120vAc to 12vDc@4A for temp regulated fans

Thread Starter

mpdube113

Joined Apr 2, 2011
22
Hello I'm looking for some guidance. i currently have 3 "T5 electronic ballast" that i'm in the process of building a air cooling system for. I have mounted aluminum heat sinks on metal housing of these 3 ballasts via some 6-32 screws an some thermal paste. I have 3-12vDc .43A brushless fans that I'm wanting to control with a temp sensor.
EASY RIGHT! well heres the catch i've searched all my salvaged parts an can't find any IC that could make this really simple.(i won't be purchasing any parts) i have tons of salvaged power supplies from TV's, COMPTERS, AND MANY other different types of electronics.

please give any advice

thankyou
 

R!f@@

Joined Apr 2, 2009
9,918
Welcome to the forums

you can make a temp sensor with LM339 as a comparator and some diodes as a sensor. Pretty simple
 

R!f@@

Joined Apr 2, 2009
9,918
There is this LM34, a temp sensor. you can use this instead of a diode.
Rest is just basic comparator. Whether it be a μC or a simple op amp comparator like LM339

You do know what a comparator is, don't you?

The temp sensor and fan switching circuitry is nothing too fancy. It's basically what I said one way or the other
 

Wendy

Joined Mar 24, 2008
23,415
One of the questions you need to answer is how deep your electronics expertise is. I like to design stuff from scratch, some people can assemble things if given a schematic, while others want to know what those little arrows mean next to the diode.

We can better answer your questions if we knew your expertise. Rifaa's replies made sense to me, but they may not help you much.
 

R!f@@

Joined Apr 2, 2009
9,918
I did made it using diodes and comparators as level sensors. Quite easy. And it was way before I join here.
 

Thread Starter

mpdube113

Joined Apr 2, 2011
22
i'm not an expert by any means. but i have a good understanding of basic electronics. its my hobby. i have no training of any sort. i'm a licensed master electrician. so with some guidance from these forums i'm hoping to learn more.
a comparator seems like a very simple concept. i'm going to do some digging an see if i can find one. if not what are my other options?
 

R!f@@

Joined Apr 2, 2009
9,918
Actually this is the simplest option as far as I can see.

I will give you by design. I do not have a schema as of now but if you follow what I say and Google it you will learn a lot more. Reading and experimenting will teach u a lot.

First you have to decide which sensor. There is NTC , PTC and ready made temp sensor like LM34. Silicon diodes can also be used but their variation is very little. You will have a large margin if you use thermistors or stand alone sensors.

Next is the comparator designed around a Voltage comparator opamp such as LM339.
This circuit basically compares two voltage levels. One input senses the sensor voltage drop at a specified or required temperature and compares it to a reference voltage at other input.

This reference determines the triggering point. A hysteresis should be given between the max temp trigger and minimum temp trigger. This will prevent the opamp triggering errors.
U can use either input for the threshold and sensor, and the design can be an over voltage type or an under voltage type.

This the complicated part.

Next is easy part.
The output of the opamp can be coupled to any thing, an indicator, or a transistor driven relay or mosfet maybe. no big deal here.

Other concern is actually where the sensor is located. for example is it far away to the comparator input or close. Precautions should be taken if far away. like noise filtering to prevent erratic triggering
 
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Thread Starter

mpdube113

Joined Apr 2, 2011
22
ok this are the IC's i've come up with

http://pdf1.alldatasheet.com/datasheet-pdf/view/251927/FOSLINK/FSP34063N.html

http://pdf1.alldatasheet.com/datasheet-pdf/view/12713/ONSEMI/UC3845BN.html

http://pdf1.alldatasheet.com/datasheet-pdf/view/33711/WINGS/KA3842A.html

http://pdf1.alldatasheet.com/datasheet-pdf/view/3073/MOTOROLA/LM358N.html

and the thermistor I've come up with is a TTC-103 it's in a little Aluminum housing with a mounting hole ( PERFECT ) Covered in Thermal paste

now a little direction :)


 

R!f@@

Joined Apr 2, 2009
9,918
Have you decided what to get or checked what you have.
did U know that u can salvage parts for ur problem from a computer power supply.

try it first
 

Thread Starter

mpdube113

Joined Apr 2, 2011
22
the parts listed on my previous post are salvaged parts i have in my possession :) just need some help applying one of the 4 listed IC's to my specific situation
 

R!f@@

Joined Apr 2, 2009
9,918
OK ..let's see now..
{ed}
You have a dc to dc converter and some SMPS PWM chips. Which cannot be used for ur current project.
But the LM358 can be used as a comparator.

Post a pic of the thermistor that you have.
and try to find a 4 pin or 8 pin IC labeled LM339. I bet there will be one if you have some PC junks.
 
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Thread Starter

mpdube113

Joined Apr 2, 2011
22
i'm sorry i don't have a camera ATM. um... i'll describe It it's green and labeled TTC 103.. i think i remember seeing another one i'll try and dig it up..
but as far as the LM339 i searched all my stuff the first time you mentioned that IC. i couldn't find it. Can we make use of the LM358
 

R!f@@

Joined Apr 2, 2009
9,918
We can use the 358.
You have to take some measurements.

Tell me the resistance of ur thermistor. at room temperature. Do not touch the thing when measuring.
Make a table. Heat the thermistor and note down it's resistance variations.

Post the table
 

Thread Starter

mpdube113

Joined Apr 2, 2011
22
room temp (60-70F) = 10.55k Ohms

heated temp (soldering Iron about 3" from the Sensor ) = 8.76k Ohms

do i need to take more precise measurements or are these sufficient
 

R!f@@

Joined Apr 2, 2009
9,918
So what you have is a NTC.
Which R drops to the applied heat.

Now ask your self how should and when should the fan operate
 

Thread Starter

mpdube113

Joined Apr 2, 2011
22
well i don't wanna make it to complicated but.. if possible i want them to Turn on when a set temp is reached (low speed) and then Climb in RPMs ( or just jump to a set RPM)as the temp rises, and then once the heatsinks on my ballast (where my temp sensor will be mounted) start to cool down i want the fan to throttle back down to Low speed and turn off..
but if that is to much i can settle for just a on off set up
 

R!f@@

Joined Apr 2, 2009
9,918
Hmm!! Just what I thought.

For dual speed you have to utilize both the op amps.
How do you plan to give power to the chip. Stand alone former or tapping into the current circuit.

You can run a fan from the current circuit. It's no big deal. If the fan is a standard PC PSU type of fan.
 

Thread Starter

mpdube113

Joined Apr 2, 2011
22
umm the fans are 12vdc .43A each and there's only 2 of them but i want to Keep enough room in the Circuit For an extra fan around the same Amp rating. i've got tons of Transformers that i can make a regulated PS from. i've got a few of these guys also along Caps in every shape an size
http://pdf1.alldatasheet.com/datasheet-pdf/view/14721/PANJIT/GBU4K.html

i haven't made a Regulated PS yet so i think this would be a good Time to practice ??
 

R!f@@

Joined Apr 2, 2009
9,918
OK then..Let's see what I can cook up.

You have to give me the trigger points. Like say the resistance of the NTC at the low speed start temperature.
Since I cannot find any data related to the NTC and you haven't shown me the thing, I cannot speculate.
So you have to mount the thermistor on the sink and measure the resistance. Note down the value at which you like the fan to start and toggle speeds.

The sensor should be mounted in a position where air does not flow. In other words , do not mount the thermistor anywhere between the fan and the sink
 
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