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Author Topic: How to determine how much power needed for x4 7950's in one rig  (Read 1593 times)
gregyoung14
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April 22, 2013, 04:34:07 AM
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Hey guys, I'm looking to build my first experimental rig, I've analyzed all of the hash rates for all the ATI cards, the best bang for your buck, or most hashes per dollar, is looking like a 7950. Bringing in 600 Kh/s assuming its LTC mining and 10x if its BTC, regardless, I'm trying to have 4 of these in one rig. Which is totally due-able because plenty of motherboards support 4 pcie slots and windows 7/ubuntu won't have issues with it either. Now my question is, how on earth do I measure how much power is needed to run these babies. I know that they each hit about 355watts at peak power, which I presume if I'm mining 24/7 that they would be at peak power if not close. So is it right to assume that (355x4)=1420watts just for the 4 cards? Plus whatever power the cpu and motherboard needs? Which means I'd have to buy one hell of a powersupply. Or do I not actually need this much power? I read somewhere that when you do crossfire with ATI cards that the second one doesn't need as much power, or something along those lines. If someone can shed some light on this, that'd be awesome. If you have any suggestions to another card thats fine, I'd love to here it. Or any ideas in general.

Edit: Oh, idea. What if I bought x5 400 watt power supplies, like cheap $20 ones and used one for each card and one for the board?

Thanks
Greg
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April 22, 2013, 04:48:17 AM
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Get two nice 1000 watt power supplies.
gregyoung14
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April 22, 2013, 05:00:45 AM
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Get two nice 1000 watt power supplies.

Would each one power two cards and then one would also have to power the board? Theres no way I could get by with each card having its own 400w supply even if it was a decent one?
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April 22, 2013, 05:09:38 AM
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I would say one 7950 need about 220W. A sempron need 45W. The rest of the PC maybe 100W. So a 1200W PSU from a good brand should do it.

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April 22, 2013, 05:14:50 AM
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The 7950 has a Power (Max TDP) of 200 watts.  But you need to OC it to get that.  The Default TDP is 160 watts.  I'm running 4x7950 on an 850 watt Gold PSU.  I have no plans to OC those cards as I expect to make them available for resale in the future.  I don't want to burn them out.  If you want to give yourself some room then I would go with a 1000 watt PSU but anything more than that it overkill.
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April 22, 2013, 06:07:34 AM
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The 7950 has a Power (Max TDP) of 200 watts.  But you need to OC it to get that.  The Default TDP is 160 watts.  I'm running 4x7950 on an 850 watt Gold PSU.  I have no plans to OC those cards as I expect to make them available for resale in the future.  I don't want to burn them out.  If you want to give yourself some room then I would go with a 1000 watt PSU but anything more than that it overkill.


Is that Max TDP for this model of the 7950 "SAPPHIRE HD 7970 3GB GDDR5 (21197-00)" or for all of them in general? And I didn't plan to OC for the same reason as you, so if I could get by with an 850 gold PSU that'd be great. If you don't mind me asking what kind of hash rates do you get with that setup? I'm trying to get a ball park feel for how much I could mine a day/week/month with that setup. Also how much power does 850 watt PSU draw on your electric bill, is it just 850 watts an hour, 20.4kwh a day, and so like 612 kwh a month? Or is that not calculated correctly. My apartment doesn't have an electrical cap and utilities are included, but If I had 10 of these rigs sucking up 6,120 kwh a month I think they would have a problem lol.
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April 22, 2013, 10:22:23 PM
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Is that Max TDP for this model of the 7950 "SAPPHIRE HD 7970 3GB GDDR5 (21197-00)" or for all of them in general? And I didn't plan to OC for the same reason as you, so if I could get by with an 850 gold PSU that'd be great. If you don't mind me asking what kind of hash rates do you get with that setup? I'm trying to get a ball park feel for how much I could mine a day/week/month with that setup. Also how much power does 850 watt PSU draw on your electric bill, is it just 850 watts an hour, 20.4kwh a day, and so like 612 kwh a month? Or is that not calculated correctly. My apartment doesn't have an electrical cap and utilities are included, but If I had 10 of these rigs sucking up 6,120 kwh a month I think they would have a problem lol.

