Is Heat-shrink Fool-proof

[tom_pay]

Hi Guys,

Yesterday I built a small circuit to remind me to turn the headlights off, and then covered the whole circuit board in heat-shrink.

If something went wrong in the circuit and a transistor started to smoke or get really hot, would the heat-shrink protect it long enough for it to burn out and stop making the heat and smoke?

Whilst I have thoroughly tested this circuit and I am sure that nothing should go wrong, I really don't want to burn down the car!!

Thanks

Tom

 

[gots2no]

It would not protect against heat. It would melt.

 

[tvtech]

Here is a spec sheet for typical heatshrink. Note it passes the flamability test.

Cheers

 

[alec_t]

You could do a simple test (well away from anything flammable!!) by connecting a single film-wrapped sacrificial resistor to a variable power supply and cranking up the volts.

 

[Reloadron]

One downside to this method is the components do not see any airflow for natural cooling. Not a big deal if you have all cool running components.

Ron

 

[tom_pay]

Thanks for the data sheet tvtech.

It says it passes the flammability test, does this mean that it passes catching on fire, or passes resisting fire? I'm confused!!!!

Overall the circuit should, at all times draw less then 3 mA. So heat shouldn't be a problem.

I'm still worried about putting this circuit in the car, does any one know of a test that I should do to convince me to install it?

Tom

 

[ericgibbs]

if you are concerned about the circuit failing short circuit, fit a suitable fuse in the power line.

 

[4pyros]

Yes use a fuse at the power source and all is good.

 

[tom_pay]

Ahhh, a fuse sounds good!!!!!

I might try that!!!!

 

[4pyros]

I might try that!!!!

No you NEED that.

 

[Sceadwian]

Put the finished device in an oven set to 200F, that's about worst case as far as being inside an automobile, it's roughly the temperature a dashboard will get on a cloudless sunny day. If it can survive a few hours in that it should be fine. I'd be more worried about extreme cold.

 

[carbonzit]

I'd be more worried about extreme cold.

Does heat-shrink get brittle and crack in the cold?

 

[Sceadwian]

I was more thinking of the circuit itself not the heat shrink.

 

[KeepItSimpleStupid]

I did headlight reminder alarms that's SO SIMPLE. Just a 12V buzzer and a diode. That's it. Connected to the right terminals, it buzzes when the driver's door is open and the lights are on.

Lights are +12 when on.
Doors may be diode isolated and a switch to ground. Mine was.
The buzzer is OR'ed with the original diode (connected at the switch)

Done, you just have to replace the buzzer every 5 years or so. The one I used could not handle the temperature.