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Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)
- Thread starter bushtech
- Start date
73's de Edd, haven't done enough start ups to tell. I now did a hot startup (cap still charged?) and installed a 1A fuse and switched, it survived that and I am now letting it run for a while to see what gets hot. When R1 or R2 start crisping I'll switch off.
Audioguru, how long does the big stay charged, isn't there a drain resistor in the circuit?
Yep, got some spare computer power supplies in the junque box, will go digging
Audioguru, how long does the big stay charged, isn't there a drain resistor in the circuit?
Yep, got some spare computer power supplies in the junque box, will go digging
When the project has no load then the 28V transformer produces 29VAC which is rectified and makes +40V. Then the heating in R1 is (40 squared)/2200 ohms= 0.73W. A 2W resistor will be fairly warm.
R2 is part of a half-wave rectifier so it draws current for half the time and is in a voltage divider with R3 so its heating is about 0.72W. If the diodes, C2 and C3 are not leaky then the heating in R2 is [(40V/2 squared) x 0.27]/82 ohms= 1.3W. A 2W resistor will be very warm.
R1 drains the big capacitor. If the capacitor is 12000μF then it is discharged in 13.2 seconds.
R2 is part of a half-wave rectifier so it draws current for half the time and is in a voltage divider with R3 so its heating is about 0.72W. If the diodes, C2 and C3 are not leaky then the heating in R2 is [(40V/2 squared) x 0.27]/82 ohms= 1.3W. A 2W resistor will be very warm.
R1 drains the big capacitor. If the capacitor is 12000μF then it is discharged in 13.2 seconds.
I now let it run for an hour (Still 1Amp fuse) switched off and did the tongue tip test (not really). Everything cool including the 2 infamous resistors, which really surprised me.
However, straight after switchoff I switched it on and off twice at about 2 sec intervals. At the second switchon the 1A fuse went.
At that sort of frequency the caps could not have discharged so hmmmmm.
However, straight after switchoff I switched it on and off twice at about 2 sec intervals. At the second switchon the 1A fuse went.
At that sort of frequency the caps could not have discharged so hmmmmm.
Herr bushmeister . . . .
You say . . . . .
At a stone cold turn on it . . will be serving as an 8 Ω surge cushion and constantly declining in resistance, as is being related to its current passage.
Then within 1/2 of a min it has stabilized at downwards of 1/2 Ω.
That . . . . . then is being as insignificant as a gnat " hitching a ride" *** on a pachyderms arse.
***
73's de Edd
.....
You say . . . . .
Why . . .'soitanly . . .when being tasked at its prior application in its handling of 3-400 watts of a comp power supply,as being compared to your mere 75-100 watts now.
At a stone cold turn on it . . will be serving as an 8 Ω surge cushion and constantly declining in resistance, as is being related to its current passage.
Then within 1/2 of a min it has stabilized at downwards of 1/2 Ω.
That . . . . . then is being as insignificant as a gnat " hitching a ride" *** on a pachyderms arse.
***
73's de Edd
.....
Use a higher rated fuse. Alternatively find a fuse with a longer delay (TT, TTT,...)
If you're using an NTC thermistor to limit the switch on current, then rapidly cycling the power also won't let it cool down.
Another option is to have a resistor in series with the mains, and a relay to short it out after a small delay. You may still have the problem if you cycle the power before the relay has a chance to drop out.
In my recent repairs I've had the opposite problem to yours. Even with the rectified secondary shorted, the fuse did not blow.
If you're using an NTC thermistor to limit the switch on current, then rapidly cycling the power also won't let it cool down.
Another option is to have a resistor in series with the mains, and a relay to short it out after a small delay. You may still have the problem if you cycle the power before the relay has a chance to drop out.
In my recent repairs I've had the opposite problem to yours. Even with the rectified secondary shorted, the fuse did not blow.
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