# So is a 240v Variac considered a tool as well?



## silverforgestudio (Feb 11, 2017)

OK guys- I know enough to be on the lookout for tools and tooling- but when it comes to the electrical stuff I'm really lost!

This was part of a free load of stuff I got for helping clean out a barn. I know eventually I will need a Variac for anodizing Titanium as well as electro-etching stainless steels.

It is in a home-made galvanized box with screw corner enclosures- no markings, no dial, no face, no knobs... I had to open the box to figure out what it was.

Here is a link to a seller of these things: http://www.newark.com/staco-energy-products/1520/variable-transformer/dp/05F310

And here are a couple of pics in the album: View media item 95759
SO- my questions are- is this a 0-240 V @ 9.5 Amp variac??? Is this TOO powerful for etching?

With a approx. 500 USD price tag I don't want to toss this if I can eventually use it.  And no- I'm not interested in killing myself with it so that is why I'm asking about it here first! (I was the kid who put the fork in the outlet... yes- that one...) HA!


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## markba633csi (Feb 11, 2017)

Oh it will work but it's probably way more voltage than you need. I doubt you would need more than about 30 volts at a few amps for etching.  Also be aware that variacs are not isolated from the power line like a transformer is, so be careful of shock hazard.
It would probably best to have a step-down transformer connected between the variac and the bridge rectifier and then you would have a 0-30 volt isolated DC supply.
Mark S.


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## silverforgestudio (Feb 11, 2017)

OK Mark- thank you! 


markba633csi said:


> Also be aware that variacs are not isolated from the power line like a transformer is, so be careful of shock hazard.
> It would probably best to have a step-down transformer connected between the variac and the bridge rectifier and then you would have a 0-30 volt isolated DC supply.
> Mark S.



So in the big picture- I'm not messing with this thing. Anyone have a need for it?


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## Bob Korves (Feb 11, 2017)

Variacs control the voltage.  It is like a giant potentiometer.  The question is the upper limit input voltage, and maximum current as well.  Is there a reason you think it is for 240V input or is that what you are hoping for?  It is difficult to try to determine the size of the variac, the terminals, and the wiring in your pic.  No writing at all on it?


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## f350ca (Feb 11, 2017)

It may be rated for 220 v but you can feed it with 110 v and get 0-150 v out. I have a couple of them, one mounted in a case with an outlet. Handy to slow down a die grinder or router.
Greg


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## markba633csi (Feb 11, 2017)

I'm sure someone here could use it as a simple motor speed controller- or monkey shocker! LOL  The evil that men do...
Mark S.


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## Bob Korves (Feb 11, 2017)

I have two variacs.  One says 110V in, 0-132V out, 297 VA,  It is about three inches diameter and tall.  The other one says 120V in, 0-140V out, 1 KVA.  The second one is pretty big and about 10 pounds.


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## silverforgestudio (Feb 11, 2017)

Bob Korves said:


> The question is the upper limit input voltage, and maximum current as well.  Is there a reason you think it is for 240V input or is that what you are hoping for?  It is difficult to try to determine the size of the variac, the terminals, and the wiring in your pic.  No writing at all on it?






Hey Bob- nothing on the box- this is the pic of the terminal board on the rear of the unit- it didn't load to the album for some reason in the first posting- sorry. I'm not hoping for it to be 240v- the Stayco data sheet on Newark Supply says:
*The 1520 is a 1-phase manually operated voltage doubler Variable Transformer with accurate AC voltage control.*

*Input Voltage: 240VAC                                                              *
*Output Voltage: 280VAC                                                              *
*Output Current: 9.5A                                                              *
*Constant Current Load: 9.5A* 

The housing for it is about 14" square and 8 inches deep- plenty of room for it inside the box- the coil is about 7-7.5 inches diameter and about 5 inches tall-



markba633csi said:


> I'm sure someone here could use it as a simple motor speed controller- or monkey shocker! LOL  The evil that men do...
> Mark S.



