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Unread 09-12-2002, 04:01 PM   #1
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Default 300w + 300w = 600w?

I have a fair idea why hooking up a pair of 300W wouldn't quite produce 600 Watts, but I'll put the question out there for discussion.
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Unread 09-12-2002, 06:29 PM   #2
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Is the issue of peak wattage a real concern, or amperage on a particular rail?
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Unread 09-12-2002, 07:35 PM   #3
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Sounds like BigBen is looking for dual "redundancy" in a possibly cheaper PSU. In other words, taking two PSU and making them one BIG PSU; both units taking half the load of the whole system.

Problem is I would believe that it would be more expensive in the long run and would take up A LOT of space.

However it does have great advantages; overal less stress on a single PSU and even some redundance if one should die.

hmmmmmmm................
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Unread 09-12-2002, 09:25 PM   #4
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A buddy of mine did something similar: he has one 300W PS dedicated to the motherboard and the other powers all the other components: hd's, cdrom's, fans...
So it's not exactly redundant but for our purposes might be the ticket... he did have to tap into the mobo control wire to get them both to power up at the same time...

As for the making two into a 600W:
If you are pulling say 400W and one of your PS's go out, then poof... your other one will definately friy as soon as all the 400W is transferred over to it... "kerzittttt!"

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Unread 09-13-2002, 09:04 AM   #5
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Hum... this isn't going where I wanted it to...

I'm trying to find an alternative to buying a very large PSU, which would be terribly expensive. Not that I need that much power, I'm just trying to cut costs.

I didn't have redundancy in mind. If I did, then I'd be talking about 3 * 300W PSUs, so that if one fails, I could keep going and swap out the dead one.

Ok, the issue with merging 2 300W PSUs is the load distribution: if there is, for example a 400Watt load from my system (don't ask me how), then off-hand we'd believe that the load would be split equally between the two PSUs, right?

Wrong.

Electronic components have this funny thing about them, where they are made within a 5% margin of error (aka tolerance). That means that if one PSU puts out 4.75 volts on the 5V rail, and the other one puts out 5.25 volts, then the 400Watt load would be proportionally distributed, where the first would be handling 190 Watts, and the other, 210.

But that wouldn't be an issue, with a combined power rating of 600 Watts, because even at 210 Watts, it still doesn't tax one of the 300 Watt PSUs beyond what it can handle.

A 300 Watt PSU can be had for less than $20 these days. A 600 Watt PSU however, will always cost more than $100.

Space isn't an issue in my case (meant redundantly), because I'm fixing to get the big Chieftec case, the one that's about 26 inches tall.

I don't expect one of those PSUs to suddenly go dead, anymore than I would expect a single one to do so, so that's a non-issue.

Peak wattage or amperage isn't an issue either: I'm just being a cheap bastard, that's all...

pHaestus *not, it was OnDaEdg* has a great article up, on merging PSUs, so I'm not worried about the wiring. I could even do the half height PSU mod, for space's sake, but I'm not that desperate.

Last edited by bigben2k; 09-13-2002 at 10:25 AM.
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Unread 09-13-2002, 10:07 AM   #6
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me? OnDaEdge I think. You sure you want to wire two PSUs together and then plug em into a motherboard?
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Unread 09-13-2002, 10:26 AM   #7
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Quote:
Originally posted by pHaestus
me? OnDaEdge I think. You sure you want to wire two PSUs together and then plug em into a motherboard?
Fixed, sorry.

Of course I'd wire 2 PSU together! How else am I going to get around spending a huge amount of money on a fat power supply?
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Unread 09-13-2002, 11:35 AM   #8
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Quote:
Originally posted by tokamac
A buddy of mine did something similar: he has one 300W PS dedicated to the motherboard and the other powers all the other components: hd's, cdrom's, fans...
So it's not exactly redundant but for our purposes might be the ticket... he did have to tap into the mobo control wire to get them both to power up at the same time...

Tokamac
I like that idea, except that I'd have to get into calculating how the load splits up, where if I combine the 2 PSU, I don't have to do anything but wire them together... hum...maybe I should think that one over...
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Unread 09-13-2002, 12:12 PM   #9
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Here's OnDaEdg's article.

Ok, here's the problem: when OnDa hooked up the 2 PSUs together, he got "almost 13V" on the 12 V rail. That might be good for a Pelt, but it's no good for a PC.

The link in the article suggests using a power diode to prevent currents from flowing back into the PSUs, which is good, but it drops the output by 0.7 volts (as all diodes/junctions do), bringing down the 12 V line to 11.3. Still no good.

On the other hand, if I experiment with this, and I do get 13 volts, I can bring it down to 12.3 with the power diodes.

For reference: 12V +/- 5% tolerance gives a range of 11.4 to 12.6.

Anyone?
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Unread 09-13-2002, 03:37 PM   #10
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Bigben,

Not be rude but if you are building this "super sysytem" then why be a "cheap bastard" with all that very expensive equipment and go cheap on one of the most IMPORTANT parts!?!?!


