Powering A 5v Device

[Finite]

Guys Im looking at using an unused PC fan controller for monitoring the temperatures of my AG system. THe fan controller has 4 probes all raited -50C to 90C. The power cable that comes with it plugs into a standard molex PC plug. The controller has a small fan on it which uses 12v (0.09A) a ground and another wire which is 5V which I assume runs the display and such. The fan isnt really essential as it will be outside in a project box but my question is, how can I wire this up to run without the need of a PC power supply.

 

[kook]

http://www.jaycar.com.au/productView.asp?I...mp;SUBCATID=381

That'll give you both 12 and 5, but it's not cheap.

 

[Sammus]

you could get a nokia phone battery charger, I think there is a slight difference between the old one and new one, one is 5.7V but I think the older style is 5V. If thats the case then you could maybe use one of those, I dont think the fan controller would draw too much current. If theyre all 5.7V then I dont think the extra 0.7V would hurt it, seeing as the 5V on a computer PSU can vary upto 0.5V or so. Don't blame me if your house burns down and explodes if you try it though (read: you might want to wait for someone to clarify this fact )

And I know you sad you didnt want to use a computer PSU, but I just did this which comes in handy a lot to power various devices. Ive done it to a 250W PSU, but that can only handly 8A on the 12V rail, so is not enough to use on a cordless drill I salvaged (batteries were f*cked), but if speed isnt an issue the 5V rail can handle upto 22A. plus Ive got a 350W and 400W PSU waiting to get the same mods, and i think they should have the grunt to run it....anyway I digress, I just thought it was an interesting article

 

[bonj]

You need a 5V regulator such as a 7805, which should be fine if it's just for an LCD display or similar. You'll need a couple of capacitors too... I'll try and find a schematic for you.

 

[Sammus]

You need a 5V regulator such as a 7805, which should be fine if it's just for an LCD display or similar. You'll need a couple of capacitors too... I'll try and find a schematic for you.

I imagine the phone charger or the computer PSU are already regulated...from what I understand charging batteries with pulses isnt a really good idea, and I know computers need super stable voltages too.

 

[bonj]

Looks like we were replying at the same time... didn't see your post, Sammus

My nokia charger is only 3.7V

 

[PostModern]

You can get old AT computer power supplies for next to nothing. $10 or so. If you can be bothered to come down to Bulli or meet me in the City next week, I'd give you one out of my old PC bits cupboard. Is there some reason other than cost that puts you off PC PSU's?

 

[Wortgames]

from what I understand charging batteries with pulses isnt a really good idea

Actually most batteries benefit from being pulse charged! Many of the more expensive chargers deliver pulses. Don't know about Nokia chargers specifically.

You could get something like this: http://www.jaycar.com.au/productView.asp?ID=MP3035

It's total overkill but the price is good and it is a handy thing to have around if you tinker with electronic gadgets. The 4.5v output would probably be perfect.

Alternatively, just get a used PC PSU from an old PC on hard rubbish day or from a spares place, and plug it straight in.

 

[warrenlw63]

The computer fan in my fridge has been buzzing away on a Nokia charger for the last 2 years. Hasn't skipped a beat. It will be fine.

Warren -

 

[newguy]

Have a look in electronic shops......there used to be a chain in Canada called Radio Shack but they've changed their name to The Source by Circuit City (crappy name). Anyway, they carry various adapters (sometimes called wall warts), and I have one that features an adjustable output voltage. See if you can find one rated for 5V DC somewhere. Other good stores to check are liquidation and surplus outlets and second hand stores.

This is what I'm talking about: 5V Adapter

 

[Keifer]

would a 4.9vdc (450mA) sony ericson phone charger work with a PC CPU fan ?

 

[newguy]

would a 4.9vdc (450mA) sony ericson phone charger work with a PC CPU fan ?

Depends if the fan is rated for 5V or not. If it is a 5V fan, 4.9V is close enough, just as long as the current draw of the fan is less than 450mA.

 

[razz]

The computer fan in my fridge has been buzzing away on a Nokia charger for the last 2 years. Hasn't skipped a beat. It will be fine.

Warren -

Hey Warren, do you have any pics of your fridge/fan set up? I would like to do this in my chest freezer.

 

[Simon W]

Any old mobile phone charger plugpack will do, Hockshops/pawnbrokers like Cash Converters usually have a boxfull of them for around $2 each.
Check the print on the charger for a 5.1 or 5.7 volt one, and make sure its a DC plugpack, not all are. (DC is signified after the output voltage with two lines, a solid one with a dashed one parallel to and below it)

eg:
_____
- - - -

Try and get a switchmode one as they have a much higher current handling capability, they are very compact and lightweight compared to the old style wall-warts.

BTW, not all rechargable batteries like a pulsed charge. Sanyo's R's (AR, SCR etc) loved it, their E's hated it, some of the current crop of Sanyo NiMH's, like the 3300's dun like it either. Reflex charging is something else altogether(short charge, rest, very short discharge, rest, short charge, etc etc), most batteries do like this.

 

[sstacey]

I'm no electronics wiz, but cant you just add some resistors into the circuit to reduce the current to 5V?
Then it could be powered by a 9volt battery or something simple and cheap.

 

[Simon W]

Voltage and current are different things, an analogue is that Voltage is like water pressure, whereas Current is like the flow rate.

Yes resistors can be used to drop the 9v to 5v, depending on the current drawn, but if this current draw changes for any reason, so will the voltage dropped by the resistor.

A voltage divider using two resistors is better for stability, but is wastefull of power with the limited capacity of a 9v battery.

 

[Finite]

You can get old AT computer power supplies for next to nothing. $10 or so. If you can be bothered to come down to Bulli or meet me in the City next week, I'd give you one out of my old PC bits cupboard. Is there some reason other than cost that puts you off PC PSU's?

Thanks for the offer PostModerb, I do have some spare PSU's lying about, its the size I was concerned about, that and I wanted to be able to leave it outside, maybe if I can find a project box big enough or I might build one out of some waterproof marine ply which I have in the gararge, glue with araldite and give the edges a hit with some waterproof silicone?

Thanks for all the replies guys, makes it much easier to consider options.

P.S: heres a teaser of what it looks like (it will be mounted on the brew stand somewhere)

 

[warrenlw63]

Hey Warren, do you have any pics of your fridge/fan set up? I would like to do this in my chest freezer.

Razz

Straightforward stuff. I use a chest freezer with a wooden collar. I've just got the fan screwed to back part of the collar. I'll try and find a pic.

Warren -

 

[Screwtop]

Blake, lots of silly advice here, fact is yes you can use it, but like bonj says to run a device such as a display you'll need a regulator.

 

[jupiter]

You need a 5V regulator such as a 7805, which should be fine if it's just for an LCD display or similar. You'll need a couple of capacitors too... I'll try and find a schematic for you.

yup. just get a 12V regulated DC wallwart and wire a 7805 into a bit of choc-bloc with the filter caps to get your 5 volt. the circuit to wire it is in the DataSheet which can be found on the national semiconductor website www.national.com.

otherwise you can get multi output switchmode power supplies reasonably cheap from places like altronics, jaycar or computronics. or even ebay. i picked up 10 small 5v switchmode power supplies a couple of years ago for $10 which i use in my projects for doing exactly what you want to do -> to power digital electronics circuits