HA! problem is I'm the monkey...


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## silverforgestudio (Feb 11, 2017)

f350ca said:


> It may be rated for 220 v but you can feed it with 110 v and get 0-150 v out. I have a couple of them, one mounted in a case with an outlet. Handy to slow down a die grinder or router.
> Greg



Would that also lower the torque with the voltage drop?


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## markba633csi (Feb 11, 2017)

Pretty beefy unit you got there, would fetch a good price but heavy to ship
MS


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## f350ca (Feb 11, 2017)

Unfortunately Yes. Cant change the laws of physics. 
I've used it on my die grinder to carve wood with HSS burrs, at full rpm they burn, at half speed they cut beautiful, and it still has lots of torque.
I added a bridge rectifier similar to the one in your photo to get pulsed DC. That operates a gear motor on a gearbox for a weld positioner. Mounted a 3 jaw chuck to hold pipe or hubs. Get the speed set then pull the trigger on the mig and get smooth consistent weld beads.
Lots of uses for them.

Greg


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## cathead (Feb 11, 2017)

I have several used in different places.  They work great for soldering irons to control the temperature.  Also I use one on
my Croc-Pot as a warmer as the low control is still too hot.  I have one in the shop to put in line with a battery charger. 
That way you can give a battery a slow charge or a boost if the battery doesn't draw any current when trying to charge it.
Also I have used  a Variac on a 4.5 inch angle grinder for less robust operations.


Edit:  By the way, some Variacs control from zero volts up to line voltage only and others
         control from zero to line voltage plus about 20 percent.  Also be aware that some can
         have more than one configuration.  The markings on the terminal posts usually tell the
         story.


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## silence dogood (Feb 11, 2017)

Variacs are very useful.  I have two.  Add an AC amp meter for repairing the old transistor power amps and power supplies.  They are great for resistance type loads such as heaters, soldering irons, the old light bulbs, etc.  Work pretty good for universal motors.    Do not use on AC motors and fluorescent lights.


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## Bob Korves (Feb 11, 2017)

The 2.66 KVA that it says on yours is some respectable power, silverforgestudio.  That is watts times volts divided by 1000.


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## silverforgestudio (Feb 12, 2017)

OK- thank you all!

And I like the use on the grinder- understood about the torque- I am NOT anything electrical (heck- just started putzing about with machine tools a couple of years ago!) so I am definitely getting an education and direction to head- thank you ALL (even Monkey-shocker Mark!) HA!

Guys thanks- as I "gear up" and learn I am blessed to have several storage-boxes of stuff for free from older guys I helped clean things or shut down their shops- I know I am in the dark about some of this stuff- thanks for the compass points!


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## markba633csi (Feb 12, 2017)

Another point: I believe that whole upper circular plate is electrically "live"- usually those units are enclosed and there's an insulated knob assembly that mounts on the top, so again, be careful if you do decide to use it. 
Sorry I'm fresh out of monkeys today.
Mark S.


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## silverforgestudio (Feb 12, 2017)

Understood Mark- I will be putting it back in the case it was in and getting a proper dial/face for when I get it back out- As I'm discovering exactly what these things are I'm making notes and putting them with the item so later I can remember/understand or know what part(s) I need to make these things work for me.

Think I'll break out the "barrel of monkeys" and glue them around the shop- and Ill shock one in your honor! HA!


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## dulltool17 (Feb 12, 2017)

silence dogood said:


> Variacs are very useful.  I have two.  Add an AC amp meter for repairing the old transistor power amps and power supplies.  They are great for resistance type loads such as heaters, soldering irons, the old light bulbs, etc.  Work pretty good for universal motors.    Do not use on AC motors and fluorescent lights.



I use that exact model to control heaters in test equipment I've build.  They work very well for resistive loads; I'd try not to use them too much for inductive loads, although they've been used to conduct high line/low line tests on some of our equipment.

 They're built like a tank!


