how to use a Thermaltake 750W Toughpower PSU without motherboard

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how to use a Thermaltake 750W Toughpower PSU with no motherboard

guys and girls,
I know others have asked similar questiosn but this is a little
different. THis powersupply has the works - sensing, min load and
anything else you could imagine to make it hard to power on without a

My problem is i am trying to build a 20 drive external case that will
not have montherboard in it.   To power the drives i need a very large
powersupply as the drive put all their startup load on the 12v line
(close to 60A!).

So i need this powersupply and i thought it would be easy to turn on by
just shorting 2 pins but now i read the sensing needs to be shorted and
loads put on some channels but not others etc.

Can anyone help me work out exactly what i need to do to make this
work?  I will have a few fans on the 5v channela nd nothing on the 3.3v

Is there a device out there that will fix the sensing, shorting and
load for me?

Here is the info on the powersupply.

I hope someone can help.


Re: how to use a Thermaltake 750W Toughpower PSU without motherboard

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They do make power supply testers.  Other than that, I'd probably just hook
up an old dead mainboard to it.  I mean, even if you don't intend to use a
motherboard, your case probably has room for one, unless you are doing some
kind of mod.  :)  -Dave

Re: how to use a Thermaltake 750W Toughpower PSU without motherboard

On 12 Sep 2006 02:39:12 -0700,

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Most supplies have this sensing, though many omit it on the
3.3V rail.  Whether yours has this 3.3V option might
determine if it's a problem, since in this use you have no
load (but for a minimal load resistor inside, "maybe") but
if you need a load, simply select a load resistor and
connect across a 3.3V (normally orange) an ground (normally
black) lead.  It is generally easier to mount this load
resistor if the type encased in an extruded aluminum 'sink
that is then 'sunk to a metal chassis by screwing it down
onto an area with as thick a metal area as reasonably
possible, even better to have heatsink grease between the
two surfaces.

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That estimate seems a littlel high, have you measured the
startup current?  Normally it's closer to 2A per drive, but
some controllers also allow staggered spinup which will
obviously reduce current quite a bit.

Keep in mind that while the 12V rail load is substantially
higher at the turn-on spin-up period, it's not as though
there is nothing on the 5V rail, each drive should be
expected to draw somewhere in the neighborhood of 0.3-0.7A
on 5V rail as well.

If your PSU doesn't have 3.3V rail monitoring, it could be
that the load on the 5V rail is enough and you need nothing
more, don't need the load resistor mentioned above, or have
you tried it (this supply and the drives) already and found
a problem?  Measure the voltage as the unit is powered on,
the 3.3V, 5V, and 12V rails.

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Yes that will turn it on, but IMO, a nicer solution would be
to take the PSU's power-on pin, run a lead from that to the
main system PSU power-on pin, then when the system is turned
on it will turn on this external PSU too.

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I doubt "shorted" is what you wanted, but if you are adept
at reverse engineering a PSU and just wanted a short-term
hobby, you could look at the PSU's power sensing circuit and
devise a means to circumvent it's protection (alter the trip
points and ignore 3.3V if applicable) BUT the protection is
there for a reason, you may not want to do that rather than
the load resistor mentioned above, "IF" a load resistor is
required at all.

If (contrary to what I expect) your 5V rail is also too
lightly loaded, you could put a load resistor on that rail
too, but I would try it without first and measure voltages
before concluding that one is needed on 5V rail.

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"Fixing" the sensing is only done by having the appropriate
loads, unless you were to open up the PSU and modify it
(which is probably beyond most people's skill level or
reasonable safety level).  "Shorting" would only be
applicable to the PS-On pin, and that needs nothing special,
if you didn't care about remote turn-on then you could
simply solder the PS-On and Gnd wires together.  

As for the load, what addt'l load you need is determined by
what load you already have and this is something no
manufacturer could randomly know... since after all, these
PSU are designed to power a whole system.

