Why your 12-volt video card won't run.
Last response: in Graphics & Displays
You say you have bad drivers, a crummy card, and crappy games? I’ll bet you may have a bad power supply.
With that new 12-volt plug video card addition does your computer:
Garble boot screen text?
Lock up with greater than 64meg-memory aperture setting?
Not hold an FSB or AGP/PCI overclock after you add a your new video card or add another component shortly after?
Have 12.0-volt and 3.3-voltage rails that have funny looking voltage dropouts with your PC-probe program running?
Freeze for “no” reason playing games?
The power supply companies are lethargic in addressing the needs of the enthusiast’s market As a result we have a grim situation on our hands. To understand the transition that has taken place with 12-volt video cards and power supplies, you have to dig into a little history.
The early Intel and AMD 486 type CPUs rode on the 5.0-volt rail. Later CPU’s moved to the 3.3-volt rail. But power supplies stopped their development after adding the 3.3-volt rail to the already existing 5.0-volt and 12.0-volt rails. So what, you say? So far…so what it is until the arrival of P4 and Barton CPUs. We have the same power supplies, and voltage rails as the PIII and AMD thunderbird CPU days. Your power supply is “P4” ready? We call out power supply P4 ready only because we throw a 4-pin plug on the 12-volt cord set and expect a 3.3-volt AGP video card power solution. Think 430 watts is enough? The manufacturers say so don’t they?
A modern desktop PC is riding the 12.0-volt rail like never before. The 5.0-volt rail, built for earlier system, is hugely out of spec based on today’s needs. A power supply is rated for “shared” service yet they spec the rails for independent service. A 430-watt supply seems to be able to supply over 700watts if you add the power advertised by each voltage rail. Clearly then, we have a problem. Put a 9800pro, P4 CPU, and dual RAID SATA 10,000 hard drives on the 12-volt bus and we’re in trouble. A “power user” system is really a dual CPU system as far as the power supply is concerned. To run efficiently, you should load a power supply to no mote than 60%-70% of the rated rail current. So even in a system with NO dual drive RAID array, were perilously close to power rail instability. Add in heat, and cheap power supplies with high internal resistance windings may do OK at 25C, but will sag when the internal resistance drop kicks in. As much as 50% of the power can be lost at 45-50C. You PC is no where near 25C inside the power supply. A 35C-40C number is more accurate. I’ve measure 120F air exiting the back of my power supply. The 12-volt rail collapse will pull down the other two rails as well. The next to go is you 3.3 volt rail, the one that runs your CPU! While the silly Old World 5-volt rail runs your “silent” fans as happy as a clam. All told, you’ll see about 70% (430 watts) of the single rail wattage total (600+ watts) in reality. So don’t forget to factor that in. My 3.3-volt rail is probably at or near collapse, too. Do the math and you’ll see I’m pulling 71 watts with only a 27.45 watt (8.3amp) margin. All channels have to be no more than 430 watts, total.
430-(21.8 * 12) – (14 * 5) = 98.4 watts remaining for the 3.3volt rail or 29.8 amps. I’m pulling about 21.5amps, which is over the 60% of maximum of 17.8 amps (0.6 (98.4watts/3.3volts)) remaining.
Does it show? You bet it does. My voltage rails are dead flat until the games or benchmarks start. Then, the 12 and 3.3-volt rails show marked voltage dropouts while the 5-volt rail run merrily along smooth as glass. Why? My over current situation is at 25C! I don’t even have this much power at 40C. That’s why the 60% factor is in the suggested load factor ratings.
The change to the ATX Power Cool will work.
510watts-(21.8*12)-(14*5) = 178.4watts for the 3.3 volt rail (54 theoretical amps). I’ll get the full rated 30 amps needed then, and at about the right load factor of about 72%. Make it better than 72%? Yes if a supply existed. But no good supplies are out there with the guts to do the job except PC Power and Cooling’s offering in my situation.
