing the blade etc from the bottom of the mower) with 3 or so drops of good oil (we used Mobil-1). After reassembly the 'bad mower' was down to about 26 amps, so not sure if we've helped much. The 'good mower' battery is only 26AH, so it's possible that the electronics don't like a battery with the ability to put out more current, or simply that they are a bit fried. We hope that lubrication buys us a little more headroom before the silly thing shuts down due to 'overload'.

If anyone has the schematics please direct us to them! (we have 2 'version 5' controller boards...and I have a version 3 I got from a junked unit).

By the way, we run our mowers off 100% solar (easy to do with one smallish solar panel...see my site:http://solarpowermower.wikia.com/wik...wer_Mower_Wiki

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