A while ago, I was sent a package from Germany by Lucas who does Street lighting maintenance there and one of the items included was this igniter module. It's a three terminal igniter designed to be used with the matching ballasts and I Thought it would be quite interesting to look at because although discharge lamps like high pressure sodium and metal halide are kind of fading away with the onslaught of LED and it's it's not 100 reliability. Um, it's kind of interesting to look at the circuitry that controlled them because there's a lot of these still in use. and if you actually do maintenance, it's useful to know what's in these rather than just sticking in a mysterious black box.

So let me show you the schematic of a ballast that uses the signator system. So I shall Zoom down in this and focus and we'll explore. So the ballast. In this case, it's not an electronic balance, it's a traditional wire wound ballast Uh current coil type things they sometimes call them and uh, it.

Basically, it's a steel core with a copper windings on it and in this case, because it's a European one, it caters for the well European and many other countries it caters for 220 to 240 volts. It's good to match the ballast to the lamp if you say. For instance, in the UK If you had 200 40 volt Supply and you're stuck at the 220 input. It would run the lamp brighter, but it would potentially shorten its life significantly so you can have to match it.

So it's useful having those two taps. So in this case, on 240 volts, we'd go to the 240 volt tab, but the 220 volt would go to the igniter and it's going to use this 20 volt winding section here to increase the voltage to strike the lamp if you connect the incoming live. If you're in another part of Europe say 200 to 220 volts, you simply take the igniter over to the other spear terminal only one workers into each of these terminals. You just basically as this iron indicator, just swap these accordingly.

There is a perfect correct capacitor that works with mainly inductive loads like this, where it's got a perfector 0.5 and this capacitor can easily compensate for that. Nice, simple inductive load. Uh, you can just cut this capacitor out and get rid of it, but it's not recommended. If you have a big long run of street lights or a warehouse with loads of Lights uh, High Bay lights, then it's useful to have these capacitors because although they're quite unpleasant and they do go bang when they fail, sometimes when you're working on them, it helps keep the perceived current and the wiring down, which means that you're not going to get issues with voltage drop along the long run.

That can result in the lighting at the far end actually causing intensity or flickering issues. So in this case we take the 240 volt to the 240 volt tap and it then is limited by this inductor over to the lamp. When you power up initially, the lamp will not light because it usually has to have a high voltage pulse inside to actually initiate the arc within the quartz tube inside. So what happens is because the voltage across this goes High Because it is open circuit, the igniter kicks in and the igniter basically acts like a dimmer that is fine at the top of each half of the sine wave.

And what it does is it's got a capacitoring series, puts a capacitor in series with the the spare tap, and either on our 50 hertz. Supply It happens 100 times a second. on 60hz, perhaps 120 times a second, it pulses the spare pin down to the neutral via the capacitor, which limits the amount of current that can flow to a controlled portion of energy. And what happens is that induces a pulsive current in this coil, which is then multiplied by this Transformer and then strikes a lamp.

When the lamp is struck, the voltage across this drops and because the common Uh to the lamp and the igniter are common together, the voltage across the igniter drops and it can see the voltages dropped and it stops trying to ignite the lamp. A common failure of, well, partly the ballast default igniters is that uh, if a lamp fails or even gets loosen its socket, this igniter will just keep trying to later and that puts a lot of strain the ballast. It's only designed for a modest amount of use at that high voltage. Another approach to this is that you'd get ballasts that go in line.

The igniter should say that go in line here and they ingest the high voltage externally. but they too the little ignators often feel when the lamp fails. Um, but the ballast is probably more expense component so let's take a look at the shocket board. I shall zoom out a bit for this and I'll show you the key components of Interest I shall Zoom back in just a tiny bit so you can see more.

So components of Interest are this Big Fat Juicy 180 nanofarad capacitor. It's rated 1000 volts and that's the one that gets put in line with the Uh spare winding the ballast. You've also got this fuse in series of that I'm guessing the reason for that is that if this capacitor short circuit it could potentially result in a lot of current uh going through the ballastin track circuitry and it blows the fuse just to protect the ballast problem more than anything else, we have a Big Fat resistor here. I Think the reason it's big, it's going to be disappearing a fair amount of power, but it's also just well rated and it is charging this 10 little capacitor down here amongst other things.

And when that capacitor reaches a certain voltage threshold, there is a divider based on this resistor and this resistor. I'll show you in the schematic afterwards. This little diac is uh triggered because it reaches its threshold and it fires this track. and that's what dumps this capacitor across a near peak of the sine wave on every half wave.

If you want to have a bit of reverse engineering yourself, here is the back of the circuit board. It's just a single-sided circuit board. Um, and now I shall show you the schematic: I'm just going to grab the schematic here. The schematic: I shall Zoom down on it again.

and there is something in here that is perplexing. Feel free to weigh in and give your thoughts on this. So this on the right hand side of this line is the igniter. There is the LIE of going to the ballast.

It's going to the 240 volt tap. There's the tap from the 220, taken to the igniter circuit, and there is the connection at the other end of the ballast to the lamp. and then there's a common neutral at the bottom. When this unit is in operation, this resistor that's a big fat juicy one charges up this capacitor.

uh, as it travels across the sine wave and there's this resistor here forms a potential divider. And what that means is that only at full Mains voltage, full open circuit voltage with the lamp, not let the voltage across this capacitor will rise up to round about, say 30-ish volts. Um, near the top of the sine wave. When it does, this Diac suddenly conducts because it conducts in both directions and dumps this capacitor through this resistor.

Network a 47 ohm to limit the current into the gate of the track and that 1K pull down resistor and what that results in is the track is turned on when the track turns on. Uh, live. It causes current to flow through the short section of winding through the fuse and charge up that capacitor with respect to neutral which the track has switched it down to and this Uh will continue until like the current has I'm not not sure what to happen here. Let me think, as this shunts to ground, it would cause a high current spec.

but I think current will continue to flow through that capacitor just the rest the same wave but the zero crossing point. Then the strike will turn off and the same thing will happen because then the polarity reverses. Now these components here are water perplexing me. What are these? Are these? A snubber to protect the track? I'm not really sure how to do that.

Uh, this is a metal oxide varista, but it doesn't have a normal numbering system. The 593-ph is correct. That means it's the series 593 series and it's made by Philips But normally you'd have a voltage like say 100 for 100 volts, but they've got 90016 I'm not sure what that's for and this is just a fixed value resistor there that is a potentially just perhaps assisting the track and turning off or clipping spikes from the circuitry. I'm not really sure.

Let me know what you think. Um, when the lamp has struck the voltage across here Falls the current will still be flowing through this resistor, but it will never reach the threshold in this capacitor the diet can trigger and therefore the track will stop. Uh, firing. That's very straightforward.

It's very simple. Um, but there we have it. I Really don't know about that. The fact is a metal oxide varista looks like it's going to clamp a spike of some sort and maybe it is just protection for the track to perfect against a little spikes.

I'm not sure. or maybe it's to cap the maximum voltage goes across that I Do not know. that would kind of work. It would add a slight shunt.

Um, but that is it. So thanks to Lucas for sending this, it was very useful to explore. Um, we're all a bit wiser for that. We now know what's in that mysterious little box.

It's this circuit here and the way it works. It's just using that tap in the winding just to basically use the ballast as a Step up Transformer to light the lamp. Very clever, Very neat.