shitty chinese psu kit

[m3vuv]

Well the bjt 2sd1047 is rated at 12 amps max,so less than half there rated current at 30a,i suppose the voltage drop will depend as to where the output voltage is set to, and which transformer tap is switched in,,hopefully the opamps are fast enough to protect it,we shall see.

[magic]

It's all about SOA of the transistors, check the datasheet. Opamps are quite fast, but relays aren't - I suppose it's some milliseconds to switch them.

Did you fix the potentiometers?
DId you check what happens when you set CV to zero with a 12V battery on the output? No, definitely don't do it

[m3vuv]

well for the pots i fitted 10 turn 10k jobs,when i charged a car battery using it even on full current output the cc led was on for about 3hrs until the battery got to 13v then went off,at this point i took it as charged and cisconnected it,one thing that did happen tho was the output shot up to 32v,this was charging at 1.5a,the heatsink was burning hot,one pass transistor had gone sc,the wire had melted off the other but it was still ok,thats when i decided on the big copper pc heatsink and more x pass transistors.

[m3vuv]

getting there slowly.

[m3vuv]

still have 1 more 2sd 1057 to fit+ the current sharring resistors etc.

[m3vuv]

Well i did all that,heres the issue,it outputs max 10ma,as soon as the load draws 10ma the relay/relays click and the output volts drop to zero,same goes if i try and draw more than 10ma from the pass transistor driver too,ive looked all over and cant see any faults,ive renewed the tip42 driver and the op amps,diodes test ok(havent tested zeners tho,just basic diode test on those,but measure 0.7v drop foward and ol reverse) at my wits end,any ideas what to check,i was going to look and see what fed the relay coils but the schematic is missing big parts,emailed the supplier,they say they cant get the rite schematic,what a shower of brown stuff!.

[m3vuv]

Also when it all drops out,relays etc,i still have the volts/amps display so that is ok supply wise,also i can pull 40amps from the bridge rectifier ok into a load so the input voltage isnt sagging.

[xavier60]

Check to see if it's going into CC mode regardless of what the LED shows. Measure the output voltage of the CC opamp WRT the positive output terminal before and after.
In other words, measure it with the PSU unloaded then loaded.
Measure the output of the CV opamp also.

[m3vuv]

What would be what then as regards op amps and outputs,would i be right in thinking ul1A iout is high for cc and low for cvor is it u1B,i assume u2A+B are to do with the relay tap switching,the schematic is very poor.TiA

[m3vuv]

anyone? TIA

[MK14]

anyone? TIA

I can't speak for everyone else. But I will speak for myself, at least.

If you want help, it would be much better, if you supplied a complete and clear schematic, which includes all the modifications you have made. Along with a specification of the PSU, you are trying to achieve.

Otherwise, it would be very difficult, at least for me, to actually give you much useful help.

You seem to be saying things like, added a transistor or so. Not sure how transformer is wired. This or that component(s) burnt out, exploded or smoked. Changed this and that, etc.

Also, you are supplying photographs, but they seem to not really help that much.

In another thread, you seem to have said your PC, can't handle schematics (actually you were referring to PCB design software, which often/usually includes schematic creation capabilities).

Without a schematic (small/simple ones, can be done by drawing them on paper, and photographing them. But, I don't think that would help here, as it is too big/complicated a schematic, and you probably would supply a sub-par photograph, which is too unclear to be especially useful).

As it stands, I can't make much sense of what exactly is going on, what has been damaged, what has been replaced, how the thing is wired up, what you intend to make (specification wise). Even the original schematic seems to be way too blurry, to make much/easy sense of.

You don't seem to pay much attention to peoples comments, either. Which further muddies the water.

Don't get me started about easily readable forum posts (grammar etc).
E.g. What is a TIA ? (Probably Thanks In Advance, I suppose).

[m3vuv]

This is the schematic that arived with it,but not complete or !00% correct,the mods i have done is fit 2 more pass transistors and emitter resistors,a 50a bridge rectified off board and a 1000000uf 63v filter/smoothing cap,all that seems ok,i havent checked the aux supply yet tho,maybe its that,before it maxed out at about 33v now its about 23v max,no current tho,it only outputs 10ma before it drops the relay out and goes to zero.TIA

[MK14]

What power supply specifications are you aiming for, when it is working correctly. I.e. Maximum output voltage, and maximum output currents ?
I'm presuming the maximum voltage and currents are available at the same time (which is not always the case, some limit the maximum output power, usually for switch mode supplies, rather than linear types, like yours).

