1. ## Lowering/Increasing voltage on the 12v rail

Hello, I am currently using 2 PSU's to run an amplifier for a subwoofer that I will be purchasing soon. This is more of an experiment than anything. Now, here is the dilemma I'm having:

I have 2 PSU's wired in parallel, as to combine the amperage of their respective 12v rails. One is 17, the other is 19, so effectively, I want to pull at least 30 amps out of these bad boys. Now, I've run across a problem; due to the PSU's internal voltage detector, the 19A one is always doing the work, as they are both the same voltage, so the weaker one is 'cancelled' out, per say. What I want to do, is increase the voltage, or lower it, by a little bit, so that the voltage won't cause this problem and I can harness all the amps I need. Now, where would I put a diode or resistor to do this? Would I only do it to 1 of the PSU's, or would I have to solder the diodes/resistors onto both of them? Any other input is appreciated.

Note: I'm well aware that using a regulated AC to DC power supply is alot safer and worth it in the long run. I have one of these, this is just an experiment, as stated.

Thank you!

Here is a little diagram I made in paint to show you how I have it wired currently:

edit: I suppose I can't post pictures whilst being a new user. Remove the spaces and go here to view picture. h t t p : / / i41.tinypic.com/2jds2e1.jpg

2. ## Re: Lowering/Increasing voltage on the 12v rail

You would want to put a diode on the 12v wire of each power supply. I would do at least 6 of them in parallel because a diode will drop a consistent voltage of about 1.2v. You don't want that.

3. ## Re: Lowering/Increasing voltage on the 12v rail

Originally Posted by www.eCrack.net
You would want to put a diode on the 12v wire of each power supply. I would do at least 6 of them in parallel because a diode will drop a consistent voltage of about 1.2v. You don't want that.
Wouldn't he still get a drop of 1.2V no matter how many he puts in parallel?

4. ## Re: Lowering/Increasing voltage on the 12v rail

So, I could solder a diode onto each 12v, directly onto the wire? I tried doing this a couple days back but on the cathode and the wire extending from the cathode, I was getting a voltage of 1.2 on my DMM. So it was like I was picking up the diode's voltage but none of the current from the PSU was getting thru. Did I wire the diode on backwards perhaps? Thank you very much for your input.

Edit: Also, about putting diodes on both, seems like that would lower both voltages, but they would still be the same. I'm trying to get a slightly different voltage from one so the voltage detector on the other won't recognize the first as a PSU, and 'accept' it's help, so to speak. :P

5. ## Re: Lowering/Increasing voltage on the 12v rail

Originally Posted by bubbagumper6
Wouldn't he still get a drop of 1.2V no matter how many he puts in parallel?
The answer is no, but why would you think that?

6. ## Re: Lowering/Increasing voltage on the 12v rail

Originally Posted by MikePresJr
So, I could solder a diode onto each 12v, directly onto the wire? I tried doing this a couple days back but on the cathode and the wire extending from the cathode, I was getting a voltage of 1.2 on my DMM. So it was like I was picking up the diode's voltage but none of the current from the PSU was getting thru. Did I wire the diode on backwards perhaps? Thank you very much for your input.
The stripe on the diode goes in the direction of ground. So put the side without the stripe facing the 12v side.

7. ## Re: Lowering/Increasing voltage on the 12v rail

Originally Posted by www.eCrack.net
The answer is no, but why would you think that?
I would just think if each diode has a constant drop of 1.2V it wouldn't matter how many are in parallel, each will still drop 1.2V resulting in the same dropped voltage on the other side...

8. ## Re: Lowering/Increasing voltage on the 12v rail

Originally Posted by bubbagumper6
I would just think if each diode has a constant drop of 1.2V it wouldn't matter how many are in parallel, each will still drop 1.2V resulting in the same dropped voltage on the other side...
Diodes

Forward Voltage Drop

Electricity uses up a little energy pushing its way through the diode, rather like a person pushing through a door with a spring. This means that there is a small voltage across a conducting diode, it is called the forward voltage drop and is about 0.7V for all normal diodes which are made from silicon. The forward voltage drop of a diode is almost constant whatever the current passing through the diode so they have a very steep characteristic (current-voltage graph).

Wiring them in parallel reduces the amount of dropped voltage. If you try it yourself you will see. I use that a lot when making PCM's for alternators.

9. ## Re: Lowering/Increasing voltage on the 12v rail

I can tell just from this thread that, I'm going to like it here. I've asked this question on multiple boards, and this is the only one with anyone who actually knows what they're talking about, so thank you. Okay, so, as an overview, I need to solder diodes on all the 12v wires on the first PSU, and this will only drop my voltage by about 1.2 or so? I don't want it to be running at 8 volts or some odd voltage.

10. ## Re: Lowering/Increasing voltage on the 12v rail

Originally Posted by MikePresJr
I can tell just from this thread that, I'm going to like it here. I've asked this question on multiple boards, and this is the only one with anyone who actually knows what they're talking about, so thank you. Okay, so, as an overview, I need to solder diodes on all the 12v wires on the first PSU, and this will only drop my voltage by about 1.2 or so? I don't want it to be running at 8 volts or some odd voltage.
Yep that should be about right. Obviously measure the voltage once you've soldered them up but you should be in good shape.

11. ## Re: Lowering/Increasing voltage on the 12v rail

Are you saying simply if you can get the current draw small enough you'll get down into the non-linear portion of the curve so the voltage drop decreases?

12. ## Re: Lowering/Increasing voltage on the 12v rail

Originally Posted by bubbagumper6
Are you saying simply if you can get the current draw small enough you'll get down into the non-linear portion of the curve so the voltage drop decreases?

no

13. ## Re: Lowering/Increasing voltage on the 12v rail

Alrighty! Well thank you guys, I appreciate it. I'm currently studying over this type of stuff so I thought this experiment would be a cool learning experience. I will definitely be around here more often.

14. ## Re: Lowering/Increasing voltage on the 12v rail

Originally Posted by www.eCrack.net
no
Then how about explaining? You do this everytime...You claim that I'm wrong yet never go into detail as to how. Don't ask me questions to try and lead me to the answer (you're not my teacher). Just explain it. I know how diodes work so be as technical as possible, I'll ask questions if I don't understand something.

15. ## Re: Lowering/Increasing voltage on the 12v rail

Originally Posted by bubbagumper6
Then how about explaining? You do this everytime...You claim that I'm wrong yet never go into detail as to how. Don't ask me questions to try and lead me to the answer (you're not my teacher). Just explain it. I know how diodes work so be as technical as possible, I'll ask questions if I don't understand something.
You asked me a specific question. I answered it. You always get butthurt and insulting and start flaming. I already told you what to try to observe the results. If I'm not your teacher don't ask me questions at all feglet.

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