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Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Something else to point out here, it uses a carbon brush contact.
Exceeding the power handling by a large amount causes that brush to get very hot and burn the winding, and the brush, so I would recommend exceeding that rating only conservatively and for brief periods of time.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Hazmatt_(The Underdog) wrote ...
Something else to point out here, it uses a carbon brush contact.
Exceeding the power handling by a large amount causes that brush to get very hot and burn the winding, and the brush, so I would recommend exceeding that rating only conservatively and for brief periods of time.
See page 1 for a overload curve, %overload vs. time ,%20M5%20,%20M10,%20and%20M20%20Variac%
20Autotransformers.pdf
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
Get the coil up and running with the 8A variac, it'll do fine for low power testing.
Assuming it's a DRSSTC all you need to get higher power later is to build up a phase controlled rectifier - A Dual SCR brick (or maybe some discrete SCRs) is all you need for oodles of power. I think steve conner's site has a schematic floating round using a couple of 555s.
Bigger Variacs do occasionally pop up on trademe, but they're not common. I got my 15A one for $150 NZD, which is a bargain (though it doesn't have a proper dial).
Could probably get a SCR brick on ebay - mine are unfortunately packed away back home (I'm in the UK right now), otherwise I'd be happy to give you a couple.
Registered Member #42796
Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195
Hydron wrote ...
Assuming it's a DRSSTC all you need to get higher power later is to build up a phase controlled rectifier - A Dual SCR brick (or maybe some discrete SCRs) is all you need for oodles of power. I think steve conner's site has a schematic floating round using a couple of 555s.
i built that using a 91A dual thyristor module and it works ok the main advantage of using a phase controlled rectifier is that it can also work as a doubler while still maintaining thr "variac"function
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hydron wrote ...
Get the coil up and running with the 8A variac, it'll do fine for low power testing.
Assuming it's a DRSSTC all you need to get higher power later is to build up a phase controlled rectifier - A Dual SCR brick (or maybe some discrete SCRs) is all you need for oodles of power. I think steve conner's site has a schematic floating round using a couple of 555s.
If i did this would it allow me to run my coil at higher output without having to get a higher rated wall outlet installed?
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
I don't think you'll have to upgrade your wall outlet, unless it's running continuously. I double checked, and we use the same outlet design as NZ. I regularly pull >20A from the 10A outlets in my workshop (usually the MIG welder). They're wired with 2.5mm^2 cable and 20A breakers, so nothing generates any heat at all. I've pulled more than 50A from the 15A outlet in short bursts of a few seconds, and invariably the breaker trips long before the outlet gets warm.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
GrantX wrote ...
I don't think you'll have to upgrade your wall outlet, unless it's running continuously. I double checked, and we use the same outlet design as NZ. I regularly pull >20A from the 10A outlets in my workshop (usually the MIG welder). They're wired with 2.5mm^2 cable and 20A breakers, so nothing generates any heat at all. I've pulled more than 50A from the 15A outlet in short bursts of a few seconds, and invariably the breaker trips long before the outlet gets warm.
OK thats sweet, ill just look out for a bigger variac for operating at full power 20A would be its absolute max
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
nzoomed wrote ...
OK thats sweet, ill just look out for a bigger variac for operating at full power 20A would be its absolute max
Yeah, the winding and carbon brush will likely see more stress than the outlet. Power outlets seem to endure lots of rough treatment without problems. The breaker should be sized correctly to protect the house wiring, not the outlet itself. It's a good idea to check the condition and size of the wiring behind the outlet before unleashing abuse beyond it's ratings.
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How cruical is a VARIAC?