Max TDP should be for the 7950 model.  not specific to an one card.  But I can see where mileage may vary, it depends on quality of parts.  I'm mainly mining LTC and FC now.  I get about 2,250kH/s average running intensity -19 on cgminer per rig.

I orders a kill-a-watt meter off amazon so I can get a real idea of how much juice I'm pulling on these machines.  The machines probably draw about 700 to 800 watts each.  But you have to figure out how much your apartment can handle.  You might trip a breaker if you load up too many machines.  For example I cant run 3 machines in the same room.  The circuit is 15AMPs  so 15 * 120 volts is 1800 watts.  I can put two in the room but I do trip the breaker when I add the 3rd one.

I've been running these machines for about a week.  Still new to all this, and it was mostly tweaking the first few days.  So I haven't received the electric bill.  But an estimate of what it will cost me.  2400 watts or 2.4kW per hour.  at .10/kW  = $0.24/hr or $5.76 per day.  So I'm adding just under $200 a month. 

Also consider that the increased usage might alert the electric company and they might reprice your service.  That happens in some places.  If you are in an apartment it might not affect you much but if the landlord sees a big spike in his bill you might not have the free electricity option for long.
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April 22, 2013, 10:24:36 PM
 #8

get two 650W

cause the 1250w ones are not so cheap

You wan´t to mine bitcoins but dont have any Hardware?
https://bitcointalk.org/index.php?topic=183111.0
anderl
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April 22, 2013, 10:25:14 PM
 #9

I've been toying with the idea of buying 2 PCIx8 to PCIx16 converters for the additional slots I have on the motherboard and an additional 300w power supply for each rig.  Its about cost.  Not sure if it will be effective to get the PSUs and the adapters or just buying another rig instead.
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April 22, 2013, 10:26:21 PM
 #10

get two 650W

cause the 1250w ones are not so cheap

right.

newegg has RAIDMAX RX-850AE 850W ATX12V v2.3 / EPS12V SLI Certified CrossFire Ready 80 PLUS GOLD Certified Modular Active PFC
 for $109 each.
gregyoung14
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April 24, 2013, 09:03:38 PM
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Is that Max TDP for this model of the 7950 "SAPPHIRE HD 7970 3GB GDDR5 (21197-00)" or for all of them in general? And I didn't plan to OC for the same reason as you, so if I could get by with an 850 gold PSU that'd be great. If you don't mind me asking what kind of hash rates do you get with that setup? I'm trying to get a ball park feel for how much I could mine a day/week/month with that setup. Also how much power does 850 watt PSU draw on your electric bill, is it just 850 watts an hour, 20.4kwh a day, and so like 612 kwh a month? Or is that not calculated correctly. My apartment doesn't have an electrical cap and utilities are included, but If I had 10 of these rigs sucking up 6,120 kwh a month I think they would have a problem lol.

Max TDP should be for the 7950 model.  not specific to an one card.  But I can see where mileage may vary, it depends on quality of parts.  I'm mainly mining LTC and FC now.  I get about 2,250kH/s average running intensity -19 on cgminer per rig.

I orders a kill-a-watt meter off amazon so I can get a real idea of how much juice I'm pulling on these machines.  The machines probably draw about 700 to 800 watts each.  But you have to figure out how much your apartment can handle.  You might trip a breaker if you load up too many machines.  For example I cant run 3 machines in the same room.  The circuit is 15AMPs  so 15 * 120 volts is 1800 watts.  I can put two in the room but I do trip the breaker when I add the 3rd one.