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## silverforgestudio (Feb 12, 2017)

Thanks Dulltool17- nice to know I have something that is in use (not from the 1950's like a lot of the things I got from this fellow)- and relatively well built!

Now I need to learn the difference in inductive versus resistance... back to the monkey-mix!


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## hman (Feb 12, 2017)

Quick rule of thumb - if the device (usefully) converts electricity to magnetism (and then to motion), it's inductive.  The prime example would of course be a motor.  If the device converts electricity into heat or (incandescent) light, it's resistive. 

OK, exceptions/details: 
1. You can use a Variac to run a transformer, which is basically an inductive "middle man" between the variac and something else.  So look at the "something else." 
2. Be aware that lights which use solid state circuitry (fluorescents, CFL, and many LED bulbs) are not resistive loads.  The circuitry requires full voltage.  LED bulbs that are labeled as dimmable might work with a variac.
3.  As Silence Dogood pointed out, a "universal" motor is OK with a variac.  Universal motors have brushes to get voltage directly to the windings of the rotor, so they'll work, but lose torque as well as speed.  Motors without brushes depend on the field (fixed) windings _inducing_ current in the rotor.  Speed is mainly a function of frequency.  If voltage is reduced, the motor will still try to run _at the same speed_, but at severely reduced output power, and may well overheat.
4.  Solid state devices contain internal voltage regulators, so that the circuit elements can be fed the correct power levels.  Reducing the input voltage will have almost no effect at first.  Then when it drops below the level the voltage regulator can handle, the device will precipitously stop working.

Hope this helps.


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## Bob Korves (Feb 13, 2017)

So, John, what about an electromagnetic chuck?  Inductive or resistive, or something else?


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## hman (Feb 13, 2017)

Geez, Bob .... ya nailed me fair and square!  Gotta admit, that's the trouble with rules of thumb.  

Yes, an electromagnet converts electricity into magnetism.  Maybe I can weasel out of the dilemma by pointing out that the magnetism isn't used to produce motion.  Though an electromagnetic chuck would indeed be an inductive load on the variac, it should work OK (as would a universal motor), with the holding power being approximately proportional to the voltage.

I guess the difficulty lies with the earlier "blanket" statement that a variac should not be used with inductive loads.  Maybe we can make silverforgestudio's life a little simpler by restating the rule as variacs being generally OK to use with resistive loads, *sometimes* Ok with inductive, and generally not OK with solid state electronics.  Yes, there'll still be exceptions.  But short of a detailed course in electronics and/or motor theory, I'm hoping it will be useful.


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## silverforgestudio (Feb 13, 2017)

Hman (John) and Bob- I get the rules of thumb do not apply universally- The use of this unit may not be an issue for now as I have no idea what/how to apply it... but the time will come. And the best part is I know enough to NOT use it till I understand it...

And I am seeing a base in electronics/motor theory is very useful!


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## Bob Korves (Feb 13, 2017)

hman said:


> Geez, Bob .... ya nailed me fair and square!  Gotta admit, that's the trouble with rules of thumb.
> 
> Yes, an electromagnet converts electricity into magnetism.  Maybe I can weasel out of the dilemma by pointing out that the magnetism isn't used to produce motion.  Though an electromagnetic chuck would indeed be an inductive load on the variac, it should work OK (as would a universal motor), with the holding power being approximately proportional to the voltage.
> 
> I guess the difficulty lies with the earlier "blanket" statement that a variac should not be used with inductive loads.  Maybe we can make silverforgestudio's life a little simpler by restating the rule as variacs being generally OK to use with resistive loads, *sometimes* Ok with inductive, and generally not OK with solid state electronics.  Yes, there'll still be exceptions.  But short of a detailed course in electronics and/or motor theory, I'm hoping it will be useful.


