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Author Topic: AC bulbs on DC?  (Read 1997 times)

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MaxAsh

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AC bulbs on DC?
« on: August 13, 2014, 01:18:31 pm »
Hey all - helping a friend with a project and ran into what I think is just a general electrical question. I did some googling, and came up with a variety of answers, so I wanted to ask folks here just in case. I'm guessing this is likely just me overthinking things, but better safe than sorry. I'd just try it out, but don't want to damage anything.

The existing cabinet has a row of 14V AC (yes AC) fed bulbs. The wiring was literally a direct wire feed off an old transformer from what I understand. No electronics or board in between. Is it possible to simply feed them off the 12V DC, PC power supply? I recall reading that a bulb, directly fed, doesn't really care about AC vs. DC much. My google searches resulted in mixed opinions. Thoughts?

Malenko

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Re: AC bulbs on DC?
« Reply #1 on: August 13, 2014, 01:38:43 pm »
bulbs for what? the marquee?  Just put an LED strip in there and tap the 12v.
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MaxAsh

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Re: AC bulbs on DC?
« Reply #2 on: August 13, 2014, 01:45:29 pm »
bulbs for what? the marquee?  Just put an LED strip in there and tap the 12v.

That's what I've done in the past, and already have a LED strip handy. My buddy wanted to try and keep the marquee looking "classic" if possible and re-use the old bulbs in there. Once I found out they were fed with 14VAC instead of 12VDC, I told him it was probably not worth the hassle. Figured I'd double-check to see if I could wire it up to the PC (without an inverter or anything special) before telling him LEDs would be best.

Malenko

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Re: AC bulbs on DC?
« Reply #3 on: August 13, 2014, 01:52:29 pm »
I think it could be done, but I dont think it'd be worth the hassle
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Ken Layton

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Re: AC bulbs on DC?
« Reply #4 on: August 13, 2014, 01:58:39 pm »
Incandescent bulbs don't care about ac or dc.

pbj

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Re: AC bulbs on DC?
« Reply #5 on: August 13, 2014, 02:10:13 pm »
Would have been easier to test it out yourself rather than run to the computer and start this thread.


MaxAsh

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Re: AC bulbs on DC?
« Reply #6 on: August 13, 2014, 02:19:53 pm »
Incandescent bulbs don't care about ac or dc.

Thanks Ken. I'll splice them into a 12V off the PC power supply and give it a try.

Would have been easier to test it out yourself rather than run to the computer and start this thread.

Actually no, it wouldn't in this case. I don't have access to my friend's home at the moment, and he's away. I was working on ordering some pieces and parts for his project (including replacement bulbs), and this thought crossed my mind. All of the existing bulbs are dead, so before ordering new ones I thought I would find out if it was worthwhile. My major concern was some sort of unexpected blowback on the power supply. I did some searching, found some conflicting answers, and turned to the community. As always, they were helpful and quick with a response, for which I'm thankful.

dkersten

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Re: AC bulbs on DC?
« Reply #7 on: August 13, 2014, 04:43:10 pm »
I imagine if you have 14 v ac, you have like 8 bulbs in series?  I would bet that 8 14v bulbs in series will barely light off 12v, they will get like less than 2v each.. I would think you would want to rewire them in parallel and they will probably light up great with 12v.. And if they are too bright all parallel, then do half parallel and series the two halves to get 6v to each.. they will dim down quite a bit..

MaxAsh

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Re: AC bulbs on DC?
« Reply #8 on: August 14, 2014, 07:52:36 am »
I imagine if you have 14 v ac, you have like 8 bulbs in series?  I would bet that 8 14v bulbs in series will barely light off 12v, they will get like less than 2v each.. I would think you would want to rewire them in parallel and they will probably light up great with 12v.. And if they are too bright all parallel, then do half parallel and series the two halves to get 6v to each.. they will dim down quite a bit..

You're probably right, I'll check that, thank you!