Hello everyone,
I managed to get a good deal on eBay (or so I thought) on a pair of variacs. The reason they were cheap, I believe, is because they had no specification.
In the photos below it is difficult to see, but the output is a US style 2 hole socket. The adjustment knob has 'YAMABISHI' printed on it. I am assuming therefore that it is intended for the US or Japanese market. The dimensions of the case are 13cm diameter, 11cm tall (not including the knob). The unit weighs about 3.8kg.
I live in Australia where the voltage is 230-240 50Hz. I am guessing that even if this unit was made for the US or Japanese market, it would not be that critical using it on 240 volts as long as I remained within the current limit? This leads to next question, what would be a sensible current limit for this device given the dimensions and weight?
I intend to house it in an insulated box with fuse protection, a voltage and current meter, and a proper line cord and socket for the device under test if the variac can be used.
Thanks in advance,
Chris
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I managed to get a good deal on eBay (or so I thought) on a pair of variacs. The reason they were cheap, I believe, is because they had no specification.
In the photos below it is difficult to see, but the output is a US style 2 hole socket. The adjustment knob has 'YAMABISHI' printed on it. I am assuming therefore that it is intended for the US or Japanese market. The dimensions of the case are 13cm diameter, 11cm tall (not including the knob). The unit weighs about 3.8kg.
I live in Australia where the voltage is 230-240 50Hz. I am guessing that even if this unit was made for the US or Japanese market, it would not be that critical using it on 240 volts as long as I remained within the current limit? This leads to next question, what would be a sensible current limit for this device given the dimensions and weight?
I intend to house it in an insulated box with fuse protection, a voltage and current meter, and a proper line cord and socket for the device under test if the variac can be used.
Thanks in advance,
Chris
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If the unit was designed for 60 Hz, and you intend to use it on 50 Hz, you may have a problem, as the core could saturate. Might want to place a current meter in series with the excitation voltage and slowly increase voltage to the final desired value (yes, this would require an additional variac to perform the test). The idea is that current excitation will quickly increase as the core nears saturation. Unfortunately, this variac doesn't have the 260V end tap that you could use.
As far as current capability, you have two choices: compare the size and weight to new units in a Newark or Mouser catalog, and assume the capability to be the same. Or, get an approximation of the wire size and reverse engineer. I prefer the former.
Edit: I see you actually bought two of them. Good, now it will be easier to test.
As far as current capability, you have two choices: compare the size and weight to new units in a Newark or Mouser catalog, and assume the capability to be the same. Or, get an approximation of the wire size and reverse engineer. I prefer the former.
Edit: I see you actually bought two of them. Good, now it will be easier to test.
Strictly based on size, using a similar ballpoint pen for scale, your unit is the same size as my Calrad 45-740, which as a nameplate rating of 5 amps.
But, that's at an AC input of 115 volts, with an output range of 0-130v
-regards
art
But, that's at an AC input of 115 volts, with an output range of 0-130v
-regards
art
Chrish,
How do you know you can use this unit at 240 volts, 50 Hz? If it is designed for 120 volts and you apply 240 to it, you will have big trouble.
How do you know you can use this unit at 240 volts, 50 Hz? If it is designed for 120 volts and you apply 240 to it, you will have big trouble.
I don't know I can use it, and have not yet...
My assumption is that it is a transformer, and that if it was designed for 110 volts and 50 Hz, it might be able to be used for 240 volts 60 Hz, but with limitations. I am guessing that the issues will be:
1. Breakdown voltage for the insulation. I am hoping that if it is mains rated, 240 will still be low enough not be an issue.
2. Current rating of the windings.
3. Saturation of the core for lower frequency.
I think I read in Building Valve Amplifiers that variacs generally have a amperage limitation due to winding gauge rather than a VA rating. Any idea if that would translate to having to halve any 120 volt rating for 240 volts input?
My guestimate was 5 amps (even if it is at 120 volts), thanks for the confirmation of that at least UncleArt.
I am hoping that with these limitations, the units might still be usable for my purpose, testing amplifiers etc. As I am not an engineer, I am hoping that if I am about to do something stupid by trying, one of you knowledgeable gentlemen might warn me 😉
Thanks for the input so far!
Regards,
Chris
My assumption is that it is a transformer, and that if it was designed for 110 volts and 50 Hz, it might be able to be used for 240 volts 60 Hz, but with limitations. I am guessing that the issues will be:
1. Breakdown voltage for the insulation. I am hoping that if it is mains rated, 240 will still be low enough not be an issue.
2. Current rating of the windings.
3. Saturation of the core for lower frequency.
I think I read in Building Valve Amplifiers that variacs generally have a amperage limitation due to winding gauge rather than a VA rating. Any idea if that would translate to having to halve any 120 volt rating for 240 volts input?
My guestimate was 5 amps (even if it is at 120 volts), thanks for the confirmation of that at least UncleArt.
I am hoping that with these limitations, the units might still be usable for my purpose, testing amplifiers etc. As I am not an engineer, I am hoping that if I am about to do something stupid by trying, one of you knowledgeable gentlemen might warn me 😉
Thanks for the input so far!
