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Heat generator simple circuit

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Dino1400

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looking for a simple circuit to generate heat to keep my device inside an enclouser abouve 0C, in outdoor application winter time.

I'm thinking about a resistor and MOSFET controlled by a GPIO of a proccessor.


I approciate your help in advance
 

Hi can we have specifics? Heat generation in essence is wasting energy.

outdoor application winter time
Click to expand...
Is this battery operated, if so then it won't last long. Or do you have a power source?
The concern here is the efficiency of heat conversion.
Is this isolated? If not, I think the best cource of action is a simple heat pump or a peltier element. Also give high regard on insulation.
 

the story is that we have a NiMH batteries that have a discharging current rated for 0C to 70C. those batteries are just backup power not the main power, we need to keep them warm in the cold winter, so now we have to sense the temperature of the device and trigger the heat mechanism if are below 0C. the processor has a tem sensor but it set few inchs away however that shold matter because we are not looking for an accurate reading. the main concern is to generate the heat and to control it.
 

Hi,

Do you want the resistor to generate most of the heat (switched, PWM operation) or the Mosfet (linear operation).

Klaus
 

Either one should work, I'm looking for something sample.
Can you guide me where to look at both options and what's the difference, advantage and disadvantage
 

Either one should work, I'm looking for something sample.
Click to expand...

First you need to do a power analysis: how much the device uses as power: with suitable insulation, you can keep the device warm.

If the device is off most of the time, you will need a heater to bring it up to working temp; again good insulation will help. You will also need a temp sensor to decide whether the heater should be turned on.

It is not clear whether the heater is just for the battery or for the complete circuit. But if the battery is on with a small duty cycle perhaps it will stay warm inside. Again some insulation will help.
 

The processor will check if the temperature below 0C will trigger the heater to warm the device.

IMG_0766.jpg

Any suggestion or cautions on this
 

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Any suggestion or cautions on this
Click to expand...

1. you need to keep some window just to prevent the battery losing too much power; say 0C heater on and 10C heater off.

2. 5W is lot of power. If you place it judiciously, perhaps you can get away with a 1W heater. A lower power resistor will have a lower heat capacity.

3. What about a cold start?
 
You also generate heat in batteries while charging and discharging them. The greater the current going through them, the more its internal temperature rises. (I have a charger that sends 100 mA through AA, C, D size, and it makes them noticeably warm.)

You can only take it so far, so you should stop charging when the battery is full. A full battery starts to generate more heat because it no longer converts electrical energy to electrochemical storage.

Therefore this method requires a careful schedule of heating a resistive load with the aid of the batteries, then charging them to generate heat in them.
 
Hi,

You may use simple software controlled ON/OFF control. With or without hysteresis....
...
up to a some_10_Hz PID PWM control.
...
Or you use a digital sensor which can control the heating element on it's own. Like an LM75.

Klaus
 
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