How cruical is a VARIAC?
nzoomed, Thu Sept 17 2015, 09:43PMIm having trouble finding a large enough variac for my coil, and from what i read, they are not totally necessary.
I have been working on coil specs from people using 120v mains power and i thought if their power supply would run at say 3000w, then i would only need 1500w to run the same powered coil since our mains is 240v.
Now ive been told that my coil could run at up to 20A so this may be a problem, since i thought i would only need 6A at the wall and i managed to score an 8A variac.
perhaps i can do without the variac and just adjust the breakout from the midi controller instead?
I was going to use voltage doubled mains output from a variac that would let me get up to 270vac from the overwind on the variac itself, so the bus voltage would be somewhere around 680v.
The other problem is i may need to wire in a 20A outlet in my garage, but ill worry about that later i guess.
The specs for my coil are here:
Re: How cruical is a VARIAC?
Ash Small, Thu Sept 17 2015, 11:10PM
The rating for variacs is 'continuous rating'.
Most can be pushed a bit continuously, but all seem to be ok at up to twice rated current for short periods, from what most people say.
It will certainly be ok at low power for initial testing.
Only run it for short periods and check it's not getting hot (after disconnecting, of course)
Personally, I'd try it on a 13 amp socket and fuse, the worst that can happen is the fuse will blow as you turn the power up.
Just my opinion, though.
Ash Small, Thu Sept 17 2015, 11:10PM
The rating for variacs is 'continuous rating'.
Most can be pushed a bit continuously, but all seem to be ok at up to twice rated current for short periods, from what most people say.
It will certainly be ok at low power for initial testing.
Only run it for short periods and check it's not getting hot (after disconnecting, of course)
Personally, I'd try it on a 13 amp socket and fuse, the worst that can happen is the fuse will blow as you turn the power up.
Just my opinion, though.
Re: How cruical is a VARIAC?
Signification, Fri Sept 18 2015, 02:35AM
Years ago, I had a big problem with my TC popping the circuit breaker (120VAC@15A). I would have to cut the primary current by -something like- 40%...?
Then, I connected a power factor correction capacitor bank to the primary connection of the neon sign transformers (a lot of 15kV 30mA and 60mA all in phase-corrected parallel), and the breaker remained intact...never tripped again from that point on. The primary needle Ammeter (20Aac) no longer slapped a peg again either!
I don't recall the total current at 15kVAC, but I got hot 4' sparks. I remember one run, where the air must have gotten highly ionized and sparks of over 4' reached out like an arm and hand with fingers, as if attempting to grip my head! FREAKY!
The thing is stored in the corner of my shop, as the huge grounding system must have worn out--did wonders for the lawn in that area, though.
Signification, Fri Sept 18 2015, 02:35AM
Years ago, I had a big problem with my TC popping the circuit breaker (120VAC@15A). I would have to cut the primary current by -something like- 40%...?
Then, I connected a power factor correction capacitor bank to the primary connection of the neon sign transformers (a lot of 15kV 30mA and 60mA all in phase-corrected parallel), and the breaker remained intact...never tripped again from that point on. The primary needle Ammeter (20Aac) no longer slapped a peg again either!
I don't recall the total current at 15kVAC, but I got hot 4' sparks. I remember one run, where the air must have gotten highly ionized and sparks of over 4' reached out like an arm and hand with fingers, as if attempting to grip my head! FREAKY!
The thing is stored in the corner of my shop, as the huge grounding system must have worn out--did wonders for the lawn in that area, though.
Re: How cruical is a VARIAC?
Hazmatt_(The Underdog), Fri Sept 18 2015, 03:55AM
I run 720-1000W and even with a cheap 10A Chinese variac the fuses blow after a while. Anything under 20A is not going to cut it.
Maybe for a rotary gap speed control that would be fine, but not on the power side.
There are cheap Chinese 20A variacs out there, so you might want to pick one of those up, rather then splurging on a Powerstat/GE/GR unit.
For 3000W of power, you're going to either need a stack of two units, or a big 1256D ( 8kw unit) which can be pricey.
