Car battery as power source

[SteveP]

A contractor is asking about using a car battery to power 12v landscape lighting fixtures (for a boat).

I'm guessing that the lamps will function normally since 12v DC is practically equivalent to 12v AC in terms of the power equation (impedance would be a factor but at the fairly low Hz of 60, impedance is negligable).

However, there are differences in that 12v AC actually peaks higher than 12v since the AC voltage is an RMS calculation (not peak height).

Also, I've heard that heat build-up can be a bigger issue with DC.

Any thoughts?

[Paul]

Steve, not only is the DC current an issue, (the fixtures will operate just fine though) unless the fixtures are suitable for underwater use, they can't be located within 10' of water.

[SteveP]

Paul, after checking with my IES guide, 'Recommended Practice for Marine Lighting', I see there are two UL classifications, 595 and 844, that deal with marine lighting fixtures. These are not underwater classifications, but include several other classifications relating to inside/outside and fresh water/salt water installations. In all cases, the fixtures need to be UL labeled as "Marine-Type...".

[FrankT]

One thing to watch for on a boat, if he's running the lights etc. with just a deepcycle battery and not a genset, will be voltage drop. On mine with batteries only, and the fridge, and stereo on, I'm down to about 10 volts within 4 hrs if I don't fire up and move or start the genset.