Also (if you already stated it, I missed it). What the specifications of the mains transformer is. I.e. Type, AC output voltage (per tap if applicable), Max AC output currents, number of taps.

[magic]

I see nothing obviously missing.

J1,J2 are the relay coils and T1,T2 drive them under control of that LM358.
The other LM358 controls CC/CV by stealing R4 current through diodes away from the pass transistors.

It couldn't be simpler.

[m3vuv]

dont know the exact specs on the transformer but it weigs about 6kg,its a big ex milatary job,it has taps at 36v-25v-17v+ others,ive powered 4 diesel glow plugs from it no problem,guess 50+ amps,the original kit was 5A at 30v,but it lists it as 50v as well,its not clear bit like the schematic,magic can you say what opamps do what,ie u1a u1b + u2 a+b?.Tia,i wonder if its trying to get its power from the small auxillary transformer for some reason,ive not looked into that yet.,the paperwork that came with the kit is in chinglish and the seller is as much use as tits on a bull!.

[m3vuv]

Also magic,you say the relays are driven by t1+t2,i see t1 but no t2,am i going blind?.

[MK14]

Also magic,you say the relays are driven by t1+t2,i see t1 but no t2,am i going blind?.

Yes.
Take the following image, twice a day, after meals with water, it should fix it.

[MK14]

Also magic,you say the relays are driven by t1+t2,i see t1 but no t2,am i going blind?.

If you mean the transistors themselves. T1 is labeled as T1. But T2, seems to have had the 2 shaved off it. It not only is blurry (entire schematic), but seems to have had the right hand section, removed almost entirely.
It's right by T1, just look an inch or so, to the right of it, for a T, missing the 2 bit (T2).

[magic]

Good catch

I didn't even notice that they cut the number, just guessed it's T2

Anyway, obviously, I mean the transistor which pulls down on J2. Look for J1/J2 labels on the schematic and draw connections between them - that's two transistors driving those two relays.

It looks like divided output voltage goes to IN+ of the opamps and you are supposed to set switching thresholds with pots going to IN-. If you simply insert pots without adjustment, it will change transformer windings at some random output levels.

[m3vuv]

So magic are you not going to tell me what section of what opamp does what?

[ledtester]

The youtuber Steve Wagner is current building the same supply and he's redrawn the board layout and schematics which you can find on his web site:

https://gswagner.com/35%20V%205%20A%20Supply/

Look at the files named "35 V 5 A Power Suppl..>".

The schematic that's been posted here is also present in that directory under the file name "Wrong but similar Schematic".

His build videos (so far):

Part 1: https://youtu.be/P2_CoiQThQ8

Part 2: https://youtu.be/3yn66h7hS5A

Part 3: https://youtu.be/gbecNRaFl8g

[m3vuv]

Thanks for that,thats brilliant,should be able to sort it out with that propper schematic etc,cheers.

[xavier60]

Well i did all that,heres the issue,it outputs max 10ma,as soon as the load draws 10ma the relay/relays click and the output volts drop to zero,same goes if i try and draw more than 10ma from the pass transistor driver too,ive looked all over and cant see any faults,ive renewed the tip42 driver and the op amps,diodes test ok(havent tested zeners tho,just basic diode test on those,but measure 0.7v drop foward and ol reverse) at my wits end,any ideas what to check,i was going to look and see what fed the relay coils but the schematic is missing big parts,emailed the supplier,they say they cant get the rite schematic,what a shower of brown stuff!.

What are you using to load the PSU? Does the output voltage recover when the load is reduced?
If there is always voltage present on the large filter cap, there is no reason to look for problems in the tap changing area.

[magic]

So magic are you not going to tell me what section of what opamp does what?

U2 is doing nothing clever, it's a comparator. IN+ is half of output voltage, when it goes above the level set by the pot at IN- the output goes up and T1/T2 collector goes down. This energizes the relay and also decrease the IN- threshold voltage by means of D7,R26 so that the opamp won't switch back until the output voltage decreases a little. This prevents relay chatter.

I suppose you can figure out which opamp goes to which relay from the schematic. Or, better, from the board

[m3vuv]

Well so far i have found the voltage on the filter caps goes up in steps as each relay pulls in,if i i wind the current pot fully ccw the led comes on+ output drops to zero,seems fine without a load on the output,any load makes the output drop to zero and the relays drop out, both tip 42 trannys have full rail power on there collectors and the main pass transistors too,they get enough current to light a 12v 21 watt bulb .any ideas? tia.