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Old 12th May 2003, 03:50 PM   #11
moamps is offline moamps  Croatia
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Hi,

something is faulty. Test transformer without bridge and caps.
Whitch voltage rating have caps?
Are caps warm?

Regards
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Old 12th May 2003, 08:59 PM   #12
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Did you connect the diodes correctly?
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Old 13th May 2003, 03:01 PM   #13
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I did check the orientation of the diodes and it's correctly connected. The caps are 6,800uf/63V per rail. I get +/-61.55 using a DMM. The diodes and caps are not even warm. Only the transformer is warm.

I did load it last night with a mono test amp and worked for about 8 hours. It is still working but when I turn the volume up, the transformer really gets warm.

Can this be normal? Maybe I should buy a bigger one.
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Old 13th May 2003, 07:18 PM   #14
dhaen is offline dhaen  Europe
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JojoD818,

To determine whether there is a problem, you must estimate the following:

What is the temperature rise unloaded?
What is the temperature rise loaded?
What will the ambient temperature be where it will be installed?

A way of determining whether it is overrunning is to check the secondary voltage drop when loaded. The manufacturer should supply a figure for "regulation".

Cheers,
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Old 14th May 2003, 11:16 AM   #15
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Default temp rise

dhaen,

It seems odd but the transformers temp unloaded and loaded seems the same. I mean, I plug it to the wall socket unloaded and leave it for an hour and it gets warm. Then I connect the amp and play it for an hour (moderate volume) and the transformer temp feels just a little warmer. I will find a way to measure it's temp unloaded/loaded to really see if somethings wrong.

BTW, at zero volume i get +/-62V, at loud volumes it drops to +/-55V! I know that the power delivered to my speakers also drops but is there anything I can do about it?

1. Add caps.
2. Change from 4 diodes to one metal bridge diode.
3. Buy new, higher amp transformer. (I hope not )

Jojo
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Old 14th May 2003, 01:47 PM   #16
dhaen is offline dhaen  Europe
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JojoD818,

If your transformer gets hot without a load, there are only 4 possibilities I can think of:

1. The transformer was built for 60Hz only, and you are using it on 50Hz. - Unlikely: Most toroids are for both.
2. It's incorrectly wired.
3 It's faulty or badly designed.
4 You have run a cable or bolt through the hole in the centre, and it is acting as a "shorted turn". The centre bolt must be fixed on one side only, and not be allowed to touch anything else conductive.

The transformer will have a regulation figure in the region of 10% to 20%. Depends on the size and quality. Check this against the voltage drop you experience "on-load".

Cheers,
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Old 14th May 2003, 03:24 PM   #17
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Another possibility is that your mains voltage is high or you have wired the primary for a little lower voltage...
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Old 14th May 2003, 07:49 PM   #18
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Default Voltage measurement

In our country the standard mains voltage is 220VAC/60Hz. However, I can only measure 208-210VAC at noon and about 215VAC at night. Maybe that is why I don't get the transfrmer to output enough voltage?

What do you mean by 10%-20% regulation?

Example, theoretically, 44-0-44 X 1.4142 = +/-62.22V rail voltage. Does 10% regulation mean that if under load, 62.22VDC-10%=55.998V? If so then my measurements are correct.

Maybe the transformer is just old. I forgot to tell you that it is about 10 years old. Do transformers react to old age?
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Old 14th May 2003, 07:54 PM   #19
dhaen is offline dhaen  Europe
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JojoD818

Yes you understand the regulation figure

I have not seen deterioration of toroidal transformers with age.

Cheers,
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Old 14th May 2003, 08:41 PM   #20
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I think you might be looking at the transforemr from the wrong direction though, as most transformers are specified with voltages under load. And from your readings under load yoou would get a nominal 40 - 0 - 40 transformer (which is a fairly standard spec unit). However, under no load condidtions, the voltage will rise by some ammount (due to the regulation as dharn said), in you case around 10%.

However, I would in general say that if a transformer ran as hot under no load as it did under load that there was a problem with it. BUT, I would also say that if this was the case you wouldn't be able to run it for eight hours under heavy loading, so for now I would not worry too much and just make sure you put it in a well wevtilated case, as far away from your other ocmponents as possible.
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