Stop being cheap, get some GOOD insurance, and BUY a 600W PSU!
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Unread 09-13-2002, 03:44 PM   #11
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Quote:
Originally posted by jtroutma
Bigben,

Not be rude but if you are building this "super sysytem" then why be a "cheap bastard" with all that very expensive equipment and go cheap on one of the most IMPORTANT parts!?!?!

Stop being cheap, get some GOOD insurance, and BUY a 600W PSU!
Are you calling me a cheap bastard?

That's Ok, I called myself that (above)...

Money is an issue, all the time. The monster sized case is only $56. I was looking at a 430 Antec PSU, but it's $79, so I'm still looking. I couldn't help noticing that 300W PSUs are dirt cheap ($20), probably because there's tons of them out there on the market, and fewer and fewer people are buying them.

I'm crazy enough to hack this case to slap an array of 3 PSUs, for redundancy, but I don't really care to take the time to make them things hot-swappable, like I should. Call me lazy

(of course that might be what I end up doing anyways!)
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Unread 09-13-2002, 04:19 PM   #12
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I would be concerned about the line noise and fluctuations; if you have the equipment to check it out though by all means go ahead.

For serious overclocker's price/performance I recommend the Sparkle 400W. The heatsinks in it are probably 2x the size of any of these "2 fan" PSUs, and they take considerable pains to make sure that the power is clean and constant. PC Power and Cooling is too much money for me to justify, and PSUs of lesser price all are of lesser quality. I think the old Antec 400W PSUs had pretty beefy reputation as well.

My instinct is that there is no difference in HEC, Enermax, or Antec's newer models other than some minor features and colors. Given the track record of Enermaxes that would give me pause with the other two...
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Unread 09-13-2002, 04:24 PM   #13
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That's a good point.

If there's any ripple in the voltage because of the mains, then it would be amplified by using two PSUs that way.

I need a cheap oscilloscope!
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Unread 09-13-2002, 06:30 PM   #14
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Every time I hear about Sparkle PSU, I cringe and get mad. I got one of their 350W models and that thing was a piece of crap. It would work fine until you turned the machine off. After that, you had to pray to God and offer a virgin sacrifice to get the thing to turn on again.

Probably just a dud. But then I tried to RMA it and the frickin company shipped it back, said that there was nothing wrong with it, and charged me the shipping.

Sold the thing to a friend and the same thing happened to him. Now it is nothing but a good door stop.

Sorry, just had to express my experience.

But BigBen, it looks like your best bet is to get 3 300W PSU and just do it. At least then you can sleep well at night knowing that if one fries, it wont take the system with it.

And yes, I am a college student so I KNOW all about the "no money" situation
EDIT: How about this; college student with Child Support due every month. Can we say POOR BOY HERE!!!
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Unread 09-14-2002, 08:05 AM   #15
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Quote:
Originally posted by jtroutma
But BigBen, it looks like your best bet is to get 3 300W PSU and just do it. At least then you can sleep well at night knowing that if one fries, it wont take the system with it.

And yes, I am a college student so I KNOW all about the "no money" situation
EDIT: How about this; college student with Child Support due every month. Can we say POOR BOY HERE!!!
Yeah, that's what I'll do, 3 * 300W, then the half height mod, then the hot-swap connector. I'll just have to deal with the voltage diff when it comes up.

Actually, I meant that I'm always looking out for a bargain.

college and CS? Yikes!
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Unread 09-19-2002, 12:10 PM   #16
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Basically, your wattage equals your voltage by amperage. What you're doing is keeping the voltage the same (if you're doing it right) but upping the max amperage. There are no problems here with what you're thinking. Basically, 300W*3 = 900W.

What you're going to have issues with is that you're going to want to use identical PSUs when you hook them up together. I suspect it'll give you less line fluctuation since they are all regulated the same. Be warned, though, that any modifications you do will lower the overall voltage of the system by adding resistance. You'll need to do VMods on all three PSUs to get your voltage back up.

What'll end up happening is your amperage will be the sum of the three PSUs, but your voltage will be lowered by the connecting hardware. Your 12V line will run at 10-11V, for instance. This is why you'll need to install pots on your voltage regulators in the PSUs (or buy PSUs with them already installed).

What'll happen, though, when one goes out, is it'll suddenly remove its resistance from the circuit. All of a sudden, that 10V circuit that you modded up to 12V will be running at 13V or so. If a PSU goes out, you're probably f*cked with a setup like this. That is why normal "redundant" power supplies are basically two power supplies with a switch between them ... they aren't simultaneously supplying power, but are set up so that if one drops the other will seamlessly take over. You can do this, but it'll be tricky to get the precise voltage values you'll want, and if something goes wrong, you'll probably have a 40 lb paperweight.
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Unread 09-19-2002, 12:14 PM   #17
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Sorry if this has been mentioned, but have you considered just buying a stack of cheaper than $hit generic 400W PSUs ($30 all over the place) and running different parts of your machine off different PSUs? You'd avoid this completely. Run your mobo off of one, your drives and such off another, and your 28x120mm fans and LEDs off a third.
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Unread 09-19-2002, 01:14 PM   #18
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Hum... many options, much info.