Have you ever added it up? I didn’t think so. Let’s do it. I didn’t add it up when I bought my Enermax EG 465P-VE supply, either, by the way. Now I’ve ordered a PC Power and Cooling ATX510 turbo-Cool.
Here is a typical system (mine).
SUPPLY VOLTAGE.....................................................................(3.3V).(5.0V).(12.0V)
Component........................Requirement.........Line(s) Used...................WATTS
AGP Video Card..................30 – 50W.............+3.3V or +12V...........X.....X.....70...............9800pro
Average PCI Card................5 – 10W..............+5V.........................X.....20.....X...............56K US Robotics
10/100 NIC.......................4W......................+3.3V.......................4.....X.....X................Onboard 10/100 Ethernet
SCSI Controller PCI Card......20W....................+3.3V and +5V..........10....10......X................Adaptec AHA-2940
Floppy Drive......................5W......................+5V.........................X.....5......X...............1.44MB TEAC
CD-ROM...........................10 – 25W.............+5V and +12V.............X.....10....10...............SCSI PX32-TS
DVD-ROM.........................10 –25W .............+5V and +12V.............X.....X.....X...............N/A
CD-RW............................10 – 25W.............+5V and +12V.............X.....X.....X...............N/A
7200rpm IDE Hard Drive.......5 – 20W..............+5V and +12V.............X.....5.....15...............Western Digital 800JB
10,000rpm SCSI Drive.........10 – 40W..............+5V and +12V............X.....10....70...............Cheetah 4.5GB / 9.1GB
Case/CPU Fans....................3W (ea.)............+12V.........................X.....X.....27...............7- 80MM fans
M.board (w/o CPU or RAM)...25 – 40W.............+3.3V and +5V............25....10....X...............ASUS P4PE
RAM.................................8W per 128MB.......+3.3V.......................32.....X.....X............... 512MB
Pentium III Processor..........38W....................+5V..........................X......X.....X...............N/A
Pentium 4 Processor...........70W.....................+12V.........................X.....X.....70...............2.4MHz Intel
AMD Athlon Processor.........70W.....................+12V.........................X.....X.....X...............N/A
TOTAL WATTS............................................................................71.....70.....262
TOTAL AMPS...............................................................................21.5....14....21.8
ENERMAX EG465P-VE LIMITS..........................................................38A.....44A...20A
ANTEC True Power 550..................................................................32A.....40A...24A
Cool Power Turbo 510 LIMITS.........................................................30A.....40A....34A
The 510 Cool Power is nothing but a server supply with an ATX wiring harness. Fine, because the 12-volt rail on a HUGE number of desktop PC systems look like server 12-volt amperage loads (two CPU’s per say, one GPU / VPU and one CPU). ANTEC has admitted to me that they are out of step with the current crop of simultaneous RAID / P4 / 9800pro or F5800 series card systems out there. And, most low spec power supplies fail when the heat is on. Don’t believe the 300watt rhetoric from ATI or NVIDIA. It will more than likely result in a bad power supply buying decision. Tom’s guide on power supplies? Well, good power verses power in the right place is what he fails to address. The 12-volt buss is woefully inadequate on a modern PC. Even with a standard HD, your still over the 70% load recommendation on the 20amp rated 12-volt rail (16amps are 2 amps over the 14amp suggestion for stability). And because high current causes heat which in turn causes internal voltage drop across the supply your lucky if your 50% efficient where my Enermax is running right now. It gets HOT! The Enermax doesn't have the power where I need it. A “real” 50C rated supply is what you need. The heavy transformer windings won’t drop so much voltage across the supply providing more current at the output end.
What will happen? Server power supplies will eventually be dropped down to the desktop PC space with 30-36amps of 12-volt rail current. That’s all PC Power and Cooling has done, added ATX capability to a good server supply at heart. We could also ask power supply companies to add three digit (XX.X) amp meters to their supplies with a voltage rail switch. A quick run through the voltages would tell you what’s really going on and at what temperatures.
