Running power tools on reduced power

300jk

Well-known Member
In a post over on tractor tales there was a post about removing
rust. George had posted about using a grinder and using a diode
or dimmer to reduce power to the tool. Is that healthy for the
tool ? I have heard in the past it isn't good. Kinda like
running too many appliances on a generator during a power
outage. I know a little about electric but am unsure on this
one. George if your out there please chime in on the topic. I
did respond to you in that post but was affraid you might not
see it. Thanks folks for your thoughts.
 
If loaded to the point they are slow, they do heat.
Reduced fan speed, and the fact that one cycle of the AC is taking the whole applied load can affect the tool's life. Running a tool with a speed control based on sokid state trigger electronics usually fries them. Jim
Jim
 
If you lower the voltage on a motor it can overheat, not something Id recommend in general.

John T
 
Work is watts, if you reduce the voltage without reducing the work requested the amps go up, and it overheats.
 
If these tools have "universal" motors with brushes, those options wouldn't be real different than how such a tool equipped with a variable speed "trigger switch" work, and (very likely) if not loaded to the point that they overheat with the reduced speed of the cooling fan they'd survive just fine, IMHO.
 
(quoted from post at 15:31:21 11/25/18) If these tools have "universal" motors with brushes, those options wouldn't be real different than how such a tool equipped with a variable speed "trigger switch" work, and (very likely) if not loaded to the point that they overheat with the reduced speed of the cooling fan they'd survive just fine, IMHO.

Forgot to mention, many years ago, a friend of mine built a Heathkit speed controller intended to be used with just such tools, essentially an overgrown light dimmer.

He used it for all sorts of tools and projects, and I bought it from his brother at this estate sale and still use it on occasion with NO issues.

Just a matter of using common sense and not working the tool long and hard enough to grossly overheat it.
 
Hello 300jk,

Like Bob said:Universal motor and common sense!
I much prefer air tools, just reduce air pressure, and again common sense applied to them too! A 7" grinder will do the heavy work.....

Guido.
 
There is a speed reducer made just for AC brush type motors.

You do have to watch the load as the torque diminishes along with the speed.

This just plugs into the wall outlet, the tool plugs into the controller.
Speed Controller
 
Ok I understand what you are saying. Now that I think of it I have a Makita oscillating tool that has a variable speed control. Must work on the same principal. Thanks
 
Thanks Guido. I really wasn't interested in trying it myself, but it seemed like a good question. We have an older Hobart welder/generator. A few times when welding with it I plugger s 4 1/2 grinder into it. Rpms of grinder seemed slower than if plugged into the wall. Didn't want to hurt it so I didn't use the welder to run the grinder any more. I was just curious about the whole concept. Thanks !
 
So in theory it can be done as long as the tool isn't overloaded for the power being supplied to it correct ?
 
Hello 300jk,

Welding and grinding go hand in hand. Grinder should do just fine,

Guido.
 
Guido- Oh I know ! Most of my welding is done in my garage or the shop at the farm. We used that welder to build our 40x60 building. No power close by at the time and with it on it's own frame with wheels it was real handy. Good for welding in field repairs, or heavy steel. The old Jeep industrial engine just won't give up !
 
A tool will "try" to produce a torque to do a job, this is watts, so if voltage is lower then the amps have to be higher. You can get away with this if the tool is lightly loaded, or if the voltage reducer also reduces the amps, or in effect limits the watts. Either way, the tool will stall or overheat or both. VFD's vary the frequency, but also will compensate the volts and amps to attain the required torque, but simple voltage reducers cannot do this. I like VFD"s, but they really only work well with 3 phase motors because of the starting windings that are needed to start a single phase in the correct direction.
 

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