Regards,
Chris
I've also got an old (problably 40+ yrs)10A one off of eBay last year, same ht. (11cm) and 16cm wide. 5.4 kg. The way its hooked up it doesn't give more than the line voltage 121-123V at max setting. Had pay almost as much for shipping as the unit as it came from the U.S..
Why not try using both for your 240V 50HZ. One each in parallel so you are spreading the load on the two units. Maybe only would work with the two in series. Hook up a cheap voltmeter to see what your getting. Maybe 50HZ won't matter if you don't put a big load on them either.
Maybe totally wrong! Just a thought and probably out to lunch!
Are there any converter devices available that you could borrow to try them on 120V first to make sure it is designed for that voltage?
Randy
Why not try using both for your 240V 50HZ. One each in parallel so you are spreading the load on the two units. Maybe only would work with the two in series. Hook up a cheap voltmeter to see what your getting. Maybe 50HZ won't matter if you don't put a big load on them either.
Maybe totally wrong! Just a thought and probably out to lunch!
Are there any converter devices available that you could borrow to try them on 120V first to make sure it is designed for that voltage?
Randy
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If you don't know it's 240V rated, assume it's only 120.
In order to know if it is in fact 240V rated, you must run the excitation current test.
In order to know if it is in fact 240V rated, you must run the excitation current test.
The Yamabishi I owned was not confidence inspiring, in fact mine appeared to have been built for the 100V Japanese market and it was real marginal thermally on 120V .. I believe these were sold here as cheap competition to the rugged and expensive Genrad Variacs that were common lab equipment here back in the day.. (I have one of those Genrad it is now about 50yrs old, I've owned for about half that time.)
I'll keep my fingers crossed but I suspect it may mis-behave at 240V/50Hz. I would just stick a 100W or larger lamp in series with the AC to the variac, if it cannot handle the voltage and frequency the lamp will just light up quite brightly signifying that the core has saturated and you'll know - no need even for a second variac to do this test. (This is a non destructive test.) If this passes then I would proceed to the excitation current test mentioned, anything over a hundred mA or so would be very suspect IMHO.
Good luck!
I'll keep my fingers crossed but I suspect it may mis-behave at 240V/50Hz. I would just stick a 100W or larger lamp in series with the AC to the variac, if it cannot handle the voltage and frequency the lamp will just light up quite brightly signifying that the core has saturated and you'll know - no need even for a second variac to do this test. (This is a non destructive test.) If this passes then I would proceed to the excitation current test mentioned, anything over a hundred mA or so would be very suspect IMHO.
Good luck!
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Thanks Zigzag,
How should I conduct the test with the two variacs? First variac - ammeter - second variac, have first variac set for minimum voltage, second for max and then slowly wind up voltage of first variac watching current? Should I place a load on the second variac? I have several DMMs, so can watch amps at input of first variac too if required.
Thanks for the advice so far,
Chris
Thanks, you posted while I was writing...
These were pretty cheap, about $25 for the pair, so not such a problem if they do not work out.
How should I conduct the test with the two variacs? First variac - ammeter - second variac, have first variac set for minimum voltage, second for max and then slowly wind up voltage of first variac watching current? Should I place a load on the second variac? I have several DMMs, so can watch amps at input of first variac too if required.
Thanks for the advice so far,
Chris
Thanks, you posted while I was writing...
These were pretty cheap, about $25 for the pair, so not such a problem if they do not work out.
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Chris,
If these were intended for 115V Ac 60Hz then they are not safe to connect to a 250V AC 50Hz supply - not safe from a overheating failure point of view that is.
Variacs of any description, even correctly rated units, have no input to output isolation, they are a single variable tapped winding, an inductive voltage divider if you like - so from an electrical safety point of view, no variac can be called safe anyway. I won't have one in my workshop even though it is properly wired with Residual Current Breakers (or Earth Leakage breaker or whatever you like to call them).
I must admit to a certain trepidation each time I see posts about using Variacs. I wonder how many people who use them understand that the variac output has exactly the same inherent safety risks as the power connections on their input. I have used variacs in the past, powered from an isolation transformer.
Cheers,
Ian
If these were intended for 115V Ac 60Hz then they are not safe to connect to a 250V AC 50Hz supply - not safe from a overheating failure point of view that is.
Variacs of any description, even correctly rated units, have no input to output isolation, they are a single variable tapped winding, an inductive voltage divider if you like - so from an electrical safety point of view, no variac can be called safe anyway. I won't have one in my workshop even though it is properly wired with Residual Current Breakers (or Earth Leakage breaker or whatever you like to call them).
I must admit to a certain trepidation each time I see posts about using Variacs. I wonder how many people who use them understand that the variac output has exactly the same inherent safety risks as the power connections on their input. I have used variacs in the past, powered from an isolation transformer.
Cheers,
Ian
Thanks Gingertube, I take your advice seriously! Now, not to question your wisdom, just to enlighten me some, what makes having a variac more dangerous than say plugging your new amp project in to the wall directly? I understand a variac is not an isolation transformer, just a tapped primary winding, and the amp under test would be isolated by its power transformer. Looking at the connections on these things, I realise they look dangerous as a shock hazard from wires and leads, but if it were housed properly with, say an earth leak breaker, a proper power cord and plug, a proper socket for the power cord of the device under test and volt/current meters to observe if there is too much current draw would that be acceptable?