Notice I don’t even have and DVD-ROMs and -RW and/ or + RW drives, either, both 12-volt devices.
Before we cut down a manufacturer’s product(s) we have to be certain the problem isn’t of your own making. With most 12-volt video cards, it is! In God we trust, all else bring data!
Regards,
rower30@earthlink.net
With that new 12-volt plug video card addition does your computer:
Garble boot screen text?
Lock up with greater than 64meg-memory aperture setting?
Not hold an FSB or AGP/PCI overclock after you add a your new video card or add another component shortly after?
Have 12.0-volt and 3.3-voltage rails that have funny looking voltage dropouts with your PC-probe program running?
Freeze for “no” reason playing games?
The power supply companies are lethargic in addressing the needs of the enthusiast’s market As a result we have a grim situation on our hands. To understand the transition that has taken place with 12-volt video cards and power supplies, you have to dig into a little history.
The early Intel and AMD 486 type CPUs rode on the 5.0-volt rail. Later CPU’s moved to the 3.3-volt rail. But power supplies stopped their development after adding the 3.3-volt rail to the already existing 5.0-volt and 12.0-volt rails. So what, you say? So far…so what it is until the arrival of P4 and Barton CPUs. We have the same power supplies, and voltage rails as the PIII and AMD thunderbird CPU days. Your power supply is “P4” ready? We call out power supply P4 ready only because we throw a 4-pin plug on the 12-volt cord set and expect a 3.3-volt AGP video card power solution. Think 430 watts is enough? The manufacturers say so don’t they?
A modern desktop PC is riding the 12.0-volt rail like never before. The 5.0-volt rail, built for earlier system, is hugely out of spec based on today’s needs. A power supply is rated for “shared” service yet they spec the rails for independent service. A 430-watt supply seems to be able to supply over 700watts if you add the power advertised by each voltage rail. Clearly then, we have a problem. Put a 9800pro, P4 CPU, and dual RAID SATA 10,000 hard drives on the 12-volt bus and we’re in trouble. A “power user” system is really a dual CPU system as far as the power supply is concerned. To run efficiently, you should load a power supply to no mote than 60%-70% of the rated rail current. So even in a system with NO dual drive RAID array, were perilously close to power rail instability. Add in heat, and cheap power supplies with high internal resistance windings may do OK at 25C, but will sag when the internal resistance drop kicks in. As much as 50% of the power can be lost at 45-50C. You PC is no where near 25C inside the power supply. A 35C-40C number is more accurate. I’ve measure 120F air exiting the back of my power supply. The 12-volt rail collapse will pull down the other two rails as well. The next to go is you 3.3 volt rail, the one that runs your CPU! While the silly Old World 5-volt rail runs your “silent” fans as happy as a clam. All told, you’ll see about 70% (430 watts) of the single rail wattage total (600+ watts) in reality. So don’t forget to factor that in. My 3.3-volt rail is probably at or near collapse, too. Do the math and you’ll see I’m pulling 71 watts with only a 27.45 watt (8.3amp) margin. All channels have to be no more than 430 watts, total.
430-(21.8 * 12) – (14 * 5) = 98.4 watts remaining for the 3.3volt rail or 29.8 amps. I’m pulling about 21.5amps, which is over the 60% of maximum of 17.8 amps (0.6 (98.4watts/3.3volts)) remaining.
Does it show? You bet it does. My voltage rails are dead flat until the games or benchmarks start. Then, the 12 and 3.3-volt rails show marked voltage dropouts while the 5-volt rail run merrily along smooth as glass. Why? My over current situation is at 25C! I don’t even have this much power at 40C. That’s why the 60% factor is in the suggested load factor ratings.
The change to the ATX Power Cool will work.
