Possible to turn a 5v 350mA mobile phone charger into a 12v power supply to drive a computer fan?

Thread Starter

MkkDdd

Joined Sep 11, 2017
10
I know computer fans can be run with mobile phone chargers because I've got it to work just by finding and joining the relevant wires (live and ground). That's about the limit of my knowledge and experience, though, I'm afraid; but I'd like to build on that. I want a bigger, better fan now. The ones I've done are noisy little 5v. blowers which aren't really man enough for the job. I understand I can get a 12v. fan to run from a mobile phone charger the same way as the 5v. ones do, and it will run slower and quieter. That's good; that's what I want. I understand a 12v fan may not start without an initial voltage of 5v., and if it does it may stall (and burn out) and this could be caused by a seemingly insignificant obstruction, or without any obstruction at all. If I'm not mistaken I also read somewhere that a simple diode or resistor could be worked into the circuit somehow somewhere to stop that happening, but I can't find where I read that now. That's what I want to find out about here: how can I do that?

Then, when I started thinking about it, it occurred to me that I might actually be able to make it a bit better and get exactly what I want: I'd like to be able to run the 12v. fan at full blast if necessary for short periods and then turn it down when things have cooled down. Is there any way I can do that: 1) make a 5v mobile phone charger put out 12v., 2) put a control on it to reduce the voltage, and 3) make it so it won't stall the fan? The fan I have in mind (this one: https://www.arctic.ac/eu_en/arctic-f12-tc.html) is designed to be run at variable speeds.
 

panic mode

Joined Oct 10, 2011
1,782
your charger can produce up to 0.35 A at 5V. that is 5V*0.35A = 1.75W
your fan draws 0.24A at 12V. that is 12V*0.24A = 2.88W
any conversion will only add losses. say you have something that is 80% efficient, that means you would need to use supply that is 2.88W/0.80 = 3.6W which is more than double of that your charger can put out.
 

Thread Starter

MkkDdd

Joined Sep 11, 2017
10
your charger can produce up to 0.35 A at 5V. that is 5V*0.35A = 1.75W
your fan draws 0.24A at 12V. that is 12V*0.24A = 2.88W
any conversion will only add losses. say you have something that is 80% efficient, that means you would need to use supply that is 2.88W/0.80 = 3.6W which is more than double of that your charger can put out.
OK, so is there anything I can do to the charger to increase its capacity? Presumably not, so I'll just have to run the fan at 5v from this charger, which will make it slower and quieter. That's OK, but it's back to the original question: how can I stop it from stalling?
 

panic mode

Joined Oct 10, 2011
1,782
run it from proper source.

that fan is rated for 12V, so run it from a 12V source that can deliver at least 1/4A

Note that power can also be expressed in terms of voltage:

P=V^2/R

Note the square factor...

So doubling voltage, quadruples power (4x).
Tripling voltage, increases power to factor 9x.
Reducing voltage, reduces power (5V/12V is 41%).

Running 12V load from 5V source means that this fan only gets 17% of power (that is 41% of 41%). No wonder it is under powered... hamster farts can reverse it.. :)
 

philba

Joined Aug 17, 2017
959
Well, you can do what you want but it would be far cheaper to just go to a thrift store and pickup a 12V wall wart. Typically one or two dollars.

To reduce the speed/noise, look into a PWM speed controller. ebays has lots of listings for < $10. Search for "pwm speed controller".
 

Thread Starter

MkkDdd

Joined Sep 11, 2017
10
run it from proper source.

that fan is rated for 12V, so run it from a 12V source that can deliver at least 1/4A

Note that power can also be expressed in terms of voltage:

P=V^2/R

Note the square factor...

So doubling voltage, quadruples power (4x).
Tripling voltage, increases power to factor 9x.
Reducing voltage, reduces power (5V/12V is 41%).

Running 12V load from 5V source means that this fan only gets 17% of power (that is 41% of 41%). No wonder it is under powered... hamster farts can reverse it.. :)
Yes, very amusing – thank you!
Well, you can do what you want but it would be far cheaper to just go to a thrift store and pickup a 12V wall wart. Typically one or two dollars.

To reduce the speed/noise, look into a PWM speed controller. ebays has lots of listings for < $10. Search for "pwm speed controller".
Now that IS helpful; thank you, philba!
 

