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cordless mower smoked and died

Discussion in 'Troubleshooting and Repair' started by monching, Sep 16, 2010.

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  1. monching

    monching

    7
    0
    Sep 16, 2010
    Hi. I have the Remington (bankrupt) 60v mower. It is powered by 5 12v batteries and also a 120v cord. I used the corded mode when the thing started smoking, now I can't use the cordless feature as well. The motor is still working but the circuit board is fried. Is there a way to hook up the battery to the motor using a third party board or even a DIY one? I don't think hooking it straight to the battery works. I don't want to buy another mower if this is still fixable. Thanks.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,505
    2,852
    Jan 21, 2010
    Take a series of photos for us. One showing the wiring and the board (if possible), another showing just the board, and a third a closeup of the burnt area. It may be helpful to see both sides of the board.

    The important thing is that the photographs are in focus.

    From those photos we can either get some idea of what has failed, or give you more specific instructions of what to photograph, measure, or test.
     
  3. monching

    monching

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    Sep 16, 2010
  4. Tesla

    Tesla

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    May 10, 2010
    What's the deal with the cut red wire? Could that have caused the failure?

    I wonder if that is was a single part that smoked or just a couple a resistors?

    I have seen high-amp boards burn traces like this, simply because the traces were too small (they end up acting like fuses). Repaired the traces with more wire or metal, check/replace any obviously bad descrete components, and they worked again. Sometimes, it's just the trace since it was a fuse that kicked in when things started to go wrong.

    At some point you should check each battery for proper operation (charging, voltage, and operation under load).
     
  5. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Huh, that was some piece of action... At least a MOSFET, two resistors, and a control IC is blown. Then there's the PCB.. Charred like that it'll start to conduct.
    You'll have to remove all charring (after first having charted the tracks), then rebuild the circuit "in thin air" with stiff wire. I've done it like that before and it works.

    I'd believe the motor could be run straight from the batteries via a simple switch, but the original setup may incorporate some safety features that may be unwise to defeat.
    Then there's the question how you'd charge the batteries w/o the original circuit.
     
  6. monching

    monching

    7
    0
    Sep 16, 2010
    Tesla, the cut red wire is the 60v + power which I cut to free up the board for photographing it. It's not the cause of the failure. It was only when I plugged it in to use the 120V AC.

    I just confirmed that 3 resistors were fried by looking thru the bottom PCB. I will post the pictures really soon.

    Resqueline, I hope only the resistors are destroyed and not the IC & MOSFET. I don't see any burn or bleeding marks on them. Also, the motor is a 60VDC Ametek, I tried hooking the motor straight to the batteries but it doesn't run continuously. Would it need a pulse to turn the motor first?

    BTW, I have an external battery charger, so actually, if I can run the motor straight from the battery, I'd probably settle for that. Thanks.
     
  7. monching

    monching

    7
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    Sep 16, 2010
  8. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    One possible & very common scenario is that the MOSFET failed first, followed by the resistor(s) and then the IC.
    One other possibility is that there was moisture/contamination on the PCB which caused a creep current and then a burn/ flashover.
    Either way the state of the resistors is an indication of the current going in/out of the MOSFET gate & the IC. Imho there's no way they could've survived that.
    Ohming the transistor pins I'm sure you'll find them all shorted. The IC is not so easy to measure out, w/o comparing it with a known good device.

    What kind of motor is it? I figured it was an ordinary series-wound brush motor. If so it should run as well on DC as AC. Maybe the brushes are worn out? Shoot a pic' of it.
     
  9. monching

    monching

    7
    0
    Sep 16, 2010
    Resqueline, the transistor is indeed shorted and the IC is probably damaged as well.

    Here is the picture of the motor:
    http://www.flickr.com/photos/raphee/4998223173/sizes/l/in/photostream/

    So I connected the battery to the motor and it doesn't start right away, and if it did, it hesitated like, it would speed up for a few seconds and slow down for a few as well. And after it ran continuously for a minute, I cut off the power and waited for it to fully stop. Then, I applied the power again but it won't start anymore.

    Does the board have a special starter feature to run the motor, perhaps? I really wish it just runs straight from the battery with an on & off switch so I can salvage it.
     
  10. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    It definitely sounds like worn-out brushes. The picture doesn't reveal everything but it does say 60VDC, and it has the looks of a permanent magnet motor.
    I figure you'll have to remove the shroud over the fan to gain access to the brushes (they're located where the wires are connected to the motor).
    Maybe the sparking from the worn brushes was what killed the transistor. Your initial challenge is to locate a pair of brushes of the same size/type as are in there.
    A switch is "all" that's needed to run it off the batteries, but there may be a challenge in retaining a decent set of safety features.
     
    Last edited: Sep 17, 2010
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,505
    2,852
    Jan 21, 2010
    I guess the obvious question to monching is whether the original controller provided a "throttle" and whether the mower was ever used at other than full throttle.

    If it required a lower setting then a switch is not going to solve the problem.

    On the other hand, if the throttle was always just slammed to the end stop, a switch would be ideal.

    For safety, I would use a switch with a spring return, so if you release it the motor stops. Not necessarily the most complex of safety features, but a worthwhile one.
     
  12. monching

    monching

    7
    0
    Sep 16, 2010
    Thanks, Resqueline. I will try replacing the brushes but I haven't actually opened a motor before so I hope I won't damage it. What is the primary function of the brushes anyway?

    Steve, the board actually offers a faster or more powerful rotation of the blades. When I was using the corded mode, its speed (and noise level) is almost twice than with the battery. So the board must be supplying it more than 66v (battery's reading). If the battery can power up the motor when fixed then I will just use the spring lever on the handle to stop the motor.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,505
    2,852
    Jan 21, 2010
    You will probably find that the control on the handle is not rated for the motor current.

    The simplest approach may be to use a relay controlled by that lever.
     
  14. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Sometime has to be the first. W/o better/ more detailed picures I can't make a guess at how it's done on that motor. Maybe the shield has to be bent in some spots.
    The brushes carry the electric current to the rotor. Just Google something like <commutator brushes> and you'll come up with lots of information, pictures, and suppliers.
     
  15. monching

    monching

    7
    0
    Sep 16, 2010
    Thanks to you both. I'll see what I can come up with this weekend. I'm hoping to make the motor work, then the relay issue.
     
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