510watts-(21.8*12)-(14*5) = 178.4watts for the 3.3 volt rail (54 theoretical amps). I’ll get the full rated 30 amps needed then, and at about the right load factor of about 72%. Make it better than 72%? Yes if a supply existed. But no good supplies are out there with the guts to do the job except PC Power and Cooling’s offering in my situation.
Have you ever added it up? I didn’t think so. Let’s do it. I didn’t add it up when I bought my Enermax EG 465P-VE supply, either, by the way. Now I’ve ordered a PC Power and Cooling ATX510 turbo-Cool.
Here is a typical system (mine).
SUPPLY VOLTAGE.....................................................................(3.3V).(5.0V).(12.0V)
Component........................Requirement.........Line(s) Used...................WATTS
AGP Video Card..................30 – 50W.............+3.3V or +12V...........X.....X.....70...............9800pro
Average PCI Card................5 – 10W..............+5V.........................X.....20.....X...............56K US Robotics
10/100 NIC.......................4W......................+3.3V.......................4.....X.....X................Onboard 10/100 Ethernet
SCSI Controller PCI Card......20W....................+3.3V and +5V..........10....10......X................Adaptec AHA-2940
Floppy Drive......................5W......................+5V.........................X.....5......X...............1.44MB TEAC
CD-ROM...........................10 – 25W.............+5V and +12V.............X.....10....10...............SCSI PX32-TS
DVD-ROM.........................10 –25W .............+5V and +12V.............X.....X.....X...............N/A
CD-RW............................10 – 25W.............+5V and +12V.............X.....X.....X...............N/A
7200rpm IDE Hard Drive.......5 – 20W..............+5V and +12V.............X.....5.....15...............Western Digital 800JB
10,000rpm SCSI Drive.........10 – 40W..............+5V and +12V............X.....10....70...............Cheetah 4.5GB / 9.1GB
Case/CPU Fans....................3W (ea.)............+12V.........................X.....X.....27...............7- 80MM fans
M.board (w/o CPU or RAM)...25 – 40W.............+3.3V and +5V............25....10....X...............ASUS P4PE
RAM.................................8W per 128MB.......+3.3V.......................32.....X.....X............... 512MB
Pentium III Processor..........38W....................+5V..........................X......X.....X...............N/A
Pentium 4 Processor...........70W.....................+12V.........................X.....X.....70...............2.4MHz Intel
AMD Athlon Processor.........70W.....................+12V.........................X.....X.....X...............N/A
TOTAL WATTS............................................................................71.....70.....262
TOTAL AMPS...............................................................................21.5....14....21.8
ENERMAX EG465P-VE LIMITS..........................................................38A.....44A...20A
ANTEC True Power 550..................................................................32A.....40A...24A
Cool Power Turbo 510 LIMITS.........................................................30A.....40A....34A
The 510 Cool Power is nothing but a server supply with an ATX wiring harness. Fine, because the 12-volt rail on a HUGE number of desktop PC systems look like server 12-volt amperage loads (two CPU’s per say, one GPU / VPU and one CPU). ANTEC has admitted to me that they are out of step with the current crop of simultaneous RAID / P4 / 9800pro or F5800 series card systems out there. And, most low spec power supplies fail when the heat is on. Don’t believe the 300watt rhetoric from ATI or NVIDIA. It will more than likely result in a bad power supply buying decision. Tom’s guide on power supplies? Well, good power verses power in the right place is what he fails to address. The 12-volt buss is woefully inadequate on a modern PC. Even with a standard HD, your still over the 70% load recommendation on the 20amp rated 12-volt rail (16amps are 2 amps over the 14amp suggestion for stability). And because high current causes heat which in turn causes internal voltage drop across the supply your lucky if your 50% efficient where my Enermax is running right now. It gets HOT! The Enermax doesn't have the power where I need it. A “real” 50C rated supply is what you need. The heavy transformer windings won’t drop so much voltage across the supply providing more current at the output end.