Try to scrounge around surplus dealers in your neighborhood and you'll eventually find them. I never thought I would have half the stuff I have, it just takes some time.
Hazmatt_(The Underdog), Fri Sept 18 2015, 03:55AM
I run 720-1000W and even with a cheap 10A Chinese variac the fuses blow after a while. Anything under 20A is not going to cut it.
Maybe for a rotary gap speed control that would be fine, but not on the power side.
There are cheap Chinese 20A variacs out there, so you might want to pick one of those up, rather then splurging on a Powerstat/GE/GR unit.
For 3000W of power, you're going to either need a stack of two units, or a big 1256D ( 8kw unit) which can be pricey.
Try to scrounge around surplus dealers in your neighborhood and you'll eventually find them. I never thought I would have half the stuff I have, it just takes some time.
Re: How cruical is a VARIAC?
nzoomed, Fri Sept 18 2015, 04:56AM
I found a cheap GR variac on Ebay for $20, but cost $200 in shipping to New Zealand, considering small 2A chinese Variacs cost that here i figured out it was a bargin, 8A may do it, are you running on 240v or 110v mains?
nzoomed, Fri Sept 18 2015, 04:56AM
Hazmatt_(The Underdog) wrote ...
I run 720-1000W and even with a cheap 10A Chinese variac the fuses blow after a while. Anything under 20A is not going to cut it.
Maybe for a rotary gap speed control that would be fine, but not on the power side.
There are cheap Chinese 20A variacs out there, so you might want to pick one of those up, rather then splurging on a Powerstat/GE/GR unit.
For 3000W of power, you're going to either need a stack of two units, or a big 1256D ( 8kw unit) which can be pricey.
Try to scrounge around surplus dealers in your neighborhood and you'll eventually find them. I never thought I would have half the stuff I have, it just takes some time.
I run 720-1000W and even with a cheap 10A Chinese variac the fuses blow after a while. Anything under 20A is not going to cut it.
Maybe for a rotary gap speed control that would be fine, but not on the power side.
There are cheap Chinese 20A variacs out there, so you might want to pick one of those up, rather then splurging on a Powerstat/GE/GR unit.
For 3000W of power, you're going to either need a stack of two units, or a big 1256D ( 8kw unit) which can be pricey.
Try to scrounge around surplus dealers in your neighborhood and you'll eventually find them. I never thought I would have half the stuff I have, it just takes some time.
I found a cheap GR variac on Ebay for $20, but cost $200 in shipping to New Zealand, considering small 2A chinese Variacs cost that here i figured out it was a bargin, 8A may do it, are you running on 240v or 110v mains?
Re: How cruical is a VARIAC?
Hazmatt_(The Underdog), Sat Sept 19 2015, 12:41AM
I'm running on 110. You will have less current with 220, but power is still power and the variac has to be rated for that or close ( 120% maximum of rated for short periods of time)
If I ever get my universal supply done, thought this up 20 years ago, then I can run 220 to 8KVA or 110 to 5KVA, maybe someday.
It's been on the back-burner for a long time, just got the box 4 months ago.
Hazmatt_(The Underdog), Sat Sept 19 2015, 12:41AM
I'm running on 110. You will have less current with 220, but power is still power and the variac has to be rated for that or close ( 120% maximum of rated for short periods of time)
If I ever get my universal supply done, thought this up 20 years ago, then I can run 220 to 8KVA or 110 to 5KVA, maybe someday.
It's been on the back-burner for a long time, just got the box 4 months ago.
Re: How cruical is a VARIAC?
Signification, Sat Sept 19 2015, 09:57AM
Also, I saw a youtube video reporting that this (exactly what happened to me) was a possibility in the guy's 10A model. He reported that his particular variac design, IIRC, used 'careless' earth grounding techniques, focusing mainly on the HOT wiring. I am going to check the internal wiring.
Signification, Sat Sept 19 2015, 09:57AM
Hazmatt_(The Underdog) wrote ...
There are cheap Chinese 20A variacs out there, so you might want to pick one of those up, rather then splurging on a Powerstat/GE/GR unit.
