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LAN_403

D1G1T4L3CH0

Sat Aug 21 2010, 07:24AM

Registered Member #3124 Joined: Tue Aug 17 2010, 10:25AM
Location: 127.0.0.1, US
Posts: 19

I opened an old power supply (12v 4amp) I've had for years because it stopped working. When I opened it, I realized then just how old it is. It had some kind of tube in it though. At first I thought it may be a mercury tube, but there is no mercury and I don't see a purpose for a mercury tube in a power supply anyway. But I checked all the parts inside and it all looks to be in working order, turns out the problem was with the power leads outside the power supply. Heh. I guess I kinda wanted to open it anyway. I also checked the tube... It has continuity. There is a picture below, let me know if you know what it is, I'm just curious about it is all. Maybe it could be something fun to play with when the power supply does finally break (or maybe I'l break it just for that ;).

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Edit: 9.25.2010 (To add links to images on another server since tinypic is not showing in some countries.)

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Chris Russell

Sat Aug 21 2010, 08:34AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

Hard to tell from just the one angle, but I once had a power supply with a vaguely similar looking gizmo. It was the overcurrent protection. When I tried to draw too much current, a bimetallic strip inside heated up and eventually opened the circuit, effectively shutting down the power supply for ten seconds or so. Looks to be in just about the right place for it.

Proud Mary

Sat Aug 21 2010, 08:39AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

This superannuated relic uses a centre-tap transformer and two early solid-state diodes (on the paxolin strip board at left) to work as a full wave rectifier.

At first I thought the two terminal glass device might be a neon stabiliser, or safety spark gap/gas discharge safety device, but if it conducts as you say (and it does seem to be in series with the output, from your pictures) then I would agree with Chris Russell.

But there is a vented (i.e. open to the air) spark gap at bottom left.

D1G1T4L3CH0

Sat Aug 21 2010, 09:02AM

Registered Member #3124 Joined: Tue Aug 17 2010, 10:25AM
Location: 127.0.0.1, US
Posts: 19

Yeah I think you may be right about the over-current protection because I can short the leads and the power supply turns the power off while remaining in the on state. I turn it off then back on and it's back up and running. Just guessing though, this switches power off at 4amps since that's the power supply's rating, or would it be more than that? I think this may actually be useful for limiting current on something else. I would get another angle, but I already have it closed back up and put up for now. The model number however is SB608E3H from what I can tell. It's hard to make out though and that could be wrong. I couldn't find anything for it on google.

I also didn't notice any spark gap in there anywhere though, are you looking at the power switch maybe (power switch connections are on the bottom left)?

Proud Mary

Sat Aug 21 2010, 10:05AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

D1G1T4L3CH0 wrote ...

I also didn't notice any spark gap in there anywhere though, are you looking at the power switch maybe (power switch connections are on the bottom left)?

Yes, it must be a switch, as you say, if it comes out on the front panel.

D1G1T4L3CH0

Sat Aug 21 2010, 12:33PM

Registered Member #3124 Joined: Tue Aug 17 2010, 10:25AM
Location: 127.0.0.1, US
Posts: 19

Well, thanks for the help on this Chris and Mary. If anyone happens to know the exact name for this device (just curious), go ahead and post it, I should probably get an email to check this.

Chris Russell

Sat Aug 21 2010, 08:00PM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

My very first thought was neon, too. It does have that shape about it, and the equipment is certainly the right age for a neon indicator or safety gap.

Perhaps unsurprisingly, they're just called "circuit breakers." Literally, they break the circuit when the current is too high. More specifically, this is a self-resetting thermal circuit breaker, if my guess is right. Sadly, though I've seen one or two before, I was not able to dig up any pictures of glass-encased thermal circuit breakers.

It probably kicks in around 5-6A, but it might be higher or lower than that. Keep in mind that if it is a thermal circuit breaker, it will take a long time to open when the overcurrent is slight, and will open very quickly in large overcurrent situations. It works well enough to protect the diodes and transformer windings from excessive heat, but I would not trust it to do any serious current limiting.

Turkey9

Sun Aug 22 2010, 12:40AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

I had one of those in a model train power supply, but it was pretty new. It was a cheap model and it's purpose was to protect the power supply (or speed control) from a short across the track. Blow dryers also have a similar switch except it shuts off purely from the heat of the heating coils.

D1G1T4L3CH0

Thu Sept 23 2010, 09:58AM

Registered Member #3124 Joined: Tue Aug 17 2010, 10:25AM
Location: 127.0.0.1, US
Posts: 19

Nice, thanks for the extra confirmation on what it is and how it works Chris and Turkey9.

Renesis

Thu Sept 23 2010, 08:12PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

It seems Firefox cant open the images.

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