Author Topic: Filament bulb to heat PCB enclosure  (Read 1178 times)

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Offline EEEnthusiastTopic starter

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Filament bulb to heat PCB enclosure
« on: November 19, 2019, 07:07:12 am »
Friends,
I am in need for a heat source for my PCB which is enclosed in a metal case. The heat source needs to be controlled using an ON-OFF control using a MOSFET. I was looking at adding a large power resistor, then it stuck me that I could use a filament bulb as well. The objective is to heat the air inside the enclosure, in order to maintain a constant temperature which is higher than the ambient.

Does anyone has experience using a filament bulb for this purpose? Any drawbacks using this idea?
I plan to use a 12V bulb powered by a 5V source, so that the bulbs life time is extended.

thanks
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Online mikeselectricstuff

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Re: Filament bulb to heat PCB enclosure
« Reply #1 on: November 19, 2019, 07:11:49 am »
What benefit would the bulb have over a resistor?
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Offline EEEnthusiastTopic starter

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Re: Filament bulb to heat PCB enclosure
« Reply #2 on: November 19, 2019, 07:21:41 am »
Well, it might add some coolness to the product in addition to the warmth.
I am wondering if the filament bulb may be a more effective radiator of heat than the resistor.
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Offline Psi

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Re: Filament bulb to heat PCB enclosure
« Reply #3 on: November 19, 2019, 07:42:42 am »
Well, it might add some coolness to the product in addition to the warmth.
I am wondering if the filament bulb may be a more effective radiator of heat than the resistor.

Resistor = 100% heat
LED = 70% heat  30% light   (roughly)
LAMP = 95% heat 5% light  (roughly)
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Offline Berni

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Re: Filament bulb to heat PCB enclosure
« Reply #4 on: November 19, 2019, 08:08:31 am »
Well a lamp does spread its heat out more because the light it is radiating turns to heat once it hits other things.

But yeah since incandescent lamps have really poor efficiency means the majority of the heating is the lamp itself rather than the light. And since lamps burn out eventually it makes more sense to just use a big power resistor instead.
 

Offline EEEnthusiastTopic starter

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Re: Filament bulb to heat PCB enclosure
« Reply #5 on: November 19, 2019, 08:13:26 am »
Thanks guys, i will stick with the resistor as I need not worry about lamp life times.. Will add an Orange LED for the glow.
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Offline macboy

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Re: Filament bulb to heat PCB enclosure
« Reply #6 on: November 20, 2019, 06:17:07 pm »
One problem with a lamp is that the cold resistance of the filament is much lower than the hot resistance. This can cause a current surge at startup of maybe 5x to 10x the nominal current. This in not the case for a simple power resistor. You might also consider that a bright light can affect operation of components. Not only will they be directly heated by the radiant energy (large dark components may get hotter than small or light colored ones, when the light is on), but semiconductors are light sensitive. Any glass package diode will behave differently depending if the light is on or off for example.
 
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Offline EEEnthusiastTopic starter

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Re: Filament bulb to heat PCB enclosure
« Reply #7 on: November 21, 2019, 05:36:18 am »
Thanks all for the responses. Those were very helpful. For now it a 2W resistor that will do the heating duties.
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