12V 10A CCTV camera system power supply pulsating

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

The reference voltage for tl431 is 2.5v

And install the TL817 ortron correctly (1-2 pin on the cold side, 3-4pin on the hot side).

Hi, it was installed correctly, it is me that reversed the reading. And when installed (correctly), we are back to square one whereas the output pulses between approx 4V to 6V-7V.

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Installed a third TL817 (correctly) and doing the same thing, this time pulsing from 3V to 6-7V with sometimes showing 4V - 5V erratically.

[R_J]

Re: 12V 10A CCTV camera system power supply pulsating

Was this power supply working at one time? It is not that complex of a circuit, with most semiconductor parts replaced it does not leave much.

How much does adjusting the pot effect the output voltage?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Yes it was working fine and all of a sudden stopped powering the cameras. Pot on one side goes from 2.5V to 5.7V (remember it oscillates) and completely turned to the other side 3V to 4.5V oscillating in both cases.

[R_J]

Re: 12V 10A CCTV camera system power supply pulsating

I would remove the output diode and replace it with a single diode even a 1 amp should be fine for a test without load, maybe it is breaking down under even a small amount of current.

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Boy R_J you are creative, I love that! Ok, so I see what you mean...what does the other diode serve for? I might have some replacement diodes I used once to repair another type of power supply, I'll check and give you the references before installing anything.

Ok so I checked and what's there is a sr30100ct, datasheet attached. Can I install any type of diode where you indicated?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

I think the one that is in there SR30100ct is a dual 30A Shotcky diode. I have some EN220A (20A I believe) or some MBR2020CT or individual SB5200TA.

[CapLeaker]

Re: 12V 10A CCTV camera system power supply pulsating

I had to read up on this to see the progress.
RJ suggested to unsolder the primary side of the optocoupler and you got a ramping up and down 14 to 21V. That shouldn’t be. You should have full bore 21V straight, since nothing is regulating the PWM, no nothing ramping up or down. So I would think there is something wrong in the primary side.

[R_J]

Re: 12V 10A CCTV camera system power supply pulsating

Without feedback from the secondary, the feedback pin would go high to 6v and the ic would detect that and at 4.4v it would go into power limiting mode. you might be able to install a resistor from FB to hot ground without the opto, but I'm not sure what value would hold it to about 3v
As for the diode I suggested, this is just to test the circuit, it doesn't need to supply 10 amps of current just to test the circuit.

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

So R_J for the test, should I use MBR2020CT (dual diode) or individual SB5200TA (5A) like you indicated in the photo?

[R_J]

Re: 12V 10A CCTV camera system power supply pulsating

You can use either one I would just use an individual diode, The other section of the dual diode would not be necessary for this test, this is just to eliminate the dual diode as being the problem. We are running out of components to suspect.

[petehall347]

Re: 12V 10A CCTV camera system power supply pulsating

is it plugged direct into the mains or through a current limiter ?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

I would remove the output diode and replace it with a single diode even a 1 amp should be fine for a test without load, maybe it is breaking down under even a small amount of current.

Ok, removed the output diode and installed a single diode 5 amps, and the result is similart oscillating at a lower voltage i.e. from 2.8V to 4.5V erratically and everything in between.

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

is it plugged direct into the mains or through a current limiter ?

It's plugged into the 110V mains. That's where it was plugged in before.

[harp]

Re: 12V 10A CCTV camera system power supply pulsating

Can this mains socket provide enough current, maybe wires are loseing inside wall or psu switch, is voltage stable till operation of psu?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

Can this mains socket provide enough current, maybe wires are loseing inside wall or psu switch, is voltage stable till operation of psu?

Oh yes it does provide enough current, I mentionned in a previous post that voltage on the main capacitors is a steady 163V, very steady.

The mains is plugged into the wall, electricity provided by Hydro Quebec.

[CapLeaker]

Re: 12V 10A CCTV camera system power supply pulsating

Without feedback from the secondary, the feedback pin would go high to 6v and the ic would detect that and at 4.4v it would go into power limiting mode. you might be able to install a resistor from FB to hot ground without the optocoupler, but I'm not sure what value would hold it to about 3v
As for the diode I suggested, this is just to test the circuit, it doesn't need to supply 10 amps of current just to test the circuit.

Geez... not sure anymore on what else to come up with to proof that the feedback section in the secondary part on this PSU is o.k. or not.

If we disconnect this PSU from power mains, inject rated DC voltage from a variable PSU into the secondary of this PSU. Then we can measure the resistance of the optocoupler on the primary side. By adjusting the voltage up to rating or lower should make the output of the optocoupler on the primary work or not. This should proof that all components in the feedback circuitry on the secondary side are working correctly and the actual problem is in the primary. I also like the your idea of disconnecting the optocoupler and limiting the voltage on the FB pin to 3V with a resistor and see what the PSU does.

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

I'm pretty much open to try anything, what does R_J think?

[stj]

Re: 12V 10A CCTV camera system power supply pulsating

check the transformer for poor connecton to the board or windings?

[rddube]

Re: 12V 10A CCTV camera system power supply pulsating

check the transformer for poor connecton to the board or windings?

OK, will do that...i'll unsolder it to make a thourough inspection and will report back