then this works pretty well.

Curious. Have you tried that? How do the electronics work with reduced power?

 

Curious. Have you tried that? How do the electronics work with reduced power?

Hello there,

It all seems to work pretty well as noted. By that i mean that the cooking power comes down as well as the input power, and so i can achieve a slow cook without having the power turning on and off as the oven does normally.
I have read that the element coating on the filament of the tube can degrade, but i've used ovens at lower power for years now because the electric in this area goes down quite a bit in the summer time, and the ovens have lasted at least 5 years each.

The cooking power level is a little tricky to adjust though. You have to kind of watch it with a meter if you want best results. What i find is that once you adjust it, the power has a tendency to increase a little so you have to be there to turn it down a little again. It does not regulate the power, it just lowers it, so you have to watch it if you want optimum power control. If you can put up with some power variation though then you dont have to watch it, and you can sort of get a better idea how to adjust it next time too with experience.

It took me quite a few years to test this because i already had an inverter microwave oven. I got the variac when i had this oven, so i didnt need to test right then. But then i happened to spot a sale on a small oven that was not an inverter type, it was around 30 dollars USD. I like to have a spare one anyway, so i went out and picked one up then came home and tested it with and without the variac. I was able to get good results with the variac and so i got continuous heating power in an oven that was made for pulsed heating for lower powers simply by setting it on high and then using the variac to control input power. I monitored the input power with a watt meter, but you can also use a current meter. You can test efficiency by heating a small cup of water so you get some idea what cooking power you are getting with a given input power, if you care to go that far.
It is very interesting. I was able to cook down to very low levels like 200 watts with a 1000 watt oven. That's low enough for anything. As i get down that low though the adjustment becomes more important because if i go too much lower it wont cook much at all. This means the food might be cooking TOO slow and could be allowing bacteria to multiply, so the lowest setting should be where you see some reasonable cooking even though it is much slower than usual.

We talked about this more in another thread here on this site too.

 

Sort of overkill on that last one. You can buy a cheap dimmer switch at any home improvement store for a few bucks and control a soldering pencil. Most hand held electric drills include a speed control built into the trigger.

Years ago a variac was popular for testing line regulation of the older linear power supply regulation but I seldom if ever see that anymore. The ones I have just sit around and collect dust. Unless you have a specific need and know a variac will suit that need I would spend the money on something else.

Ron

Yes, and that is just what i don't want. Let it sit to collect dust.

 

As mentioned before, I use my variac to repair equipment - especially the oldest ones where anything can go "cabooom" if the full power is applied to it. Something the older technicians replaced with an incandescent lightbulb in series with the equipment's power cord.

I also use it to characterize unknown transformers - I usually have a few around and the variac is perfect to get the various parameters of a transformer - something similar to what is shown here.

However, it is not an everyday tool (just like my frequency counter, insulation tester, ESD voltmeter and others), thus it gathers dust from time to time but it is certainly nice to have when you need it.

 

Thanks guys for all you're comments. I will read all you'r post again and then decide if i will get one. I think it will be useful in my small research lab to control mains. I also think it is useful at home to reduce the speed of fast motors like a grinder, to use the grinder as a polisher etc. Thanks again.

 

As mentioned before, I use my variac to repair equipment - especially the oldest ones where anything can go "cabooom" if the full power is applied to it. Something the older technicians replaced with an incandescent lightbulb in series with the equipment's power cord.

I also use it to characterize unknown transformers - I usually have a few around and the variac is perfect to get the various parameters of a transformer - something similar to what is shown here.

However, it is not an everyday tool (just like my frequency counter, insulation tester, ESD voltmeter and others), thus it gathers dust from time to time but it is certainly nice to have when you need it.

Yes testing a unknown transformer is also a very good purpose for the Variac. Nice

 

That means that the fan motor is an universal motor. I've read that you can't control the speed of an induction motor with the variac, because the speed of an induction motor relates to the frequency of the AC current, am i correct??

The variac don't change frequency. The fan thing works.

 

I used a variac to match a guitar amplifier to the juke box speakers in a bar. They had a high impedance line feeding a bunch of speakers, and connecting the amplifier directly produced very little sound. So i wired the variac as a step-up device and it worked and the band people were happy and so was the bar owner, because it worked without changing anything.I think that it was a 5 amp device, and a 50 watt amplifier.That was back in 1966, so some of the details may not be available.

 

The variable don't change frequency. The fan thing works.

You are right indeed. As the voltage is lowered the slip increases and the fan slows. And I would never use a 120 volt fan with a universal motor, except in a vacuum cleaner.

 

Hi,

Now that i read some of the other posts i remember using it for other things too, like a regular 120vac fan that had a regular fan motor and not a universal motor. I used the variac to slow the fan speed, and it did not seem to hurt the fan because it lasted for years. Never investigated why it worked so well for so long. Dont use it for that anymore though as i dont need that function anymore.

 

Most mains powered hand tools are Universal motor driven, usually RPM control is via triac control, I have used the Variac on one such Universal motor power tool that did not have Triac control.
Max.