Thread Starter

MkkDdd

Joined Sep 11, 2017
10
Yes, indeed, philba; that (http://www.ebay.co.uk/itm/DC-1-8V-3V-5V-6V-12V-2A-Low-Voltage-Motor-Speed-New-Controller-PWM-1803B-/111531021357?hash=item19f7c4542d:g:lqAAAOSwnDxUds8K) and this (http://www.ebay.co.uk/itm/AC-Power-Adapter-12V-DC-Supply-2a-amp-regulated-Wall-Wart-Charger-5-5-X2-5-mm-EU-/282121706292?hash=item41afc39b34:g:LGYAAOSwZVlXoa7M) are exactly what I'm looking for. Just wish I could find the 'wall wart' things a bit cheaper. I don't suppose there's any way I can modify phone chargers to do the same thing, is there? I had thought perhaps it might just be a question of soldering in a resistor or something, but it would seem ignorance has got the better of me there.

In any case, your contribution has given me the clarity I was looking for, for which I am very grateful. Thank you.
 

dl324

Joined Mar 30, 2015
8,891
Welcome to AAC!

Friendly bit of advice. Wait until you have a few posts under your belt before you start getting snarky with senior members.
I don't suppose there's any way I can modify phone chargers to do the same thing, is there?
Get one that can provide at least 1A and use a switching regulator to step voltage up to 12V.
I had thought perhaps it might just be a question of soldering in a resistor or something, but it would seem ignorance has got the better of me there.
Won't work. With resistors, you can only get less than the input voltage. Even going the other way, from 12V to 5V, couldn't be done efficiently with just resistors.
 

Thread Starter

MkkDdd

Joined Sep 11, 2017
10
Welcome to AAC!

Friendly bit of advice. Wait until you have a few posts under your belt before you start getting snarky with senior members.
Get one that can provide at least 1A and use a switching regulator to step voltage up to 12V.
Won't work. With resistors, you can only get less than the input voltage. Even going the other way, from 12V to 5V, couldn't be done efficiently with just resistors.
What, you mean the 'hamster farter'? One man's amusement is another's banal.

That's the thing with the phone charger route: they don't provide 1A, which makes philba's suggestion the way to go; just don't want to fork out five bucks half a dozen times for 'wall warts' right now. I will with time, eventually replace the phone chargers driving the fans bravely into the face of hamster farts with these wall wart things and the potentiometer thing (motor speed controller) – exactly what I want.

Actually, it's all worked out very well for me here because I've got two 5v fans driven by 5v phone chargers (power sources) which make a hell of a noise because they're running at full blast. That motor speed controller I found for two bucks as a result of philba's suggestion is a godsend – just what I need to control those noisy fans. The other, bigger (12v) fans can run at 17% power for a while.

Yes, I rather thought what you wrote about resistors must be the case; was just hoping maybe there might be some magical work round, but it's all worked out for the best now. Thank you very much for your input.
 

Thread Starter

MkkDdd

Joined Sep 11, 2017
10
Using a mobile phone charger to provide a 5v. 350mA supply, wouldn't this 'Mini 3V/3.3V/3.7V/5V/6V to 12V DC-DC Boost Step-up Converter Power Supply Module' (http://www.ebay.co.uk/itm/Mini-3V-3-3V-3-7V-5V-6V-to-12V-DC-DC-Boost-Step-up-Converter-Power-Supply-Module-/263025181008?) do the same thing as a 'wall wart', i.e. provide a 12v. supply which I could then run through the motor speed controller to drive the bigger (12v.) fans? At £1.18 (a buck and a half) it looks like a real winner to me. I think it will do the job, won't it?
 

philba

Joined Aug 17, 2017
959
Not sure I understand the insistence of starting with 5V when 12V is dirt cheap. Seriously, go to a thrift store. 12V multi-amp WWs are there for less than the cost of a bad cup of coffee. Look for ones from wifi routers. I picked up 3 the other day for $4 and they all work just fine.
 

Thread Starter

MkkDdd

Joined Sep 11, 2017
10
Do not include political commentary (particularly in technical threads)
Not sure I understand the insistence of starting with 5V when 12V is dirt cheap. Seriously, go to a thrift store. 12V multi-amp WWs are there for less than the cost of a bad cup of coffee. Look for ones from wifi routers. I picked up 3 the other day for $4 and they all work just fine.
Yeah, you're right. I was put off at first because I couldn't see any with EU plugs for less than five or six dollars. After a bit of fishing around I've found one for £2.40+ £0.49 postage – ~$3.80 all in – so I've gone ahead and ordered a couple of them.

Question answered, problem solved, thanks again.

