The Amp Garage Light Bulb Current Limiter

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Structo
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The Amp Garage Light Bulb Current Limiter

Post by Structo » Tue Feb 05, 2013 3:06 pm

This was originally posted by Martin Manning.

Great tool to add to your arsenal.
This can really prevent harm to your new build.
Martin Manning wrote:This unit was originally constructed by TAG member rp, and then rewired, photographed, and documented by me.
I like this design because it uses standard parts (no metalwork required), and the series-wired duplex outlets let you plug in any sort of incandescent fixture.
The adapter shown works for standard bulbs, or you can use a night-light (the old-fashioned kind with a 7W bulb and no auto-on feature) for candelabra-type bulbs which are available in 25-60W.

Internal wiring details are in the .pdf.
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Last edited by Structo on Wed Feb 18, 2015 7:36 pm, edited 3 times in total.
Tom

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Cantplay
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Re: The Amp Garage Light Bulb Current Limiter

Post by Cantplay » Tue Feb 05, 2013 3:15 pm

Would a dimmer be better than a switch here?

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Structo
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Re: The Amp Garage Light Bulb Current Limiter

Post by Structo » Tue Feb 05, 2013 3:17 pm

A dimmer is going to emit a lot of noise and hum.
Plus I don't think they like an inductive load.

Really, as it's built, it is a very simple and easy to use tool.
Tom

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Scumback Speakers
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Re: The Amp Garage Light Bulb Current Limiter

Post by Scumback Speakers » Tue Feb 05, 2013 3:23 pm

Tom, thanks for the pdf file. That "reported attack page" warning came up on Firefox on my Mac...I downloaded anyway, but figured you should know it's still popping up.
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Re: The Amp Garage Light Bulb Current Limiter

Post by surfsup » Tue Feb 05, 2013 5:23 pm

Another drawing I had...Tom, your build looks exactly the same as mine. Nice work...
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M Fowler
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Re: The Amp Garage Light Bulb Current Limiter

Post by M Fowler » Tue Feb 05, 2013 5:48 pm

Here is a pdf someone posted before.

Also, a photo of mine built with crap I had on hand.
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Phil_S
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Re: The Amp Garage Light Bulb Current Limiter

Post by Phil_S » Tue Feb 05, 2013 9:00 pm

You guys are shaming me into rebuilding mine so it is "just right." I see that mine is not properly grounded.

Excelled info on mA - bulb wattage equivalency. To be clear here, for an appropriate upper wattage limit for the bulb, we are looking at the rating on the primary side of the PT, the VA rating, is that right?

Would this be improved by adding a 1A fast blow fuse? Or is the bulb the fuse?

I suppose a GFCI duplex won't work properly?

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roberto
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Re: The Amp Garage Light Bulb Current Limiter

Post by roberto » Tue Feb 05, 2013 11:05 pm

No, the bulb is not the fuse. The bulb is a variable resistor.
It changes its resistance with current: the more the current the more the resistance. It's used as a safety for tweeters too. It also compress the sound.

The bulb becomes a fuse if you choose to use a 12 or 24V bulb instead of a 120//230V one.

Yes, you have to choose the bulb to limit the current to your needs.

So, imagine the bulb like a resistor: a 25W bulb is like a resistor with 208 mA at 120 V (109 mA at 230 V on my part of the pond). So, even if the primary of your trafo is shorted, you'll never have more than 208 mA through it.

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Structo
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Re: The Amp Garage Light Bulb Current Limiter

Post by Structo » Wed Feb 06, 2013 1:40 am

You guys are welcome but the credit goes to Martin Manning.

I just posted it as a sticky. :wink:
Tom

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Phil_S
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Re: The Amp Garage Light Bulb Current Limiter

Post by Phil_S » Wed Feb 06, 2013 1:50 am

roberto wrote:No, the bulb is not the fuse...
I did not state my question clearly. I understand the bulb as a variable resistor. I was wondering, when you draw more current than allowed by the bulb, does the filament burn out...open circuit like a fuse? I suppose you'd have to be pretty dull minded to see the bulb glowing extra bright and not turn it off at the switch. So, maybe the question is moot. I imagine if you let the bulb burn at such intensity, it wouldn't last long, so it could behave somewhat like a slow blow fuse. Lotta words to this thought....answered my own question. Besides, the amp has a fuse, don't need another.

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martin manning
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Re: The Amp Garage Light Bulb Current Limiter

Post by martin manning » Wed Feb 06, 2013 3:28 am

Phil_S wrote:
roberto wrote:No, the bulb is not the fuse...
I did not state my question clearly. I understand the bulb as a variable resistor. I was wondering, when you draw more current than allowed by the bulb, does the filament burn out...open circuit like a fuse? I suppose you'd have to be pretty dull minded to see the bulb glowing extra bright and not turn it off at the switch. So, maybe the question is moot. I imagine if you let the bulb burn at such intensity, it wouldn't last long, so it could behave somewhat like a slow blow fuse. Lotta words to this thought....answered my own question. Besides, the amp has a fuse, don't need another.
You can't draw more current than a direct short, right? Let's say your amp has such a short in the primary circuit of the power transformer and you power it up with your light bulb limiter. Now what have you got? The normal situation where a 120V bulb is connected to a 120V supply, with the current limited to the wattage rating of the bulb divided by the 120V supply voltage.

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Phil_S
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Re: The Amp Garage Light Bulb Current Limiter

Post by Phil_S » Wed Feb 06, 2013 1:44 pm

martin manning wrote:You can't draw more current than a direct short, right?...
D'oh! <head slap moment> Thanks, Martin!

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Cygnus X1
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Re: The Amp Garage Light Bulb Current Limiter

Post by Cygnus X1 » Fri Feb 08, 2013 10:11 am

Built mine with a romex box.
Hard to see but it has a female IEC and a fuseholder.

Along with some industrial terminal blocks.

[img:546:364]http://img829.imageshack.us/img829/2519 ... lfront.jpg[/img]

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Structo
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Re: The Amp Garage Light Bulb Current Limiter

Post by Structo » Fri Feb 08, 2013 2:01 pm

What does the transformer do for you?
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M Fowler
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Re: The Amp Garage Light Bulb Current Limiter

Post by M Fowler » Fri Feb 08, 2013 3:20 pm

Structo wrote:What does the transformer do for you?
Heats up his coffee :)

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