Inrush current limiter component (what is this thing called ?)

[Dannyx]

Having repaired many power supplies lately, I've come once or twice across a component which, to my shame, I cannot figure out what it's called. I don't have a picture of it on hand sadly (maybe someone can post one), but it looks like a regular glass fuse (only a bit smaller), with two electrodes at each end and this thing makes a spark inside that glass envelope when you first plug the supply in. I know what its general purpose is: it's an inrush current limiter (or at least I think so). It's placed in parallel with the AC input, so I'm assuming it's like a spark gap: it takes away the initial surge and dissipates it in the form of a spark, which, because it's inside a vacuum tube, can't really do anything to "nasty". It's actually pretty satisfying to see that spark forming whenever I plugged the thing in.
Funny story: when I first came across one of these, I was dealing with a faulty inverter on an LG monitor and as I was constantly plugging the supply in and out, taking measurements, until I saw this spark coming from near the AC inlet, so you can imagine I nearly soiled myself The supply was still ok, so that's when it clicked "OOOOOOH, I see what this thing does"
I think it was labeled RA or RS on the board, though I can't figure out what it stands for (Rush arrestor/suppressor ?) It's definitely not an NTC thermistor - it can't be, since it doesn't look the part. Can anyone provide some more info ? No real reason, other than to enrich my knowledge

[stj]

Re: Inrush current limiter component (what is this thing called ?)

the glass thing is a spark gap to suppress spikes,
it's not a surge suppressor / inrush limiter.those look a bit like a large ceramic capacitor with a rough finish - usually dark green or black.
and they connect inline like a fuse.

[Dannyx]

Re: Inrush current limiter component (what is this thing called ?)

the glass thing is a spark gap to suppress spikes,
it's not a surge suppressor / inrush limiter.those look a bit like a large ceramic capacitor with a rough finish - usually dark green or black.
and they connect inline like a fuse.

Ok, so I was partly right. So when I search for those should I look for "spark gaps", or are they called something else ? To me, spark gaps are those zig-zagged traces placed close together Also, yeah I know about the NTC thermistors

[stj]

Re: Inrush current limiter component (what is this thing called ?)

the zig-zag / forks are cheap attempts to avoid fitting real spark-gap devices.

the difference is the tracks will leave carbon burns and need to be fixed afterwards - the glass ones work in a sealed space and dont need to be replaced!

[Dannyx]

Re: Inrush current limiter component (what is this thing called ?)

the zig-zag / forks are cheap attempts to avoid fitting real spark-gap devices.

the difference is the tracks will leave carbon burns and need to be fixed afterwards - the glass ones work in a sealed space and dont need to be replaced!

Oh wow, so I was wrong about that little sh!t LG monitor - it was actually built pretty well then, with a bit of quality, considering they bothered to add such a component at all

[PeteS in CA]

Re: Inrush current limiter component (what is this thing called ?)

They're also called gas discharge tube, as they have a gas inside that controls the trigger voltage and forms a plasma path for the discharge.

I'm sure I've given this summary on BCN before, but here are the three common voltage surge suppression devices:

* Gas discharge tube - relatively slow but able to absorb considerable energy;

* Transient Voltage Switch (TVS) - looks like a diode, very fast, less able to absorb energy, comparatively expensive;

* Metal Oxide Varistor (MOV) - almost as fast as a TVS, can absorb almost as much energy as a gas discharge tube, inexpensive, gradually deteriorates - the trigger voltage gradually goes down until the MOV starts conducting at normal AC line voltages.

All in all, MOVs are the most common. Cheap and effective are a good combination. MOVs can become a problem, however, in power environments where there are frequent line voltage surges. Examples would be areas that have lots of thunderstorms (= lightning strikes) or industrial areas where machinery generates line voltage surges. When an MOV deteriorates badly enough, the continual conduction soon becomes high enough to destroy (crack or blow apart) the MOV and blow the input fuse.