My question was completely practical, not a gotcha.  I am planning to use a variac to control my electromagnetic chuck, I am not an electrical/electronic genius, and want to make sure I am not trying something stupid...  I am also planning to try to use the variac and a drum switch to reverse the current to the chuck multiple times while reducing the voltage in steps to zero, to try to demag the chuck and parts after grinding or machining or scraping or whatever.  Are those reasonable ideas?


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## chips&more (Feb 13, 2017)

Bob Korves said:


> My question was completely practical, not a gotcha.  I am planning to use a variac to control my electromagnetic chuck, I am not an electrical/electronic genius, and want to make sure I am not trying something stupid...  I am also planning to try to use the variac and a drum switch to reverse the current to the chuck multiple times while reducing the voltage in steps to zero, to try to demag the chuck and parts after grinding or machining or scraping or whatever.  Are those reasonable ideas?


Hi Bob, You would build a power supply that has a DC output for creating magnetism. And an option on the power supply to change its output to AC for demag. That’s the simple power supply. There are more elaborate power supplies that pulse the AC and such, but just a switch to change from DC to OFF to AC (mag-off-demag) works pretty good…Dave.


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## Bob Korves (Feb 13, 2017)

chips&more said:


> Hi Bob, You would build a power supply that has a DC output for creating magnetism. And an option on the power supply to change its output to AC for demag. That’s the simple power supply. There are more elaborate power supplies that pulse the AC and such, but just a switch to change from DC to OFF to AC (mag-off-demag) works pretty good…Dave.


Yes, Dave, I am using a bridge rectifier for AC to DC, along with a electrolytic capacitor, etc. to mag the chuck.  I think I have that figured out pretty well.  I am not quite sure how to wire it for AC as well, I guess just bypass the DC circuit completely with the AC, no capacitor or anything else, and then dial the voltage down to zero with the variac to demag(?)  Any important details I am missing?


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## chips&more (Feb 13, 2017)

Bob Korves said:


> Yes, Dave, I am using a bridge rectifier for AC to DC, along with a electrolytic capacitor, etc. to mag the chuck.  I think I have that figured out pretty well.  I am not quite sure how to wire it for AC as well, I guess just bypass the DC circuit completely with the AC, no capacitor or anything else, and then dial the voltage down to zero with the variac to demag(?)  Any important details I am missing?


Hi again Bob, I would first run the 120vac through an isolation transformer (for safety, especially if you ever decide on using coolant). And then yes, just tap of the transformer for the AC source. I would use a 2 pole 3 position switch for the DC-off-AC. The switch would have 1 momentary position for the AC. Momentary means, it’s only on when your thumb/finger is on the switch. Makes it handy for pulsing the AC if you need to. Sometimes just non-pulsed AC is enough to demag. Depends on the type of metal on the chuck at the time. This kinda switch is not your regular garden variety, but can be found. As far as the Variac, don’t know if it’s needed? And I don’t think it isolates either (can’t remember for sure). For me, I would want all the magnetism I can get and not some dialed down percentage of it. Maybe there are some jobs applications out there that work better with less magnetism/pull? Some jobs require shimming because it’s warped. And if not shimmed correctly the magnetism will do its own warping. But that just means it was not shimmed correctly and not because it had too much magnetism. If you have ever had a part fly off the chuck, it’s one of those never forget moments...Dave


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## Bob Korves (Feb 13, 2017)

chips&more said:


> Hi again Bob, I would first run the 120vac through an isolation transformer (for safety, especially if you ever decide on using coolant). And then yes, just tap of the transformer for the AC source. I would use a 2 pole 3 position switch for the DC-off-AC. The switch would have 1 momentary position for the AC. Momentary means, it’s only on when your thumb/finger is on the switch. Makes it handy for pulsing the AC if you need to. Sometimes just non-pulsed AC is enough to demag. Depends on the type of metal on the chuck at the time. This kinda switch is not your regular garden variety, but can be found. As far as the Variac, don’t know if it’s needed? And I don’t think it isolates either (can’t remember for sure). For me, I would want all the magnetism I can get and not some dialed down percentage of it. Maybe there are some jobs applications out there that work better with less magnetism/pull? Some jobs require shimming because it’s warped. And if not shimmed correctly the magnetism will do its own warping. But that just means it was not shimmed correctly and not because it had too much magnetism. If you have ever had a part fly off the chuck, it’s one of those never forget moments...Dave


