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Indicator Lamp on Weathertron 3AAT80B1A1 Thermostat Jeff Wisnia 11-13-2008
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Posted by Stormin Mormon on November 17, 2008, 11:12 am
Last time I measured the resistance of a half wave rectifier for a DC bulb,
the half wave rectifier was about 2k ohms resistance. Depending on the
amperage draw of the bulb, that could be the correct dropping resistor
value.
--
Christopher A. Young
Learn more about Jesus
www.lds.org
Stormin Mormon wrote:
show/hide quoted text
Its a halfwave rectifier for a DC bulb.
Posted by Jeff Wisnia on November 17, 2008, 3:24 pm
Mark wrote:
show/hide quoted text
Mark, I think you may have got me there!
I probably got lucky when I grabbed bulb from the leftovers from the
kid's model railroading experiences of some 20 years ago, and it
probably was one intended to be run on higher than 12-14 volts. (No
markings on it.)
But, after I soldered it in I looked at it lit (from the back) before I
replaced the thermostat on the wall and compared its color to that of
the "emergency heat" bulb when that one was turned on. The filament of
the bulb I installed was lit to just about the same color as the
"emergency heat" one, so I guess it's a "right fit", huh?
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.
Posted by Mark on November 17, 2008, 6:56 pm
show/hide quoted text
yep sounds like you are OK then...
I remember this from a long time ago we had a temperature chamber that
ran off of 240V and used a 240 V bulb inside for light...the bulb
burned out and we didn't have a 240 V bulb to replace it...one of the
engineers got the bright idea to use a diode and a standard 120 V
bulb, seemed logical,,, so we all got to learn by experience why that
didn't work...
Mark
Posted by Don Ocean on November 17, 2008, 10:33 pm
Jeff Wisnia wrote:
show/hide quoted text
God looks out for fools and drunks.. ;-)
show/hide quoted text
Posted by Fartikus on November 17, 2008, 11:15 pm
> Jeff Wisnia wrote:
>> Mark wrote:
>>>> I soldered in a new bulb yesterday. Tracing the circuit showed that
>>>> here's a single diode in the common return lead of both bulbs so the
>>>> bulbs effectively see only half of the nominal 24 volt AC supply.
>>>> I used a 12-14 volt "grain of wheat" bulb and it works fine now.
>>>> Jeff
>>>> -
>>> that is a common wrong mis-conception. A 12V bulb hooked up to 24 V
>>> AC with a diode does not see 12 V. It sees 24 Volts for 1/2 of the
>>> time. During the time it sees 24V, it is getting 4x the power because
>>> P=V^2/R. But since it seeing 4x power only half the time, the net is
>>> 2x power. So a 12V bulb hooked up to 24 VAC through a diode is
>>> seeing 2x the correct power, it should be very bright and will burn
>>> out soon.
>>> If you don't belive me, try it with a 120V bulb and a diode hooked up
>>> to 240V. It does not work. The bulb will burn out in a short time.
>>> Mark
>> Mark, I think you may have got me there!
>> I probably got lucky when I grabbed bulb from the leftovers from the
>> kid's model railroading experiences of some 20 years ago, and it probably
>> was one intended to be run on higher than 12-14 volts. (No markings on
>> it.)
>> But, after I soldered it in I looked at it lit (from the back) before I
>> replaced the thermostat on the wall and compared its color to that of the
>> "emergency heat" bulb when that one was turned on. The filament of the
>> bulb I installed was lit to just about the same color as the "emergency
>> heat" one, so I guess it's a "right fit", huh?
>> Jeff
> God looks out for fools and drunks.. ;-)
Then this group is in good shape.
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