Noting Gingertube's advice as to the poor safety etc, I did the amp meter test described by zigzagflux. I hooked up the input of the first variac to line AC (240 volts, 50 Hz) and then hooked up my Fluke meter set to AC Amps between the first and second variac. Results are:
up to 140 volts output from first variac, current to second 22 mA
160v 30mA
180v 31mA
200v 35mA
210v 39mA
220v 44mA
230v 52mA
240v 72mA
250v 110mA
255v 150mA
260v 202mA
So it looks like the current is just OK at 240 volts input?
It would be handy to be able to ramp voltages up for testing amps. My current project has seen me pop about half a dozen LM317 regulators as I teach myself how to do a MAIDA reg 😉
Thanks for the advice and help so far, much appreciated.
Noting Gingertube's advice as to the poor safety etc, I did the amp meter test described by zigzagflux. I hooked up the input of the first variac to line AC (240 volts, 50 Hz) and then hooked up my Fluke meter set to AC Amps between the first and second variac. Results are:
up to 140 volts output from first variac, current to second 22 mA
160v 30mA
180v 31mA
200v 35mA
210v 39mA
220v 44mA
230v 52mA
240v 72mA
250v 110mA
255v 150mA
260v 202mA
So it looks like the current is just OK at 240 volts input?
It would be handy to be able to ramp voltages up for testing amps. My current project has seen me pop about half a dozen LM317 regulators as I teach myself how to do a MAIDA reg 😉
Thanks for the advice and help so far, much appreciated.
Wow, you're gutsy. The idea was to test before slamming the variac with full line voltage. But, okay, it looks like the variac is fairly happy with 240V.
You can see that the v/i curve is very linear up to 230V, and it just starts to 'knee' at 240V. I would have no problem using it with 240.
Looks like internally your variac does have an outside winding connected to the wiper; that is, the 240V connects between one end of the winding and an inside tap (not at the other end). The wiper is allowed to move from 0 to 260V because it wipes past the inside tap to a few additional turns, which acts as an autotransformer and gives you some voltage boost.
IMHO, as long as the user realizes that the variac isn't there to protect THEM, but rather their EQUIPMENT, they are a "must have" for working on sooo many different things.
Many, many times, a greatly reduced line voltage will allow tests on a circuit that would otherwise blow a line fuse, or an entire bank of expensive transistors, or just go up in flames when connected directly to the Mains.
But, as mentioned, there is no input/output isolation. Again, if the user has any business being inside their gear, they sure shouldn't be pretending the Variac is there for any reason remotely related to their safety... it's a troubleshooting tool.
That having been said, I'd much rather ramp up an unknown Estate Sale Treasure to 30 volts or so AC input and find B+ shorted to the chassis that way, than to plug in on in and find the FULL B+ shorted where it doesn't belong.
That is all.
over
Regards,
art
Many, many times, a greatly reduced line voltage will allow tests on a circuit that would otherwise blow a line fuse, or an entire bank of expensive transistors, or just go up in flames when connected directly to the Mains.
But, as mentioned, there is no input/output isolation. Again, if the user has any business being inside their gear, they sure shouldn't be pretending the Variac is there for any reason remotely related to their safety... it's a troubleshooting tool.
That having been said, I'd much rather ramp up an unknown Estate Sale Treasure to 30 volts or so AC input and find B+ shorted to the chassis that way, than to plug in on in and find the FULL B+ shorted where it doesn't belong.
That is all.
over
Regards,
art
Thanks again for the assistance.
Before use I intend to enclose the unit. Those terminals on the front look a little too easy to brush up against for my liking. Will also add fuse, current and voltage meters.
Cheers,
Chris
Before use I intend to enclose the unit. Those terminals on the front look a little too easy to brush up against for my liking. Will also add fuse, current and voltage meters.
Cheers,
Chris
Chris,
What Art said.....
You will have to forgive me for being a bit sensitive about electrical safety.
Blame it on my training - I did my electronics training in the Biomedical Engineering Dept. of a major teaching hospital where I had to consider such things as:
"is there a direct electrical connection to the heart"?
"are there electrodes strapped to the patient such that he/she can't get away"?
A little paranoia does'nt go astray.
This has carried over into the hobby.
For example, I always switch and fuse both active and neutral - a bit over the top, but then if it ONLY ever saves your life once!!!!
Cheers,
Ian
What Art said.....
You will have to forgive me for being a bit sensitive about electrical safety.
Blame it on my training - I did my electronics training in the Biomedical Engineering Dept. of a major teaching hospital where I had to consider such things as:
"is there a direct electrical connection to the heart"?
"are there electrodes strapped to the patient such that he/she can't get away"?
A little paranoia does'nt go astray.
This has carried over into the hobby.
For example, I always switch and fuse both active and neutral - a bit over the top, but then if it ONLY ever saves your life once!!!!
Cheers,
Ian
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