Electronic ballast for 7w UV bulb

10-10-20

Who knows how ballasts work with fluorescent lights?

I have a UV pond steriliser which has a two-pin PL-S 7w bulb (below) and an external IP44 potted ballast.

The ballast suffered a leak and it's now popping the RCD, even after drying it out. I'm trying to source a replacement ballast so that I don't need to replace the whole filter unit, but they aren't easy to find. I'm going to fit a standard ballast into a waterproof box rather than have the same type of IP44 ballast.

The existing ballast has three wires on the output side, two running to the pins on the bulb and one earth which is running to a metal strap over the face of the bulb. The only ballast that I can find typically has four output pins rather than the two that I need. Example is this ballast from RS:

https://ie.rs-online.com/web/p/lighting-ballasts/6692964?gb=b

Can I connect my two-pin bulb to this ballast or can anybody tell me what I should be looking for to source the correct ballast?

kirk.

The way I remember it is 2-pin ballasts work with 2-pin lamps and some 4-pin lamps

4-pin ballasts work with 4-pin lamps

That's an American one I've forgotten most of ballast details could be wrong

https://ballastshop.com/cc579tp-keystone-compact-fluorescent-ballast/

kirk.

If I remember correctly those PL lamps just had a 2-pin ballast in series with the lamp , nothing else ?

10-10-20

Thanks Kirk! My head is melted from it now. I need to get the UV working as I can't see my fish!! 😂

I found this Phillips PL-S ballast but it's showing the wiring diagram for 4-pin wiring and no mention of 2-pin.

https://www.lighting.philips.co.uk/prof/lighting-electronics/fluorescent/fluorescent-fixed-output-gear/hf-matchbox-red/913700422866_EU/product

The datasheets on it are poor too. I've googled this to the end of the earth and back now!

10-10-20

https://www.boards.ie/discussion/comment/120972877#Comment_120972877

Yes, this lump which must be an electromagnetic ballast as opposed to an electronic one.

Whether that's an issue or not, I don't know!

I oven-cooked it at 50c for 7hrs to try dry it out, all to no avail!!

kirk.

That electronic ballast works with 4-pin lamps

The 2- pin PL needs a magnetic ballast in series with lamp afaik , the ends then connect direct to supply

Might be time to look at upgrading the lighting

10-10-20

After further googling it seems that the answer is that the 2-pin ballasts are specifically called "magnetic ballasts" and they were outlawed in around 2005 in favour of 4-pin electronic types. Magnetic ballasts are those bulky transformer types which you'd commonly see in ceiling tube fixtures of old.

From what I can see the newer electronic ballasts have a requirement that one side of the supply to the tube is less than 30cms away, while the other side can be more remote, but this doesn't suit pond UV situations as they prefer to have some distance between the wet side and the dry. So as the pond UV clarifier is a specialist device they have remained using 2-pin as it allows the ballast to be more remote than 30cms from the bulb.

Anyway, after learning all of this I then recalled that I had a bench worklight which I recalled had 2-pins... so I just opened it there now... and what did I find...?

...a magnetic ballast for 7w, 9w or 11w bulbs!

So I'm sorted for now!

kirk.

Ya that's the setup I'd be familiar with , it was quite common, 2-pin lamp and magnetic ballast in series

There's a 4-pin PL-S which works with that electronic ballast

Not familiar with the original ballast you have . What's the story with the earthing , is that connected to the metal base on the lamp ?

Just edited my posts there to avoid confusion with no. of wires and pins

10-10-20

https://www.boards.ie/discussion/comment/120975670#Comment_120975670

So the earthing is the oddest thing...

The IP44 ballast obviously has earth running through it, it's showing a resistance now of between 40k to 60k ohms between L and E, so I think that's the water causing that within the sealed unit. But that same earth runs out to the bulb in the UV unit and connects directly to this metal finger which is installed right up against the base of the bulb:

I think it's a type of discharge pathway, not sure, but I suppose it also acts as a method of causing an RCD to trip should water ingress into the UV enclosure as the finger is right up against the bulb conductors.

10-10-20

That bench worklight has a sticker on it saying "This appliance must not be earthed" and as you can see there is no earth within, only L and N to the magnetic ballast.

So when I move that ballast over to the pond UV clarifier I'll run the earth through the new waterproof enclosure and straight out so that it connects up with that metal finger at the bulb. I think that's best?

kirk.

Assume it's fault protection if the holder gets wet , is the area around the lamp normally dry ?

I think there used to be something similar related to ignition , can't recall exactly

Bruthal.

The 2 pin type bulb has the starter contacts built into it. So it ignites via the wire wound choke/ballast setup in series, (mag field collapse upon start contacts opening and all that), similar to the old florescent tube setup where the starter was a seperate item.

10-10-20

https://www.boards.ie/discussion/comment/120975831#Comment_120975831

The lamp is normally dry, it's enclosed within a quartz tube which keeps the pond water out and then there is an end-cap with rubber seal on the fitting which keeps the rain out of the clarifier.

kirk.

https://www.boards.ie/discussion/comment/120975902#Comment_120975902

Ya that basic setup in pic above was used for at least a few lamp types

The 2-pin 2D lamp with internal starter

The 2- pin PL lamp

Sodium lamp with internal ignitor

10-10-20

Well, it's working now with that ballast! Delighted!

I might even upgrade the bulb from 7w to 9w now and put it on a timer to run overnight.

Thanks to you all, eventually got there!

kirk.

Not sure what that metallic part is for , it's there for a reason probably something obvious

I think I recall something similar to do with assisted striking

Really no need for fault protection there doubt it's that now