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Jonpro03 01-29-2011 05:00 PM

Any electronics guys in here?
 
I know it's a shot in the dark, but I need help with this. I'm the cheapest guy you'll ever meet. So spending money on a DC to DC power supply for my carputer is not an option for me. Why buy it when I can build it? So I've spent a couple of weeks in multisim building circuits, and I can't get anything reliable. Plus I have to account for the fact that voltages in a car can range form 10-14 volts or whatnot.


So my next thought was to just add 12V from the car to the point on the power supply after the rectifier. So I started researching power supplies. Then I found this:

http://reference.findtarget.com/sear...ower%20supply/

More specifically this:


An SMPS designed for AC input can often be run from a DC supply (for this would be ), as the DC passes through the rectifier stage unchanged. It's however advisable to consult the manual before trying this, though most supplies are quite capable of such operation even though nothing is mentioned in the documentation. However, this type of use may be harmful to the rectifier stage as it will only use half of diodes in the rectifier for the full load. This may result in overheating of these components, and cause them to fail prematurely.

Now, I've heard this before. Simply run the 12Vdc to the AC input of a regular PC powersupply. It sounded retarded to me when I heard it. Then I learned a little more about it and now I'm curious.

I understand why the diodes (I believe Zener) would burn up, and it's no problem for me at all to replace those with some more appropriate ones.

GXP Venom 01-29-2011 05:30 PM

IS this the same guy in almost in tears over his XBox with the wires soldered everywhere..... doesn't sound like this person is saving himself any money. Sorry, but BAHAHAHAhahahahahaha. It will work. It will create heat. That heat will compound as you go along, resistance builds heat builds more resistance builds more heat....... Just because something will work in itself. doesn't account for dealing with everything that goes on as it works. This is your XBox talking to you Jon, I hate you.......

Changing out the diodes is a step, but will circuits and paths take the heat. Kinda like punching out a block to accommodate a piston without figuring out if the wall thickness will still take the heat/compression. I believe those cheap Dollar Store phone chargers use this and they fry quickly, often taking a phone with it.

sawgunner 01-29-2011 05:33 PM

want a power inverter for you car i'll sell mine for cheap

Jonpro03 01-29-2011 05:44 PM

I have a DC to AC converter. I just don't want to use it because then I'm going from DC to AC back to DC and loosing a lot of power in the process.

GXP Venom 01-29-2011 05:46 PM

Why use an inverter then. Why not a DC transformer?

Jonpro03 01-29-2011 05:58 PM

That's what I'm working on... but dropping voltages to 12V, 5V, and 3.3V when your input voltage is anywhere between 10-14V is not easy, that and I need at least 3 amps for each voltage. The thing is, I'm pretty sure that after going through the rectifier on a PC power supply, the output is 12V. So that's where I want to apply voltage and say screw you to the rectifier side of the powersupply.

GXP Venom 01-29-2011 06:24 PM

Saying screw you usually results in unwanted side effects. LOL . I haven;t been around hobby electronics in quite the while p\but it seems to me I remember dc transformers that allow you to tap into "legs" along the windings. This would be ideal for your project. Don't know the availability or cost.

Jonpro03 01-29-2011 06:50 PM

So in order to get an ATX power supply to work on a DC input, you have to input ~220V. That's not gonna work...


Back to working on applying DC voltage after the rectifier.

StealthGXP 01-29-2011 06:57 PM

Your cheap ???

How much time have you put into this ??

I bet you could of picked up a nice inverter big enough to power what you need !!!

I mean I know that your learning .. But idk.

Jonpro03 01-29-2011 07:03 PM

Well like I said, I have a 400W DC to AC inverter that I'm currently using. I just don't want to use it anymore. LOL


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