Hi, I have to design a 12VDC lunchbox warmer with cut off tempreature control. I planned to use 2 units of PTC heater. can anyone help me for the circuit. I have no idea how to start. Thank you in advance.

 

PTC (Positive Temperature Coefficient) heating elements come in a wide variety of shapes, sizes and designs. You make no mention of which element(s) you plan to use. This all starts with the element and how you plan to measure temperature. This also sounds like a school project and we have a section for those. Anyway the element needs to be specified and a data sheet for the element so those wishing to help know the current the element will draw and how to choose a battery. This is a PTC heater pad and this also is links to a dozen more heaters. What you need to do is figure out your lunchbox size and thermal insulating properties, then determine the temperature you want to maintain, how much power will be needed, a method of control including a sensor. Temperature control can be a simple On/Off using a voltage comparator circuit which you can read about here. As it stands now you have not provided enough information for anyone to work with. Again, is this a school project and if yes, exactly what is the assignment?

Ron

 

Hi, I have to design a 12VDC lunchbox warmer ...

Is this homework?

The biggest challenge is the power storage, assuming this is meant to be mobile. What do you plan to use as the source of energy to heat the lunchbox?

 

Is this homework?

The biggest challenge is the power storage, assuming this is meant to be mobile. What do you plan to use as the source of energy to heat the lunchbox?

I planned to use 12V Rechargeable Batteries as a source of energy. but when i experiment the flow of project< ( From Battery directly to PTC heater, suuply voltage dropped from 12V to 2V. When i Switched Off the supply and measure, voltage of battery remains +12V. ).

 

I planned to use 12V Rechargeable Batteries as a source of energy. but when i experiment the flow of project< ( From Battery directly to PTC heater, suuply voltage dropped from 12V to 2V. When i Switched Off the supply and measure, voltage of battery remains +12V. ).

Do you have the data sheets for both, the battery and the heater element? Making heat with a battery can use quite a bit of current and if the battery lacks the current capability the battery voltage will drop rapidly under the load. This is why I mentioned data sheets for any heaters you planned to use. For general example here is a 12 VDC automotive baby bottle warmer. Take note the power is about 24 Watts.

• Cable: 1.5Meter Voltage: 12V/DC Power: 24W ±1W

A large and heavy 12 Volt 7 Amphour would likely last maybe 3 hours depending on the battery data discharge curve found on the battery data sheet. Then a 12 Volt maybe 7.5 AH battery is also a heavy battery. Without you providing data sheets and some drawings there is no way to help you or diagnose your problems.

Ron

 

Do you have the data sheets for both, the battery and the heater element? Making heat with a battery can use quite a bit of current and if the battery lacks the current capability the battery voltage will drop rapidly under the load. This is why I mentioned data sheets for any heaters you planned to use. For general example here is a 12 VDC automotive baby bottle warmer. Take note the power is about 24 Watts.

• Cable: 1.5Meter Voltage: 12V/DC Power: 24W ±1W

A large and heavy 12 Volt 7 Amphour would likely last maybe 3 hours depending on the battery data discharge curve found on the battery data sheet. Then a 12 Volt maybe 7.5 AH battery is also a heavy battery. Without you providing data sheets and some drawings there is no way to help you or diagnose your problems.

Ron

thank you for your respon. I will try start with power supply and keep study about all the components that should i used in the circuit