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Author Topic: Power Supply Question  (Read 3640 times)
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Antifragile


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October 12, 2013, 09:52:10 AM
 #1

Hey Guys,

Wonder if some of you knowledgable with Power Supply's can answer some question for me (and our GB) please?

I'm going to be having a Drill Bit mini plane with 4 boards coming in a few weeks. https://bitcointalk.org/index.php?topic=266235.0

It is not real clear which power supply we should use as the boards use only the 5V side. A 4 board (8 chips X 4) setup is going to use around 80 - 100 or 120 watts (normal to overclocked) and need around 20-25 amps.

A few problems we are looking at:
1 - Not all mid range (450-650w) PS's give the needed amperage (Cutting it close maybe). And when you go up above this range, I'd imagine the 5V efficiency takes a dive.
2 - Not all mid range PS's give more than 100 watts at 5V. (Again maybe cutting it close)
3 - Not sure if running all the 5V and next to none of the 12 V (maybe a fan here) is inefficient or the like? (I don't see this in reviews as who runs just the 5V channel of a PS?)

Maybe a custom wired 5V only PS like this would be better (and just use a 5V fan), if one could do the wiring? http://www.meanwell.com/search/sp-150/default.htm
(This is a 70 buck or so PS, pretty much the mid range, price wise of PS's in general.)

The GB leader mentioned this, if it helps:
Quote
All the 5V pins are connected in the ATX. Standard ATX24 pin layout. Recommended to connect to all 5V pins to support the current.
All grouund pins in the ATX connector are connected. Recommended to use all ground pins to connect.
Estimated that each 8 board will consume up to 5A max, unconfirmed. Will need to test with hashing.
Using a 5V 25A power per miniplane you should be good but need to test the hashing first.
Running at lower hash rate will reduce the power consumption.
Any stable regulated 5V supply should be OK. So its OK to have a converter going from the 12V from an ATX to make 5V for the boards.


Once the test units are hashing we'll know the power requirements exactly, but the above is pretty much a close range.

Any ideas guys? Any suggestions would be greatly appreciated.

Thanks,
IAS

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October 12, 2013, 09:56:29 AM
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200W Dedicated AC voltage to 5 volt DC PSU: $65



http://www.vozopca.com/index.php/power-supply/5v-power-supply/5v-200w-switching-power-supply-110v-240v-ac-to-5v-dc-40-amps.html

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October 12, 2013, 04:46:15 PM
 #3

The choice of having the boards run at 5V is horribly bad.  I can't believe it was even considered.

The problem is that most ATX PSU today only produce 12V "natively.  To meet the ATX spec they then use very tiny DC to DC converters to convert some of the 12V into 5V or 3.3V.  There are two problems with this.  The first is to save cost the max load on those rails are usually tiny something like 100W or less.  Also they often don't increase with PSU size.  So a 500W PSU might be 100W max on 5V rail and a 1200W PSU from the same company is still only 500W on the 5V rail.  The second is that efficiency at 5V is going to be lower due to the double conversion.   At first this might seem like a bad choice but the reality is that on a modern computer 90% to 100% of the load is 12V.  So making the 12V rail as powerful and efficient is the best route.

The problem with dedicated 5V devices like the meanwell is that they tend to have bad efficiency.  The unit you listed is 77% avg efficiency.   A cheapo 80Plus Bronze PSU will be 82% to 85%.  The other problem with 5V is it means higher current for the same amount of power.   125W @ 5V is 25A.  125W @ 12V is only 11A.   Higher current means larger (or more) wires, more voltage drop, more power lost in the wires.

There is a third option and that is a high efficiency 12V to 5V converter.   This could be put close to the ASIC module(s) to limit the length of the 5V runs.   I need to run to a wine festival but I will see if I can find an example this evening.

If at all possible I would they would reconsider the input power choice.  It isn't like the ASICs are running at 5V o they are already converting from 5V to ~1V anyways.  Swapping that component out for one which converts from 12V to 1V will make it a better device.


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October 12, 2013, 04:58:26 PM
 #4

The choice of having the boards run at 5V is horribly bad.  I can't believe it was even considered.

The problem is that most ATX PSU today only produce 12V "natively.  To meet the ATX spec they then use very tiny DC to DC converters to convert some of the 12V into 5V or 3.3V.  There are two problems with this.  The first is to save cost the max load on those rails are usually tiny something like 100W or less.  Also they often don't increase with PSU size.  So a 500W PSU might be 100W max on 5V rail and a 1200W PSU from the same company is still only 500W on the 5V rail.  The second is that efficiency at 5V is going to be lower due to the double conversion.   At first this might seem like a bad choice but the reality is that on a modern computer 90% to 100% of the load is 12V.  So making the 12V rail as powerful and efficient is the best route.

The problem with dedicated 5V devices like the meanwell is that they tend to have bad efficiency.  The unit you listed is 77% avg efficiency.   A cheapo 80Plus Bronze PSU will be 82% to 85%.  The other problem with 5V is it means higher current for the same amount of power.   125W @ 5V is 25A.  125W @ 12V is only 11A.   Higher current means larger (or more) wires, more voltage drop, more power lost in the wires.

There is a third option and that is a high efficiency 12V to 5V converter.   This could be put close to the ASIC module(s) to limit the length of the 5V runs.   I need to run to a wine festival but I will see if I can find an example this evening.

If at all possible I would they would reconsider the input power choice.  It isn't like the ASICs are running at 5V o they are already converting from 5V to ~1V anyways.  Swapping that component out for one which converts from 12V to 1V will make it a better device.




