Is it possible for transformer substitution?

[mikey5791]

Hi all,
Got this local made DC power supply (12/14V) given free as the transformer has melted. There is no marking or indication to identify what type or rating of transformer used.
Fyi,. I had a busted autogate mainboard with transformer with marking 13-0-13 . Is this the 13v dc type transformer?
My questions are
1. How do i test to see if the transformer is in good working condition?
2. Can this transformer (marking 13-0-13) be used to replace the melted transformer on the DC power supply?
Hope you guys understand what i was asking. My intention is not to let all this stuff to go to landfill but instead to reuse and recycle. Any suggestions and assistance is highly appreciated.

[stj]

Re: Is it possible for transformer substitution?

the burned transformer has 2 secondaries - both 13v ac

you need to look at the traces on the board to see if they are used seperatly, connected in parallel to double the current, or connected in series to get 26v ac
maybe clean all the crap off the board with solvent and post another picture

[petehall347]

Re: Is it possible for transformer substitution?

board looks burned

[kasfamily]

Re: Is it possible for transformer substitution?

Compare the sizes of transformers.
There are 3 ampere diodes in DC power supply

[eccerr0r]

Re: Is it possible for transformer substitution?

Are you sure the homemade PSU's transformer is fried? Does it work at all?

The donor board transformer looks like the two 13V windings are in series. You will likely still need them in series and hook diodes to the outer two terminals (two inner terminals should be connected to stay in series).

As for the primary side, not sure if you will still maintain the functionality, looks like the homemade supply has some sort of voltage setting on the front panel. I don't think the donor transformer has the same connections though it may...highly doubt it... so you'll end up with just one voltage.

[mikey5791]

Re: Is it possible for transformer substitution?

Stj,
Looks like the burned transformer is connected in series to get the aux power ac24v needed. Correct me if i am wrong. I tried using solvent to clean as much as possible but the burned part from the ac input (live and neutral) is charred. Hope the picture is clearer.

Kasfamily,
The donor transformer (13v-0v) is slightly smaller compared to the 3 amp transformer on the local made dc power supply.

eccerr0r,
The local made psu does not power on anymore. I suspect the transformer is fried as i noticed few areas started to melt the outer body.
You are saying about hooking diodes to the outer terminals. May i know what spec of diode to use? Something like 3A 200V or other type. Sorry i have not much clue on this and i do hope you can guide me on the wiring.
You were right on the local made psu, it has 12v or 14v dc selection on the front panel. I do not mind having just one voltage say 12vdc as long as the donor transformer is put to good use.

[mikey5791]

Re: Is it possible for transformer substitution?

Dear all,

Attached i drew a rough sketch of how the donor transformer was connected in its board. I guessed the ac live and neutral was shorted causing the primary side of the transformer charred and some tracks are unreadable.

On the other hand, the fried trans on the local made psu is about 6.5cmx4.5cm while the donor one measures about 4cmx4cm which is smaller. Not sure if this can be the donor. Kindly advice.

[stj]

Re: Is it possible for transformer substitution?

clarify for me,
are you trying to fix the pcb or the metal box one?

i am not sure the transformer on the pcb did that damage,
transformers these days have a thermal fuse in them and anyway, the windings/body doesnt look heated

[stj]

Re: Is it possible for transformer substitution?

looking closer - the pcb i think is o.k. - other than the burned tracks/fiberglass - i suspect water got under it.
or it got spiked by very high voltage - but water is my main suspect

the metal kent unit - is the primasry or secondary open or shorted - whats your meter readings?

[mikey5791]

Re: Is it possible for transformer substitution?

stj,
Thank you for your response.
Fyi i am trying to fix the metal box unit (Kent Star) by hopefully getting the transformer from the burned pcb as replacement.
On the metal Kent Star unit, I am using my digital multimeter on resistance 200 ohm scale and naming the left most black wire as 1, the middle blue wire as 2 and the right side yellow wire as 3. The primary side terminal 1&2 reads 6.7 ohm while 2&3 reads 5.8 ohm
The primary side readings seem unusual to me.

Also naming the secondary side left most terminal as 1, middle one as 2 and right side as 3,i got readings of 1&2=3.9 ohm while 2&3=3.8 ohm

Appreciate your assistance and kind help and hopefully get the Kent Star metal unit psu can work again.