What will happen? Server power supplies will eventually be dropped down to the desktop PC space with 30-36amps of 12-volt rail current. That’s all PC Power and Cooling has done, added ATX capability to a good server supply at heart. We could also ask power supply companies to add three digit (XX.X) amp meters to their supplies with a voltage rail switch. A quick run through the voltages would tell you what’s really going on and at what temperatures.
Notice I don’t even have and DVD-ROMs and -RW and/ or + RW drives, either, both 12-volt devices.
Before we cut down a manufacturer’s product(s) we have to be certain the problem isn’t of your own making. With most 12-volt video cards, it is! In God we trust, all else bring data!
Regards,
rower30@earthlink.net
More about : volt video card run
With so much load being displaced from the 5v rail to the 12v rail, why don't video card companies use a 5v connection instead of a 12v connection? The voltage is being stepped down before use anyway, well bellow 5v!
Yes, I know watts and current, 5v would require higher amperage, but would it be so high as to fry a 5v wire from the molex connector to the power supply?
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Yes, I know watts and current, 5v would require higher amperage, but would it be so high as to fry a 5v wire from the molex connector to the power supply?
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<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>
I apologize for the screwed-up chart. This is one of the harder Email edit programs around. Do the columns look as bad to you as it does to me? They were all lined up in the edit mode.
Funny, a post that can really help people out is all but ignore while a simply post on a memory question can collect over 127 threads. Go figure.
The question was why not use the 5-volt rail.
1.0 Probably could if the current stayed below 40amps. Remember, the insulation on available wires have a 60C to 105C rating but the cost of the wire is much higher at 105C. The supply companies are really stingy and won't budge unless they are forced to on cost.
2.0 Here is the next problem (like you said);
40 amps into 5V is 200watt of power
40 amps into 12 volts is 480watts.
So you move over twice the power with the same current at 12volts. This is why Auto power is going to higher voltage (48 volts). The wire can easily stand the voltage breakdown, but not the current unless you use 105C insulation.
3.0 Insulation temperature rise at over 40amps would be unaccceptable to the consumer. I forgot my little cheat chart to tell you the degree C rise with AWG, or I would. This is readily available from a good wire company (Belden) So to get as much power as you can, and keep wire cost low, higer voltages are better.
4.0 105C wire is not very flexible since it has low plastisizer content to avoid driving off the light molecular weight oils when things get toasty. This keeps the tensile and elongation characteristics over the UL 60% aged test limits for internal component wiring.
5.0 Two independant 12-volt rails would be much more efficient. Many Server supplies already split the load into two, keeping the status quo intact.
I guess my beef is that too many people don't want to work with the facts, or find them out. If I weed out name calling and guessing, these posts are really thin on information.
It too bad, because most people's problems are emotional ties to X<Y<Z mostly based on dumb luck that those components happen to work. If you dable in high end components, you better make sure you understand all the requirements. And go use the information before condeming someone's product.
OK, the Sapphire at least runs with my too small Enermax supply compared to the PowerColor, but most likely with the PC Power& Cooling, Inc Turbo-Cool 510 ATX-PFC, both would have run just fine.
One last thing, A server power supply that yield 30+ amps on the 12volt rail can be converted to a standard ATX or AMD power plug with a converter. So, if the 510ATX-PFC is too salty, and you need more power but not that much, an ANTEC, Sparkle and/or Enermax server supply can work. The Enermax does come with the converter cords. Enermax is a little up to date and also offers the same 36amp server supply with an ATX harness. ANTEC does not, so go fish for the converter cords.
Be careful, though. Enermax is at least honest and shows that the power drops to ZERO with a 70C temperature with losses all along the way. So be sure to use the 60% ambient load factor on these supplies. The 45C rated PC Power & Cooling supply still requires you to manage your supply rail voltage load splits, though.
Sorry if this post is too technical, but the truth hurts, and it hurts us all equally just as it helps us all, too. Name calling need not apply to a good factual post.
