Starting a farm with OptiPlex computers possible?

[MinimumJargon]

I have a mix of 20 OptiPlex 7020 and 9020 PCs and I was wondering if I could start a mining farm by adding a GPU and supporting them with a separate PSU.

The CPUs in them are i5 (4th Gen) 4570or4590 / 3.2 GHz/3.3 GHz and 1 16xPCIexpress slot.
The power supply is only 255w so I was thinking of powering 3 or 4 cards independently with an 850w gold PSU I have to start.

I was thinking this might be I cheaper way to start mining Altcoins as my only initial cost would be for the graphics cards,
but I'm unsure how these would compare to built rigs and if it would even be semi-profitable.


Any input would be appreciated.
Thanks

[Suslived]

It would be optimal to run denser mining rigs with less CPUs with more GPUs.

If you have a single GPU for each computer then the profits of your single GPU would be eaten up by the cost of running your CPU, motherboard, HDD/SSD, fans, etc. This is why people have 8 GPUs or more on a single motherboard (to maximize power efficiency and profits).

Might not be such a good time to buy GPUs though. Do your research first.

[joblo]

Sure but replace the old PSUs instead of adding a second one.

[MajMongoose]

seems like a lot of work - 

I have 2 - 9020's that I use for testing software/hardware updates or changes, before i move it to my H110 BTC+.

Trying to wrangle 20 of them would be a bit much, but as long as you have room and cheap electricity, why not.

[edwardceng]

yeah, possible as long as your PC has PCI-ex1/x16 slot and if want to combine two PSU you can use add2Psu or use jumper technique with a paperclip