Thermostat heated seats

[raresvintea]

Hello everyone. I've installed in my car heated seats. I've put in seats a NTC 10K&15K sensor. The potentiometer from dashboard can make a course between 5kOhms at "low" and 2.2kOhms on "max".
I've tried to make a thermostat using a lm741 but the point of stop was really hard to manage, and i've put some swiches, now in the winter. I want to make a better device!

The problems are:
-long wires from sensor to the "control unit'- 3meters
-already installed NTC sensors
-the limmited course of the pot from dashboard.

All i want to make is a device that can handle temeperatures below -15C, to menage voltage fluctuations because of electrical system and hard conditions. The circuit that i've already maked was based on a voltage comparator, that commands a small power transistor and after that a P channel mosfet to minimise looses and to avoid noise from a relay. What i want to make is a circuit that can handle this.

I think that i need to put a voltage stabilizator LM7805 to be sure that all the time i have a constant voltage for voltage reference. And to use a circuit that can handle -20 degres and to be perfect functional... military ones, because i don't want to fail when outside is very cold, because otherwise i will fail I need to say that i made a small series-parralel resistor circuit to put the value from the ntc sensor in Comparison with the one set onthe potentiometer.


PLEASE come with ideeas and with recomandations. There are some specialized circuit to do this?

 

[alec_t]

What is the dashboard pot connected to? And why can't it go to zero Ohms?

 

[raresvintea]

It's connected to wires, is a button with two seapate pots. It can't go to zero because of the construction of the rotary button, but when the pot has 5k, the minum temperature is set, a warm seat, and at max 2.2k a hot seat. most important are 2-3 "positions of the pot", because i don't want to can't stay on the seat. Now outside are -10C and tommorow i will measures the exact values where it needs to stop...

 

[Reloadron]

Do you have a link to a data sheet or something on what you bought?

Ron

 

[raresvintea]

Datasheet for what? LM741?

 

[Reloadron]

No my bad, I now see what the sensors are. Actually the 741 isn't a real good choice. If you are after a comparator circuit this link may be useful. What I was actually asking for is if you have a schematic or drawing of what you have.

Ron

 

[KeepItSimpleStupid]

Something like this ought to be your final control element.

There was a website with nice heated seat kits that did modulate the heaters. Bang, Bang control is VERY BAD for the heating elements. I know.

You really didn't give us much to go on.

The 741 OP amp is essentially obsolete. It was one of the first IC OP amps.

 

[alec_t]

As Ron says, a schematic of your present setup would be helpful. It's difficult for us to suggest improvements if we don't know exactly what the starting point is and what constraints (apart from a weird pot) there are.

 

[raresvintea]

Same question, but if you have a better ideea. A digital thermostat using a mosfet and a pot. Any ideea?

 

[alec_t]

A digital thermostat

Do you mean one (a) using digital (logic) ICs, (b) having a digital display, or (c) controlled by a MCU?

 

[KeepItSimpleStupid]

This kit https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_120539_-1 could likely work to modulate the heater power.