Author Topic: Contant Voltage Transformer  (Read 307 times)

Offline kamelryttarn

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Contant Voltage Transformer
« on: July 13, 2017, 03:55:26 PM »
I have had a 500VA (I could be wrong and it may be a 300VA) constant voltage transformer for a couple of years but never really had any use for it. When I connected it the other day and hooked up a computer (SMPS) and a 40 inch LCD TV (also SMPS) to it the picture flickered as soon as the computer started working. I don't think a healthy CVT should act this way so I suspect the capacitor may be ready for retirement. The heat generated by these things could probably limit the life expectancy of the capacitor, but what kind of capacitor would most likely be optimal? I think motor run caps would probably be a good bet but do you guys have any other recommendations?

http://www.aelgroup.co.uk/faq/faq001.php

My unit is an old 70's or 80's unit labelled Ulweco but was actually produced in France.

Offline Mads Barnkob

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Re: Contant Voltage Transformer
« Reply #1 on: July 13, 2017, 05:33:21 PM »
I do not know those old type of capacitors, but from what I could find it seems people are just replacing them with motor run capacitors of same capacitance/voltage rating: http://www.antiqueradios.com/forums/viewtopic.php?f=6&t=133396&sid=75670d7389c6e1bee3009f51cbcc4ca0&start=20
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline Hydron

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Re: Contant Voltage Transformer
« Reply #2 on: July 14, 2017, 01:05:05 PM »
One thing to remember with these transformers is that if presented with an large (~200%+) overload on the output then the voltage will drop significantly. If the computer SMPS draws a large inrush current when plugged in then maybe it is causing the voltage to droop very low for long enough to upset the TV.

Does it happen when plugging the PC in, or just when turning it on from the front panel? If it's the latter then inrush is not to blame.

If the problem is in fact the capacitor then you can probably tell by checking the capacitance - if it reads OK then also check that it's not getting hot during use. As Mads said, motor run caps are likely to be fine, as they are rated for continuous mains use. Required voltage rating can be fairly high, so check this carefully!

Offline kamelryttarn

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Re: Contant Voltage Transformer
« Reply #3 on: July 18, 2017, 09:50:09 AM »
Thanks guys. The flickering was constant as soon as the CPU started working as far as I could tell. I measured the caps (that were surprisingly large physically) and they measured alright with my LCR meter but I had no way of measuring the current when it was under load. New caps should arrive this week. Probably no harm in replacing them after all this time.

[edit]
I received the caps the other day and installed them. The transformer is much quieter now. I haven't been able to test it it much but it seem to be running much better. CVT's really are quite amazing.
« Last Edit: July 25, 2017, 09:19:35 PM by kamelryttarn »

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Re: Contant Voltage Transformer
« Reply #3 on: July 18, 2017, 09:50:09 AM »

 


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