shitty chinese psu kit

[xavier60]

D17 could be replaced with an LED but the current might be too high for it. A better way is to put an LED and resistor in series between the 12V control rail and the output of the CV opamp. Start with 10K or a bit lower to see how the LED brightness is.

[m3vuv]

is that u1a pin1 or 7? and the amp control rail or volts control rail?,thanks.

[xavier60]

is that u1a pin1 or 7? and the amp control rail or volts control rail?,thanks.

If you want the LED to indicate CV status, it needs to connect to the CV opamp U1B output pin 7.
The power source needs to be 12V from the 7812.
What did the reference voltage measure??

[m3vuv]

what ref voltage are you talking about?,i havent checked any,is that not how the led is alread conected?

[xavier60]

what ref voltage are you talking about?,i havent checked any,is that not how the led is alread conected?

Im still curious about the 2.5V reference I asked you to measure yesterday. In case the TL431 really has been damaged.

[m3vuv]

didnt check it as the psu was working ok,well up to 10a anyway,i am more concerned over the cv connections,although thats icing on the cake imho.

[xavier60]

didnt check it as the psu was working ok,well up to 10a anyway,i am more concerned over the cv connections,although thats icing on the cake imho.

I'll standby until you get a chance to check it.

[m3vuv]

whats the point in risking shorting pins probing to check the ref voltage when the psu is working fine,i just want to know where to connect a cv led.

[ebastler]

Wow, five weeks of tinkering and nine pages of forum dialog on a $20 power supply kit. I guess we can't complain about the value for money one gets out of this kit... 

[m3vuv]

at least it gave you some reading!

[MK14]

Wow, five weeks of tinkering and nine pages of forum dialog on a $20 power supply kit. I guess we can't complain about the value for money one gets out of this kit... 

I suppose, it shows that there are many different types of people, in this world.

A reasonably decent kit, with PCB and decent enough supplied components, should be able to be constructed, reasonably quickly and tend to work, first time.

They (presumably) are either buying sub-standard quality kits and/or need to improve their construction techniques, so it doesn't short out and blow components up, every 5 minutes and/or they just can't listen to good advice, and so end up with something so badly bodged together, that it keeps on failing.

[MK14]

at least it gave you some reading!

You have got to be joking. The gist of the way it looks to me, is that you keep on saying you swapped this component for another component. This kit for another kit. This component or that component smoked, burnt out, got too hot, etc.
Making it extremely difficult or not possible, to follow/help or get anything sorted out.

It really needs you to supply a schematic, and keep that schematic updated with any changes you make.

[m3vuv]

well mines been a bit of a battle mostly due to doubling the output,was a good learning curve tho,at the end of the day i have a 0-36v 10amp+psu with cc control for about 30 quid!,whats not to like?.

[m3vuv]

at least it gave you some reading!

You have got to be joking. The gist of the way it looks to me, is that you keep on saying you swapped this component for another component. This kit for another kit. This component or that component smoked, burnt out, got too hot, etc.
Making it extremely difficult or not possible, to follow/help or get anything sorted out.

It really needs you to supply a schematic, and keep that schematic updated with any changes you make.

if you look the schematic + links have been posted.

[MK14]

if you look the schematic + links have been posted.

But the problem is, I keep on seeing posts, such as this one:

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.

Which keep on changing components, component values and possibly circuit configuration.

Leading to confusion, misunderstandings and difficulty with following what exactly is going on.

[m3vuv]

So am i correct in thinking the cv led goes to the lm7812 output via a dropper resistor and u1 pin7?

[m3vuv]

well i left this running overnight charging a car battery at 14v 1 amp,woke up this morning to find zero output,left it disconnected for an hour and its working againe,could that be the 7812 shutting down thru heat?,if so i plan on building this and fit offboard,is that a good plan?or just fit the existing reg offboard on a bigger heatsink?

[m3vuv]

Seems mr wagner made a ballsup with u3 +u7,he has 2xu3 but no u7. on the board layout etc.

[m3vuv]

seems we have a u6 on the schematic but not on the pcb!

[not1xor1]

well i left this running overnight charging a car battery at 14v 1 amp,woke up this morning to find zero output,left it disconnected for an hour and its working againe,could that be the 7812 shutting down thru heat?,if so i plan on building this and fit offboard,is that a good plan?or just fit the existing reg offboard on a bigger heatsink?

Unless you attached the wrong schematic or are just trolling that circuit will never work because you will never get 14V and 1A out of 2 78L12 ICs.

[xavier60]

well i left this running overnight charging a car battery at 14v 1 amp,woke up this morning to find zero output,left it disconnected for an hour and its working againe,could that be the 7812 shutting down thru heat?,if so i plan on building this and fit offboard,is that a good plan?or just fit the existing reg offboard on a bigger heatsink?

Unless you attached the wrong schematic or are just trolling that circuit will never work because you will never get 14V and 1A out of 2 78L12 ICs.

"m3vuv" is suspecting that the LM7812 supplying the 12V control rail is shutting down.

[m3vuv]

well i fitted a bigger heatsink to the 12v reg but after steve wagner corrected his pdf docs i realised i had fitted it to the wrong 12v reg,gonna redo it now,may fit a usb charger port hung off of the 5v reg too.

[m3vuv]

i see the shutdown as a heat issue as the output reterns when its cooled,my board is different to the last as in u3 is hard up against the tl431 voltage ref so dare say heat could cause issues there,going to mount the 12v u3 offboard on a heat sink with caps on the in+ out and try that.

[m3vuv]

hope the corrected pdf files help if anyone is planning on building one of these.

[Terry Bites]

Will this saga ever end?