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B&D dh1245 bench grinder capacitor match problem

Discussion in 'Troubleshooting and Repair' started by marcyb, Jan 14, 2021.

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  1. marcyb


    Jan 14, 2021
    Hi guys, im new here so please bear with me.
    I have an old black & decker HD1245 bench grinder that has been a great little servant to me over the years. Recently it has stopped spinning but still hums (it does spin a little but with no force), i can spin it manually and it'll turn on its own, but it doesnt pick up any speed. After doing some reading on the subject, I believe the capacitor may be faulty and will try to switch it out first, problem is.. i don't know which one or where to get it. I don't know if its a run cap, a start cap, or both - or even if that's relevent anymore.
    The capacitor says:
    124-138 uf
    110V RMS
    MSDA J4 18S
    I cant find anything relating to it on google, but if i can match the figures as best i can, it should be alright - there must be a modern equivalent for it, i assume as long as im within certain ranges (even higher in some cases), it could even be a good upgrade. I jusr can't identiy it, and am not up with these things, so can't source a replacement. I really don't want to put the wrong part in it.
    Any help would be greatly appreciated

    Here are the grinder specs if that helps:
    Black & Decker HD1245 6" (150mm) Heavy Duty grinder
    1 ph
    3000 / min
    Type H2

    Capacitor and id plate pics attached

    Attached Files:

  2. Martaine2005


    May 12, 2015
    Hi, it appears to be a start capacitor.
    Modern equivalents seem to be 124 - 149μF. And 110 - 125V.
    Stay within the specs above but the voltage can be higher without any issues.

    marcyb likes this.
  3. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir marcyb . . . . .

    Let's try out a bit more involved testing, SINCE you did menton of a proclivity of the motor, in attempting to try to turn, with a slight bit of hand assistance to its shaft.
    The motor starts with it then always rotating in ONE direction, and I hope that after AL L L L L L of those years that you have noticed in which direction that the grinding wheels "sparks were a' flyin' ". Assuredly in viewing the shaft end, towards the grinding wheel, a counter-clockwise ratation.
    On your attempting another motor start up, take a rope / cord of a dimensional variance of the lightest gauge, being that of a kids tops twisted 3 ply cord on up to the largest gauge, being that of a venetian blinds cord.
    Make the initial few turns tight enough so that the tension to the motor shaft keeps it from slipping or unwinding and then go on and put on upwards of 15-20 turns and hold taunt..
    FIRST . . . . being sure that in the winding on of the cord and then on the pull of the cord, will have the motor shaft rotating in the SAME direction as was normal in its working times.
    THEN you have one hand at the ready to flip on AC power to the motor, just after you have uniformly put a tug on the pull cord end, to get the motor runnig as fast as it wil go.
    Then flipping on the switch applies AC power, and if all is normal, a metal load, work piece, pressed to the grind stone should find torque level being at its norm.
    See If your motor is now running normally now, with this much heftier start up assist and its faster speed.

    If not, then the non - self starting condition should be related to . . .
    Lowered or very little capacitance assistance from the starting capacitor.
    With that high level of capacitance value it is being two heavy duty electrolytic capacitors of twice the needed capacitance value, that are then being seies inter connected reverse polarity to each other to end up with half of either of their capcitances and being a nonpolarized (AC use ) capacitor.

    OR and that's heavy on the OR . . . . of there is being a bad ( non closing ) centrifugal switch, located inside the motor.
    Or, sometimes as in my motors past situations it has the contacts being kept from electrically closing contact by a fine layer of "insulating" sawdust.

    Now, being shown in the references is a centrifugal switch and yet a different switch variant , on the right.

    HOW IT WORKS . . .

    Using the left illustration is the mechanical aspects where a set screw affixes the unit to the shaft of the motor and it is being positionally aligned such that the insulated molded black bakelite collar presses into the tandem leaf switch bracket It is being adjusted such that the collar presses the leaf switch closed.
    That then has the start capacitor switched in circuit with an unpowered motor.
    Upon power up the, then dormant cap gives enough hard torque to the motor to get it started up to speed.
    Now examine what just happened electro-mechanically.
    Initially, the RED arrow switch was being closed and engaging the start up capacitor for initially zipping the motors rotor up to speed, at some point in speed up,
    the springs( BLUE square) are then affected by the increasing centrifugal force upon the set of RED square counterweights and the black collar pushes to open the switch and disconnects that starting capacitor.
    That is true, all on up until the moment of AC power disruption, when you turn the unit off.
    Then the turned off motors slowing speed decreases the counterweights extreme outer positions, move inwardly, until the two springs tensioning actions LOUDLY SNAPS the switch closed, until the final end of motor rotor speed run down.
    The unit is then ready for the next start up, just as it was being, initially.
    WITH THE EXCEPTION . . . . .
    If those contacts might have a contaminant or loose deteris that is keeping them from electrically closing.
    If so, one might try high air presssure blasts from a compressor.
    Spread the contacts and pull a strip of fine silicon carbide paper / wet and dry thru the tensioned contacrs and then swap abrasive sides and pull thru again to thereby clean both contact sides.
    Use an ohmmeter to see if the normally closed.contacts are REALLY being closed.

    ILLUSTRATIONS . . . . .


    Motor Start Capacitor . . . . .

    73's de Edd . . . . .

    Even a mosquito doesn't get a slap on the back, until getting deep into the work at hand.

    Last edited: Jan 15, 2021
    marcyb likes this.
  4. marcyb


    Jan 14, 2021
    perfect - thanks Martaine
  5. marcyb


    Jan 14, 2021
    Thank you so much for the detailed answer, im finding it a little difficult to decifer but i'll take it all on board. i already tried the 'cord' trick (i actually used a loosely attached drill on the shaft rather than cord - as it's a much much easier way to do it, and turns at a higher rate) - but it didn't help.
    I will try the capacitor first, then go from there if that doesnt work.
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