Electronics > Power/Renewable Energy/EV's

IR lamp resistance

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--- Quote from: Faringdon on May 22, 2023, 03:44:51 pm ---Thanks, how about dimming the output of the IR lamp?

Also, for inrush when turned on at low temperatures, we need an NTC

--- End quote ---

How many 'engineers' does it take to replace turn on a light bulb?

So here's a few relevant observations about turning on an incandescent light bulb. 

First, if you limit the current to the amount that the bulb will draw when warmed up--in your case about 2 amps--the bulb will turn on a bit slower but typically not enough to matter.  You might not even notice in the case of smaller bulbs.  So if you had a huge bulb or bulbs in parallel that drew current that was a large fraction of your circuit breaker or fuse ampacity, inrush limiting might not be totally insane, although I personally haven't seen it done on anything short of large commercial devices like theatre lighting where they soft-start via dimmers.  A single IR-heater that draws 2A on a 16A circuit really shouldn't need anything at all.  I have 500W (250W x 2) IR heaters in my bathrooms that run off of a 15A 120V circuit (not dedicated) so they draw ~4.5A when on. 

Second, if your bulb does fail at turn-on and even if it goes short, those faults clear very quickly--at least the ones I've seen.  Also, I think the IR bulbs like the one you mention aren't all that likely to fail short and they typically have pretty long lifetimes. If you still want to incorporate short protection without blowing your fuse (and you absolutely need a fuse...)  you'll need to passively limit the current to something below what would blow your fuse in less then 1 cycle and then have an overcurrent detection system that will shut the power off at the end of the current half-cycle.  That's assuming you are using a triac.

Third, bulbs like that have fairly long thermal time constants.  Both soft-starting and dimming could be accomplished by cycle-skipping rather than phase control.  Perhaps a 5-cycle (100ms) period with dimming levels from 1 to 5.

Thanks, i dont suppose anyone knows offhand what is the stray inductance of the IR lamp in the top post...there will be some stray L which will need dealing with if turned ON/OFF with high current.
Will get the LCR on it when i can find it.

The LCR45 isnt going to measure it too well unfortunately

An old HP 4192A is what you want for these sorts of measurements, or an old gen rad or HP impedance bridge, but if you are dimming then you will need a honking great series inductor anyway, so the lamp inductance becomes insignificant in comparison.

Thanks, we are hoping to do symetrical phase cut dimming, with no series inductor added.

Just  another nonsense post by FTTS. Of course there is no "We" who are "doing" anything for a "customer"  its just FTTS imagination to waste our time.

1/ IR lamp filament resistance is function of filament temperature and PTC so cold/hot R is perhaps 5..25 :1 ratio.
See 1930s..1950s General Electric IR lamp data.

2/ IR lamps are never dimmed, no reason. On or off.

3/ Outdoor /restaurant/patio space heaters gas or electric are banned in many parts of EU and surely soon in UK, USA, CA, AU etc by environazis laws and regs.
Moot project.

Another 5 min lost to FTTS toilet bowl of time.

Thanks again!



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