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Gavlar

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hi all

one for the electrical engineers please...

The transformer in my pond filter/UV unit has burned out and spares are not available from Hozelock - who will instead happily sell me an entire replacement unit at 75 quid or so. Nor will they tell me what the transformer spec is so I can source one myself (the writing on it is also burned off).

The transformer feeds a 6W UV fluorescent tube with a ballast. Lamp voltage is 42V and its nominal current is 0.16A.

There are multiple units on ebay, RS etc which output at 42V and 0.2A but which describe themselves as LED drivers. Will these be OK or is there some quality that would make them unsafe for use with a fluorescent tube?

thanks
Gavin
 

Sandyn

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There should be a rating plate on the failed transformer? if so take a picture of it. Is is a separate unit?. I would guess it's a IP 64 or 68 transformer, (traditional transformer, heavy-ish) double insulated, which is fully submersible and safe from the original reliable source. Is is AC or DC output?
The bad news, I personally wouldn't touch any equipment sold on ebay for such a safety critical application and I wouldn't substitute an alternative manufacturers power source, unless I could satisfy myself that to do so would not compromise safety of the complete system. What is the configuration of the system? separate cabled transformer? or included in the filter? Does mains go to the pond??
It is very very important not to do the wrong thing here.
 

Spectric

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You do need to be careful like Gavin has said, electricity and pond water are not a good combination.

You say the lamp voltage is 42 volt, but what is the voltage rating of the ballast unit?

An LED driver is a constant current device, a fluorescent tube is entirely different in that the ballast provides a strike voltage to get it going and then just the running voltage.

I have always disliked the idea of using mains powered devices in domestic ponds and such, why they could not use 12 or 24 volt Dc equipment and onshore PSU I do not know.
 

Gavlar

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thanks for the replies...see pictures of the setup and the burned transformer, which has lost its writing so the spec is unknown, but it's not IP anything I don't think! The double-ended lamp is sealed with O-rings inside a glass tube, and the pond water rushes past in the annulus between that and the plastic cylinder. None of the electrical kit gets wet, since the whole lot is also inside a weather proof casing.

Does any of this help, dare i say shed some light? :D
IMG_20210408_144010472.jpgIMG_20210408_144021280.jpgIMG_20210408_144030598.jpgIMG_20210408_144043556.jpgIMG_20210408_144058186.jpg
 

Spectric

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Having given you a diagram I should also explain.

When power is applied a current will flow through the ballast, the filament at one end of the tube, through the starter which heats up the bi-metalic contact and through the other filament at opposite end of the tube with the filaments emitting electrons as they heat up. The starter then opens and interupts the current flow which causes the ballast to apply a high voltage( the strike voltage ) across the ends of the tube to Ionise the gas, which then emits light.
 

Gavlar

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thanks again - I'd never really thought about the mechanism of fluorescent tubes but consider myself better informed now!
 

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