Further, if such a device existed it would be a niche
product and quite expensive for what it is, if it provided
enough of a load to keep PSU voltages ideal with 20 drives
spinning up.  You're just as well off to buy the PSU,
measure the voltages, and then know if you need anything
more at all (besides grounding the PS-On lead).  If you need
a load on the 3.3V rail, something like a 1 Ohm, 20W
resistor should suffice- if it even needs be that low an
ohmage which it probably wouldn't, but I'm being

For the 5V rail I doubt you'd need anything, but you could
try a 2.2 Ohm 20W power resistor there too.

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Pretty expensive, do you need a PS2 form-factor PSU
(casing)?  In this price range you might get a better supply
as one meant for a server, though hunting one down by
digging up specs or web searches is a bit more work since
they're normally found the other way around, by part numbers
listed by server manufacturer.  Plus, the server supplies in
this wattage will be larger form-factor but that's not
necessarily a bad thing, more room inside for components
tends to mean a better built supply.

Re: how to use a Thermaltake 750W Toughpower PSU without motherboard

Thanks for the reply.
If i can get a cheaper server powersupply for around the same price i
would be interested.  Note that site link i gave you was an Australian
PC store with $AU prices incase you were comparing to $US prices.  I
will look into it anyway.

Sorry about the wording i used it seems like shorting etc were the
wrong words to use though i still get a lot of the information that i

On the link i posted before it states the min loads on all the
channels.  Am i correct in understanding that you think i may not need
to meet the min load on all the channels?  Will not meeting the min loa
don a channel damage a PSU or jsut turn it off if it has monitoring?

I don't have the PSU yet.  I am looking at getting it today or
tomorrow. I want to make sure i can use it the way i want to first.

As to the HD loading the 5v channel as well as the 12v channel i am not
so sure.  I had the same expectation as you in that it would load both
channels but if you look here,1085,765,00.html
and the 320 sata II disk it lists 2.8 amps on the 12v rail and nothign
on the 5v rail.  It does say some watt's under that.  maybe the watts
are on the 5v rail but i thought they may be the 12v rail.  Guess i am
not too sure.  interested in your view.

I know you can get a cord that connects to the MB connector on your
secondary power supply and will turn on your second power supply when
your main one turns on.  I thought of getting this but i was a little
worried if it took into acount the sensing and min loads that the
toughpower PSU may have.  (Read somewhere that atx 2.2 compliant PSU
should have sensing but that could be wrong)

Thanks for the info on the resistors.


Re: how to use a Thermaltake 750W Toughpower PSU without motherboard

On 12 Sep 2006 20:05:41 -0700,

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I have not been inside that particular PSU so I can only
generalize about it having the same common arrangement of
electronic topology as many others.

Minimum loads are spec'd to specify the environment under
which the supply is supposed to keep the rail voltages
within tolerance - in this case the ATX spec.

If your 3.3V rail, which you don't need to use, were
floating at a higher voltage than spec'd but you didn't need
(use) that rail at all, it's not a problem per se unless the
PSU is using sensing (feedback) on that rail as one point of
it's safety/shutdown circuitry.  Some PSU do use 3.3V, more
often better quality ones, but even though that PSU has a
lofty price, it might not be THAT high a quality unit to
have it, or it might have so little real-estate inside that
it was all they could do to squeeze what they did in.

Considering 5V rail, certainly all those drives will exceed
the 2A minimum, BUT, with such a high 12V current draw if
the weighting on the switching controller has a 12V bias, it
will tend to raise the 5V, voltage any/every time the 12V
has a high load (should be an issue, IF it is, only at
initial power-on, drive spin-up).  IF the result was that
the 5V rail rose too high, it could potentially trip the
overvoltage protection but generally that trip point is high
enough it wouldn't be a problem- so the best course of
action here is to try it and be measuring the voltage with a
multimeter if one is available, to determine if any load
resistors are required.

