Question about Black & Decker 19" Electric Lawnhog Mulching Mower with Rear Bag

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Wiring problem Have a Black$&Decker MM850 electric mower. While cutting one day the switch burned up. When I installed a new switch it worked for afew seconds then stopped. If I cross the wires the mower comes on when plugged in without depressing the switch. Is there a wiring diagram available for tis mower?

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  • Lawn Hater May 15, 2008

    I have the same problem with the B&D switch. Mine didn't burn up, it just stopped working. Initially I put a coin on top if the switch button to allow the handle to push the button farther into the switch. This worked for about a year but then also went bad.



    I want to hot wire the motor using a seperate switch, but there are four wires and I'm not sure how they operate. I know that there is some type of of electric brake that stops the motor when the swiutch is disengauged. Does anyone have a wiring diagram for the switch and motor?

  • Robsspen Jun 24, 2008

    I had the same problem and ended up taking apart the switch. It appears that there is buildup of a black oily substance on the contacts in the switch box that eventually interfers with the contacts. I too need a wiring diagram or a new switch. Can I get either one?

  • bill34655 Aug 02, 2008

    Hi. I have just bought a replacement switch for a black and decker lawnhog. but i did not mark where the wires are attached. there are 2 black, 1 red and 1 white, can you tell me which goes where? please help. i keep playing around but can't seem to get the right connection. lawn mower keeps tripping the circuit breaker in the house.

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I have same problem with my MM850 B&D Mower. But I have decided to replace push switch with flick-switch. So far this is what I have found out about wires. Push swith has 2 sliding conntacts and it makes RED and WHITE connected in OFF position and RED / BLACK + Black AC LINE connected in ON position. Everything sounded easy so I bought ON-OFF switch and connected RED and BLACK on one side and BLACK AC LINE on other side. I did not connect WHITE wire thinking that it's there only to stop motor in OFF position. But with big suprise mower worked about 5 secons and than quit. Well I am not going to give up so now I am in search for good replacement flick (Toggle) switch that has same function since I do not want to go back with push switch. Ok, guys help me here. Thanks.

Posted on Jul 28, 2008

  • KORGMASTER Jul 28, 2008

    Well that would be the place if you want to go with same push switch, but I do not want to. I need to find what can replace same push but in form of Toggle Switch. If anyone has any info please let me know. Thanks.

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I'm sure you can find parts many places online. I got mine from www.ToolPartsDirect.com. If you type in the model number, you can see a complete parts diagram. The switch is part 9 on the diagram; about 15 bucks. When I was mowing, I smelled a burning electric parts type of smell. The motor brushes wore down from use. Now my wife can't tell me I don't mow enough!

Posted on Jul 24, 2008

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Its unsafe to hot wire the switch. contact me at 204-783-7294 i will send you a wiring diagram ask for dennis

Posted on May 29, 2008

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The problem with the system is not the switch, but the poorly designed switch box housing. Often, there is nothing wrong with the switch. I tested mines and it works fine. The problem is the switch box housing does not keep the switch in the correct position for the higher tension spring lever to press against it to operate. I use small washers to stack between the rear of the switch inside and reassembled the switch box upside down by turning the handle upside down, so the washers and switch do not fall out. Once I am finished assembling the switch box and position it on the handle, then I position the handle back to the normal top side and attach the handle back to the lawn mower. I am finished.
http://en.wikipedia.org/wiki/AC_motor#Split-phase_induction_motor

"Split Phase Motors
Split phase ac motors are widely used for low power applications as for example in oil burners, furnace blowers, garage door openers and major appliances. Such motors employ separate run and start windings connected in parallel across the acpower source. When the motor is initially energized both windings are energized, and when the rotor speed reaches about eighty-five percent of the normal running speed the start winding is disconnected from the circuit. Various devices are utilized forthis latter purpose and include centrifugal switches and current and voltage relays.

A problem which is characteristic of these motors is that they have a relatively short operating life. The principal reason for this is the failure of the switching devices used to cut out the start windings when the rotors approach the normalrunning speeds.Failure of these switching devices in turn cause the start windings to burn out.

One of the reasons for the failure of these switching devices is the high currents which they are carrying at the time the contacts open. Attempts to increase contact life by use of improved designs and materials have not been altogethersuccessful. Another disadvantage associated with these switching devices is that they are necessarily quite large and occupy a substantial space in the motor housing." -from another web site.

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