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It is a gold rated PRO1050w XFX Black Edition http://www.amazon.com/gp/product/B0066AH46G/ref=oh_details_o04_s00_i00?ie=UTF8&psc=1

Sapphire Radeon HD http://www.newegg.com/Product/Product.aspx?Item=N82E16814202030

Other than that, just a hard drive and case fans.

I wouldn't try to go beyond 3 cards with 1050w, wouldn't be stable.
4 cards would mean pushing the PSU to a level of load which would only result in failure.
Also, PSU's tend to get less efficient as they age.

3 cards it is!

i have free electricity and was hoping a bunch of people would sell their mining rigs but I guess interest in minning is higher than ever...

So 3 7950s on 1050w, what about 4 on a 1200w (gold rated)?

Or would that be pushing it...

3 cards. You may be able to get away with 4 cards if you under volt - get a electricity energy meter plug and check how much 3 cards consume when you under volt and make sure to take measurements when your box is at full load.

Railgun.

7950s draw 200w, absolute maximum. If we're talking real power (Gold rated PSUs), then 1000w is more than enough for 3 cards. If you're using a budget or low power CPU (like Intel S and T processors) then you should be able to power 4 cards with a bit left over. I recommend the i5-3470T - at 35 watts you could easily run 4x 200w video cards.

Have to call you on that, the 7950 under bitmining (BTC) load is around 175w on a reference card, and 186-188w on a weak factory OC to 900mhz (see charts here for evidence: http://www.tomshardware.com/reviews/radeon-hd-7950-review-benchmark,3207-9.html ). With significant overclocking, they can easily get close to the 7970's 250w TDP.

While it is quite possible to stay under 200w, if you are going for the most hash's, it is far from being an absolute maximum.

Also, I have heard in multiple places that LTC has a slightly higher power usage, but that could be hearsay, I have not borrowed my friends kill-a-watt to test my computer under BTC vs LTC mining. I will be borrowing it soon though (or relatively soon, as I live in rural Alaska, and he is almost 100 miles away) to test it.

Edit: 1000 quality watts should be fine for 3 cards easy, I wasn't trying to contest that evaluation. Just trying to point out that it can be a significant load.

simple
3 on 1050w
4 on 1200w

better to be safe than sorry and your PSUs will last longer if you dont max them out

Not one of the tests in the charts you link show power usage above 200w for the 7950. If you were overclocking to the point where you're using close to 250w per card - you've got way bigger problems than an undervolting power supply.

I built 2 rigs yesterday with 3 hd7950s each (same ones as OP listed) on 860w seasonic platinum and they are running just fine overclocked and mining 1750KH/s LTC. I used sempron 45w CPUs.

A rig with four  7970 that are overclocked by 100mhz will draw 1130 watts at the wall.

Each PCIE connector will draw between 10 and 12 amps at 12v.

Also the nearer to the limit of the PSU the less efficient it is - a cheap PSU will suck over an amp just for itself  near full load.

Go big on the PSU

I'm nowhere near an expert on all this (just started researching and building about a month ago), but I've got a 3-card 7950 rig on an 850 gold power supply. With the current Afterburner settings, it's running under 770 watts. (The processor should be about 65 watts of the total) I've attached pics for reference.

Side note: The reason I've got the "power limit %" on +9 is because it smooths out the GPU usage. For some reason, the Sapphire Radeon HD 7950s seem to jump all over the place at stock "0", and are stable at +9.

http://i1302.photobucket.com/albums/ag124/joephoto221/msi-shot_zpsdf6525ef.jpg (http://s1302.photobucket.com/user/joephoto221/media/msi-shot_zpsdf6525ef.jpg.html)

http://i1302.photobucket.com/albums/ag124/joephoto221/rig3_zps6b767996.jpg (http://s1302.photobucket.com/user/joephoto221/media/rig3_zps6b767996.jpg.html)

http://i1302.photobucket.com/albums/ag124/joephoto221/2bdb8519-a227-40b7-ab0f-60aac7fd5165_zps4cbc7a15.jpg (http://s1302.photobucket.com/user/joephoto221/media/2bdb8519-a227-40b7-ab0f-60aac7fd5165_zps4cbc7a15.jpg.html)

Nice case lol.

Yeah they ain't pretty, but they're cheap, easy and keep the temps down. Just ordered four more. ($13 for two at Walmart)

EDIT: The Walmart collapsible crates are a little smaller...damn!

@JoeRigs  How are you getting 560-570 out of a 7950? 

Best i can do is ~525 

What cards are you using? Also, are you using Afterburner to tweak them?

I used two gigabyte hd 7950s in my first rig and they both got 600 out of the box. Unfortunately, those cards are "voltage locked" and were harder to keep cool. So, I went with the Sapphire cards on the second rig...with some tweaking (shown in the Afterburner screenshot)  I was able to get them up to where they are now. (I'm sure there is still room for improvement, but I'm OK with their current numbers.)

Well, 3x7970 @ 1100 clock pulling +-870 watts from the socket, no undervoltage, sempron CPU and no HDD.
Using Corsair tx850 v2 PSU, so basically it's overloaded. This is one of the oldest 79** rigs, running for >12 months stable  :)
So, depends on PSU quality. I would probably burn 4x7950 on your 1050Wt PSU

I bought a AX1200i as it has the on board data logging.

The AX1200i indicates that the load of 4 slightly overclocked Sapphire 7970 is over 1250 Watts

The biggest difference to how much load they pull is down to temp of the cards.

When they get to 80 degrees the load increase quite significantly. This is partly down to the fans running at max speed but also due to electrical resistance as the cards heat up.

A good quality Digital PSU will run above its stated max with no problems and it will still be 96% efficient

Wow that is a lot of cards. Good luck

Now that's a cool case.. guess stacking a few riggs is the next thing right? ;)

id say up to 5,

i have a corsair AX750 with the following setup:
gigbyte ud5h mobo
intel i7 3770k cpu
1x 5970 - both cores at 830mhz
1x 5870 - currently at 901mhz
1x 7970 - at 1125mhz

been running stable for the last ~month also have 5 hard drives in the machine always on. i am able to game and mine with the 5870 perfectly aswell. seems perfectly stable so far, in the process of looking for a watt meter in my silly excuse for a country

3.
4 if you get under volt specific 7950's

Nooooo ... you are wrong.

7950 hogs way more than 200w max.

how many watts per card would I need to mine x11

3 cards for Scrypt, Scrypt-N, four cards of X11, X13

I love how we're giving answers to an OP who has not been on for 3 months  :D

For those newbies interested in mining a 7950 can be undervolted and would typically run just over 200W, so you could run 4 comfortably with scrypt.  The more energy efficient coins are even better.

One thing to consider though, every 10C of ambient air temp will pull another 10% of power form the card.  If you're running them in summer the resistance from heat and increased fan usage causes more power draw.  Hence winter rocks!

mine x11, x13 coins you can use as many cards as you can plug to it then.

are you selling any 7950 ? if so let me know.. thnkx ..