While there are multiple 12V rails, I doubt there are
parallel feedback mechanisms, usually it's a pseudo-separate
rail divided by internal resistors that act to limit current
per rail... it might have separate rectifier diodes for the
12V rail if their current rating is correct,but we can't
necessarily presume this as it could be (probably is to some
extent) a peak rating for all the current on the 12V rails
rather than sustained, and peak ratings for these
rectification diodes are often far higher than 72A.

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I'm sure you can use it, though it does seem a bit pricey to
me, I'd still investigate server supplies BUT they may be
even more work to reverse engineer to get running/keep
running, and then there's the difference in form factor, I
don't know what kind of enclosure you'll be using for 20

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Yes they do load the 5V, just not anywhere near the 2A or so
the 12V may have for a moment during spin-up.

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Here's a picture of a Barracuda 7200.10 320GB, PATA label,
essentially the PATA brother of the next link,
5V - 0.72A
12V - 0.52A

Here's a picture of a Barracuda 7200.10 320GB, SATA label,

5V - 0.72A
12V - 0.52A

I don't know what all 20 of your drives will be, but "most"
drives have the current on the labels, though you may note
the 12V is lower than 2 or 3A, it's not the surge but
steady-state rating.  Ultimately any drives you wonder about
should first have their labels checked- it's not unheard of
for a drive model to remain somewhat similar but the drive
itself changes somehow, and I do think Seagate has done this
with some version of 7200.9 or 7200.10, but I don't think
that would result in 2.8A @ 12V and 0A @ 5V.

I am quite sure none of their 7200.10 drives use 2.8A of 12V
current in "amps typ operating" as was suggested in that
link you gave- they'd have to start  putting heatsinks on
their drives if they generated that much heat.

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power supply and will turn on your second power >supply when your main one turns
on.  I thought of getting this but i >was a little worried if it took into
acount the sensing and min loads >that the toughpower PSU may have.  (Read
somewhere that atx >2.2 compliant PSU should have sensing but that could be

"Sensing" is not a new feature nor unique to ATX 2.2 PSU.
You could buy a dongle-adapter-something-or-other that does
as you described, plugs into both PSU and turns this one on.
You'd achieve the same thing by soldering a wire between
both PSU's PS-On wire, though it might be good to make sure
they have a common ground too, so two wires (though
presumably the data cable(s) to get to these drives will be
that common ground, there is not enough current for this to
be a problem).

The real question is whether you're willing to cut up/off
wires or another permanent modification to the supply (which
voids it's warranty).  If not, then any way you look at it
you'll have to source a mating motherboard-style connector
to interface to the PSU's plug to turn it on, whether that
connector is bought from some electronics supply house like (I'm not certain they have one but
expect they do- just a matter of wading through a gazillion
parts to find it), or whether the plug comes on a ready-made
dongle meant for the purpose, or whether you cannibalize an
old motherboard to get the connector.

The easiest way to get it off an old motherboard is as

- Plug an old worthless PSU plug into the motherboard socket

- Make sure it's plugged in all the way, locking tab locked.

- Take board outside and flip it over.

- Take smallest pencil or blowtorch avail. (or hot air gun)
and hold far enough away (if a torch) to not ignite the
board.  Move it back and forth while gently pulling straight
at 90' angle on the PSU leads and once solder is melted,
whole plug pulls out at once.

Plugging the old PSU in helps, because a tool might deform
the connector plastic as it softens (but it shouldn't melt),
and helps to keep the pins straight during cooling.  Just be
sure not to overheat it, plugging lightly should make it
easy to tell when hot enough.  If you overheat the board it
will stink badly and need be left outside- this is
destructive cannibalization, before throwing the board away.

I still don't know if you're adept at soldering though, and
that is one of the most reliable ways to get a load
resistor(s) connected.  Some of the PSU "testers" you'll see
on the web do have minimal load resistors which would be
better than nothing but aren't meant to keep the rails even
while you have ~ 20 drives spinning up, that will require
more current than those cheap little testers can handle

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