Small Heater advice

[OldTechie]

I'm starting a project in which I need a small heated container (sort of a small ovenized enclosure) heated to around 40C.
I'm looking at various ways of heating the enclosure. I've looked at adhesive-backed silicone-based heating elements and polyimide heaters and even explored the possibility of using nichrome wire and kapton tape to fashion a heater.

The heater power is small, about 5W at first estimation. The heater will need to wrap around a smalll aluminum enclosure, and the adhesive backed heaters look well suited for that.

I'm asking for recommendations as to a prefered type of heater, based on previous experiences. Has anyone here used any of these types of heating elements, and what are the pos & cons of each? For instance, does the adhesive deteriorate over time? Is one type more prone to burnout than the other? In the event of failure, are the adhesive-backed heaters difficult to remove?

There doesn't seem to be a major difference in the cost of the different types of heaters, so that's not a big issue. I'm only making a few of these, so not looking at volume pricing.

Any suggestions? Thanks for any you might have.
DaveM

 

[Diver300]

My suggestion is to use a transistor, or maybe a few transistors. TO-220 or TO-126 transistors can be bolted to the aluminium enclosure.

Transistors have the advantage that they can also control the current. You do have to make sure that the transistors are limiting the current so that the voltage across the transistor is most of the supply voltage.

You could also look at small wirewound resistors like this:- https://uk.farnell.com/vishay/rh005220r0fe02/res-wirewound-220r-1-solder-lug/dp/2678790
They are designed to be bolted to a heatsink, but without insulation they will lose more heat to the air than a transistor would.

Transistors and wirewound resistors are very reliable if they are not run beyond their rating.

 

[OldTechie]

My suggestion is to use a transistor, or maybe a few transistors. TO-220 or TO-126 transistors can be bolted to the aluminium enclosure.

Transistors have the advantage that they can also control the current. You do have to make sure that the transistors are limiting the current so that the voltage across the transistor is most of the supply voltage.

You could also look at small wirewound resistors like this:- https://uk.farnell.com/vishay/rh005220r0fe02/res-wirewound-220r-1-solder-lug/dp/2678790
They are designed to be bolted to a heatsink, but without insulation they will lose more heat to the air than a transistor would.

Transistors and wirewound resistors are very reliable if they are not run beyond their rating.

I understand your suggestion, and have already considered that approach and dismissed it.
There is no room inside the enclosure for a big resistor, and the temperature does need to be maintained rather accurately throughout the inside of the enclosure. That's why I settled on a heater that can be formed closely around the enclosure, such as an adhesive backed flexible heating element can provide. I thought about having a resistor or transistor provide the heat, but the enclosure doesn't have the mass necessary to distribute the heat and maintain the temperature.

I've been inside a number of OCXOs such as the HP 10811 and 10544 models, which have a massive machined chunk of aluminum that can do the job well. I don't hava access to the machinery and expertise to run them to manufacture such a contraption. Would be nice if I did, and having a machine shop make the parts is just too expensive.

Thanks for the suggestion,
DaveM

 

[Dick Cappels]

I once was successful using some of these placed around a metal box to stabilize the temperature of an amplifier and a current sense resistor.

Hint: Insulate your box but DO NOT USE STYROFOAM! I did so and the circuit in the box started a fire resulting in the need to replace the whole thing. Lesson learned.