Help needed to replace a microscope lighting transformer

[dolmadis]

Hi All

I need to replace a 240 volt input (UK), variable 9.5v to 12v output as a dimmer, 100 VA ancient transformer to run a 100w 12v Halogen bulb in a lamp house.

I could not find anything off the shelf in Google UK so I guess that I will now appreciate some help in sourcing the components I need to assemble one in a safe box/enclosure.

All I can say at this stage is thank you for your help if you can noting that I have just enough skill to solder components and wiring to and from as it were.

BR


John

[Pau]

100W 12V seems pretty usual.
You can buy used microscope power sources of different brands or a generic source from an electronics store.
For a halogen lamp AC or DC output doesn't matter

[dolmadis]

Thanks, I'll see what I can find via Google.

John

[ChrisR]

You could use a Chinese lab supply eg ebay 264416396384

I looked at LED power supplies, but most marked 100W Dimmable will only supply 100W at higher voltage.

It might be cheaper to use a 12V 100VA fixed supply but then you'd have to add a regulator and heat sink etc - unless the one in your scope remains usable?

[dolmadis]

Hi Chris

The halogen bulb is in the lamp house and the regulator is on the power supply unit.

So yes, I would have to add a regulator to any stand alone power unit I might purchase.

I have been looking at this from Google.

https://www.mr-resistor.co.uk/item.aspx?i=17896

Have I missed anything which might indicate that this is not a solution?

Thanks.


John

[ChrisR]

Back a step, do you know what's actually failed in your power supply?
It might be a simple fix.
If it's the transformer itself, then you could probably find a replacement, something like ebay 223027792912
otherwise use a fixed power supply to connect into the input of the regulator circuits inside your power supply.

No, I can't see any reason why the item you found would't work. You don't really need a calibrated output, and if it's spiky the filament of your bulb should smooth that out. (I'd doubt it would be OK for LEDs, they'd possibly flicker.)

[dolmadis]

Back a step, do you know what's actually failed in your power supply? It might be a simple fix. If it's the transformer itself, then you could probably find a replacement, something like ebay 223027792912

No I do not know what has actually failed. I checked the external wiring to the power box, the EU adapters, connectors from the lamp house to the power box and the bulb physically (no multi-meter or knowledge) and whilst the indicator lights on the power box did not light at least I thought that the problem was logically isolated to the power box.

I took off the casing an looked for anything obvious; nothing evident.

So as you suggest I can either try to replace the transformer as you kindly suggested or just hit the credit card for the replacement. Thanks for checking it out.

BR

John

Edit - I also checked the glass radio fuse.

[Photomicro]

Just guessing John, is the old PSU an American Optical by any chance, like that for the AO 20?

[dolmadis]

Hi Mike

Thanks for stopping by.

It is a PZO (100W Halogen) OH1 ZH100.

I must admit, as I have admitted before, that I am not competent or confident around electrics.

BR


John

[dolmadis]

If I change the radio fuse in the power supply (just in case it has blown) what amp size should I use? The glass fuse in the power supply has no markings.

BR


John

[DavyC]

For the mains fuse look at the rating printed on the body of the power supply. If its in polish look for 'Bezpiecznik' probably rated around 0.5 - 1.0 amp. Hard to see, the rating may also be on the silver metal ends on the sides of the fuse. Can't ever assume that the previous owner stuck to using the correct rating. How many times I seen silver cigarette paper in where a fuse aught to be! A cheap multimeter will let you test most of the power supply. Better to get the original psu up and running.

[soldevilla]

You can use a power supply from an old computer. All the people have one of these in the garage

[dolmadis]

For the mains fuse look at the rating printed on the body of the power supply. If its in polish look for 'Bezpiecznik' probably rated around 0.5 - 1.0 amp. Hard to see, the rating may also be on the silver metal ends on the sides of the fuse.

Thanks


John