rickconn

Hello,

My first post, please go easy on me...

I would like to use the resistance from a 'motor vehicles' engine temp sender, to controll a 12v source.

Guessing here...
If the resistance is 'infinity' at 0 degrees Celcius
and lets say, 10k at 82 degrees Celcius

I would like to put out say:
12v at 0 degrees Celcius
and
5v at 82 degrees Celcius

Any suggestions would be more than welcome.

Free free to correct me on the resistance of a temp sender, as I have not yet measured one.

Thank you all
Rick

rjvh

what do you want to control with the voltage a motor or a lamp or ????

Robert-Jan

rjvh

About the sensor
it could be a PTC or a NTC

it's a resistance based sensor with a Positive Tempature Coeficient or Negative Tempature Coeficient thats what you have to find out by measurement if you don't have any documentation of the sensor

The way you discribet it (as you said this is hypothetical) it would be a NTC the tempature goes up and the resistance come down

a resistance based sensor can't be infinity at a point as this would indicate a burn out and a permanent damage of the sensor

Robert-Jan

Gayan Soyza

Do you need to vary the 12V source in a linear fashion?

Or

Just only to detect two temperatures & control the output?

If it is 0C --->then out 12V
If it is 85C --->then out 5V

__________________
Gayan

My Website
http://gsmicro.blogspot.com/

rickconn

Good afternoon,

Wow, I wasnt expecting so quick replies..

Thank you all...

Gayan
Yes I would like the voltage to be linear between 5 to 12v.

I was hoping that as the tempreture was rising, the voltage was dropping.

Between say:
If it is 5C --->then out 12V
If it is 85C --->then out 5V

So I will guess at 45 degrees I would be getting 8.5 volts.


rjvh
PTC or a NTC

I do not know what is 'common' on a temperature sender from a vehicle, but Im hoping to use something 'generic'.

If anyone can enlighten to on the 'automobile' temp senders, that would solve that question...

Part 2:

Its controlling a filiment.

Thank you both for quick replies...

I best check back more often.

Mikebits

Thermistors are not very linear.

rjvh

what is a filiment ??

I can't picture what for device that is

how much power does it consume?

Robert-Jan

rickconn

I would like to have the element consume a maximum of 15 amps.

Its like 2 platess in a battery, but as the element heats the water, the current drain is increasing, so as the temp rises, I thought to reduce the voltage to it.

Cheers
Rick

Edit: The resistance between the plates is approw 1mg.

rjvh

now I have even more questions

I think your filiment is a heating element or not ??

if it is controling the temp of a amount of water than i would suggest that you make something with a PWM control (puls with modulating control)

the efficiency is much better than when you just lower the voltage

resistance is messured in Ω and the oposite (conduction is in siemens)

i am not familiar with mg

Robert-Jan

rickconn

Thanks Rob and Jan

No its not.

It is 2 plates, like in a battery, making contact via an electrolytic.
The resistance accross the electrolytic is at room temp, approx 1 megaohm

Using a 12vdc supply, its consuming around 5 amps

Because of the potenial difference between the plates, the electrolytic heats up. As it does, the current draw increases uncontollably till the electrolytic boils.
I have found that reducing the voltage manually to 5v, seems to limit the current drain to a maximum of 15amps, which would be as much as I could tolerate.

Really, Im seeking a simple feedback circuit to limit the voltage/current based on the temperature of the electrolytic.

Cheers
Rick

rjvh

Now i do get the picture

never thougt about a current control with a steady voltage? (battery charger)

by the way it's one person Robert-Jan (I am not offended)

Robert-Jan

rickconn

Evening,

I dont have a preference for regulating current, or voltage.

I thought that a temp sender, from a car, could be used to regulate, either current or volatage.

However, a simple schemetic, would help...

Im guessing, the sender will have a varying resistance between to 'knowns'

Some sort of voltage divder, accross the base of a tranistor, to regulate between the emitter and collector, either voltage or current.

I will have to hunts the values on the sensors, probably, to be fair to everyone.

Kind regards,
Rick

After reading a couple of forume, I think it would be safe to say, a car temp sensor may be closte to:

5000 ohms at 0 degrees C

and

200 ohms at 100 degrees C

Hope this helps

Regards
Rick

rjvh

Hi I still have to wait a few hours when it starts to be evening here

i made a small sketch that works with a FET as a variable resistor so controling the curent

as the sensor value is not known you have to experiment with the values depending on what you want
the resistor values should be preferible in the kΩ lower is not recomended

the FET have to be a type that can handle the 15Amp as you required and i would defenetly cool this component as it will be hot when it has to handle that amount of current

Robert-Jan

Attached Images

TMP20.JPG (165.3 KB, 16 views)

rickconn

Robert-Jan,

Thankyou for your sketch,

I will have a peek overr the next week or so.
I will let ou know how I go.

Again, thank you kindly
Rick