[stj]

Re: Is it possible for transformer substitution?

the kent one sounds o.k.
show more pictures

[eccerr0r]

Re: Is it possible for transformer substitution?

Are the diodes still good in the homemade/Kent PSU? If so, they can be reused and their anodes should be connected to the outer two of the donor transformer. Should not need additional parts if just the transformer is damaged.

Do note that the donor transformer is not going to give you 3 amps output. Probably will only get 1.5A or so tops, and likely you'll get around 17+V open circuit voltage or so.

Attached are schematics of what it looks like now and how I expect them to be connected with the "new" transformer, and yes I made a mistake in the "from" schematic where the center pin of secondary got shorted with one of the diodes and transformer output wires...

Note that if your switch or fuseholder or powercord are broken, it will still be broken if you swap the transformer... your measurements for the broken transformer primaries are suspicious but since they show some connectivity it should still be somewhat working.

[R_J]

Re: Is it possible for transformer substitution?

Have you applied ac to the power supply? maybe the transformer is good, or maybe the fuse is open/missing? The switch will switch the primary to provide the different voltage on the secondary so check if it is still ok.

[mikey5791]

Re: Is it possible for transformer substitution?

stj,
Attaching more pictures on the kent unit.
Note that both the primary and secondary outer plastic covering are melting.

eccerr0r,
The 5402 diodes are still tested good on the kent unit. It does not matter if the donor transformer is unable to give a full 3 amp output. Since it is expected to give out around +17v dc open circuit voltage, that is good enough for some other electronic project. On your "To" schematic, if i am putting the new trans. ,I noticed the middle primary terminal no.2 is left empty, unconnected. I assume this is correct? In addition, on the secondary side terminal no.5 &6 are joined and connected to ground. Do i need to connect this part to the metal part of body for ground?
Since you mentioned the fuseholder, i went to check the fuse. It is blown, glass type fuse rated at 3A. No wonder it is not operating but something must have shorted in the transformer. Thanks for putting effort in preparing the schematic.

RJ,
Yes, i have applied ac power but it is not powering on. Now i know the glass fuse is blown. I think it is safer to replace the kent unit transformer as it looks badly melted and may likely cause an electrical hazard.

Looking forward to all your kind feedback and guidance before i perform the transformer changeover from the burned board to the kent unit.

[R_J]

Re: Is it possible for transformer substitution?

ok, The transformer did not look that bad in the first pictures, I would say it is bad.

[mikey5791]

Re: Is it possible for transformer substitution?

Got one question though.
Since the pcb transformer(13v-0v) is converting ac mains to ac24v on the burned board, will it be also doing the same on the kent unit? Then after this transformer replacement, am i getting output in ac instead of dc?

[eccerr0r]

Re: Is it possible for transformer substitution?

Yes pin "2" of the donor transformer is unconnected because it appears unconnected on the PCB and we can't make assumptions on what that pin does... unless you want to experiment...

Pin 5+6 just connects to the black output terminal, which is your "GND" terminal. Technically I omitted the "red" output terminal, which is the same node as the anode of the LED and cathodes of the 1N5402 diodes.

And for your recent post, no, the diodes "convert" the AC to DC. It's 24V because there really is 24V (actually 26V) as the two windings are in series, but the diodes and "center tap" you're only getting half voltage. If you want a full 24V DC at even less current, you would need a full wave bridge rectifier instead of the full wave half bridge rectifier. Your original transformer is "hardwired" in series and likewise could have gotten 24+VDC with a full wave bridge rectifier.

BTW at 3A for the original fuse, that probably did in the transformer most likely, it probably should have been closer to 1A. Should probably likewise use no more than a 1A TD fuse to protect the transformer, or whatever the PCB used. Then again, chances are, these fuses won't protect the transformer, just prevent a fire...

(also as another warning... Make sure you're not reading 3AG which is the ¼"x1¼" or 6.3mm x 32mm fuse standard size... I get that messed up frequently.)

[stj]

Re: Is it possible for transformer substitution?

i think some idiot was switching the primary between 120 & 240 to change the output - thats why it melted

[eccerr0r]

Re: Is it possible for transformer substitution?

Except the original transformer windings we're for 220V vs 240V which would explain the 12V vs 14V output voltage? Usually dual 120V/240V transformers aren't tapped due to VA limit issues.

[stj]

Re: Is it possible for transformer substitution?

but it looks very bodged - so who knows - and look at the same switch handling mains and secondary - thats insane!