Thanks for pointing out what happens when one of the PSUs die, that's basically what I was looking for.

I'm down to a few options (some overlap each other):

1-Beef up the PSU myself. Since I haven't cracked one open recently, I don't know if it's going to involve a rebuild, or if it's going to be a simple add-on job. It would make a single PSU.

2-Mod the PSUs by adding a trim pot. Again, since I haven't cracked one open, I don't know if it's even feasible. (not a complete solution)

3-Up the voltages on all the rails (see #2), and add my own regulator circuit at the end of the merged outputs (parallel, yes). Kinda redundant, but it should filter everything out nicely. I guess I need to add that diode, in case one of the PSUs die.

Where's gmat when I need him?
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Unread 09-19-2002, 01:52 PM   #19
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The regulation circuits on power-supplies (of reasonable quality) already have trim pots on all the positive outputs. All you need to do is tune them until the tolerance is matched, tie the + leads together and call it a day.

And yes, 300W+300W = 600W because you have to look at the definition of W. Watts are equal to Volts*Amps. To calculate wattage, you do this for every output and add em together.

Im back from the dead (braincells)
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Unread 09-19-2002, 02:19 PM   #20
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Quote:
Originally posted by MeltMan
The regulation circuits on power-supplies (of reasonable quality) already have trim pots on all the positive outputs. All you need to do is tune them until the tolerance is matched, tie the + leads together and call it a day.

And yes, 300W+300W = 600W because you have to look at the definition of W. Watts are equal to Volts*Amps. To calculate wattage, you do this for every output and add em together.

Im back from the dead (braincells)
Welcome back!

Since I'm thinking about cheap PSUs, I guess it'll just be a chance I'll take.

I'm very clear on running the PSUs in parallel, and that 300W + 300W does indeed equal 600W. I'm writing an article on that too!

What I wasn't clear on, is the implications of running the PSUs in parallel.

1-OnDa got almost 13V when he did this. Why?

2-as I mentioned above: "The link in the article suggests using a power diode to prevent currents from flowing back into the PSUs, which is good, but it drops the output by 0.7 volts (as all diodes/junctions do), bringing down the 12 V line to 11.3. Still no good. "

I think it would solve the "dying PSU" in an array issue: "What'll happen, though, when one goes out, is it'll suddenly remove its resistance from the circuit. All of a sudden, that 10V circuit that you modded up to 12V will be running at 13V or so. If a PSU goes out, you're probably f*cked" (thanks airspirit)


I ain't done with this yet, but I'm getting closer!
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Unread 09-24-2002, 09:30 AM   #21
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I emailed OnDa. No reply yet.

I'll give 3 * 300 a shot. I'll pick up parts in a couple of weeks.
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Unread 09-24-2002, 01:31 PM   #22
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I found the link to the half height PSU mod, but the pictures are gone!

Slimline PSU mod

Good thing I printed it... (I think?)
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Unread 09-25-2002, 02:17 AM   #23
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If you want cheap redundancy you can just run a Y into everything. IE the two power supplies have all their connectors connected up together into a single plug. so if one power supply dies it is just a simple matter of unplugging it and plugging another one straight into the now empty part of the Y.

Or you could even make up a little pcb with 2x 20pin male connectors, 8x 4pin male connectors, etc etc, and have 1x 20pin female connector, 4x 4pin female connectors, etc etc on the other side.
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Unread 09-25-2002, 04:39 AM   #24
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Big Ben,

Here is a 500/525w PowerMax.I got mine from this same place back in Feb for 50 bucks. This supply rocks and runs this machine ....


Xp 1800+ @ 1725 watercooled
2- 18.3gb Barcuda's 10200rpm (SCSI)
1- 4.5gb quatum (SCSI) linux drive
1- yamaha CDR (SCSI)
1- cdrom 50x (ide)
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1- ATI Tv Wonder
1- adaptec 2940 UW2
1- voodoo 3000 (soon to be a GF3 or 4)
1- 12v pump a 1.5amp
4- 80mm fans (HDD cooling)
1- 120 on Rad


POWMAX
Info...

Power Magic 500W/525W P4 & AMD Recommanded ATX Power Supply With Dual Cooling Fan. For AMD Athlon XP2100+XP1900+XP1800+,AMD,INTEL P2,3,4. Online ordering coupon code: ( PSPMXB0012FNLP6100E)
(Part - PSPMXB0012FNLP6100E)

Price: $48


Ship: $7.00 - 10.00 Insured shipping box
Will Ship: Same - 1day


Amamax
Info...

866-426-2629
713-777-9700
TX

There here in Houston. So I got it the next day on UPS ground.
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Unread 09-25-2002, 09:08 AM   #25
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Nice, thanks!

I'm going down to Harwin tmo, so I'll try to pass by, to check them out.

hehe they also have 300W psu for $16!
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