Wow, that was very informative. Thanks so much and I look forward to your further response.

Something to consider, as I mentioned already, is for noobs like me, just plugging an ATX PS in has an advantage over the dedicated device (which must be custom wired).

Thanks again,
IAS

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October 12, 2013, 05:58:24 PM
 #5

Modern pc Power Supply's is ATX12V.
You need old (very old, and in this case definitely used) Power Supply's for AT computers . 250 watt have near 25A , 5 v line.
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October 12, 2013, 06:11:21 PM
 #6

Modern pc Power Supply's is ATX12V.
You need old (very old, and in this case definitely used) Power Supply's for AT computers . 250 watt have near 25A , 5 v line.

Interesting and cheap solution. The problem is that the miners use 24pin ATX connectors and those old connectors are 20 pin I think.
I think these old PS's are pretty loud though (this will be in the living room.)
Still a good solution, thx.

IAS

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October 13, 2013, 02:16:39 AM
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Modern pc Power Supply's is ATX12V.
You need old (very old, and in this case definitely used) Power Supply's for AT computers . 250 watt have near 25A , 5 v line.

Interesting and cheap solution. The problem is that the miners use 24pin ATX connectors and those old connectors are 20 pin I think.
I think these old PS's are pretty loud though (this will be in the living room.)
Still a good solution, thx.

IAS

I'm pretty sure the 20 pin plugs will snap right into the 24 pin connectors.  The only thing the extra four pins add is one more wire with 12v, one with 5v, one with 3.3v, and one ground.  It is my understanding that all of the different power and ground wires share a common source.  This makes me think the additional wires were just added to cover the extra amp requirements for different branches as the systems started requiring larger power supplies.  ie....After derating 18 gauge wire for temperature it might only be acceptable to carry an eight or nine amp load.  If you need to supply 15 amps you would either need to increase the wire gauge or use a second run of 18 gauge wire.

I'm sure someone more knowledgeable can step in and correct any errors.

Chad
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October 14, 2013, 06:49:32 PM
 #8

FWIW, I have a 5v 40a power supply from ebay that's running great.  Voltage adjustment from ~4.8~5.8v, 3 outputs, and has a cover fro the output terminals.

I attached several powered USB hubs to this supply and I'm drawing about 50% of it's rates output without any issues at all. 

I don't think using ATX power supplies makes sense here, since there's a lot of extra stuff (multiple 5v and 12v rails, sensors, etc.) that you're paying for which you don't need. 
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October 14, 2013, 07:12:32 PM
 #9

To run those things, you need an old ATX2.01 PSU - you're probably talking a PSU around 10 years old.  Back then they were heavily 5V biased.  I'm thinking the old Enermax 430W PSU I bought to run a SlotA Athlon would be ideal.

Now PSUs are basically a 12V unit with a few 5V and 3.3V feeds for SATA and the likes.

Some very recent OEM PCs have PSUs that ONLY output 12V - there's no other outputs, the little 5V and 3.3V are produced by the board, and the drives are run from a connector on the board.

To design a mining board that needs a 10 year old PSU spec is madness, as DeathAndTaxes said.

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October 14, 2013, 08:18:39 PM
 #10

Thanks for all the replies guys. I appreciate your time and I have a pretty good grasp on what you are all saying now.

Surprisingly, I have found some PS's, like the 70 buck Corsair 600CX that has 25amps and 150 watts on the 5v channel. If worse comes to worse there are a few others I found. I doubt the efficiency is very good though. Hopefully close to a 5V only 40amp or so PS. aznatama (or someone else) - Is it hard to wire/solder a the 24 pin atx to a dedicated 5V PS? The wiring thing is my fear.

Thanks again,
IAS

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Gerald Davis


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October 15, 2013, 02:46:04 AM
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Wires aren't soldered.  You (or someone) will need to buy a ATX 24 pin housing and 24 Molex crimp pins.  You would also need a crimper.   Essentially you crimp a connector onto the end of each wire and then insert the crimped wire into the ATX 24 pin housing.  You will need to do some research and find out what pins are being used by the board. Obviously if they aren't using all the pins there is no need to crimp and assemble full 24 wire connectors.   On the other end you just need to bundle all the 5V connectors together and crimp it into a ring terminal to attach to the PSU.  The same thing will all the ground wires.   The PS-ON pin can just be connected to ground to produce a connector which is always on when connected (no motherboard power switch).  A lot will depend on exactly how is the ASIC board wired.   It isn't "tough" but it does require a little practice plus it is expensive to do just one connector because you will need a crimp tool.   1 tool for 100 connectors is going to be cheaper then 1 tool for 1 connector.

I didn't realize in the first post that they would be using the ATX24 connector.  Given that the only easy solution is to find a ATX power supply with sufficient 5V current.   Still I have to say running high current on 5V rail is just a pointless complication for purchasers.  There is absolutely no reason to not use 12V.  It can be done but the buyers will face additional complication and cost for lower efficiency.  A lose-lose.
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Gerald Davis


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October 15, 2013, 02:48:16 AM
 #12

Some very recent OEM PCs have PSUs that ONLY output 12V - there's no other outputs, the little 5V and 3.3V are produced by the board, and the drives are run from a connector on the board.

I am using a couple of those to produce a 4.8 KW (not a typo Smiley ) ASIC powersupply although I will probably only load them 75% to gain redundancy.  My custom prototype connector boards should be arriving next week.
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