Balder Grinder won't start

[idickers]

I have a Baldor 7307D 1/2 hp bench grinder that I bought off of Craigslist several years ago. I use it with a Multitool 2"x36" belt sanding attachment, and it's worked great until this weekend, when it would not start when I flipped the toggle switch on, and then once it started in the "Off" position and turned off in the "On" position, and since then it's been silent. I opened the bottom of the case and checked the switch, and I get 120V at the input, and 120V at the two output terminals when the switch is flipped to "On". I can't start the grinder by spinning the wheel so I'm guessing it's not the starter.

Any suggestions? I really don't know much about grinders.

 

[AmericanMechanic]

Can you measure the resistance of the motor terminals (input and output)? If it's infinite resistance (in ohms) then there's likely a break in the motor winding.

 

[DSLTRK]

Any noise when the switch is on?

Also, if the motor was getting current with the switch off, you have a big issue with the switch.


Check continuity between the motor leads and the cast aluminum case. You should have infinite resistance. NO POWER IS APPLIED WHEN DOING THIS.

Check resistances between neutral and hot motor leads, for a 1/2 HP motor @ 120V should be about 35-40 ohms
NO POWER IS APPLIED WHEN DOING THIS.


Check continuity from neutral motor lead to neutral on receptacle plug. Important and often overlooked, you need a good neutral for 120v circuits.
NO POWER IS APPLIED WHEN DOING THIS.

 

[organ]

Try some Propecia...

 

[exmaxima1]

I have a Baldor 7307D 1/2 hp bench grinder that I bought off of Craigslist several years ago. I use it with a Multitool 2"x36" belt sanding attachment, and it's worked great until this weekend, when it would not start when I flipped the toggle switch on, and then once it started in the "Off" position and turned off in the "On" position, and since then it's been silent. I opened the bottom of the case and checked the switch, and I get 120V at the input, and 120V at the two output terminals when the switch is flipped to "On". I can't start the grinder by spinning the wheel so I'm guessing it's not the starter.

Any suggestions? I really don't know much about grinders.

I have the same grinder w/MT adapter. It is a capacitor run motor and has no starter winding or relays. Not sure what you are measuring, but if you get 120 volts across the switch when it is flipped "on", you have a bad switch. You should have no voltage drop across a good switch once the contacts are engaged.

Try bypassing the switch and see if that starts the grinder.

 

[idickers]

Thanks for all the good suggestions. The ON-Off switch has 4 connectors, the incoming power (red arrow) and neutral (green arrow), which measure 120V constant. On the opposite side of the switch are two tabs that I assumed would be switched power and neutral out (blue and white arrows). However, when the switch is in the On position, I read 0V between the blue and white arrow, but do read 120V between the green neutral arrow and both the blue and white arrows. Is this normal, or does the switch sound flaky?

 

[exmaxima1]

Thanks for all the good suggestions. The ON-Off switch has 4 connectors, the incoming power (red arrow) and neutral (green arrow), which measure 120V constant. On the opposite side of the switch are two tabs that I assumed would be switched power and neutral out (blue and white arrows). However, when the switch is in the On position, I read 0V between the blue and white arrow, but do read 120V between the green neutral arrow and both the blue and white arrows. Is this normal, or does the switch sound flaky?

That is a 2 pole switch (DPST), and you lost one side of the switch. If you jumper the "green" and "white" wires together, the grinder should run. If so, buy a new switch.

 

[idickers]

That is a 2 pole switch (DPST), and you lost one side of the switch. If you jumper the "green" and "white" wires together, the grinder should run. If so, buy a new switch.

We have a winner! Jumped the two pins and the grinder started. Switch is ordered, thanks for helping the electrically-challenged!

 

[jeff_gates]

I had to replace the switch in my grinder last week.

--Jeff

 

[organ]

We have a winner! Jumped the two pins and the grinder started. Switch is ordered, thanks for helping the electrically-challenged!

This is troubleshooting 101 by the way... if you think a switch is the problem, jump it.

 

[idickers]

I know, I know. I hadn't yet figured out the 2-pole angle, so the suggestion saved me a day of fiddling, and I appreciate the help.

 

[exmaxima1]

We have a winner! Jumped the two pins and the grinder started. Switch is ordered, thanks for helping the electrically-challenged!

Good for you---a new switch is cheaper than a capacitor or burnt windings.

FYI, if you are running on 120 volts (as opposed to 240), you don't need a double pole switch. You can use a single pole switch, and in this case you can leave the jumper in place and continue to use the grinder with only one electrical leg being switched. No need to switch both the black and white wires.

FWIW, if you already bought a new DPST switch you can wire both sides in parallel and still only connect one leg (typically the black wire). You will have twice the current capacity and the switch will last essentially forever. I do that alot for high current motors that are configured for 120 power.