Funny, a post that can really help people out is all but ignore while a simply post on a memory question can collect over 127 threads. Go figure.
The question was why not use the 5-volt rail.
1.0 Probably could if the current stayed below 40amps. Remember, the insulation on available wires have a 60C to 105C rating but the cost of the wire is much higher at 105C. The supply companies are really stingy and won't budge unless they are forced to on cost.
2.0 Here is the next problem (like you said);
40 amps into 5V is 200watt of power
40 amps into 12 volts is 480watts.
So you move over twice the power with the same current at 12volts. This is why Auto power is going to higher voltage (48 volts). The wire can easily stand the voltage breakdown, but not the current unless you use 105C insulation.
3.0 Insulation temperature rise at over 40amps would be unaccceptable to the consumer. I forgot my little cheat chart to tell you the degree C rise with AWG, or I would. This is readily available from a good wire company (Belden) So to get as much power as you can, and keep wire cost low, higer voltages are better.
4.0 105C wire is not very flexible since it has low plastisizer content to avoid driving off the light molecular weight oils when things get toasty. This keeps the tensile and elongation characteristics over the UL 60% aged test limits for internal component wiring.
5.0 Two independant 12-volt rails would be much more efficient. Many Server supplies already split the load into two, keeping the status quo intact.
I guess my beef is that too many people don't want to work with the facts, or find them out. If I weed out name calling and guessing, these posts are really thin on information.
It too bad, because most people's problems are emotional ties to X<Y<Z mostly based on dumb luck that those components happen to work. If you dable in high end components, you better make sure you understand all the requirements. And go use the information before condeming someone's product.
OK, the Sapphire at least runs with my too small Enermax supply compared to the PowerColor, but most likely with the PC Power& Cooling, Inc Turbo-Cool 510 ATX-PFC, both would have run just fine.
One last thing, A server power supply that yield 30+ amps on the 12volt rail can be converted to a standard ATX or AMD power plug with a converter. So, if the 510ATX-PFC is too salty, and you need more power but not that much, an ANTEC, Sparkle and/or Enermax server supply can work. The Enermax does come with the converter cords. Enermax is a little up to date and also offers the same 36amp server supply with an ATX harness. ANTEC does not, so go fish for the converter cords.
Be careful, though. Enermax is at least honest and shows that the power drops to ZERO with a 70C temperature with losses all along the way. So be sure to use the 60% ambient load factor on these supplies. The 45C rated PC Power & Cooling supply still requires you to manage your supply rail voltage load splits, though.
Sorry if this post is too technical, but the truth hurts, and it hurts us all equally just as it helps us all, too. Name calling need not apply to a good factual post.
Related ressources
- 12-volt card problems part II - Forum
- Can I use a 4pin 12volt in an 8pin slot? - Forum
- Stupid question about 12volt rails. - Forum
- Can I mix 12Volt rials on 2x SLI ? - Forum
- What video card to run off a 430 watt psu - Forum
OK you rower. But 18-gauge wire carries up to 16 amps, and the cards in question are only using it as supplemental current. Notice how the 9600 Pro doesn't need the added power, while the 9700 Pro does. I don't think there's an 80-watt difference between them, is there? In fact, I think the difference is more like 15-Watt, which wouldn't even make noticable heat on an 18 guage power cable...so again I ask, if the 5v line provides enough power supplementation, why not use it?
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<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
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Go here "http://bwcecom.belden.com/Master Catalog PDF/PDFS_links to docs/03_Hook-Up & LeadWire/3.28_3.32.pdf" and look at the lead wire current carrying capacity Table 3 on page 3 of 5.
I'd say your 18amp value is pretty close, 105C SR-PVC is good for about 20amps at 30C ambient even.
Questions, does the video card pull most of the power from the 12-volt Molex connector or the 3.3-volt AGP slot? The total power of the R9800pro is about 70 watts I've seen shown about. A good technical post from ATI would be nice to see just what power the card wants, and from where.
