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### Topic: 30VAC help (Read 993 times)previous topic - next topic

#### trellsbells2

##### Dec 13, 2012, 04:52 am
I have a 30 volt power supply that has a total of 650 mA. I also have Christmas lights that pull a total of 40 mA but require 120VAC. Is there a way I can power these lights without stepping up the voltage to 120.
Thanks I feel Kind of stupid asking this but I am not very far into my degree and haven't learned anything like this yet.

#### johnwasser

#1
##### Dec 13, 2012, 04:58 am
Your 120V 40 mA string of lights are probably all in series.  If you divide the string into 4 equal strings and put those strings in parallel they should run on 30V (120/4) and 160 mA (40*4).
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#2
Thank you

#### retrolefty

#3
##### Dec 13, 2012, 05:10 am

Your 120V 40 mA string of lights are probably all in series.  If you divide the string into 4 equal strings and put those strings in parallel they should run on 30V (120/4) and 160 mA (40*4).

That doesn't take into consideration of how the current limiting resistance is built into the existing string. If it's one resistor or if every led has a closely mounted series resistor. So you can certainly break the string up into 4 parallel wired strings you might have to wire new resistor values into each series string. There is also probably a series diode to decrease the reverse voltage the leds are subjected to, and that too might have to be duplicated for each of the four new parallel strings. Most small leds have a 5v maximum reverse voltage rating.

Lefty

#### michael_x

#4
##### Dec 13, 2012, 10:45 am
Quote
Your 120V 40 mA string of lights are probably all in series

... and perhaps consists of "real bulbs", not LED's.
This would make everything much easier : no resistor(s), no reverse diode, runs on AC

( and you could use both 30V DC and the output of a 30V AC transformer )

#### dc42

#5
##### Dec 13, 2012, 06:40 pm
If it does use real bulbs, then just one of them is probably a fuse bulb (i.e. one that goes open circuit instead of short circuit whenit fails). You need one fuse bulb in each of your four strings. Packs of replacement bulbs usually include one fuse bulb.
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