Dave, this chuck will be for general use in the shop, perhaps on the mill, and on the bench for holding work for scraping or other hand work.  I suppose I might use it very occasionally for holding a special project on the surface grinder.  I already have a nice 6x18" B & S permanent magnet chuck for general use on the surface grinder.  Part of the usefulness of this chuck will be the ability to lower holding strength for thin, delicate, or other unusual projects.  Without the grinding wheel it is no longer a safety issue.  With the grinding wheel I will use full mag power.  Thanks for the suggestion of the isolation transformer, an excellent idea, and for a switch momentary to AC.  Great ideas!


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## hman (Feb 14, 2017)

Bob -
Thanks for your clarification.  But even though you weren't intending to "gotch" me, you did correctly point out a flaw in my simplification.  No problem whatever (and even if it were intended, I took it as being in good humor).

It's been my long held philosophy that it doesn't matter whether "you" (whoever that is) are right or that I'm right.  What matters is that reality is right, and we _all_ benefit from getting there.  Anyway, it sounds like you're well on the way toward achieving your goal.  Best wishes!


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## Bob Korves (Feb 14, 2017)

hman said:


> Bob -
> Thanks for your clarification.  But even though you weren't intending to "gotch" me, you did correctly point out a flaw in my simplification.  No problem whatever (and even if it were intended, I took it as being in good humor).
> 
> It's been my long held philosophy that it doesn't matter whether "you" (whoever that is) are right or that I'm right.  What matters is that reality is right, and we _all_ benefit from getting there.  Anyway, it sounds like you're well on the way toward achieving your goal.  Best wishes!


John, we are all looking for knowledge and understanding here, and sometimes the words get in the way.  I did not know the issues with inductive and resistive loads, and I learned something important that relates to a current project from your post.  Thank you!


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## pstemari (Feb 14, 2017)

Generally speaking, motor speed is controlled by the voltage and the torque is controlled by the current.  If you lower the voltage, power output drops, but that's because the speed drops.  As long as you haven't saturated the transformer, the current should remain more-or-less constant for a given load.  Speed will drop off a bit with load on a real motor due to resistive losses in the windings.


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## Bi11Hudson (Feb 18, 2017)

My 2 cents worth, for what that's worth:

The "variac" is an "auto-transformer". You may use a lower voltage than rated, however you may *NOT USE A HIGHER *voltage.(at 60 Hz AC) I doubt you would ever face _that_ problem, with exceptions of course. The bottom line: you can safely connect to 120 VAC, just remember that current (amps, I, KVA) does not double. It is the limiting factor. If connected to 120 volts, the output would be ~140 volts max at rated current. That would give you a safe output of 0-100%=0-120volts for use with a grinder or other "sewing machine motor".  I HAVE seen an induction motor used with a lamp dimmer as a speed control, but it was an industrial application and only "sorta-kinda" worked. OK for the application but *not recommended*. 

Your clutch problem is a whole different issue. The determining factor there involves the manufacturer's spec sheet. I can only say for sure that DC would far and away do a better job than AC. A good strong DC field would be much more desirable for a clutch. (chuck) Use a full wave bridge and a good strong capacitor. A 1000MFD cap will suffice for 1 amp at power line frequency. With AC, you would get "zero crossing" at 120 times per second. Beyond that, you get into electrical theory serious and I don't have the 10 years or so to make you into an electrical engineer.

Oh, and by the way, when my name gets posted with this entry; you can add BSEE1974 in your mind. I posted an artical a few years back on the subject. But as a newbie I don't think the moderator will allow a link. Maybe later...
Try www(dot)hudsontelcom(dot)com and home shop electrics for a general overview of the subject.