Please don't take this the wrong way, I don't mean to be 'sharky' (whatever that means) or otherwise offensive, but you may genuinely not be aware that we don't have 'thrift stores' here, like they (you?) do in the States. I know because I lived in the States for many years. <snipped political commentary>
 
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WBahn

Joined Mar 31, 2012
24,692
Using a mobile phone charger to provide a 5v. 350mA supply, wouldn't this 'Mini 3V/3.3V/3.7V/5V/6V to 12V DC-DC Boost Step-up Converter Power Supply Module' (http://www.ebay.co.uk/itm/Mini-3V-3-3V-3-7V-5V-6V-to-12V-DC-DC-Boost-Step-up-Converter-Power-Supply-Module-/263025181008?) do the same thing as a 'wall wart', i.e. provide a 12v. supply which I could then run through the motor speed controller to drive the bigger (12v.) fans? At £1.18 (a buck and a half) it looks like a real winner to me. I think it will do the job, won't it?
If your step-up converter is 100% efficient, then your output would provide at best 145 mA, and more likely max out somewhere in the 125 mA range, or half what your "full blast" is looking for.
 

WBahn

Joined Mar 31, 2012
24,692
Please don't take this the wrong way, I don't mean to be 'sharky' (whatever that means) or otherwise offensive, but you may genuinely not be aware that we don't have 'thrift stores' here, like they (you?) do in the States.
Well, it's probably a bit unreasonable to expect people to be aware of what you do and don't have since you chose not to include your location in your profile. While we are very much in international site with members from all over the world, the simple fact is that the overwhelming majority are from the United States (as best I can tell) and so when there's no way to tell where a member is from, it pretty natural for most people to take the safe bet and assume that they are most likely from where most members are from.

Also, please refrain from gratuitous injection of politics into threads.
 

Thread Starter

MkkDdd

Joined Sep 11, 2017
10
Well, it's probably a bit unreasonable to expect people to be aware of what you do and don't have since you chose not to include your location in your profile. While we are very much in international site with members from all over the world, the simple fact is that the overwhelming majority are from the United States (as best I can tell) and so when there's no way to tell where a member is from, it pretty natural for most people to take the safe bet and assume that they are most likely from where most members are from.

Also, please refrain from gratuitous injection of politics into threads.
It wasn't gratuitous. I was explaining 'Why not just go to a thrift store?'.
 

WBahn

Joined Mar 31, 2012
24,692
It wasn't gratuitous. I was explaining 'Why not just go to a thrift store?'.
I'm thinking that neither the U.S. standard of living nor President Trump's position on NATO members' level of defense spending is particularly critical to the explanation of why you don't have thrift stores in the undefined place where you live.
 

Plamen

Joined Mar 29, 2015
98
I know computer fans can be run with mobile phone chargers because I've got it to work just by finding and joining the relevant wires (live and ground). That's about the limit of my knowledge and experience, though, I'm afraid; but I'd like to build on that. I want a bigger, better fan now. The ones I've done are noisy little 5v. blowers which aren't really man enough for the job. I understand I can get a 12v. fan to run from a mobile phone charger the same way as the 5v. ones do, and it will run slower and quieter. That's good; that's what I want. I understand a 12v fan may not start without an initial voltage of 5v., and if it does it may stall (and burn out) and this could be caused by a seemingly insignificant obstruction, or without any obstruction at all. If I'm not mistaken I also read somewhere that a simple diode or resistor could be worked into the circuit somehow somewhere to stop that happening, but I can't find where I read that now. That's what I want to find out about here: how can I do that?

Then, when I started thinking about it, it occurred to me that I might actually be able to make it a bit better and get exactly what I want: I'd like to be able to run the 12v. fan at full blast if necessary for short periods and then turn it down when things have cooled down. Is there any way I can do that: 1) make a 5v mobile phone charger put out 12v., 2) put a control on it to reduce the voltage, and 3) make it so it won't stall the fan? The fan I have in mind (this one: https://www.arctic.ac/eu_en/arctic-f12-tc.html) is designed to be run at variable speeds.
 

Plamen

Joined Mar 29, 2015
98
If the fan is to cool a desktop computer...it has its own 12V. If your fan is to used stand alone then you can look for a compromise - if 12V is too much for the charger and 5V is too little for the fan - get a small boost module and adjust thew voltage within the charger's capabilities.
Let us say you will be able to reach 9V - still way better than 5V
 

WBahn

Joined Mar 31, 2012
24,692
Your thinking doesn't surprise me.
If the fan is to cool a desktop computer...it has its own 12V. If your fan is to used stand alone then you can look for a compromise - if 12V is too much for the charger and 5V is too little for the fan - get a small boost module and adjust thew voltage within the charger's capabilities.
Let us say you will be able to reach 9V - still way better than 5V
If he doesn't want to get a 12 V wall wart because it costs too much, he probably isn't going to be too interested in getting a boost module.
 
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