Jump to content

12v current limiter to slow 12v fan

real_vibes

By real_vibes
in Boat Equipment

 Share

Featured Posts

bizzard Veteran II

bizzard

Posted
Posted (edited)

Is this fan a engine radiator cooling fan which are very powerful or a heater circulating fan which are much less powerful. I think by adding resistance like a rheostat to reduce the motor speed doesn't save any electricity, the rheostat just exhausts unwanted current in heat. An old fashioned model railway 12vdc rheostat speed controller like an early Triang one which took 12vdc from a mains transformer and supplied a variable 12vdc current to the track, variable between 0 and 12vdc would do.

 

eta. But don't attempt to do it with a hot cross bun though, for if you happen to tread on it a currant might run up your leg and electrocute you. closedeyes.gif

Edited by bizzard
Link to comment
Share on other sites
dor Veteran II

dor

Posted
Posted

Do you know what the current rating of the fan is? A 12V light bulb in series is an easy way of putting a resistor in the circuit, and usually cheaper than an equivalent resistor with a high enough current rating.

  • Greenie 1
Link to comment
Share on other sites
churchward Veteran II

churchward

Posted
Posted

A rheostat would be better. wink.png

 

 

Real vibes

 

This will make the fan, variable speed.

 

These were a luxury item on cars many, many years ago jut after they started fitting heaters.smile.png

Yes indeed my 1960 Morris Minor convertible has one on the heater fan.

Link to comment
Share on other sites
nicknorman Veteran II

nicknormanDonate to Canal World

Posted
Posted

the potentiometer you mention in post #5 would burn out in a second. You need something that can handle the current / power dissipation. 12v at 1A means an effective resistance of 12 ohms. Say you wanted to halve the current, you could add another 12 ohm resistor in series, but that will still be dissipating 3 watts so you need a high power wire wound resistor. Maplin do a 10 ohm 7 watt one, which would probably do. Order code L10R. 74p. Even though its rated well above the requirement, it will still get hot so don't burn yourself on it.

 

Of course if you slow it down too much, it may stall and not run at all. Perhaps it would be safer to get a lower value one say L4R7 as well, if you are going to the trouble of driving to Maplin. Then if 10 ohms transpires to be not enough, you can put the two of them in series to make 14.7 ohms.

Link to comment
Share on other sites
PaulG Experienced

PaulG

Posted
Posted

Resistors are just going to waste power and run your batteries down faster.

I suggest you look at a PWM controller, which would be much more efficient.

You need to measure the input current of your fan first, and then allow a safety margin. Here's an example of something that might be suitable:

 

http://www.ebay.co.uk/itm/12V-40V-10A-Pulse-Width-Modulation-PWM-DC-Motor-Speed-Control-Switch-Governor-UK-/121008731849?_trksid=p2054897.l4275

Link to comment
Share on other sites
ditchcrawler Veteran II

ditchcrawlerDonate to Canal World

Posted
Posted

Resistors are just going to waste power and run your batteries down faster.

I suggest you look at a PWM controller, which would be much more efficient.

You need to measure the input current of your fan first, and then allow a safety margin. Here's an example of something that might be suitable:

 

http://www.ebay.co.uk/itm/12V-40V-10A-Pulse-Width-Modulation-PWM-DC-Motor-Speed-Control-Switch-Governor-UK-/121008731849?_trksid=p2054897.l4275

How is it going to run your batteries down faster. It may not be effficent but if you double the resistance of the circuit you will have the current and the battery would last twice as long.

Link to comment
Share on other sites
nicknorman Veteran II

nicknormanDonate to Canal World

Posted
Posted

 

How is it going to run your batteries down faster. It may not be effficent but if you double the resistance of the circuit you will have the current and the battery would last twice as long.

"Run your batteries down faster" ... than if you used a PWM controller. Is true, but at a significant extra cost (10 times a resistor). Yes, this is a more elegant solution although the board doesn't seem to be CE marked and with an absence of inductors visible, I wonder what its RF emissions are like!

Link to comment
Share on other sites
PaulG Experienced

PaulG

Posted
Posted

How is it going to run your batteries down faster. It may not be effficent but if you double the resistance of the circuit you will have the current and the battery would last twice as long.

Alright. I'll rephrase it. Using a resistor will waste power and run your battery down faster than would be the case if you use a PWM controller!

 

 

"Run your batteries down faster" ... than if you used a PWM controller. Is true, but at a significant extra cost (10 times a resistor). Yes, this is a more elegant solution although the board doesn't seem to be CE marked and with an absence of inductors visible, I wonder what its RF emissions are like!

Depends whether you consider a cost of a couple of pints of beer to be significant! biggrin.png

If it's for sale in the EU it must be CE marked by law.

I wasn't necessarily recommending this board - I chose it as an example because it had good picture with dimensions.

Other (and probably better) boards are available!

Link to comment
Share on other sites
nicknorman Veteran II

nicknormanDonate to Canal World

Posted
Posted

Alright. I'll rephrase it. Using a resistor will waste power and run your battery down faster than would be the case if you use a PWM controller!

Depends whether you consider a cost of a couple of pints of beer to be significant! :D

If it's for sale in the EU it must be CE marked by law.

I wasn't necessarily recommending this board - I chose it as an example because it had good picture with dimensions.

Other (and probably better) boards are available!

Yes but its from china and the law isn't always followed on ebay!

Link to comment
Share on other sites
ditchcrawler Veteran II

ditchcrawlerDonate to Canal World

Posted
Posted

Alright. I'll rephrase it. Using a resistor will waste power and run your battery down faster than would be the case if you use a PWM controller!

 

Got you now, when I read it I honestly thought you were saying that because of the head/power wasted it would use more power with the resistor than without. Its to easy to read things and get the hot end of the soldering iron, I mean wrong end of the stick.

Link to comment
Share on other sites
smileypete Veteran II

smileypete

Posted
Posted (edited)

It

Says 12v 1A. Does that mean 1Amp?

 

Still unsure what kit I need but can't help but think there is a good and simple solution.

 

This sort of thing should do:

 

http://www.ebay.co.uk/itm/BLACK-2A-MULTI-VOLTAGE-CAR-DC-DC-CONVERTER-/270959020720

 

And this might come in handy for hooking the output up to the fan lead:

 

http://www.ebay.co.uk/itm/2x-DC-POWER-JACK-CONNECTORS-MALE-FEMALE-ADAPTER-F-CCTV-DVR-CAM-5-5mm-X-2-1mm-/160756789659

 

How much do you want to slow it down, and what's it going to be used for, some sort of eco fan replacement?

 

cheers, Pete.

~smpt~

Edited by smileypete
Link to comment
Share on other sites
Doodlebug Rising Star

Doodlebug

Posted
Posted

A resistor is the wrong way to do it, for a start as mentioned you would need a big resistor to handle the heat created, and also you will loose the torque of the motor.

 

You need the motor speed regulator from maplins, I have a fan similar to yours, and the regulator and it works very well. It works using PWM, or pulse width modulation. Roughly translated this means it turns the motor on and off at a few thousand times a second. If the motor spends 50% of the time on and 50% off, the motor will run at half the speed it does when on all the time.

 

The dial allows you to adjust (modulate) the pulse width, ranging from 1% on 99% off to 99% on 1% off.

 

A quick google will explain it. But messing around with resistors just isn't the right way to go about it.


http://www.maplin.co.uk/mfa-panel-mounted-speed-regulator-module-30310

 

^^ thats what you need.

 

Hope that helps.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.