...as for those cheap orange Chinese variacs--BEWARE!! I was recently zapped really, really, really, hard when I touched the orange thing. I think this was not noticed before since, this time, I was barefoot on the floor. The AC outlet tester (the variac had an ac outlet on it) reported HOT AND GROUND REVERSED!!!! I verified this with a meter--this was indeed the case! BTW, this was the first time I saw this particular error.There are cheap Chinese 20A variacs out there, so you might want to pick one of those up, rather then splurging on a Powerstat/GE/GR unit.
Also, I saw a youtube video reporting that this (exactly what happened to me) was a possibility in the guy's 10A model. He reported that his particular variac design, IIRC, used 'careless' earth grounding techniques, focusing mainly on the HOT wiring. I am going to check the internal wiring.
Re: How cruical is a VARIAC?
nzoomed, Sat Sept 19 2015, 10:08AM
Well i guess i should be able to push 10A through my 8A rated variac if thats the case, this is probably the most my unit will handle unless i het a higher rated power outlet installed.
Should be a bit of fun.
nzoomed, Sat Sept 19 2015, 10:08AM
Hazmatt_(The Underdog) wrote ...
I'm running on 110. You will have less current with 220, but power is still power and the variac has to be rated for that or close ( 120% maximum of rated for short periods of time)
If I ever get my universal supply done, thought this up 20 years ago, then I can run 220 to 8KVA or 110 to 5KVA, maybe someday.
It's been on the back-burner for a long time, just got the box 4 months ago.
I'm running on 110. You will have less current with 220, but power is still power and the variac has to be rated for that or close ( 120% maximum of rated for short periods of time)
If I ever get my universal supply done, thought this up 20 years ago, then I can run 220 to 8KVA or 110 to 5KVA, maybe someday.
It's been on the back-burner for a long time, just got the box 4 months ago.
Well i guess i should be able to push 10A through my 8A rated variac if thats the case, this is probably the most my unit will handle unless i het a higher rated power outlet installed.
Should be a bit of fun.
Re: How cruical is a VARIAC?
Mads Barnkob, Sun Sept 20 2015, 07:20AM
When you start pushing a variac beyond its limit, it will start to hum a lot, do not let it scare you THAT much ;)
A variac is good for bringing up the voltage slowly, usually you will see smoke if something is wrong, plugging it straight in you will see sparks and explosions.
A variac betters the power factor as it doubles as a mains choke, will maybe better it from 0.45 to 0.55. Something in that range.
Mads Barnkob, Sun Sept 20 2015, 07:20AM
When you start pushing a variac beyond its limit, it will start to hum a lot, do not let it scare you THAT much ;)
A variac is good for bringing up the voltage slowly, usually you will see smoke if something is wrong, plugging it straight in you will see sparks and explosions.
A variac betters the power factor as it doubles as a mains choke, will maybe better it from 0.45 to 0.55. Something in that range.
Re: How cruical is a VARIAC?
nzoomed, Sun Sept 20 2015, 09:41AM
OK thats good to know, it hums a bit as it is without a load!
nzoomed, Sun Sept 20 2015, 09:41AM
Mads Barnkob wrote ...
When you start pushing a variac beyond its limit, it will start to hum a lot, do not let it scare you THAT much ;)
A variac is good for bringing up the voltage slowly, usually you will see smoke if something is wrong, plugging it straight in you will see sparks and explosions.
A variac betters the power factor as it doubles as a mains choke, will maybe better it from 0.45 to 0.55. Something in that range.
When you start pushing a variac beyond its limit, it will start to hum a lot, do not let it scare you THAT much ;)
A variac is good for bringing up the voltage slowly, usually you will see smoke if something is wrong, plugging it straight in you will see sparks and explosions.
A variac betters the power factor as it doubles as a mains choke, will maybe better it from 0.45 to 0.55. Something in that range.
OK thats good to know, it hums a bit as it is without a load!
Re: How cruical is a VARIAC?
Hazmatt_(The Underdog), Sun Sept 20 2015, 03:10PM
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.
