Tom's Hardware > Forum > Old Man/Woman's Club > Other > Help electronics.

Help electronics.

Forum Old Man/Woman's Club : Other - Help electronics.

Tom's Hardware: Over 1.4 million members in 6 different countries available to answer all your high-tech questions. Sign up now! Its free!
Ask the community Add a reply
Word :    Username :           
 
svol   02-27-2002 at 01:36:16 PM

I need some help to figure out how to change the Amperage in the following setup:
<A HREF="http://home.kabelfoon.nl/~svo/rheostat2.gif" target="_new">http://home.kabelfoon.nl/~svo/rheostat2.gif</A>.

The voltage of the powersupply is 12V, with the Rheostat 0.70 I can regulate the voltage from 7V to 11.6V, the fan is an 12V 3A 120mm fan.
The problem is my Rheostat gets very hot when I set the Voltage to the lowest, as you can see in the picture there is another unused pin on the Rheostat, my question is: Can I use that pin to connect some resistors (how many Ohm?) to transfer the 'leaking' power to the resistors which I can cool with a heatsink.
My second question is: How can I adjust the setup to make the max amperage 2A instead of 3A, because the fan makes to much noise when at full load with 3A.
Can anyone who knows more about electronics then me help me with these problems, thanks a lot.

My case has so many fans that it hovers above the ground :eek:
It's not a bug, it's a feature

Add a reply
Sponsored Links
Register or log in to remove.
zpyrd   02-27-2002 at 07:13:23 PM
- 0 +

Using a variable resistor to control the voltage applied to a gate of a power silcon controlled rectifier (SCR) would be more effective.

I'll try to find you a basic schematic for you to use.

<font color=red><i>Doctor Hooter</i></font color=red> <b>(·Y·)</b>

Reply to zpyrd
zpyrd   02-27-2002 at 08:32:12 PM
- 0 +

Here is a link to some basic electronic circuits. There are few adjustable voltage control circuits here that could be used to control fan speed.
<A HREF="http://ourworld.compuserve.com/homepages/Bill_Bowden/" target="_new">http://ourworld.compuserve.com/homepages/Bill_Bowden/</A>

<font color=red><i>Doctor Hooter</i></font color=red> <b>(·Y·)</b>

Reply to zpyrd
Grizely1   02-27-2002 at 09:30:47 PM
- 0 +

i have no clue. i suppose i should learn this kind of stuff soon......

<font color=red>DO NOT LIGHT YOURSELF ON FIRE</font color=red>

Reply to Grizely1
svol   02-28-2002 at 11:01:35 AM
- 0 +

One word: AAAAAAAAAAAHHHHHHHHHHHHHHHHH.

Man those setups are far to difficult for me, I don't understand the half he is saying, I don't think I can build such circuits yet, I'll have to learn more about electronics at school first.

Isn't there a simpeler way to adjust my current electronic circuit setup in order to lower the Amperage from 3 to about 2 and to prevent the Rheostat (potentiometer) from over-heating?

Anyway thanks for your help so far.

My case has so many fans that it hovers above the ground :eek:
It's not a bug, it's a feature

Reply to svol
pike   02-28-2002 at 06:09:46 PM
- 0 +

Like Sir Grizely1, I have no clue either. This is not a useless post but it's rather to keep you from falling into desperation. You are ok, it`s us that are ignorant. :-))))<b></font color=red>

OPPS! I DID IT AGAIN!
DAMN WORDSTAR!

A little gray humanoid plus a case of probes with that sir?

Reply to pike
labdog   02-28-2002 at 06:59:21 PM
- 0 +

take off your Rheostat, buy a potentiometer for very few dollars instead of.


if you know you don't know, the way could be more easy.

Reply to labdog
Grizely1   02-28-2002 at 10:32:38 PM
- 0 +

no thank you, i said.

<font color=red>DO NOT LIGHT YOURSELF ON FIRE</font color=red>

Reply to Grizely1
svol   03-01-2002 at 01:32:46 PM
- 0 +

As far as I know a Rheostat and a potentiometer are the same: they both regulate Voltage and have 3 pins.
I was thinking of placing some resistors in the electric circuit to catch up the 'leaking' power from the third pin of the Rheostat and to use them to set the max ampere to 2 instead of 3, but I don't know if it will work or if there are better easy ways for it.

