Hard Drive Power supply voltage

[LouSir]

I have a label printer that came with a 9v 300ma power supply. I would like to some how regulate ne of my 12v hard drive power connectors down to 9v. Any Ideas? Has this been tried before? successfully?

[bassman]

Hello LouSir and welcome,
There are some very good electronics people here and I am sure they will be along soon to answer your question directly.
As for me, I would suggest NOT using any of the leads from you computers PSU to run an external unit, especialy any type of printer.
Although this printer is only 9 volt, I belive the amprage draw is a little higher then you would want pulling from you machine.

Wait for some of the others to answer to be sure this is the right idea http://www.PCGuide.com/ubb/wink.gif

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[kenja]

Well, it can be done, but I'd need a really good reason not to use the "wall wart" (transformer/rectifier).

The amount of current doesn't bother me. For example, the 12V draw of my new 24x CDRW is 2.0Amps. To do this right, we need a DC to DC converter, and going from 12V to 9V at almost a third of an amp is not a common configuration. I found this (http://www.mpja.com/product.asp?product=12776+PS), but I have no idea if you can connect two in parallel (for adequate current). Here (http://www.uoguelph.ca/~antoon/circ/car912.htm) is a schematic, but I haven't checked the current capability of the transistor.

If I was stranded somewhere and absolutely needed 9V from my PC, I could use the 3.3V as the return ("ground") for the +12V line, for a sum of 8.7V (probably close enough for the label maker).

I do not recommend doing this, because the 3.3V power is critical to the operation of the CPU and memory. I've got a computer that runs the CPU fan using the +12V and +5V leads, for a sum of 7V (lower RPM = less noise). I haven't had any problems, but I don't have a real good feeling about it. Someone said they contacted PC Power & Cooling about doing this, and they advised against it, saying it could interfere with the regulation of the +5V "rail". The guy went ahead and did it anyway, without any problem.

[kenja]

Here (http://www.mitedu.freeserve.co.uk/Circuits/Power/dcdc_con.htm) is another schematic.

[ranchdog]

A common Rheostat could be used if this is necessary for a power supply. Turn the dial and lower the voltage. Use a Volt Meter on the backside and adjust for a reading of 9V. 12V in (Yellow wire) and whatever the dial setting is will read on the out leg.

We use Rheostat's once in a while (making a Rheobus) for fan's,
etc. Reduce the voltage and reduce the rpm.

Think of it as that dial thingie on the light switch that will dimm the living room lights.

Please don't overload the PSU.

Luck.

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[kenja]

Plans (http://www.fanbus.com/) for making a "rheostat fanbus".

(Dropping 3 volts across the rheostat at 0.3 amps = 0.9 watts, which means there will be an insignificant amount of heat generated.)


[This message has been edited by kenja (edited 12-17-2001).]

[LouSir]

Thanks for all the input, I think I will go with the reostat while I tinker with some of those circuits that you guys have sent. Thank You All Again

[Mini-Me]

One question: Why don't you simply use the p/supply that came with the printer?

You can regulate the 12v rail of the computer p/s down to 9v easily using an LM317T adjustable voltage regulator IC.
These are very cheap and the ciruit is dead easy to build.

To correctly drive a regulator IC like this, you need at least 2.5v greater input voltage then the wanted output voltage.
9 + 2.5 = 11.5, so with 12v input, you can happily get stable 9v output from the LM317 up to 1 amp.

Contact me at my e-mail address for more details and a schematic.
You will need to know how to solder.
Basic electronic knowledge would help to!!!
http://www.PCGuide.com/ubb/wink.gif


G.


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