12v 300ma transformers to power pc case fans?

I have a few old transformers that output 12volts at 300milliamps. I was wondering if it was all that important to use resistors to get the current within the stated specs for a pc case fan I wanted to try to run on it. I have a fan that states 0.2amps and another that states 0.45amps. Would it matter much if I used this transformer for either of these fans as it is now? Or would it likely ruin either fan?

Reply to
psistormyamato
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This is not a repair issue.

Current is something that's available, and something that's used, not something that is forced. So if you have a power supply that supplies more current than the load requires, the load merely takes what current it needs, and leaves the rest.

It is voltage that is forced. Connect something to a voltage supply that is higher than needed, and you may burn out that something. Connect soemthing to a voltage supply that is lower than needed, and it likely won't work because there's not enough voltage.

On the other hand, some of those AC adaptors are marginal. They expect to work with a certain current load, and thus they can be made cheaper. If they aren't loaded to the specs, the voltage may be higher than it says in the specs. Those expect the load to bring the voltage down to where it should be. WIth those ac adaptors, connecting a lower current fan may mean the voltage is higher than desired, and that may be bad for the fan. It depends on how much higher the voltage.

Michael

Reply to
Michael Black

These adaptors run 12v fans fine, for fans of 0.1A to 0.3A. You cant run the 0.45A fan on one, it'll burn it up. You dont need a resistor.

NT

Reply to
meow2222

I hope you don't intend to try to run a DC fan on AC?

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Reply to
CJT

Why not use the Pc's power supply? It's there, convenient, probably able to handle quite a few more amps of load, and automatically switche4d at the right times.

Reply to
Ancient_Hacker

"Ancient_Hacker" wrote in news: snipped-for-privacy@l39g2000cwd.googlegroups.com:

because he has these xfmrs laying around waiting to be used!

;-)

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Jim Yanik
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Reply to
Jim Yanik

Maybe its not being used on a pc, who knows.

NT

Reply to
meow2222

I assumed the fan had nothing to do with the computer.

Every time I pass a computer on the sidewalk waiting for the garbage truck, I look it over. If it's recent enough and has ram, at the very least I'll extract that. Sometimes the hard drives, and usually (because they are easy to extract, and the cases can be used for building other things in), the power supplies. Hence I have a lot of fans from PC power supplies. I've made a few fans for the warm weather out of them, and have used AC adaptors to power them. They work fine, and often create enough of a breeze without me feeling like I'm facing a major storm.

Michael

Reply to
Michael Black

He's probably not using the fans in a PC.

Reply to
James Sweet

Read the labels on the fans. If they came out of a computer, they are probably DC, not AC. Make sure that your power supplies are the same. If they are just transformers, they are AC. If they are 'wall-warts', they could be either AC or DC.

Reply to
Bennett Price

Sorry, but I figured that I had better ask first before I tried this. This way it wont become a repair issue!

They are AC to DC transformers that used to be for recharging a portable spotlight and,.. I forget what the other was for, maybe that old luminare glass that broke.

I am using them outside the PC, as fart fans and such. I thought about using a power supply for it, but I thought a complete PC power supply would be a little overkill for just fans.

Yes they are PC case fans I will use.

Thanks for the feedback. I try to learn what I can, but my full attention is on world history at the moment. I got an A in physical science, but thats a Tennessee A lol.

Reply to
psistormyamato

snipped-for-privacy@FreeNet.Carleton.CA (Michael Black) wrote in news:eki36j$65k$ snipped-for-privacy@theodyn.ncf.ca:

I used two salvaged PC fans after Hurricane Charlie,Aug.13,2004,to keep cool(Florida in August!) when my line power was out for 7 days. I powered them with a 12v/20ah gel cell.It also powered a small fluorescent lamp.

The fans really helped at night when trying to sleep.

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Reply to
Jim Yanik

Jim Yanik wrote in news:Xns9889BEB6EC1F9jyanikkuanet@

129.250.170.84:

Those fans usually run on DC. The transformer puts out AC. You are likely to ruin the fans.

As for current, do NOT series a resistor to drop the current to the spec'd current.

What they are saying is that the fan will DRAW .45 amps of current when run from 12 volts. The other fan will require less current. It you have to run off of a battery, use the lower current fan. It will run longer.

If the fans DID run on AC, your 12 volt at 300 mA transformer would be overloaded by the .450 amp (450 mA) fan and would likely fail after a short time during which it would overheat.

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Reply to
bz

It only outputs 300 mA if the load demands it.

200mA

450mA

If it is just a transformer, yes, as this outputs AC and most if not all PC fans need DC.

If it is a DC mains adaptor it will be ok with the 200mA fan but overloaded with the 450 mA one.

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Dave Plowman (News)

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