Hazmatt_(The Underdog), Sun Sept 20 2015, 03:10PM
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.
Re: How cruical is a VARIAC?
Mads Barnkob, Sun Sept 20 2015, 07:38PM
See page 1 for a overload curve, %overload vs. time
,%20M5%20,%20M10,%20and%20M20%20Variac%
20Autotransformers.pdf
Mads Barnkob, Sun Sept 20 2015, 07:38PM
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.
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.pdfRe: How cruical is a VARIAC?
Hydron, Mon Sept 21 2015, 11:29PM
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.
Hydron, Mon Sept 21 2015, 11:29PM
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.
Re: How cruical is a VARIAC?
dexter, Tue Sept 22 2015, 05:55AM
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
dexter, Tue Sept 22 2015, 05:55AM
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.
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
Re: How cruical is a VARIAC?
nzoomed, Tue Sept 22 2015, 06:16AM
nzoomed, Tue Sept 22 2015, 06:16AM
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?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.
Re: How cruical is a VARIAC?
GrantX, Tue Sept 22 2015, 06:39AM
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.
GrantX, Tue Sept 22 2015, 06:39AM
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.
Re: How cruical is a VARIAC?
nzoomed, Tue Sept 22 2015, 10:41AM
OK thats sweet, ill just look out for a bigger variac for operating at full power 20A would be its absolute max
nzoomed, Tue Sept 22 2015, 10:41AM
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.
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
Re: How cruical is a VARIAC?
GrantX, Tue Sept 22 2015, 12:16PM
GrantX, Tue Sept 22 2015, 12:16PM
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.OK thats sweet, ill just look out for a bigger variac for operating at full power 20A would be its absolute max
Re: How cruical is a VARIAC?
Hazmatt_(The Underdog), Wed Sept 23 2015, 12:47AM
HAHAHAH yea, I pulled 220A from a 30A breaker for 3 seconds.
We had a 3180V transformer we used to run as a Jachob's ladder, boy did that thing pull a ton of current!
Hazmatt_(The Underdog), Wed Sept 23 2015, 12:47AM
HAHAHAH yea, I pulled 220A from a 30A breaker for 3 seconds.
We had a 3180V transformer we used to run as a Jachob's ladder, boy did that thing pull a ton of current!
Re: How cruical is a VARIAC?
nzoomed, Wed Sept 23 2015, 01:07AM
WOW, didnt think that was possible lol. I have a 3000W light bulb that would trip the breaker after a few seconds, but that was at my old home.
nzoomed, Wed Sept 23 2015, 01:07AM
Hazmatt_(The Underdog) wrote ...
HAHAHAH yea, I pulled 220A from a 30A breaker for 3 seconds.
We had a 3180V transformer we used to run as a Jachob's ladder, boy did that thing pull a ton of current!
HAHAHAH yea, I pulled 220A from a 30A breaker for 3 seconds.
We had a 3180V transformer we used to run as a Jachob's ladder, boy did that thing pull a ton of current!
WOW, didnt think that was possible lol. I have a 3000W light bulb that would trip the breaker after a few seconds, but that was at my old home.
Re: How cruical is a VARIAC?
klugesmith, Wed Sept 23 2015, 03:31AM
It's for a series of 400 Hz products, which is how a 3 kVA autotransformer can weigh in at only 13 pounds.
I bet the overload vs. time curve is reasonably valid for 50 and 60 Hz designs.
Reminds me of one company promoting 400-Hz motors (and associated 3-phase alternators) for applications like concrete drilling. Here's a 7.5 HP (5.6 kW) motor weighing 16 lbs (7.3 kg):
klugesmith, Wed Sept 23 2015, 03:31AM
Mads Barnkob wrote ...
See page 1 for a overload curve, %overload vs. time,%20M5%20,%20M10,%20and%20M20%20Variac%
20Autotransformers.pdf
Great reference there, Mads.See page 1 for a overload curve, %overload vs. time
,%20M5%20,%20M10,%20and%20M20%20Variac%
20Autotransformers.pdf It's for a series of 400 Hz products, which is how a 3 kVA autotransformer can weigh in at only 13 pounds.
