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Old 14th March 2003, 12:55 AM   #1
Boban is offline Boban  Canada
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Default Pearl - ps fuse?

Hi,
my Pearl project is very close to be completed. Tonight, I assembled the separate power supply. Voltage is 43.0 V DC solid. No problems here. It's bit modified version (I have a gif picture but don't know how to post a picture) and I doubled the caps value to 20000uF per channel. The question I have is about fuse. My transformer is 300VA 30-30 rated 5 A and I used 5 A fast fuse. Is this value correct or should I go for lower amperage? Mind you, the power supply is working fine.

I added resistors to my umbilical cord just to add some load The ps is running very cold for more than 2 hours.

The Pearl boards are completed (only parts missing are 10K resistors and enclosure - still waiting to receive my order from Mouser). The coupling caps are Auricap. Will update you with the results.
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Boban
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Old 14th March 2003, 01:53 AM   #2
Boban is offline Boban  Canada
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Ok, here is picture. Tell me if something is wrong.
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File Type: gif power supply gif.gif (9.7 KB, 323 views)
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Old 14th March 2003, 05:07 AM   #3
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You should go with a lower value fuse. You want to protect the preamp circuit should it try to draw too much. Fuse for that, not for your power supply (which has 10X the capacity required for this circuit) The transformer suggested is only 30VA.

Measure the current drawn once it's working right and double it, or use the 1A fuse suggested by Wayne in the article.
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Old 14th March 2003, 06:39 AM   #4
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300 VA

Which part burns first, the fuse or the resistors? Yes, the resistors!

If you don' t allready have the 300 VA transformer, 15-30 VA is required. More than 80-100 VA is plain overkill, just produces losses...

Use slow fuse. Calculate max load plus losses, choose a fuse which is around this current or slightly more, but the fuse must withstand the startup currents. This can easily be tested by increasing the fuse value one step if you blow the fuse now and then when you are switching the amp on.

Parts connected to the mains must be approved! X, Y-caps, VDR's etc. No PERMANENT resistors on the primary side
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Old 14th March 2003, 02:31 PM   #5
Boban is offline Boban  Canada
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Yes, I agree that 300VA is more than needed, but transformer was available locally and was cheap. It is shielded too.
The reason I used 5A fuse is that I had a couple of them at home (fast ones) and the transformer is rated 5A. Should I try with the smaller value like 1A or 2A? And why you recommend slow one? Which one (fast or slow) will suit my need better?

Thanks
Boban
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Old 14th March 2003, 03:29 PM   #6
coffin is offline coffin  Taiwan
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Slow Blown type---T
I think maybe T500mA/250V is enough.
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Old 14th March 2003, 06:12 PM   #7
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Quote:
Originally posted by coffin
Slow Blown type---T
I think maybe T500mA/250V is enough.
If you still use the 300 VA I think 500mAT _may_ be too small. But if the fuse doesn't blow every 10th start up it's OK. You should also use secondary fuses now when your transformer is so oversized. You pcb will act as fuses otherwise.
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Old 18th December 2006, 03:34 PM   #8
h_a is offline h_a  Europe
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Quote:
No PERMANENT resistors on the primary side
What do you mean with permanent? In the schematic there are clearly 4.7Ohm resistors on the primary side - do you suggest not to use them?

Sorry to pull this dinosaur-thread, but I'm curious what you mean.

With kind regards, Hannes
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Old 18th December 2006, 04:53 PM   #9
PierreG is offline PierreG  Canada
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Quote:
Originally posted by Boban
Yes, I agree that 300VA is more than needed, but transformer was available locally and was cheap
Can you telle me where locally?
And at what price?

Thanks
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