12v PSU -> 24V or 36V - help needed [Solved]

dear electronic gurus,

I would like to mod the Delta DPS-835AB, Artesyn 7001138-Y000, IBM x3650 3655 835W (12.1V 69A) Power Supply from 12V to 24V or better said 27V
The photo attached to this posting shows the wiring how to connect two PSUs together:
Obviously to raise the voltage up to 13.2 I have to solder a 1.3kohm resistor between pins 17 & 19.
To get the 24V as far as I understood I have to connect the GND from one PSU to the "+" line to the other PSU only? Due to that the ex "+" polarity (left PSU shown on the photo) is now the new GND. The right PSU on the photos shows the original polarity.

The solution shared by @BlazinH: "Just for information when you are connecting like power supplies using grd. to pos. or pos. to grd. connections you are connecting them in "series" which adds their voltages together but leaves the max. current the same. Wiring grd. to grd. and pos. to pos. is a "parallel" connection that does not add voltages but instead shares current."

something tells me I think I can see this happening

hehe, me too. Ergo better asking before than never...

Not worth spending some real dollars for a real psu ?

What do you mean? IYO the server PSU described in the OP is not a "real" PSU?

opened a thread on rcforums, too.

I have trailed them on a jrk and the Jrk caused them to drop out pretty easily didn't seem to have the balls to supply the amps quoted on them.
But could have had an old pair, as a basic desktop supply for little projects cool , but to supply a constant 50amps I need they were not up to the job, even when wire in parallel lasted about 1/3 longer before dropping out.

But some people do have success with them. Im not discouraging people from using them at all. They do work for some.

Just for information when you are connecting like power supplies using grd. to pos. or pos. to grd. connections you are connecting them in "series" which adds their voltages together but leaves the max. current the same. Wiring grd. to grd. and pos. to pos. is a "parallel" connection that does not add voltages but instead shares current.

Dear @BlazinH thank your for the explanation, now I can realize my experiments without being blown away when I power on the switch

You’re welcome pit. You probably already know this stuff but you can also combine the two and use series and parallel connections together. For example, you could use four 12v psu’s and wire the first and second ones in series to give 24v and the third and four ones in series to give 24v. Then wiring the two 24v pairs together in parallel will give 24v with double the available current. Of course, you must make sure the psu’s are set or tied so that they don’t interfere with each other’s operation which is what the resistor between pins 17 and 19 is for I suppose.

Check on the rcgroups forum as they use them to run lipol battery charges

just a note if you connect in parallel + to +, - to -, gives you same voltage double the current

if you connect in series + psu1 - to + psu2 - gives you double the voltage same current

with the series setup you need to be aware that the - psu output is connected to mains ground, so you need to isolate the earth to - connection on psu1 and leave the psu1 - psu2 + connection floating.

regards Terry

Hi @BlazinH I have a big issue: for some reason my setup doesn't work. The same PSUs do not work together, meaning one PSU is shutting down when the other is going on. One + from PSU 1 is wired to - of PSU2, the two free outputs will be used for the motor. But it does not work at all...

As I have all my equipment apart at the moment, for info wired up two of my 12VDC 40A power supplies (Led power supplies) in series and a easy 24VDC..is shown - Note DC is not connected to chassis ground in any way on these boxes. I often think that PC Power supplies are too smart for what we want to use them for (which is why I have never used them). Unfortunately I don't have a 24V motor to give it a real test. (Note these power supplies are also slightly adjustable).

I got more information what I have to do:

I have to pull out the two PCB mounting screws, then to drill out the cladding and to reinstall the screws with a nylon washer between the PCB and the lugs. Obviously I need to do the two screws nearest the output only.

yuppiiie Thank you @SeatTime

BTW PSU test passed and BB-VNH3SP30 test failed (24V)

just asking, did you do this to isolate 220V ground from the PSU case?

not sure but i remember i have read somewhere in RCgroups that if you do this config (2x12V PSU) you have to ground isolate one PSU and make that one the positive for the 24V and the other PSU the negative

NEVER, I repeat NEVEr isolate the 220V from ground. Although I am not an electrician I know that it can be your end of your life...what I did: I isolated the board from the case by releasing the two screws nearest the output only. That's all and my PSUs are running fine.

@Pit thanks for your information.You are absolutely right about isolating ground from the 220v.
i knew that we had to isolate a ground from a PSU but i thought it was the 220V ground.
so for moding PSU for 24v we have to isolate DC ground from the case not the 220V ground.
searched a bit and found this

from here

So was the power supply shutting down when connected to the driver or just the driver? Just for more info and in-case I ever have to go down this route, hooked up two 200w 12VDC motors in series (to simulate 24V motor) with my two 12Vdc power supplies (24V) and the two motors and PWR supplies worked fine.