I'm running strictly conventional on my layout. I need to provide no more than 12VAC to a relay (to help power the inside rails of a long Ross ready switch). I have a dedicated buss to most of my switches that delivers 14VAC. What size resistor will allow me to drop the voltage on a feeder wire from 14 to 12? And here's the really dumb polarity question - does it matter in what direction the resistor is connected?
Bob
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That 12 volt relay won't care if you feed it 14 volts. It will work fine.
However, if you really want to over complicate things and put in a resistor, you need to know what the current draw of the relay coil is at 12 volts. Without knowing the current draw, you cannot calculate the ohms and wattage rating for the resistor.
Resistors are not polarized...they can be installed in either direction.
Assuming it is an AC coiled relay (12VAC coiled relays are uncommon) measure the coil resistance with a meter. Add a half watt resistor about 1/7 of coil value in series to either lead. When relay coil is powered,measure voltage across it to check it . As Mr Melvin stated polarity is unimportant.
3 sets of paired diodes in series will also reduce it by 2 volts regardless of coil resistance..
Dropping voltage with diodes is explained here
www.jcstudiosinc.com/BlogShowT...=413&categoryId=
Having said the above relay coils usually take up to 50% over their rating without damage, in this case up to about 18 volts so 14 volts in should not be a problem.
Dale H
Rich and Dale,
Thank you both for your very helpful answers.
Bob
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