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Variac buying advice needed, safety concerns
Variac buying advice needed, safety concerns
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Old 27th July 2018, 08:41 AM   #11
trobbins is offline trobbins  Australia
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You could add a commercial plug and socket over the top of banana plugs to provide fully enclosed ac wiring.
do you have a plug in cheap power meter - well worth it.
also an earth leakage breaker just for your bench.
a wise person also pulls out the equipment plug, rather than relying on the switch (eg. of the variac).
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Old 27th July 2018, 09:04 AM   #12
cowbellster is offline cowbellster  Finland
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The power meter is a great idea! I have one already. Thanks!
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Old 31st July 2018, 07:46 PM   #13
mondogenerator is offline mondogenerator  England
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With a variac, always use:

RCCB or earth fault breaker
Fusing
Primary ammeter (and knowledge of the current rating of variac)
Secondary volt meter
Power resistors (BIG) Or a light bulb in series with the output from the secondary when first powering up.

I've never had any need or concern to use an isolating transformer. Best practice is to isolate supply nearest to the source (probably the RCCB or MCB in the electric box)
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Old 31st July 2018, 08:29 PM   #14
cowbellster is offline cowbellster  Finland
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Thanks!

The light bulb in series would be handy. It's just that it's not allowed to sell them anymore. I have some old 40W/230V ones left. Maybe they are a bit too small.

EDIT: Actually I found some 100W bulbs for sale.

Last edited by cowbellster; 31st July 2018 at 08:39 PM.
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Old 31st July 2018, 08:59 PM   #15
jackinnj is offline jackinnj  United States
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Variac buying advice needed, safety concerns
Quote:
Originally Posted by PRR View Post
I don't know many audio-geeks who truly need a 2KVA Variac.
That's cuz you live in Maine where there is no necessity of airconditioning!

I bought a 2KVA variac from a fellow who used it to ramp up the voltage on his window air conditioner when Jersey Central P&L had frequent brown-outs!

(We don't get no stinkin' brown-outs anymore, just black-outs!)
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Old 31st July 2018, 09:06 PM   #16
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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I have two variable transformers. One is a Variac, purchased at great expense about 40 years ago from Farnell and is an isolating 240v in with up to 270v out at 500v/A. I recently fitted new brushes and it still works a treat. The other I bought not so long ago, about 35 years I think. I purchased it from a transformer manufacturing company in the UK. I ordered a 300v/A auto variable transformer and to my surprise they sent the wrong one rated at 3kvA. For the same price as carriage back was a lot of money and it was their error, they said to keep it. Bonus I thought and that supplied, in real time, my large industrial bench at my workshop, working through a 3kvA isolating transformer, under the bench.
I don't think I have used the large one since retiring 5 years ago. The stuff we collect when in business.
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Old 1st August 2018, 03:27 AM   #17
PRR is offline PRR  United States
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Quote:
Originally Posted by cowbellster View Post
...it's not allowed to sell them anymore.....
As you say: there is usually a niche for *large* incandescents, larger than household bulbs, which are reasonably useful for large light in rarely-used spaces. My car-garage has six 150W hot-bulbs, because I need big light, and I only use them a dozen hours a year to get in and out. Such lamps are still readily available, though not at the supermarket.

The primary point of a lamp-limiter is to avoid burning the wall-wires. Any lamp you would safely use direct from your wall is obviously OK. (Lamps over 2KW might not be; but are much rarer.) A secondary use is to slow-down burn-up of the amplifier. For this you want a bulb "somewhat" larger than the expected normal power of the amplifier. For a 2*6L6 tube amp of 40W out, 100W in, a 150-250W lamp is appropriate.
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