Is it Safe to use 2 PSUs?

VarunJain

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I have a Nvidia Quadro FX 3700 and a under powered PSU(old) which currently powers my motherboard and other peripherals.
Is it safe to use a separate PSU(new) to power just the graphics card while the rest of the motherboard is powered by the same old PSU?
I had tried this set up and I switch on the new PSU first and then boot the PC which results into the graphics card being switched on before the motherboard gets any power but still, it worked.
So, is it safe to continue with this set up or is it necessary that all the components on the motherboard are fired up simultaneously?

Note: The old PSU does not have the required 6- pin PCIe power connector nor the required wattage and while the new PSU has both,
the 24-pin ATX on it is different in configuration (some pins of the 24 are blank).
 

VarunJain

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I have this PSU lying around and don't want to spend more on buying a single big PSU as I am hardly going to use the setup for even months.
 

Ra_V_en

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Not sure what you mean by safe... its not stupid as above reply would suggest, but its tricky.
Indeed using 2 power supplies is not usual configuration but I've seen some attempts.
It would be very practical to switch both units at the very same time... and its possible with some customizations of the power switching mechanism.
For this matter there is an electronic device called relay which can be used for such purpose. There are relays powered with 12 V or if its lover voltage model you just need to put inline resistor, so it is possible do do solution like this:
Connect relay power connectors with black and red wires from Molex of the PSU that is connected directly to MOBO and or the case. This one will be primary PSU which can be switched on typically by switch button.
Other 2 connectors from the relay can be attached to green and black wires (if I'm correct from ATX specification) of the other PSU mobo connector. If you short circuit black & green lines PSU turns on (I'm guessing you are doing it that way now anyways), which is exactly what relay does automatically while the current shows up on the input pins.



Btw I7Baby.. as for person with so many badges you are talking like someone for whom PC's is total magic.. especially this sarcastic sentence about insurance.
I've seen usage of multiple PSU's already ... and its far from being stupid as far as you know what you are doing.

Obviously you shouldn't connect devices which are internally connected to both PSU's as for example mobo to first and GPU to the second.
As far as voltage difference between black wire and red wire indeed is 12V within the same PSU, but from red of first PSU to black of second doesn't have to be like that. From the first lessons of the electronics you would know Voltage is difference of potentials... but indeed potentials can be different within both neutral (black) wires of those PSU's. On those first lessons you would also learn that puting 2 different power sources in parallel configuration is actually dangerous.

As far as you would use those 2 PSU's for totally different components... like fans back-lights... or maybe HDD's (I'm still concerned about SATA cable voltage) it would be fine... but if you consider summing up currents from both its NO CAN DO.
 

VarunJain

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Right now, I am just using the 6-pin PCIe from the new PSU and as soon as I plug in the PSU, it starts supplying power to the PCIe. Hence, right now, I am not short circuiting any connections.
 

Ra_V_en

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Read my updated response above... im feeling it will clear things up more.
BTw how do you switch on the second PSU as far as i know ATX has to be switched on from short circut of those wires or from switch connected to the mobo which does exactly the same?

If you really are using second one as for additional power for the GPU from 6pin you need to know that GPU is already powered from mobo by the PCIX slot which is connected to the first PSU if im correct. Its maybe working but indeed i would be worried about this card.
Just imagine situation 1 PSU breaks down and second is still on, GPU would be in not typical situation since normally if power is down then its down from all the sides.
I'm guessing GPU itself has protection for such issues (we know it does because you will get error screen if 6/8pins are not connected)
but in a critical situation that kind of instability would be unpredictable...

For this matter using relay is more safe cause if the main PSU dies the second would switch down automatically but unfortunately not other way around and thats the main reason i would not use such solution myself ;/

 

Ra_V_en

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Put Add2Psu into the google, it actually uses the solution I've said before 1 connector for molex to power up the relay, 1 connector for ATX24 to short circut the power on wires and 1 relay ;)
Indeed this solution is working... but read my posts I've sent before... it will probably work fine but I'm still concerned about general safety if one of them will break..... and it wont be the one which is controlling switching up the other.
 


^^+1

@VarunJain: Which are those PSU models?

@Ra_V_en: This is an international forum. And people from different countries have different quality standards. OP is probably from India and this is common in India. But for i7Baby, it ain't common since he's probably from some developed country
 

Ra_V_en

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I am aware of the global forum... being a citizen of highly industrialized country doesn't give you rights to talk nonsense tho... in fact I'd be expecting from such citizen to have adequate level of knowledge... they got there somehow right?

The main question is why does the author want to complicate all of this... its either no cash for proper solution or experimenting. If one of those then its acceptable attempt but author has to be aware of possible risks or cons.