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Reduce 10vac to 2.5 0r 3vac


I have a 10vac output adapter that I would like to reduce to 2.5 or 3vac to test Christmas lights.
Can I do that with resistors?



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Most Helpful Member
You can, but it may not be the best way. What is the current-rating (or wattage) of the lights?
Are the lights incandescent or LED?
What test do you have in mind?


Well-Known Member
Most Helpful Member
You could power 3 or 4 light bulbs from the 10vac adapter. 3.3V or 2.5V per bulb.
Make a short strand of 4 bulbs. Then replace one bulb with the bulb to test.
All bulbs bust be of the same type.


The current is 170mA
Wattage is .42/bulb
I just want to see if the bulbs light.
I can see a short across the filament but the bulb won't light in the socket string.


Well-Known Member
Incandescent bulbs don't care whether you feed them AC or DC.

So you can test them with DC. If you have an adjustable DC bench supply you could set that for 2.5VDC.

Or you could use a 1.5 Volt Alkaline D cell. It won't be as bright but it will tell you if the bulb is good or not.


Thanks Chris, a 3vdc button cell works.
I had already tried that on the lights I was testing and it wasn't working but when testing a new bulb it does work.
The short I'm testing is likely the shunt in the bulb.
I have a light keeper pro that I'll dig out and see if the shunts are causing the problem.

dr pepper

Well-Known Member
Most Helpful Member
Some light strips have bulbs that short when they fail, so your lights dont go out, such strings have a fuse lamp for safety.

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