With that information we could probably determine a logical answer. Or even ask ATI the question.
I'd say your 18amp value is pretty close, 105C SR-PVC is good for about 20amps at 30C ambient even.
Questions, does the video card pull most of the power from the 12-volt Molex connector or the 3.3-volt AGP slot? The total power of the R9800pro is about 70 watts I've seen shown about. A good technical post from ATI would be nice to see just what power the card wants, and from where.
With that information we could probably determine a logical answer. Or even ask ATI the question.
Sorry, to resserect this old thread while you have a newer thread but I wanted to address one question.
Intel's AGP 2.0 specification explains the need for the auxilary connector. From page 188
<b><pre>Revision 2.0 188</pre><p></b><b><pre>Table 4-14: Add-in Card Power Supply Limits</pre><p></b><b><pre>Symbol Parameter Condition Min Max Units Notes
Vddq 1.5 I/O Supply Voltage IMAX = 8.0 A 1.425 1.575 V 1
Vddq 3.3 I/O Supply Voltage IMAX = 8.0 A 3.15 3.45 V 1
VCC3.3 3.3 V Power Supply IMAX = 6.0 A 3.15 3.45 V
VCC5 5 V Power Supply IMAX = 2.0 A 4.75 5.25 V
VCC12 12 V Power Supply IMAX = 1.0 A 11.4 12.6 V</pre><p></b><b><pre>Note:
1. The Vddq current is due mostly to the AC switching transients of the A.G.P. I/O buffers. The maximum current listed
will not be seen in practice, but represents the current carrying capability of the connector. Actual average
currents will be less than 2.0 A.</pre><p></b><i>- edited for formatting purposes only</i>
Notice the upper limits on power draws of the 12V and 3.3V lines from an AGP connector, of 1.0 amp (12 watts) and 6.0 amp (19.8 watts) respectively. Add the 2.0 amp for +5 volt rail and you only get a max combined power of about 40 watts via the AGP connector.
I don't know how much total power is truly needed but it is clear that not much will be coming from the +3.3 volt rail since the AGP port doesn't support much current.
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Quote:
Questions, does the video card pull most of the power from the 12-volt Molex connector or the 3.3-volt AGP slot? The total power of the R9800pro is about 70 watts I've seen shown aboutIntel's AGP 2.0 specification explains the need for the auxilary connector. From page 188
<b><pre>Revision 2.0 188</pre><p></b><b><pre>Table 4-14: Add-in Card Power Supply Limits</pre><p></b><b><pre>Symbol Parameter Condition Min Max Units Notes
Vddq 1.5 I/O Supply Voltage IMAX = 8.0 A 1.425 1.575 V 1
Vddq 3.3 I/O Supply Voltage IMAX = 8.0 A 3.15 3.45 V 1
VCC3.3 3.3 V Power Supply IMAX = 6.0 A 3.15 3.45 V
VCC5 5 V Power Supply IMAX = 2.0 A 4.75 5.25 V
VCC12 12 V Power Supply IMAX = 1.0 A 11.4 12.6 V</pre><p></b><b><pre>Note:
1. The Vddq current is due mostly to the AC switching transients of the A.G.P. I/O buffers. The maximum current listed
will not be seen in practice, but represents the current carrying capability of the connector. Actual average
currents will be less than 2.0 A.</pre><p></b><i>- edited for formatting purposes only</i>
Notice the upper limits on power draws of the 12V and 3.3V lines from an AGP connector, of 1.0 amp (12 watts) and 6.0 amp (19.8 watts) respectively. Add the 2.0 amp for +5 volt rail and you only get a max combined power of about 40 watts via the AGP connector.
I don't know how much total power is truly needed but it is clear that not much will be coming from the +3.3 volt rail since the AGP port doesn't support much current.
<b>56K, slow and steady does not win the race on internet!</b>
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