Joining 12v + 5v = 17v?

....or pufff!! there goes the psu.

Hi guys!

I have two PSU on my case right now. One powers only my MOBO and video card. The other one the rest of my system.
If I get a 12v line from one and a 5v line from the other one, and combine them to power a TEC. What would happen? A) I blow up both PS. B)Nothing happens C) TEC is powered up to 17v.
I thought about using the two PS because I didn't think it would work using just one (12v + 5v from the same PS). Or will it?

If the above is a horrible mistake. How would I go about powering a 172w 24v TEC between 15v-18v max (which is what I have read to be the best compromise) using my two current PS's?

I'm planning to buy an X800XT PE and modding/Overclocking the living crap out of it . For this I have decided to go to TEC for the first time.
I think I'll do "OK" with a MCW50-T modded to 172w pelt using this guide

This is the water setup I'm using right now:
- White Water
- MCW20
- MCW50
- 1/2 Clearflex
- 2-342 heater core (2" shroud on both sides)
- 4 Panaflos 120mm L1A push/pull (1 extra for burners)
- Iwaki MD-15RLT (shrouded)
- Lian-Li Pc 70 case (very moded)


Thanks in advance for any help that you can give me.

Well a way you could do it would be to use the +12v as the hot lead, and the -5v as the ground. I'm pretty sure that will add up to 17v, but I'm not sure if the PSUs can take it. I know if you use the +12v as hot, and +5v as ground you get 7v. That's the method for 7v modding a fan.

TECs pull a lot of AMPs. I don't know if your PSUs could handle the load. If the dual PSu method will not work, it's best just to get a separate universal power supply. Meanwell makes one that is popular for pelts.

he's right, voltage is a difference in potential.. and the difference between 12V and 5V is 7V. Running the 12V and the -5V line would give you 17V, BUT the -5v line won't stand more than 1A. So yes, you would fry the -5V line and maybe the whole PSU .

Is there a way I could do this using my current PS's? I wouldn't want to buy another PS. I already have 2

if you use two different unit and make their common float (take off the ground from psu), then you can wire then in serie and add voltage. It has been done before, but you have to make sure both psu can supply the amps your TEC will take at 17V. Some precautions have to be taken when connecting two psu in series, here is a little how-to
Hope this help.

I found this very good article here. Maybe it will help somebody else too.

But I still have a doubt after reading the article.
According to the article I should rig my PS's in series to get 18v. But I would have to disconnect the ground of one of the PS in order to get it to work. Would that affect the rest of the devices connected to that particular PS?

For example, I have one of the PS hooked up to the MOBO and VID card. If I disconnect the ground on that one, will it affect the MOBO and VID?

The author of the article doesn't specify if he used his modded PS's as stand alone units for TEC use only or if he used it for the rest of his system also.

Do not use the psu for anything else, most devices will have a longer life with a ground connections - unless you dont mind loosing a few devices due to static discharge or leakage current throught all the devices at different "0"!!
Dont forget the whole case is (and should be) grounded.

So, do you guys think this would be the most reasonable thing to do?

Use the larger of the two PSUs to power EVERYTHING in the system except for the tec. Make sure that the second PSU is ground isolated and hook it in series for your 17v. Power your TEC from that.

Click to expand...

I also found this info now:

Output
DC Voltage Ripple & Noise Total Reg. Output current rating Min / Max
+3.3V 50mV +5%, -4% 0.5A/20A
+5V 50mV +5%, -4% 0.3A/22A
+12V 1 120mV +5%, -4% 1.0A/20A
-12V 120mV ¡Ó10% 0A/0.5A
+5Vsb 120mV +5%, -4% 0.1A/2.2A
+12Vsb 50mV +5% N/A
+3.3V & +5V 145W
Total Power 270W

Over Voltage Protection
+5V: 5.5V~7.0V
+3.3V: 3.7V~4.3V
+12V:13.4~15.6V

Click to expand...

Does this mean that if I mod this PSU I can get the 12v line up to 15.6v without a problem? Could I power the TEC @ 15.6v with this single PSU?

You might find these links useful if you're thinking of modding your PSU.