I bet the overload vs. time curve is reasonably valid for 50 and 60 Hz designs.
Reminds me of one company promoting 400-Hz motors (and associated 3-phase alternators) for applications like concrete drilling. Here's a 7.5 HP (5.6 kW) motor weighing 16 lbs (7.3 kg):
Re: How cruical is a VARIAC?
Mads Barnkob, Wed Sept 23 2015, 06:23AM
The 400Hz rating slipped my eye, it was the first curve I found :)
I remember seeing other curves where it was more conservative, as in 300% maximum overload at 30 seconds, 200% for 5 minutes .
Mads Barnkob, Wed Sept 23 2015, 06:23AM
klugesmith wrote ...
It's for a series of 400 Hz products, which is how a 3 kVA autotransformer can weigh in at only 13 pounds.
I bet the overload vs. time curve is reasonably valid for 50 and 60 Hz designs.
Reminds me of one company promoting 400-Hz motors (and associated 3-phase alternators) for applications like concrete drilling. Here's a 7.5 HP (5.6 kW) motor weighing 16 lbs (7.3 kg):
Mads Barnkob wrote ...
See page 1 for a overload curve, %overload vs. time,%20M5%20,%20M10,%20and%20M20%20Variac%
20Autotransformers.pdf
Great reference there, Mads.See page 1 for a overload curve, %overload vs. time
,%20M5%20,%20M10,%20and%20M20%20Variac%
20Autotransformers.pdf It's for a series of 400 Hz products, which is how a 3 kVA autotransformer can weigh in at only 13 pounds.
I bet the overload vs. time curve is reasonably valid for 50 and 60 Hz designs.
Reminds me of one company promoting 400-Hz motors (and associated 3-phase alternators) for applications like concrete drilling. Here's a 7.5 HP (5.6 kW) motor weighing 16 lbs (7.3 kg):
The 400Hz rating slipped my eye, it was the first curve I found :)
I remember seeing other curves where it was more conservative, as in 300% maximum overload at 30 seconds, 200% for 5 minutes .
Re: How cruical is a VARIAC?
Ash Small, Wed Sept 23 2015, 09:36AM
450Hz is commonly used on aircraft, for this very reason.
50/60Hz was only chosen for mains supply because it was the limit of technology (3000-3600RPM) at the time the decision was taken.
(I live in 50Hz land, but regularly crank my 7.5kVA 50Hz generator up to 3600RPM, 60Hz@300V)
Ash Small, Wed Sept 23 2015, 09:36AM
klugesmith wrote ...
It's for a series of 400 Hz products, which is how a 3 kVA autotransformer can weigh in at only 13 pounds.
I bet the overload vs. time curve is reasonably valid for 50 and 60 Hz designs.
Reminds me of one company promoting 400-Hz motors (and associated 3-phase alternators) for applications like concrete drilling. Here's a 7.5 HP (5.6 kW) motor weighing 16 lbs (7.3 kg):
It's for a series of 400 Hz products, which is how a 3 kVA autotransformer can weigh in at only 13 pounds.
I bet the overload vs. time curve is reasonably valid for 50 and 60 Hz designs.
Reminds me of one company promoting 400-Hz motors (and associated 3-phase alternators) for applications like concrete drilling. Here's a 7.5 HP (5.6 kW) motor weighing 16 lbs (7.3 kg):
450Hz is commonly used on aircraft, for this very reason.
50/60Hz was only chosen for mains supply because it was the limit of technology (3000-3600RPM) at the time the decision was taken.
(I live in 50Hz land, but regularly crank my 7.5kVA 50Hz generator up to 3600RPM, 60Hz@300V)
Re: How cruical is a VARIAC?
Signification, Thu Sept 24 2015, 04:27AM
220A, where 30A is intended, would set a lot of fires in 3 long seconds. yea?
Signification, Thu Sept 24 2015, 04:27AM
Hazmatt_(The Underdog) wrote ...
HAHAHAH yea, I pulled 220A from a 30A breaker for 3 seconds.
