Isolation Transformer, Variac and Dimmer Bulb Tester, I have all three. What order would you suggest I hook them up ?
Hi BassNoid,
Ignore the dim bulb tester for starters, you have very good equipment there that allows you to control the energy input to the device under test.
I would use the isolation transformer to feed the variac. This keeps the current in the isolation transformer low unlike what you can get on the output of the variac.
It would be really nice if there was a voltmeter and current meter permanently connected to the variac.
-Chris
Edit: Install a fuse in the primary of the isolation transformer.
Ignore the dim bulb tester for starters, you have very good equipment there that allows you to control the energy input to the device under test.
I would use the isolation transformer to feed the variac. This keeps the current in the isolation transformer low unlike what you can get on the output of the variac.
It would be really nice if there was a voltmeter and current meter permanently connected to the variac.
-Chris
Edit: Install a fuse in the primary of the isolation transformer.
Hi BassNoid, dim bulb testers is what i use when repairing ss amps, it burns full bright when there is something wrong like busted output trannies, otherwise, it turns on bright then becomes very dim to signify a viable working amp.....
variacs are what i use for testing traffos under "short circuit" or copper loss testing...
isolation traffos are what i use for testing atx psu or equipment with smps psu..
i have all of the three and use them accordingly...
right now, i am making an isolation traffo for 500 watts, it will have 100v, 120v, and 220 volt secondaries...
variacs are what i use for testing traffos under "short circuit" or copper loss testing...
isolation traffos are what i use for testing atx psu or equipment with smps psu..
i have all of the three and use them accordingly...
right now, i am making an isolation traffo for 500 watts, it will have 100v, 120v, and 220 volt secondaries...
No Fuse on any of the devices ! Simple enough to add one or more of them. What value of fuse ? I have means to connect a variety of meters in the chain between the devices.
You need a fuse in the output of the Variac as the winding is the same rating all the way through so at lower voltages you can easily overload it.
Hi BassNoid,
The very first item I bought was a variac. I still have that one, it's a light duty one. I now use three depending on the current expected. The largest one is simply too big and heavy to leave on the bench. That would be for huge tube power amplifiers, or Carver power amps. I bought it under the direction of technicians that were training me. I already had a good meter and a 'scope (500 KHz - don't laugh Ray! 🙂 ). They were adamant about this, and 40+ years down the road I have to agree with them.
Some equipment can do very strange things with a light bulb in series with them, and you aren't really controlling the current with a light bulb if the device normally draws low current. With a variac, you can run the power up partially, and that allows you to troubleshoot something at lower voltages and currents than you ever could with a light bulb. The variac allows you full control over current, and allows you to correct for normal variations in your house supply. In my case, I adjust the voltage to 120 VAC and also correct for load.
The isolation transformer would work for the light bulb tester too. It can break ground loops, or allow you to work on the primary section of a device a bit more safely. They are invaluable when fixing an "all american five" type table radio as they are normally chassis hot. One side of the AC line is directly connected to the chassis. Some small TVs are that way too.
The fuse should be rated for the rating of the lowest current device in the chain. So, look at the variac's current rating, and the one for the isolation transformer. Use a fuse rated for the lowest current device.
-Chris
The very first item I bought was a variac. I still have that one, it's a light duty one. I now use three depending on the current expected. The largest one is simply too big and heavy to leave on the bench. That would be for huge tube power amplifiers, or Carver power amps. I bought it under the direction of technicians that were training me. I already had a good meter and a 'scope (500 KHz - don't laugh Ray! 🙂 ). They were adamant about this, and 40+ years down the road I have to agree with them.
Some equipment can do very strange things with a light bulb in series with them, and you aren't really controlling the current with a light bulb if the device normally draws low current. With a variac, you can run the power up partially, and that allows you to troubleshoot something at lower voltages and currents than you ever could with a light bulb. The variac allows you full control over current, and allows you to correct for normal variations in your house supply. In my case, I adjust the voltage to 120 VAC and also correct for load.
The isolation transformer would work for the light bulb tester too. It can break ground loops, or allow you to work on the primary section of a device a bit more safely. They are invaluable when fixing an "all american five" type table radio as they are normally chassis hot. One side of the AC line is directly connected to the chassis. Some small TVs are that way too.
The fuse should be rated for the rating of the lowest current device in the chain. So, look at the variac's current rating, and the one for the isolation transformer. Use a fuse rated for the lowest current device.
-Chris
fuses are good safety practice, it goes without saying....
fuses are rated based on your wire size since the fusses are there to protect your cabling....
fuses are rated based on your wire size since the fusses are there to protect your cabling....
The important thing with a variac is that it is a transformer although not an isolating type. If you set it to 12 volts and the load takes 10 amps the input of the variac will only be 1 amp at 120V. If the wire gauge of the variac can only take 5 amps there needs to be a 5 amp fuse in the output. The input fuse will not save it.
Hi Refugee1,
I've never seen a variac fused in the adjustable output. But I would assume that the pegged meter and loud hum would be hint enough to shut it down. There wouldn't be any harm in fusing both locations. I'm going to suggest using a good breaker for both locations.
-Chris
I've never seen a variac fused in the adjustable output. But I would assume that the pegged meter and loud hum would be hint enough to shut it down. There wouldn't be any harm in fusing both locations. I'm going to suggest using a good breaker for both locations.
-Chris
It is normal practice with variac power supplies to fuse the output. It is the most commonly overlooked thing and cause of burn-ups.
In our lab, students (who should have know better) have blown many Variacs by not fusing the wiper outputs. This includes $6000. high current three phase Staco variable autotransformers, the kind that stack several parallel sections per phase. The damage happens very fast, with no time to turn it down, especially since the "knob" is a 15" diameter round wheel that takes both hands to be able to turn at all. Some types of these are motor driven, and it takes a couple of minutes to go all the way up or down.
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It makes sense to fuse the output of the variac. I have one commercial unit that has breakers on both input and output. The others were unfused.
-Chris
-Chris
Hi DF96,
Why would you use the lamp? It defeats the autotransformer and may cause things to act really weird. I would suggest that the lamp is an either or thing with the variac.
-Chris
Why would you use the lamp? It defeats the autotransformer and may cause things to act really weird. I would suggest that the lamp is an either or thing with the variac.
-Chris
a variac is handy when you want to test equipment rated for 100 volts or any other voltage..
when testing for magnetizing currents, you can test using voltage from 0 to rated and above rated voltages...this is how i use my variac..
variac can also be used in livening up old unused vintage gears, performing capacitor reforming at the same time...
when testing for magnetizing currents, you can test using voltage from 0 to rated and above rated voltages...this is how i use my variac..
variac can also be used in livening up old unused vintage gears, performing capacitor reforming at the same time...
Hi Tony,
I have zero use for a light bulb type current limiter. I need to know how much voltage is applied and at what current. The light bulb limiter is just one big question mark for me.
-Chris
Yes, I also do that with a variac. Often I'll slow start unknown condition units also. That way you can prevent doing more damage to a damaged circuit.
I have zero use for a light bulb type current limiter. I need to know how much voltage is applied and at what current. The light bulb limiter is just one big question mark for me.
-Chris
One more thing, make sure that you know the actual voltage output of the Variac. Some can boost the input voltage by a substantial amount, depending on how they are wired.
Isn't the series bulb a good idea, along with the variac, when firing up something that has sat for a long time or when working with very questionable power supply parts? I'd rather wake some parts out of a coma very slowly while looking, listening, and smelling for signs of "grumpiness".
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