 

When I was doing repairs (many years ago) on things that had blown a fuse, a VARIAC with an ammeter was indispensable. Disable a circuit section. Replace the fuse with a 2x higher rated one. Plug the device into the VARIAC. Very, very slowly start to increase the voltage from zero. Watch the ammeter. If the meter needle immediately increases with the voltage (maybe only a couple of volts), you have not isolated the shorted section. Tougher to do today with everything on a PCB.

Ken

 

When I was doing repairs (many years ago) on things that had blown a fuse, a VARIAC with an ammeter was indispensable. Disable a circuit section. Replace the fuse with a 2x higher rated one. Plug the device into the VARIAC. Very, very slowly start to increase the voltage from zero. Watch the ammeter. If the meter needle immediately increases with the voltage (maybe only a couple of volts), you have not isolated the shorted section. Tougher to do today with everything on a PCB.

Ken

Hi,

Yes some things will not start up at all with low input line voltage. The trick used back in the 1980's was to power the device low voltage section with a separate power source, then run the main power up slowly. The low voltage power source would get the logic up and running, then the main power buss could be run up slowly and see if anything looks bad. This was done with high power converters.
I suppose a lot of things these days have undervoltage cutout, so we'd have to find a way to run up the low voltage section first, then follow with the main power, if that is even possible with some devices. I'd have a hard time doing that with my LCD tv set.

 

Most mains powered hand tools are Universal motor driven, usually RPM control is via triac control, I have used the Variac on one such Universal motor power tool that did not have Triac control.
Max.

Hi,

Oh yeah i think i used it on a grinder once and a power drill, but that was a long time ago.
Now all my drills have variable speed, even the Dremel.
I used it on my older Dremel though from the 1970's that did not have a speed control on it.

 

One advantage of Variac over triacs is that they (at least mine) go to 115%. Don't often need that, but a few weeks ago I was soldering 12 AWG highly flexible silicone wire to a model speed controller. It was a multi-layer board with (apparently) an embedded copper layer for heat sink. My usual soldering station was useless, as was my 25 W pencil iron. My 80 W Weller with a 1/4" tip, which I normally run at 90% to 95%, sorta of worked, but was great at 105%.

 

Hi,

Oh yeah good idea about the iron heating improvement and that reminded me of another use i forgot about also. I knew i used it for a lot of things just couldnt remember them all at once

The other use was i bought a soldering GUN from Harbor Freight. It came with two tips, one on the gun one spare. I used the gun a few times and the dang tip on the gun MELTED. I figured it would not help to use the spare tip because that would melt too, so i picked up a couple copper tips from Radio Shack i think it was. They were heavy duty. What i found though was that now the gun would overheat quickly (the transformer gets hot really fast) and i think it is because the original tip was made of something less than pure copper, and the new tip was pure copper so it conducted better and thus drew a lot more current on the primary side.
The gun still works, but i can only use it for about five minutes and then have to let it cool down for several minutes or else the transformer (that's all they are really) will burn up the insulation on the wire.
What i can do with the variac though is turn DOWN the power getting to the gun, so that the transformer does not get hot but still solders quite well. I think it was originally 150 watts, but with the new tip it will draw much more than that from the line unless i use the variac. With the variac i can turn it back down to 150 watts and not worry about melting the tip.

So that's another use. There are so many uses it's hard to list them all.

 

Did anyone mention you can use it to electrocute people due to poor mains isolation?

 

Hi,

Oh yeah i think i used it on a grinder once and a power drill, but that was a long time ago.
Now all my drills have variable speed, even the Dremel.
I used it on my older Dremel though from the 1970's that did not have a speed control on it.

If i buy it i will use it to slow down the grinder and the drill i have. I want to use the grinder to sharpen knifes etc.I don't like the high speed of the grinder. My grinder and drill do not have variable speed.

 

If i buy it i will use it to slow down the grinder and the drill i have. I want to use the grinder to sharpen knifes etc.I don't like the high speed of the grinder. My grinder and drill do not have variable speed.

Maybe consider phase angle control. It will probably be less expensive and more reliable.

 

At work we used it to cut glass. Yes, cut glass. A score and a resistance wire heater with a spring. Heat the crack and add a dab of water from a q-tip and break. It was tough cutting glass that was initially 1" x 1"

i wanted to cut a mirror tile around a rectangular heat register. So, I cut maybe a 4" x 3" area of tile. I scored it and then bent a heating element in a L and used the q-tip. Of course it didn't cut the rectangle out, but it tried really hard. I had some glass to nibble, but it worked,

My variac is a weird set-up, but I was may in high school when I did it. I have a 1000 W isolation xformer elsewhere on the bench. Got it for like $10.00 USD. My uncle gave me a 3 A variac which is generally not useful, BUT... I put an analog ammeter and analog voltmeter on it.
The switch I used was a center off. One side would bypass the Variac (Isolation at 15 A) the other side would use the Variac + isolation.

If I did it again, I would add a light or lights that turned on when the switch was on. This is where I would plug in what i was working on. Usually this was an audio amplifier.

Did the Muffin fan speed control at work.

Remeber to fuse the wiper.

Sencore made a nice unit that combined a leakage tester and Wattmeter, Volts and Amps.