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Eulogy for a Black & Decker cordless mower

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  • Eulogy for a Black & Decker cordless mower

    A few years ago I bought a Black & Decker 36V cordless mower for about $60. I only used it a couple times, and it mostly sat outside under a tarp.

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    This year, John started using it to mow the lawn, and it was working well. But a couple days ago he said it suddenly stopped working, and the blades would barely turn by hand. I looked it it today, and when I turned the blades, it sounded like the bearings had disintegrated into gravel. There was some rust on the shaft and I figured it had seized and trashed the bearing. But when I took it apart, I found this:

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    Waddya think? Some J-B Weld? Replacement motors are available for $175. Nah...

    I have started looking for cheap DC motors or free treadmills and such. I could make a DC-DC converter from 36 volts to 90 volts.
    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

  • #2
    Too bad the armature is damaged- otherwise you could have replaced the magnets with neodymium and souped it up.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

    Comment


    • #3
      jb weld have a glue rated up to 300°c: https://www.westfalia-versand.ch/sho...s-300-grad.htm

      loctite 608 is incredibly strong on materils like steel or aluminum if surface is prepared correctly (water test). on this i dont know, if you have it try on some other broken core.

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      • #4
        I wonder what actually caused the failure. These are probably ceramic magnets, and they have obviously cracked. But I would assume they had been cemented to the steel housing, and there is no obvious evidence of any adhesive. Perhaps the motor overheated and loosened the adhesive so the magnets shifted and impinged on the armature. Or perhaps something got into the motor and caused a magnet to crack. The armature might be salvageable, but I don't see how the magnets could be replaced, unless they were the exact size and shape to fit.

        I think something like a shop vac motor might be about the right size and power to work, and it would not be too hard to generate 120 VAC (or even DC) to power a universal motor.
        http://pauleschoen.com/pix/PM08_P76_P54.png
        Paul , P S Technology, Inc. and MrTibbs
        USA Maryland 21030

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        • #5
          Sometimes they don't use cement. They use a metal clip between them just to keep them in place. The metal housing serves as a magnetic way part of the circuit and the magnets tend to stay put. On small motors, the can is so thin that they wind a thin strip to increase the cross section
          Helder Ferreira
          Setubal, Portugal

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          • #6
            This is a fairly common mode of failure for some of the cordless clippers we use to prep animals for surgery in the practice. Even a surprisingly gentle blow or drop results in the magnets fracturing. I've not managed to fix one yet.
            West Sussex UK

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            • #7
              Water intrusion and freezing temperatures.

              Comment


              • #8
                Originally posted by PStechPaul View Post
                I wonder what actually caused the failure. These are probably ceramic magnets, and they have obviously cracked. But I would assume they had been cemented to the steel housing, and there is no obvious evidence of any adhesive. Perhaps the motor overheated and loosened the adhesive so the magnets shifted and impinged on the armature. Or perhaps something got into the motor and caused a magnet to crack. The armature might be salvageable, but I don't see how the magnets could be replaced, unless they were the exact size and shape to fit.

                I think something like a shop vac motor might be about the right size and power to work, and it would not be too hard to generate 120 VAC (or even DC) to power a universal motor.
                I've seen this exact type of failure before. The magnets are glued in place. The glue is hard and doesn't take the temperature changes very well. Eventually the glue let's go and a magnet turns and jams everything up.
                And and my opinion is not worth the effort. The next thing you'll be replacing are the batteries.
                The guy down the street got a brand new electric lawn mower for free. he was ranting and raving how he'll never have to buy gasoline again, the original battery wouldn't hold a charge very long so he goes out and buys a few new batteries for it and it cost him $250. I laughed and told him youll never spend $250 in gas for cutting your grass for the rest of your life. Where's the savings?

                JL...

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                • #9
                  Those magnets are like glass and as sharp when broken.
                  Batteries are fine until you have to replace as mentioned.
                  Then too, it is only a matter of time before the cost of disposal is going to catch up to the battery industry.
                  There are issues with recycling especially lithium ion batteries, as they tend to be unstable, with fires and some explosions when being put through recycle processes starting with the truck that picks them up. Most waste firms will not knowingly take lithium ion batteries for this reason. When the massive LI batteries in EVs start to fail, this will become a front line issue and consequently the costs associated with deconstructing and disposing of them will come home to roost. Gas or diesel will look like "free fuel" then.
                  S E Michigan

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                  • #10
                    Magnets are EASY to glue back, I have actually used gorilla glue, with excellent results. It's weatherproof, and holds well. Heat resistance is, well "OK" but it has held.

                    However, your armature is all chopped up, and that motor is simply toast.

                    You can see where the laminations have slid and have cut the wires and insulation on the armature.

