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e-Electric Batteries & Chargers > electronic gurus answer this!!!
 
 
white chocolate
Key Veteran
Location: Baltimore, Md.

I have done the search and read the posts. Nine out of ten people say to put the load on the 5v wire when making a charger power supply out of a computer ps. My question is why do you have to do this?

Quote 
Next choose a location on the PS case to mount the automotive light socket. Mount the light and connect it to a "Common" wire and to a +5 volt (yes plus five volts) wire. You need a small "load" on the +5 volt side of the PS in order for it to put out it's maximum voltage on the +12 volt lines. Some folks use a 1 ohm 25 watt resistor. E-zone is full of opinions on this but I find a small load works fine. If you are not getting slightly over 12 volts of output on the "posts" you can add a second light by connecting it to a "common" and a +5 volt wire.


this is from rcbatteryclinic.com. How does the load help the max voltage on the 12 v lines? Please explain in detail if possible. Not an electronic dummy!
01-20-2004 Over year old.
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Florian Uhlemann
Senior Heliman
Location: Jackson, MI USA

There is a german article how to convert it so you dont need to put a load on it..

the way this PS is made, is that you need to put a load on the 5V to be able to draw the higher amps on the 12V

don't ask ME why. i just know that's the way it is

i know. another useless post

Florian
01-20-2004 Over year old.
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white chocolate
Key Veteran
Location: Baltimore, Md.

actually...

not another useless post. I emailed the guy on battery clinic.com and he said the same thing. I was just curious why this needs to be done. He told me that if there is no current drawing on the five volt wires then it wont send the full twelve to the twelve volt wires. Somewhere round 10 he said. Thanks for the post.
01-20-2004 Over year old.
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Florian Uhlemann
Senior Heliman
Location: Jackson, MI USA

That is correct.

I can send you the pictures of the article, but it's german and you'd need to translate it by yourself I don't feel like doing it, cause it is 5 pages long sorry

In the article they tell how to modefy it so that there is no need to load the 5V and then you'd even have a higher ampere output on the 12V's

Florian
01-20-2004 Over year old.
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Data Android
Senior Heliman
Location: Fort Lauderdale, FL

Can you provide a link to that mod?
I have a load on my, but would like to take a look at this other option.
01-20-2004 Over year old.
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white chocolate
Key Veteran
Location: Baltimore, Md.

german article

Yes could you please post! Or email it to me either way.

thanks
01-20-2004 Over year old.
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Sar
Elite Veteran
Location: Kingston, NY

The power supply is designed to be run under a load, if you do not run it under a load, it will not produce full power on the 12 volt output leads. I'm curious to see how the German mod bypasses this problem, perhpas by tricking the feedback loop into thinking it is under load.

It can become very time consuming to explain technically, but the 12 and 5 volt outputs share the same power drivers inside of the power supply. The power supply monitors/samples the primary output (the 5 volt side) to determine the required power to drive the transformers with. If the load on the 5 volts is too light, the drive circuit will not provide enough power to adequately drive the 12 volt side and you'll get below-rated current from the 12V as such and possibly unstable voltages, particularly under load.

So if you put a load on the five volt side, the driving circuitry will need to drive it more strongly, which at the same time results in the 12 volts side being driven more strongly and providing the specced current.

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Jon
01-20-2004 Over year old.
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Silvashadow
Senior Heliman
Location: Bexley, Kent, UK

Try the link below. It describes how to modify an AT power supply to give full load capability without an external load on 5V rail. I never had the time to try it myself.
http://www.raptortechnique.com/12vpower.htm

Best of luck

Graham
01-20-2004 Over year old.
 
 
Florian Uhlemann
Senior Heliman
Location: Jackson, MI USA

Here we go.. have fun translating








Florian
01-21-2004 Over year old.
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IMZ Caliber
Senior Heliman
Location: Chesapeake, VA USA

Needing a load seems to be only for the newer powersupplies, with in the last 6-8 years. If you have one from the time before all the energy saver MB's came out you won't need to do this.
01-21-2004 Over year old.
 
 
Peter65
Key Veteran
Location: Roxby Downs, South Australia.

This has been discussed recently on our Aussie Forum. We have had a number of people build this project and are happy with the results

12V PSU

Laughing at yourself will lengthen your life. Laughing at me will shorten it...
01-21-2004 Over year old.
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e-Electric Batteries & Chargers > electronic gurus answer this!!!
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