How-To: Modifying the PW200

**evandude** · 08-11-2005, 08:42 PM

First off, let me say that this guide is in no way trying to get you to purchase an iTuner power supply such as the PW200. In fact, I wouldn't advise anyone to buy one, ever. This is intended for those who already made the mistake of buying one, and would like to at least make it a little more useful while they're stuck with it. It won't change the weak power output of the supply, so don't expect it will magically make the PW200 usable on P4's and athlon 64's, or anything like that.

With that said, the concept of this modification is as follows:

The reason the iTuner power supplies suck so much is that they don't regulate the 12v rail. It is simply switched with a MOSFET. Therefore, if you want it to work halfway decent, you need to feed it a voltage that is within the ATX specifications for the +12v rail (which is about 11.5-12.5v). unfortunately, feeding it directly from your car's electrical system isn't a good idea, since the voltage is often outside that range, which can damage your components, and/or cause malfunctions (random restarts, etc)

So if you use a PW200, you have to regulate the 12v line externally. However, the PW200 isn't very well designed in that regard, because the actual DC-DC parts of it are also fed from the 12v input. This means that the 12v input coming from the external regulator is powering the entire computer, and not just the 12v line. Since all the rails other than +12v are regulated anyway, there is no need to supply them with a regulated 12v input.And since the PW200 can supply up to about 60 watts on all its regulated outputs, and assuming 80% efficiency, that's up to about 75 watts of extra power that is being unnecessarily drawn from the regulated 12v input.

The specific intent of this modification is to separate the power input into two separate inputs: one +12v regulated, and one unregulated, thus reducing the load on your external 12v regulator by up to 75 watts.

This is the bottom of the PW200. The red circle shows the PMOS transistor that is used to switch the 12v rail, with "in" and "out" marked. The blue line marks the location where the trace should be cut, and the green circle marks where the new REGULATED 12v input wire should be soldered.

As you can see, the only change is that the 12v rail will now be switched from the regulated input, instead of the (now unregulated) original input.

RESULTS:

BEFORE:
12v input current before mod, epia 800 motherboard with no devices/drives attached:

before, with one 3.5" hard drive attached:

MODIFICATION:

AFTER:
regulated 12v input, no devices/drives:

with one 3.5" hard drive attached:

As you can see, it has significantly reduced the draw on the 12v regulator. Obviously, an epia doesn't draw much power either way. But on a motherboard that is pushing the limits of the +5v and/or +3.3v rails on the PW200, this will make a significant difference in the amount of power the external 12v regulator must handle.

**dragonBTV** · 08-11-2005, 09:08 PM

the disadvantage is: the 12v will NOT be isolated (switched).

you have to related(control) your 12v regulator to the PW200, same on same off

maybe harmful sometime to some mainboard. please confirm this hack.

**evandude** · 08-11-2005, 09:10 PM

Actually, it is still switched. The regulated 12v input goes through the same switching transistor that was used to switch the 12v line in the original circuit, that's why I attached the new wire to the input side of the transistor instead of the output side.

**dragonBTV** · 08-11-2005, 09:16 PM

Originally Posted by evandude

Actually, it is still switched. The regulated 12v input goes through the same switching transistor that was used to switch the 12v line in the original circuit, that's why I attached the new wire to the input side of the transistor instead of the output side.

if so, great hack!

maybe I can design a daughter board 12v (??A) regulator...

**evandude** · 08-11-2005, 09:23 PM

Just to be sure, I just hooked it up and applied power to both power inputs without booting the computer, and measured all the ATX connector pins with a multimeter. the 12v rail was not powered, only the 5vsb was (as expected).

I'm sure that if you design a small 12v DC-DC regulator, it will be much smaller and more efficient than the one I built

http://eegeek.net/mp3box/DCDC/index.htm

**dragonBTV** · 08-11-2005, 09:27 PM

Originally Posted by evandude

Just to be sure, I just hooked it up and applied power to both power inputs without booting the computer, and measured all the ATX connector pins with a multimeter. the 12v rail was not powered, only the 5vsb was (as expected).

I'm sure that if you design a small 12v DC-DC regulator, it will be much smaller and more efficient than the one I built

http://eegeek.net/mp3box/DCDC/index.htm

maybe the size is depands on the switching freqency ONLY
mine is about 230KHz...

how many A recomanded for this PW-200 daughter board in your mind, 10A?

**dragonBTV** · 08-12-2005, 02:35 AM

WE can make the daughter board for the PW-200 owners
get in touch with evandude if you need this low cost solution

**evandude** · 08-12-2005, 06:31 AM

Originally Posted by dragonBTV

how many A recomanded for this PW-200 daughter board in your mind, 10A?

Since the PW200 is very weak (only 60 watts on all the other rails), I think 10A on the 12v line would be excessive. (unless of course it wasn't much more expensive than a lower power output)

If you look in the mp3car.com store, there are two 12v regulators of this type, one 60 watt, one 90 watt.

But if you could design one that was cheaper than those, I'm sure people would be interested

**Coldfusionpower** · 08-12-2005, 01:18 PM

this mod is just to get the Amp increase right ? not the watt ? i got a pw200-v but didn't work for my setup . don't have any money to buy opus .. can get it to 150w ?

**evandude** · 08-12-2005, 01:40 PM

This mod does not in any way change the power on the 5v, 3.3v, -5v, -12v rails. The only thing this does is reduce the load on the external regulator that supplies the regulated 12v, which allows you to get more usable power on the 12v line from your external regulator.

The PW200 can only supply 6A on the 5v line, and 6A on the 3.3v line. If your computer requires more than that on either line, then the PW200 will not work for you. If your motherboard has low current draw on those lines, and high current draw on the 12v line (which is fed from the external regulator) then you may be able to use it, because you can get an external regulator with high power output (like the opus one which supplies up to 80 watts) and with this mod, use it to power only the 12v rail.