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Old 6th July 2006, 03:24 AM   #1
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Default AlephX PSU- need help

Hi,
I'm building an alexh-x but a problem appear when at the initial testing of the PSU with no load on it. It keep blowing fuse.

I'm using a crc filter with 2 bridge, 56000uF - .25R - 56000uF. The fuse I'm using is 8A slow blow. something like this: http://s37.photobucket.com/albums/e9...nt=LOIC_PS.jpg
The transfo is from ebay, initially 240V input, 4x 38V output rated at 3700VA. I'm running it at 120V and get about 19V per secondary.Let me know if you think you need some more info.

Thanks for your help
Thierry
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Old 6th July 2006, 04:52 AM   #2
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Are you using the NTC shown in the figure you referenced? If not, the initial current draw to charge the capacitors will easily blow the fuse.

Second, have you tried starting the power supply up slowly using a variac? That will give you some clues as to where the mistake might be.

Lastly, a good high wattage power resistor doesn't cost much and will provide a decent load to the power supply for testing purposes.

A few points to try and if they don't work out, we'll try some others.

Cheers, Terry
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Old 6th July 2006, 05:16 AM   #3
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I'm using 2 cl-60 one on the hot and one on the neutral
Could it be possible that 8amp fuse is not enough?

I didn't try with a variac but I'll get one tomorrow.

As for the load I have a 33R around 50-100W, would it be good for that purpose? I was not using one so far because I don't want to add more inrush til it work.

Thierry
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Old 6th July 2006, 09:05 AM   #4
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If it is 3700VA at 120V main, the current handling is about 30A on the main side. In addition, there will be very high inrush current. Probably, there should be fuses on the secondary side too. Ayo . . . have no idea how to estimate the fuse size in this case . . . Nevertheless, the 8A slow blow is considered too small.
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Old 6th July 2006, 02:21 PM   #5
TS Lo is offline TS Lo  Hong Kong
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Quote:
Originally posted by jh6you
If it is 3700VA at 120V main, the current handling is about 30A on the main side. In addition, there will be very high inrush current. Probably, there should be fuses on the secondary side too. Ayo . . . have no idea how to estimate the fuse size in this case . . . Nevertheless, the 8A slow blow is considered too small.
In this case - the transformer can only handle about 1800VA since the
copper wire used in the primary winding is only enough for (3700/240)
15 amp.

TS
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Old 6th July 2006, 04:26 PM   #6
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In the absence of a variac, try a light bulb in series with the transformer primaries. This will keep the fuse from blowing and let you look around to see if everything else is working fine.

Jeremy
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Old 6th July 2006, 10:53 PM   #7
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Problem solve, I happen to had a short capacitor who was pulling the juice. The variac was very handy in troubleshooting it.

Thank you all for your reply

Thierry
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