Ballast wiring

[Steve]

I recently replaced the UV lamp in my mum's pond filter. But a few days later I went back to find both filaments completely detached. Not sure what's caused this. It's a 36w PLL lamp. A very very expensive PLL lamp.

I have another new lamp to try. But if the same happens again I'll have to replace the ballast (and order another lamp). The ballast is sealed in a small black box and joined to the lamp holder with 3 core flex. It appears the middle two terminals on the lamp holder are commoned. This presents an issue. All the ballasts I have seen have four terminals with no instruction which terminals can be combined. And it looks very difficult to rewire the lamp holder. Any ideas?

I'll obviously buy a suitable enclosure and glands etc for the ballast.

 

[Echo the husky]

If the middle 2 pins were joined the lamp would not be able to light as both ends of the tube would be at the same potential.

 

[Steve]

It just appeared to be the same colour wires on the middle two pins. You're right. But how does this fitting work then? Could there be a starter behind the lamp holder? If so it's gonna be a t**t to change. As there is no obvious way to remove the lamp holder from the screw cap of the filter. The ballast does appear to be just that. A dense heavy block of black plastic with no removable parts. So I guess there has to be a starter somewhere. I shall have a closer look if this new tube fails to light tomorrow.

To clarify, the cable states on it that it is 3 core only and one of the cores appears to be green and yellow and attached to one pin of the lamp holder.

 

[oldbutnotdead]

Looking at the things it would make sense that the centre 2 pins of the 4 pole connector are common- not sure if the filaments do any light generation or are just exciters for whatever gas is inside the envelope.

Have a look at your ballast- usually there are some hieroglyphics on the side indicating what should connect to what.

BTW, £14 is not very very expensive

 

[Steve]

OK I've taken the end of the fitting apart. Couldn't believe it when I found a starter - a consumable part - in the fitting but it was permanently wired in. It was wired between the two middle pins with the outer pins connected to the ballast and an earthed metal plate in the Base.

Rather than duck about replacing the starter I've ordered a reputable branded unit instead. One I can actually change the starter in. Don't buy cheap pond equipment.

 

[Steve]

And my mum was charged much more than that at the local pond supplier.

I watched the lamp through the little spy hole and the filaments did light but I think they were being run too long too hard so it flickered out and the filaments broke again.

 

[ericmark]

I can only guess, but having worked with UV lamps in the past they are often use far greater currents than the equivalent size white light lamp. Since both pins (1, 2) (3, 4) are connected together I will again guess it is a HF ballast which does not use the heaters to start. I will again guess that the watts on the old lamp don't match the watts on the new lamp may be same physical size but not the same power size. Looking at this web site it would seem there are three sizes of PLL lamps 18, 36, and 55 watt.

This image

shows how to use LED instead of a fluorescent tube so ignore the right hand image. The left hand image shows how it is wired with a magnetic ballast and how the heaters are connected, the starter only shorts pins 2 and 3 for a short time when it starts, clearly any fault on the starter could blow the start filaments.

I note with my 18W reading lamp which is PLL states only for magnetic ballast, not a clue why?

 

[Steve]

Odd that both the filaments completely detached from the lamp on both occasions though. They must have had a fair bit of current through them. This type of lamp generally sits there with the ends glowing indefinitely once the starter fails.

 

[Echo the husky]

This type of lamp generally sits there with the ends glowing indefinitely once the starter fails.

Indeed, perhaps the ballast has shorted turns and is no longer limiting the current available to the filaments during starting, causing them to blow.