I've been running these machines for about a week.  Still new to all this, and it was mostly tweaking the first few days.  So I haven't received the electric bill.  But an estimate of what it will cost me.  2400 watts or 2.4kW per hour.  at .10/kW  = $0.24/hr or $5.76 per day.  So I'm adding just under $200 a month. 

Also consider that the increased usage might alert the electric company and they might reprice your service.  That happens in some places.  If you are in an apartment it might not affect you much but if the landlord sees a big spike in his bill you might not have the free electricity option for long.

Very good info, I'm liking what I hear so far. I got my first two cards yesterday, two 7950's and popped them in. With my pre existing 650w corsair, that was a no go. It booted but only one card, and the drivers were crashing and the system was locking up horriably. So I took one card out, and problem solved. 850w psu gets here any minute now, its 80 gold certified so hopefully I can run at least 3 if not 4 with it. I ordered some pcie x1 to x16 extender cables so I'll aslo be testing to see if I can take advantage of the two x1 slots I have on top of the other two x16 slots.

As for the power thing, I live in a "huge" apartment complex that all shares power, like 1000 units. So I don't think coporate is going to see a spike in the bill from just me and convientantly enough summer is approaching in sunny florida and everyone is cranking the AC up so it should just blend right in with that. As for flipping a breaker, yeah theres a good chance that happens if all the machines are coming from the same room. Right now I'll only have a rig and a half but come a couple weeks from now I want to build 3-5 more with hopefully x5 or x6 a piece and If I can't power them in my place I have friends down the hall I could pay like $10/week to have plugged in and running in the corner of there room lol

I have another concern though, I'm having a hard time pulling high hash rates with my currenrtly running 7950, I can only pull about 380kh/s with auto settings, after some tweaking and very high fan speeds, like 100% and i 20 I was pulling high 500's but I was trying all sorts of different setups from what people had recomended for 7950's and couldnt get stable high hash rate and a high U and MU I think it is? I was pooling with wemineltc and my hash rate was like 450 but my to U rates were 0? and the site was showing that I was only pulling like 20kh/s so I don't know whats up with that.

Can anyone recommend a good profile for a 7950 and a good pooling service to go with it? Im in the US so I know some sites offer US servers and that tends to help a little.

Any recommendations and input is highly appreciated!  Smiley
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April 24, 2013, 09:27:47 PM
 #12

I have 2 rigs, each running 4 Sapphire 7950s. Each machine has one 950w power supply, and I have had zero problems. Here is the supply I'm using...
http://www.newegg.com/Product/Product.aspx?Item=N82E16817703028
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April 24, 2013, 09:57:58 PM
 #13

How are people measuring the power consumption of their graphics cards?  Is there an application or is it a hardware solution?

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April 25, 2013, 01:54:23 PM
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Quote
I ordered some pcie x1 to x16 extender cables so I'll aslo be testing to see if I can take advantage of the two x1 slots I have on top of the other two x16 slots.

if it doesn't work (cgminer reports the card SICK/DEAD) you need to short the PCI slot.  There is a thread on the forum somewhere.

Quote
I'm having a hard time pulling high hash rates with my currently running 7950

What is the make and mode of the card? 

This is what I used to use when it was just 3 cards...
C:\guiminer-scrypt\cgminer\cgminer --scrypt -o YOURPOOLURL -u USERNAME -p PASSWORD -I 20 -w 256 --lookup-gap 2 --thread-concurrency 21712 -g 1 --auto-fan --auto-gpu --temp-target 75

I added  --gpu-vddc YOURVOLTAGE(1.0) and tweaked it and -I (20) until I could get all 4 cards running stable.

Quote
How are people measuring the power consumption of their graphics cards?  Is there an application or is it a hardware solution?

Kill-a-watt meter.  $20 and you can get it at newegg or amazon.
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April 26, 2013, 06:42:45 PM
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The system with 4 Gigabyte HD7950 @1100MHz is 'eating' about 5A from 220V wall outlet or 1100Watt
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