shitty chinese psu kit

[xavier60]

Well,i just tested the led that came with the kit,its way brighter and has a vf of 1.97v,could that be the issue?,everything else looks good.

That wont cause a problem. Carefully test the PSU's output with the LED removed for now.

[m3vuv]

Hi,your answer isnt clear,how exactly do you want me to test it?

[xavier60]

confirm that the voltage regulation is ok then see how much current it can safely supply before the voltage drops.

[m3vuv]

how can the voltage drop without the led connected?,i dont want to try it without,the transfo is huge,testing max without any regulation will destroy things,the transfo can deliver 100 amps +.

[xavier60]

With the LED missing, there will be no current limiting. It will be safe to test the PSU so long as it's not overloaded.

[m3vuv]

thats my pont,sounds iffy to load it untill the v out sags,that will be a lot of amps without the led,what if i stop at say 10 amps?

[xavier60]

thats my pont,sounds iffy to load it untill the v out sags,that will be a lot of amps without the led,what if i stop at say 10 amps?

If it has been designed to supply up tp 10A then it should be safe regardless of the current limiting not working.

[m3vuv]

well it will supply 20a ok before the voltage drops,its od tho if i connect the load of 1 ohm then wind the  volts up it gets to 13v and tops out,if i wind the voltage upto 20v first then connect the load it sits there happily untilthings get hot then fan starts,10a is the most i can measure on my fluke or avo 8,thats without the led.

[m3vuv]

Well just an update,i changed the led for a decent one,adjussting vr1 gives me 12amp before current limiting,i will leave it at that,seems better than the stock 5a,goes up to 36v too,i class it as a good result,thanks for everyones help.

[xavier60]

That sort of odd behavior can be caused by loop instability resulting in oscillations.

[xavier60]

Well just an update,i changed the led for a decent one,adjussting vr1 gives me 12amp before current limiting,i will leave it at that,seems better than the stock 5a,goes up to 36v too,i class it as a good result,thanks for everyones help.

What actually fixed it though? Is the 7812 over heating? Is there a separate 7812 for the tap changer?

[m3vuv]

i'm not sure,the vreg seems not to be getting too hot,the tap switching is stock.

[m3vuv]

in a nutshell i used four BUW49 transistors as the pass elements,fitted a 50amp bridge offboard,a 22000 uf offboard filter cap and changed r4 too a 1 watt item.the pass transistors are on an old amd pc heatsink with an old ps2 fan.Just need to fit some vents on the case now,its an old pc speaker sub case.

[xavier60]

I wouldn't be surprised if it has some instability.  R6 and C4 are positioned in a way that does nothing useful. Series RC are usually for frequency compensation, so should connect back to the CV opamp's input.
The position of R5 makes R33 totally redundant as a bleeder for the CC pot's wiper. The top of R5 should connect to the bottom of the CC pot.

[m3vuv]

one thing i notice is when the led illuminates i can stil increase the output current using the volts pot!,is that normal?

[xavier60]

one thing i notice is when the led illuminates i can stil increase the output current using the volts pot!,is that normal?

Not normal. Check the stability. Or there could be some sort of interaction between the 2 pots. Check the 2.5V reference.

[m3vuv]

how do i check that then?

[m3vuv]

I assume thats the tl-431?

[xavier60]

I assume thats the tl-431?

That's it.

[m3vuv]

When two of the 2sd 1047 trannys going sc killed the tl430 as well?

[xavier60]

When two of the 2sd 1047 trannys going sc killed the tl430 as well?

No. What does the reference  voltage measure?

[m3vuv]

I dont know yet as i am getting ready for a hospital visit,at least as it is i can set the current output using the led,i dont see that as an issue,ie set the voltage then adjust the current pot to whats needed?.

[xavier60]

When two of the 2sd 1047 trannys going sc killed the tl430 as well?

On second thoughts. Any fault that causes the PSU's output to go to max voltage can cause a strong reverse bias to be applied to the TL431 when the voltage pot is set to minimum. The TL431 needs a protection diode across it.

[m3vuv]

Well,i have this fitted into the case finaly,i am just charging my clansman battery ,feeding it 28v at 400ma,its working perfect,i must of been having a brain fart before! lol.

[m3vuv]

would it be possible to fit a cv led to this,if so where to connect,is it same place as the otherone just polarity reversed?