My case has so many fans that it hovers above the ground :eek:
It's not a bug, it's a feature

Reply to svol
zpyrd   03-01-2002 at 05:59:06 PM
- 0 +

A rheostat uses a copper wire winding for resistance. Two posts terminate the winding and the wiper the third. The wiper aka brush makes contact to the copper winding where the insulation has been removed. Similar to the commutator on a DC/Universal motor. Rheostats are general purpose load control devices. They have low total resistance >1K.
Their most common commercial use is on a residential appliances such as electric ovens.

Potentiometer uses a carbon strip for resistance. Two posts terminate the carbon strip and the third is the wiper. The wiper brushes over the carbon strip to very resistance. Potmeters are low power devices 1/4 to 1/2 W where as rheostats are high power devices 5W to 1000's of KW.
Potmeters come in two varieties. Linear and non linear. Linear potmeters are used where the application requires a constant gain control. ie voltage regulation. Common application would be a dimmer switch on a lamp. Non linear pots are used where exponential control is required. Common application would be the volume control on an audio amplifier.

The simplest circuit to use for your application would use a general purpose power scr with a 5W rating using a cathode gate. Take 4.7k 1/2W carbon resistor and connect it in series with a 1/2W 47k linear pot. The 4.7k resistor is the current limiter so the gate does not burn out. The 47k pot will control how much current flows through the scr.
Connect the 4.7k resistor to ground. Connect one terminal post of th 47k pot to the 4.7k resistor. Connect the other terminal post of the 47k pot to the gate of the scr. The wiper post of the pot must also be connected to the gate of the scr.
The anode terminal of the scr is connected to +12vdc. The cathode of scr will be connected to the positive terminal of the fan. The negative terminal of the fan is connected to ground.

I can't guarantee this will work because it's been over 12 years since I studied basic electronic circuits in college.
If you want me to draw this out for you I can scan the drawing and send it to a e-mail address. I'm not putting it on the web. Too much work for something I'm not sure will even work.

<font color=red><i>Doctor Hooter</i></font color=red> <b>(·Y·)</b>

Reply to zpyrd
svol   03-03-2002 at 10:59:33 AM
- 0 +

I made a drawing myself to see if I understanded your setup, you can find it here, it is still a .bmp so you can edit it easily:
<A HREF="http://home.kabelfoon.nl/~svo/potmeter.bmp" target="_new">http://home.kabelfoon.nl/~svo/potmeter.bmp</A>.

I'm going to use the 12+ V of my PSU as powersource and my fan is original 36W, you think they will do?

My case has so many fans that it hovers above the ground :eek:
It's not a bug, it's a feature

Reply to svol
labdog   03-03-2002 at 08:08:06 PM
- 0 +

this is right but if you want 2A max, use a 6K omhs instead of the 4.7 (12/6 = 2A).


if you know you don't know, the way could be more easy.

Reply to labdog
svol   03-04-2002 at 12:24:22 PM
- 0 +

Thanks, and thanks to Zpyrd also.

My case has so many fans that it hovers above the ground :eek:
It's not a bug, it's a feature

Reply to svol
svol   03-11-2002 at 08:16:33 PM
- 0 +

Ok I tried this setup but it doesn't work, the fan will only run when I remove the resistor and I set the pot-meter as close as possible to the left side (where it is connected with the PSU), does anybody know what is wrong?

My case has so many fans that it hovers above the ground :eek:
It's not a bug, it's a feature

Reply to svol
Ask the community Add a reply
Tom's Hardware > Forum > Old Man/Woman's Club > Other > Help electronics.
Go to:

There are 1165 identified and unidentified users. To see the list of identified users, Click here.

Forum map
Bestofmedia Forum ©
2000-2009 Bestofmedia Group
Page generated in 1.120 seconds
Please mind

You are about to answer a thread that has been inactive for more than 6 months.
If you still wish to proceed, please ensure that your posting is original and does not duplicate or overlap any prior responses to this thread.

Add a reply Cancel
Sponsored links
  • Ask the community now
  • Publish
Ad
Related Topics
See all relatives topics
Related Content
They won a badge
Join us in greeting them
How do I win badges?