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## angelfj1 (Feb 18, 2017)

f350ca said:


> It may be rated for 220 v but you can feed it with 110 v and get 0-150 v out. I have a couple of them, one mounted in a case with an outlet. Handy to slow down a die grinder or router.
> Greg



Generally speaking, a variac makes a very poor speed control.  The torque developed by an ac motor is proportional to the square of the voltage. So, if you reduce the voltage by 20%, the motor will only produce 64% of rated full voltage torque.  In addition, running ac motors act like a constant volt-ampere load, so a reduction in voltage will draw additional current proportionally.  The best way to kill a motor is to feed it with lower than rated voltage.


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## angelfj1 (Feb 18, 2017)

pstemari said:


> Generally speaking, motor speed is controlled by the voltage and the torque is controlled by the current.  If you lower the voltage, power output drops, but that's because the speed drops.  As long as you haven't saturated the transformer, the current should remain more-or-less constant for a given load.  Speed will drop off a bit with load on a real motor due to resistive losses in the windings.



No.  AC motor torque is a function of voltage, actually the square of the voltage, not the current.  That's why voltage reduction, regardless of how it is reduced, is such a poor way to control speed.  See my previous post in response to f350ca!  In addition,  when you reduce the voltage to an ac motor, the motor will try to maintain a constant volt-ampere, but the power factor will decrease, motor curre  The speed of the motor


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## hman (Feb 18, 2017)

Bi11Hudson said:


> Oh, and by the way, when my name gets posted with this entry; you can add BSEE1974 in your mind.


Good to know!  I'm more-or-less a "seat of the pants" electricker myself, and try not to post info I'm not sure of.  But I do try to be of help. Glad to have you here.  I'm sure you'll be valued by many of us!


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## silverforgestudio (Feb 18, 2017)

Bi11Hudson said:


> My 2 cents worth, for what that's worth:
> Try www(dot)hudsontelcom(dot)com and home shop electrics for a general overview of the subject.



Thank you! I am WAAAAY under the learning curve now- and I will hopefully be pulling the books out way before using this thing. good in fo and I appreciate the thoughts and advice to ALL that have posted- THANKS GUYS


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## f350ca (Feb 18, 2017)

angelfj1 said:


> Generally speaking, a variac makes a very poor speed control.  The torque developed by an ac motor is proportional to the square of the voltage. So, if you reduce the voltage by 20%, the motor will only produce 64% of rated full voltage torque.  In addition, running ac motors act like a constant volt-ampere load, so a reduction in voltage will draw additional current proportionally.  The best way to kill a motor is to feed it with lower than rated voltage.


Routers and die grinders use universal motors that will operate on AC or DC. The motor speed is directly proportional to the applied voltage.

Greg


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## Bi11Hudson (Feb 27, 2017)

Just be sure to account for loss of torque as you account for loss of speed. Torque will fall off dramaticly as speed falls off. That comment is for series universal motors, such as drills, routers, die grinders, sewing machines, and the like. Induction motors like on a drill press, lathe, mill, etc. are a whole different subject. As said, if you try to run an indiction motor on a variac, it will try to maintain speed and get _*very hot*_ in the process.


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## silverforgestudio (Feb 27, 2017)

Thank you Bill! Good to know-


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## pstemari (Mar 2, 2017)

angelfj1 said:


> No.  AC motor torque is a function of voltage, actually the square of the voltage, not the current.  ...



AC motors have problematic characteristics, in particular they're locked to line frequency and you can't change the speed without changing the frequency, but torque is still directly proportional to current. That's basic physics.

If you start varying the voltage into an AC motor, you'll get reduction in current, and hence torque, but that's a fairly limited behavior because the back EMF is proportional to speed, and speed in turn is locked to line frequency. Once you start dropping the voltage below that level, the motor quickly stalls out. 

Sent from my Nexus 6 using Tapatalk


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