I have a bench mount grinder, and a typical electric angle grinder. Both work fine, but sometimes there 'on' speed is just to fast for what I want to do. Is there anything I can plug items like these into to be able to adjust there speed? Like something that decreases current, or whatever? I was watching "Mythbuster" yesturday and they had a device like this, not sure if it was homemade or not though.

Thanks

Not an electrician but you might try a lamp dimmer switch. Use a short drop cord that's heavy enough to support the draw of your tools and cut it and splice in a plastic AC box with a dimmer switch mounted in it. The only problem I see is if the dimmer isn't able to handle the amperage the tool draws.

I picked up an old variac which adjusts the voltage and that works fine on my unit. This does work but be careful as it doesn't work for all situations. The dimmer switch probably would work for lower current devices but depends on the unit you have.

No electrician either but (on 12v dc atleast) as the voltage drops going to a device, the current required increases so just be carefull not to fry anything.

Be careful on how much you are taking away from the device. Sometimes having a low voltage condition is just as bad or worse than a spike or high voltage. Kinda like when there's a brown-out...if anyone has experienced that.

Sorry, but normally, to safely vary the ac motor rpms, you need to use a frequency driver to alter the frequency of the input power, and those aren't cheap. graemlins/sad.gif

Just like as posted above, if voltage is decreased then the amps will go up, if the amps go up it will build up more heat that will cause the insulation to break down and burn up your equipment. You need to vary the frequency but variable frequency drives are expensive. I think that if it were me I would either buy another different speed grinder or maybe a variable speed grinder like this one. It is a little spendy for me. graemlins/beers.gif
http://www.arizonatools.com/catalog/browse/2137-3530,2/detail/15975/

[ 01-02-2004, 01:47 PM: Message edited by: J Meadows ]

Dang electricity! You guys give me nothing but bad news. J/K, thanks for the help, I'll probably leave it be graemlins/beers.gif .

yes, as was said really the only way to do it would be with a vfd (variable freq drive). motors dont like to have voltages applied that they aren't meant to run at, overheating will be the result. bummer huh? its never as easy as it should be ;)
on a side note, if you have a grinder or somthing of the sort you cant live without, vfd's are getting cheaper for fractional horsepower motors. i believe they can be had for around 300$ or so now. they are trick as hell, you can program them to do all sorts of cool stuff, ramp up slow or fast, ramp down slow or fast, and adjust volts/amps/freq at the touch of a button. very cool indeed, especially on a several hundred horse motor :D

Can you post a link to one of those vfd's?

One link here (http://www.saftronics.com/)

IMO, J Meadows, has the right link to the tool you need. VFD's are pricey, and are mostly used in comericial applications. That Delta grinder would be perfect for your needs. If you were to buy a VFD, Saftronics makes a pretty good Drive, but I would look into ABB, in my line of work we have used both for years, and the ABB has held up better. Sometimes hooking up a Drive to an existing used motor, will mean it's time for a new motor, (one with the smoke still in it. ;) ) Just my .02...Mike smile.gif

There are some cheap (relative term) VFD's at www.automationdirect.com. (http://www.automationdirect.com.) Figure spending about $200 per HP though. They also only work with 3 phase motors. Some will take 120 single phase in and produce 208 3 phase out. They can be run manually, or under remote control.

Heres a link one of the smaller units rated for a .5HP motor:
Getting Started Chapter of VFD Manual (http://web1.automationdirect.com/static/manuals/gs1m/ch1.pdf)

Zuma1211 is right, graemlins/thumbsup.gif if you hook up a vfd to a motor that is not inverter rated then the varying frequencies can burn the motor up. We use Allen Bradley at my place of employment, easy to work with IMO. Also 3-phase and sell for about $900 I think.

check out this page i found. vfds (http://www.controlsupply.com/monitor.htm)
while as was stated, there are issues you need to consider with them and the motor in question, there are cheaper "homeowner" (for lack of a better term) type vfds being produced now. of course fractional horsepower 1phase is going to be cheaper than say a 20-30 horse NEMA 3R allen bradley for daily use at a factory.
another good point like mark pointed out you can buy a vfd to run a three phase motor of choice (lathe, etc.) from a single phase supply. this is another nice use for these you'll see, that way you can run 3 phase motors in say a residential area that cannot be hooked up to 3 phase supply.
and i too like the allen bradley stuff, any of it really, it is nice to work with, and seems to be a very good reliable product. most the stuff i have used in my work is the much larger horsepower applications, in factories that require a motor that continues to run or millions are lost, so they buy the best.
another excellent entirely non related camaro discussion, BTW graemlins/thumbsup.gif

I am no expert on electric stuff, but any motor with brushes like a drill or grinder can be run on DC. I often use a hand grinder on our DC welder which has an outlet plug for 110v DC.

Look on your nameplate and I'll bet it says AC/DC on it. A variable speed control that converts voltage to DC then reduces the voltage with a variable control will do the job and should be available from electric tool vendors like Sears. They were more commonly available a fiew years back when only constant speed drills were sold, now variable speed drills are cheap to buy.

Your grinder will lose power as you reduce speed, be careful not to oveload it and don't block the tools air vents by grabbing it with heavy gloves covering the vents.

I saw a ham-fisted guy with oversized gloves fry a grinder that way! :eek:
Gee! what's that smell???

Here's a link to a variable speed controller for up to 15 amps:
http://www.toolking.com/grip/view.asp?id=3955
David

[ 01-04-2004, 10:18 AM: Message edited by: davidpozzi ]

Thanks Dave, that's alot more in my price range.

good point dave. i can't say i've ever seen one of those speed controllers, but that is a very nice option for any ac/dc motor graemlins/thumbsup.gif
just make sure its an ac/dc motor, or you won't be happy with the results ;)

My angle grinder says AC Only, :(