DC Bulbs not working in some circuits?

Truax McFarland

1 Posts

Jun 16, 2008 07:43 am

DC Bulbs not working in some circuits?

Hello everyone! I am running some compact florescent bulbs at a camp off the grid. I was using an inverter and running 120 V AC, but I switched to 12 V DC to try to reduce waste.

Here's the weird thing - one fixture that works with 12O V AC bulbs from the inverter, will not run 12V DC bulbs directly from the battery. The other fixtures work fine. I didn't do the wiring so I don't know all the details, but its not a very long run of wire to the mystery fixture. Can any one suggest a reason for this?

Thanks!

184 Posts

Jun 16, 2008 09:20 am

Re: DC Bulbs not working in some circuits?

The long wiring run seems to be the problem. Your losses when trying to run 12VDC a long way are greater than they are when you try to run 120vac the same distance. An easy test would be to measure the voltage across the light bulb at the distant fixture with the light turned on. You might measure something like 9 volts, which means that 3 volts is lost in the wiring.

John

184 Posts

Jun 16, 2008 09:24 am

Re: DC Bulbs not working in some circuits?

If you need to go back to using an inverter, try to eliminate waste by:

Choosing an efficient inverter.
Operating the inverter close to it's capacity.
Choosing an inverter that goes into standby or power-saving mode when there is no load.

John

184 Posts

Jun 16, 2008 09:32 am

Re: DC Bulbs not working in some circuits?

I misread your post, thinking that you said it is a long run of wire to the mystery fixture. You can troubleshoot by:

1. trying a known-good bulb in the mystery fixture.
2. checking with a voltmeter as I previously said.

You might also look for bad connections, or maybe a bad switch or fixture. Your digital voltmeter is your best friend. The key is to see if there is a significant voltage drop across the wiring. Then you might check for a bad switch. A voltage drop across the switch, when the switch is turned on, indicates a bad switch.

john

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