                    Recycle it. Unless you can find another motor at a garage sale on a mower with a different problem. I'd not bet on that.

                    Storing things "outside" results in those problems. The devices are not intended for it. It ain't an old JD tractor. The original adhesive deteriorated from weathering, and there you are.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      Originally posted by dian View Post
                      jb weld have a glue rated up to 300°c: https://www.westfalia-versand.ch/sho...s-300-grad.htm

                      loctite 608 is incredibly strong on materils like steel or aluminum if surface is prepared correctly (water test). on this i dont know, if you have it try on some other broken core.
                      JB Weld contains powdered iron. Using it to try to epoxy magnets can get interesting trying to get it to stay where you put it.

                      Comment


                      • #12
                        Too bad it broke. We have an older 24 volt version of the same mower. It ran about 14 years on the original batteries. I changed the batteries and decided maybe it is time to replace the bearings and brushes in the motor. The brushes really did not need replacing. The bearings felt good but I am sure the lube was starting to dry up so put new ones in. It is still going strong. Somewhere along the the way I lost the key it used to use to lock it out for charging. When inquiring about a new key I was told - oh there is a safety upgrade on this mower. Take it a dealer and they will do it for free. I am taking about a 10 to 12 year old mower at that time. They did the upgrade which included replacing the cover and the upper part of the handle, a new control module and a different lockout key. If this thing ever gives up the ghost I would go out and get another. Great mower for smaller lawns.
                        Larry - west coast of Canada

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                        • #13
                          I've seen many cases where the magnets come loose. The most notorious was the winch in our freight elevator. That motor went out twice, same problem each time, magnets came loose. That was decades ago, and the motor was $800 at that time. I suspect a different expansion rate for the steel case and the ferrite magnets would be to blame.

                          Back in the day I did a fair amount of satellite system installations. The dishes were large, 15 ft diameter at the time. The actuators almost all had DC PM motors, and a good number of the actual motor failures were due to loose magnets. On one job I wedged them back in on site with pieces of wood. As the actuators got smaller, the motors tended to have full ring magnets instead of two separate segments. I can't recall even having one of those come loose, but if they had they could have rotated inside the case, killing the motor anyway.

                          For that lawnmower motor- perhaps you could carefully knock those laminations back to where they should be, and the armature might be fine. But how would you know if there is damage to the windings, and maybe if you did make that motor run again it might just develop a short or an open at a later date- possibly sooner than later. And getting all those bits of magnets out of there is not easy- it's likely that some little chunk would come back to grind away at things.

                          Personally, I'd be happy to see you fix it, but you'd have to be at least as crazy as me to try to.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                          Comment


                          • #14
                            I was able to put the motor back together, without the magnets, and the armature turns smoothly. But I don't know if the windings are damaged, although that is immaterial if the laminations have been messed up. I remembered that I had a starter/generator from an old (ca 1967) Simplicity Broadmoor tractor, and It seems to be about the same size. It's also 12V as opposed to 36V, and probably not made for continuous operation as a motor. It's also frozen, so probably a fool's errand to use it as a replacement.

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                            http://pauleschoen.com/pix/PM08_P76_P54.png
                            Paul , P S Technology, Inc. and MrTibbs
                            USA Maryland 21030

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                            • #15
                              $250 for batteries? Where, at a Batteries Plus Bulbs place? They have the absolute highest prices for everything.

                              When I replaced the cells in my B&D batteries, I was able to get full sized D NiCads for about $0.99 each. The OEM batteries had sub-sized D cells with spacers to take up the extra space that full sized Ds would occupy. And they have already lasted longer than the OEM ones. So they were not just cheap junk. If anything, the OEM cells are cheap junk that was designed to fail so the user would have to buy replacement batteries; OEM replacement batteries which would also have smaller cells that fail faster. Great way to boost your stock but an awful way to treat your customers.

                              I do not know what size cells these lawn mowers use, but I do know that they CAN be purchased for a lot less.



                              Originally posted by JoeLee View Post

                              I've seen this exact type of failure before. The magnets are glued in place. The glue is hard and doesn't take the temperature changes very well. Eventually the glue let's go and a magnet turns and jams everything up.
                              And and my opinion is not worth the effort. The next thing you'll be replacing are the batteries.
                              The guy down the street got a brand new electric lawn mower for free. he was ranting and raving how he'll never have to buy gasoline again, the original battery wouldn't hold a charge very long so he goes out and buys a few new batteries for it and it cost him $250. I laughed and told him youll never spend $250 in gas for cutting your grass for the rest of your life. Where's the savings?

                              JL...
                              Paul A.
                              SE Texas

                              Make it fit.
                              You can't win and there IS a penalty for trying!

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