Delta DPS-750PB A Over Voltage Protection Disable

Thread Starter

Shuriken

Joined Jan 14, 2022
4
Hello everyone,
I have bought a delta DPS-750PB A that has a DC-2736 board and i am trying to disable OVP as i am trying to get 14v with a 1k ohm resistor. I was expecting for it to have the DC-2179 board that many people managed to disable the ovp but on this one i can't find any info. Any help would be appreciated. I have attached a photo with the daughter board.270061722_964079957820466_7419751475602205651_n.jpg270603537_670425850640162_7310042686851227424_n.jpg271184152_459910605691073_3597317358506251343_n.jpg
 

MisterBill2

Joined Jan 23, 2018
10,533
Years ago we had a problem in a DC motor tester that the switch mode 30 amp power supply would sht down whe trying to run the motor on 30 amps, because it would trip the OVP because the remote sensing was making the output exceed the trip point as the wire resistance drop was too much. The cure was to get a higher voltage supply that had a higher OVP setting and adjust the output voltage to what we needed.
In this instance , defeating the OVP instead of just adjusting it a bit seems like a poor choice. If the circuit is available then we can suggest a re-calibration means.
 

Thread Starter

Shuriken

Joined Jan 14, 2022
4
This Delta DPS is a power supply from a PC server and from what i read, defeating the ovp is the best choice since the adjustment pot range on it is very small and won't reach 14v. I am trying to transform it into a short use car battery charger. I have been able to do so with another type of board and since i can't find anything online for the current board i am hoping someone more knowledgeable can help me.
 

MisterBill2

Joined Jan 23, 2018
10,533
You may be able to trace the circuit adjacent to the voltage adjustment pot and change the range setting resistors. Or are you able to adjust the voltage but the OVP trips before the voltage is high enough.?
 

Thread Starter

Shuriken

Joined Jan 14, 2022
4
When fiddling with the adjustment pot the change is very small from like 12.2v to 12.5v. When i add an 1k ohm resistor the voltage is around 14v but the ovp trips immediately. On the other board i shorted to ground a small resistor for the ovp thus disabling it and i am able to change the voltage with the pot from 13.8-14.2v.
 

MisterBill2

Joined Jan 23, 2018
10,533
OK, now here is a guess, based on the clue of your shorting to ground a small resistor: That resistor could have been the sense input for the OVP circuit. So now get your good magnifier and examine the package that you have, looking for a small, low-wattage, resistor connected to the output positive. One side of that resistor is tied to the output, the other side will feed the OVP circuit. If you can measure that resistor, find the resistance and tie a similar value resistor from the side of that one which is not connected to the output, to the negative output. That will raise the OVP setting quite a bit. So then try setting the voltage.
 

MisterBill2

Joined Jan 23, 2018
10,533
That board in the photo clearly contains a lot more than just the OVP circuits. The empty position marked "VR553" might be intended for an OVP setting adjustment, and may have been replaced by a single chip resistor, possibly. But t might also be for an adjustable current limit function. It looks like the two holes are in parallel with the chip resistor immediately below them. If that is the case, then measure the resistance and ad a parallel resistor to reduce the resistance a small amount, and check to see if that changed the OVP trip point. If it does, then you have found the adjustment point to raise the OVP trigger a bit, far better than disabling it completely.
 
That board in the photo clearly contains a lot more than just the OVP circuits. The empty position marked "VR553" might be intended for an OVP setting adjustment, and may have been replaced by a single chip resistor, possibly. But t might also be for an adjustable current limit function. It looks like the two holes are in parallel with the chip resistor immediately below them. If that is the case, then measure the resistance and ad a parallel resistor to reduce the resistance a small amount, and check to see if that changed the OVP trip point. If it does, then you have found the adjustment point to raise the OVP trigger a bit, far better than disabling it completely.
Thanks for your invaluable help, I'll try
 
Did the trip point voltage change with the resistor added? That was the purpose of the test, to see if that was the OVP set-point resistor. If it is, then the set-point for the OVP trip can be moved I was not intending to disable it.
Yes, I measured it always remains at: 12.44 V.
But the fans accelerate the speed ... does this mean that the current increases?
 
Very interesting indeed! The OVP trip point did not change but the fans run faster. Is there a separate output for the fans? Are they 5 volt fans or 12 volt fans? Are you able to measure the fan voltage?It might be a current limit adjustment, in which case we should leave it alone.
So now the search returns to seeking the OVP sense resistor connected to the output.
 
OK, so guess #1 did not work out as well as I hoped. It was a guess, not a declaration.
I also see two white connectors along the top edge of the board, one marked "CN702", can't see the tag on the other one. Those might be for programming the supply, as it looks like it has at least one processor IC. If it is digitally programmed then it is another game altogether.
 
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