HAHAHAH yea, I pulled 220A from a 30A breaker for 3 seconds.
220A, where 30A is intended, would set a lot of fires in 3 long seconds. yea?
Re: How cruical is a VARIAC?
klugesmith, Thu Sept 24 2015, 05:41AM
Suppose the circuit uses AWG 10 copper wire, which in ordinary applications can carry 30 amps forever.
For short circuit calculations where the wire is initially at 75 degrees C, and can briefly withstand 150 degrees C,
the I-squared-t rating for AWG10 is about 300,000 ampere-squared-seconds.
For example:
Protection device is supposed to interrupt the circuit sooner than that.
This was discussed at 4hv about a year ago:
klugesmith, Thu Sept 24 2015, 05:41AM
220A, where 30A is intended, would set a lot of fires in 3 long seconds. yea?Nay. The rate of temperature rise is limited by the thermal mass of the copper wire.
Suppose the circuit uses AWG 10 copper wire, which in ordinary applications can carry 30 amps forever.
For short circuit calculations where the wire is initially at 75 degrees C, and can briefly withstand 150 degrees C,
the I-squared-t rating for AWG10 is about 300,000 ampere-squared-seconds.
For example:
- 100 A for 30 seconds
- 1000 A for 0.3 seconds
- 220 A for 6 seconds.
Protection device is supposed to interrupt the circuit sooner than that.
This was discussed at 4hv about a year ago:
Re: How cruical is a VARIAC?
Signification, Fri Sept 25 2015, 07:15AM
I have always wanted to learn about that (I^2)t stuff. All I need is a tiny little push. I can easily handle the rate of temperature rise (dT/dt), thermal mass of materials, and can do the thermal calculations for proper heat sinks, given the thermal resistance (deg/W), in steps from junction to ambient).
In fact (kludgesmith), your comment made a big difference. A lot of this started when I was trying to learn about the so-called ("ACTION INTEGRAL") usually associated with SCR's.
In fact, this "action integral", mostly what i saw by -electroholic-, way before I joined, was reason for my VERY FIRST post here!! and a main reason I joined--Of course, now I see there is so much more here!!
EDIT, OK--got it--thanks kludgesmith. Now for that 'action integral' application.
Signification, Fri Sept 25 2015, 07:15AM
klugesmith wrote ...
Suppose the circuit uses AWG 10 copper wire, which in ordinary applications can carry 30 amps forever.
For short circuit calculations where the wire is initially at 75 degrees C, and can briefly withstand 150 degrees C,
the I-squared-t rating for AWG10 is about 300,000 ampere-squared-seconds.
For example:
Protection device is supposed to interrupt the circuit sooner than that.
This was discussed at 4hv about a year ago:
220A, where 30A is intended, would set a lot of fires in 3 long seconds. yea?Nay. The rate of temperature rise is limited by the thermal mass of the copper wire.
Suppose the circuit uses AWG 10 copper wire, which in ordinary applications can carry 30 amps forever.
For short circuit calculations where the wire is initially at 75 degrees C, and can briefly withstand 150 degrees C,
the I-squared-t rating for AWG10 is about 300,000 ampere-squared-seconds.
For example:
- 100 A for 30 seconds
- 1000 A for 0.3 seconds
- 220 A for 6 seconds.
Protection device is supposed to interrupt the circuit sooner than that.
This was discussed at 4hv about a year ago:
I have always wanted to learn about that (I^2)t stuff. All I need is a tiny little push. I can easily handle the rate of temperature rise (dT/dt), thermal mass of materials, and can do the thermal calculations for proper heat sinks, given the thermal resistance (deg/W), in steps from junction to ambient).
In fact (kludgesmith), your comment made a big difference. A lot of this started when I was trying to learn about the so-called ("ACTION INTEGRAL") usually associated with SCR's.
In fact, this "action integral", mostly what i saw by -electroholic-, way before I joined, was reason for my VERY FIRST post here!! and a main reason I joined--Of course, now I see there is so much more here!!
EDIT, OK--got it--thanks kludgesmith. Now for that 'action integral' application.
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