# Chinese Hiland 0-30V/Audioguru PSU build (down the rabbit hole)

Discussion in 'Power Electronics' started by bushtech, Oct 27, 2017.

1. ### bushtech

934
145
Sep 13, 2016
That would be R1 and R2. On the 82Ω R2 I am already using a 5 watter

2. ### bushtech

934
145
Sep 13, 2016
Aah, eagleeyed 73's de Edd. Not my proudest moment with my Dremel tool. Thank goodness you can't see the power switch on the photo, that's even worse

3. ### bushtech

934
145
Sep 13, 2016
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

4. ### Audioguru

2,789
633
Sep 24, 2016
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.

bushtech likes this.
5. ### bushtech

934
145
Sep 13, 2016
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.

6. ### Audioguru

2,789
633
Sep 24, 2016
Maybe badluck made you turn on the project twice when the mains was at the peak voltage and maybe 2 seconds between turn ons did not let the fuse cool enough.

bushtech likes this.
7. ### bushtech

934
145
Sep 13, 2016
Thanks Audioguru, that's a thought. I'm now considering 73's de Edd's inrush current limiting thermistor

8. ### bushtech

934
145
Sep 13, 2016
73's de Edd

This comes out of an old PC power supply 230V/ 6/4A. Right after incoming supply

Writing on it says SCK 082

Man enough for the job?

9. ### 73's de Edd

2,840
1,207
Aug 21, 2015
Herr bushmeister . . . .
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
.....

10. ### bushtech

934
145
Sep 13, 2016
Lol! Thanks 73's de Edd. Will install it and report back.

yeah, good ole Loxodontus Africana, not a fellah to be trifled with.

Great song btw.

11. ### bushtech

934
145
Sep 13, 2016
Installed the thermistor, switched on and fuse stayed intact. Then did 3 widely spaced switchons with fuse staying intact. But the 4th time I tried the fuse blew (0.75A fuse)

I just don't understand this, thought we had it licked

934
145
Sep 13, 2016

13. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,359
2,755
Jan 21, 2010
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.

14. ### bushtech

934
145
Sep 13, 2016
Thanks steve. Recent power ups have had long (10min+) delays between power ups, so no rapid cycling recently

15. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,359
2,755
Jan 21, 2010
Does it happen with no load on the secondary?

And presumably the fuse fails immediately you turn the PSU on (i.e. not after a couple of second delay).

16. ### bushtech

934
145
Sep 13, 2016
yes, no load connected and V and A pots turned down. Instant blow

17. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,359
2,755
Jan 21, 2010
No, disconnect the secondary.

Is it the surge when the filter caps charge?

What is the total capacitance of your filter caps?

18. ### bushtech

934
145
Sep 13, 2016
The big one is 12,000μf

19. ### bushtech

934
145
Sep 13, 2016
not sure what you mean by disconnect the secondary

20. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,359
2,755
Jan 21, 2010
The secondary side of the transformer