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

[Audioguru]

Did the series lamp just flash for a moment when the project was switched on or did the lamp light continuously?
238V at 0.75A is a power that is way too high of 238V x 0.75A= 178.5VA. The project draws only 118VA when it has its maximum output current of 3A.
A fast blow fuse might blow as the main capacitor C1 charges.
I have not seen a fuse for many years but I think a fast blow has a thin wire inside and a slow blow has a coil of wire that looks like thick wire.

 

[bushtech]

Previously the the lamp would just flash at switch on and slowly start lighting up if I raised the volts and amps.

So are you saying a slow blow fuse of 0.75A is OK or should I use a larger slow blow fuse?

 

[Audioguru]

Your 0.75A/250V slow blow fuse is fine if the project does not get hot when powered with no load.

 

[bushtech]

This is what the fuse looks like:

Busy talking with the supplier to find out if it is a slow blow fuse. If it is I have to find out why the fuse is blowing

 

[bushtech]

This is the fuse: http://www.conquer.com.tw/product/item_sel_all_set2.asp?item_assortment_no=64

 

[Audioguru]

I looked in Google Images for Glass Slow Blow Fuse and it showed photos of fuses with a thin wire, a thick wire, a coil of wire and a thin wire with two or three dots on it like yours. Some are correct and some are wrong.

 

[bushtech]

Audioguru
I stuck my DMM in in place of the fuse and fired the power supply up a couple of times. The highest reading I saw on the DMM was 0.54A. Is this within the realms of normality and is this enough to blow a 0.75A fuse? I think not. Pots turned right down but dummy lead attached

 

[Audioguru]

I think your DMM cannot measure the short duration peak current of the big capacitor charging and your fuse is a fast blow not a slow blow.

 

[bushtech]

Thanks Audioguru. Just thinking now, I had DMM in dc mode aand I was reading AC amps. Does it matter when you're reading Amps?

 

[bushtech]

Will my analog MM be able to show it?

 

[Audioguru]

The duration of the large capacitor charging is too short for a DMM or analog MM to accurately show its amount of current. An oscilloscope is needed to show it. I wonder if the core of the transformer is saturating by the high pulse of current that makes the amount of current even higher.

 

[(*steve*)]

This is what the fuse looks like:View attachment 41630

That is most definitely a slow blow fuse.

Fuses of that type should probably be able to sustain a 200% overload for some time between 2 and 120 seconds. The example below has *exactly* that specification, but yours should be similar.

See here.

 

[bushtech]

Thanks for the clarification steve. I probably made a mess up of transferring this lot into a box which is causing this problem

 

[bushtech]

I have now noticed that I don't seem to be getting any current. No matter how I turn the amp pot the meter stays on 0A. Have checked the voltages on U3 and all more or less the same as the readings I posted in post #271 apart from pin 3 which has gone from 0 to 2.5V.

 

[Audioguru]

When pin 3 of U3 has a higher voltage than the project output voltage then U3 is not reducing the current through D9 by reducing the output voltage. Measure the output voltage of U3 to see if it is wrongly reducing the input of U2.
What resistance is the project's load?

 

[bushtech]

Thanks Audioguru. I had never before noticed that the amps only loads up when a load is attached. Started working fine when I attached load.


Seems I still have a lot to learn about this power supply.

Load is a big 50Ω resistor as shown in post #226.

Still need to find out if I'm still blowing fuses. I have got 2x 1Amp fuses. I am going to sacrifice one and see if goes to magic smoke heaven

 

[Audioguru]

Let it sit for one hour with no load. Feel everything, nothing should be hot. Current times voltage equals heat.
Your current meter measures the load's current, not the entire project's current. The parts in the circuit draw a very low current when there is no load and nothing is wrong.

 

[bushtech]

Will definitely do, thanks Audioguru

Hmmmm, what about those 2 resistors that have wayward tendencies ?

 

[Audioguru]

Which two resistors are "wayward"?

 

[73's de Edd]

Methinks that you need another bezel . . . . for your meter bezel . . . . . to cover up your panel hole boo-boo's.

Is your fuse problem ONLY when he system is started up from a stone cold initial power up ?
Or will it still do it, after main filter capacitors are still maintaining somewhat of a charge being held in them ?

You gots any computer power supplies in your "Junque Boxe " .
Wherein, you might scavenge an inrush current limiting thermistor, to install in the hot leg of the AC line input that feeds the primary of your power toroid.