At 11:27 AM 3/1/2008 -0600, Jim Stone wrote:
>My parents have a gas light in front of their house that was converted years
>ago to run off DC current. The conversion seems to be through some sort of
>kit. It uses two bulbs that look to be standard 12V automotive light bulbs
>and a 24V DC transformer....
>so I replaced it with a standard Home Depot door bell transformer with
>selectable voltages of 8V, 16V or 24V.The light worked for about 10 minutes,
>then quit. I checked the transformer and it was dead. I knew my wiring was
>good, so I took the transformer back and exchanged it for another one.....
>I can try putting a new one on a different circuit, but hate to blow a fifth
>one without knowing why the first four (including the original one) have all
>died. Does anyone have any ideas or suggestions?
Jim,
My guess is that you are drawing a lot more current for the 2 light bulbs
than the door bell chime does. Is there anything on the door bell xformer
that lists is current - ie 1A or 200ma?
Next you'll want to disconnect the wires from the xformer and using the Ohms
setting of your multi meter measure the resistance between the 2 wires.
This will tell you what the cold resistance of the wire & 2 bulbs is.
>From that you can calculate about how much power you need to supply.
V = I * R , You'll now V = 24, the Resistance of the bulbs is R, so
I = V/R. Now you know the current that you'll require. Then I'd go
with a safety factor of 2 or 2 times as much current as the calculations
say.
The other possibility is, are the bulbs marked as to how many watts they
are? If so, then Power = V * I. So if we assume the bulbs are 20w each,
you are using 40W of power. So I = P/V, or 40/24V is approximately 2 amps
of current. Again, double the 2 amps and find a 24V xformer that will handle
4 amps.
I think you'll find that your bell xformer is rated at either 250 or 500 ma
or 1/4 to 1/2 amp max. So you are trying to get it to output at least 4X
what it can handle.
John
John T. Blair WA4OHZ email: jblair1948@cox.net
Va. Beach, Va
Phone: (757) 495-8229
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