Ok. So, I've got this project I'm working on, involving a 4" color LCD screen. I have a vague understanding of electricity, but the specs on the info sheet for the monitor have me confused.

It wants a 12V DC power supply, 500mA, with not more than 7W.

I get the 12V DC part, and I think I've got the information somewhere on which line I can tap into near the fusebox by the driver's feet for that. I can tap in there safely, right? I think the lights for some of my gauges are wired there. Will it be alright for this to be there, too?

And I get the 500mA part, so long as that means milli-amps, and it means I have to have a line with a fuse that's at least that, right? What happens if the fuse is for more than 500mA? Does this 500mA contribute to some total amount of amps being drawn from the line, so I need to count up what else is powered through there and make sure it's not more than the fuse rating?

Anyway, it's the watts (that's what the 'W' in '7W' is, right?) thing that has me confused. Volts I get (sort of), amps I get (barely), but what the hell are watts (other than lightbulb ratings...)? And how do I tell if the line I want to tap for the 12V is less than 7 watts?

Sorry for the rather long winded question. How come they don't teach you useful stuff like this in high school?

 

Power = Voltage * Current

6 W = 12 V * 0.5 A (500mA)

When you turn on your alternator your voltage jumps up to some in the mid 13s. That spec is saying don't exceed 14V (7W = 14V * 0.5A). I think you use a 0.5A fast blow fuse to protect your screen. (oh yeah, W is watts)

You could easily tap off of the radio fuse . . . I like to distribute where I pull power from ......

 

I'd personally put a 12 Volt regulator from Radio Shack in the mix... It keeps the higher voltage down to 12 Volts, making sure you don't fry your screen...

A generic part number is 78xx, where xx is the voltage... 7812 is a 12 Volt regulator... It may be prefixed or suffixed with letters... They shouldn't matter though.

 

good idea Pele

 

Thanks for all the information, guys.

Someone mentioned to me the other day that I ought to run a line from the battery for this, and set it up with a relay from the radio.

It sounded reasonable to me. Opinions?

 

Yeah the 7 watt rating is the monitors total power consumtion. You won't have to worry about a regulator. I've installed dozens of monitors. I actually have a caddy in the shop now that we are in the process of putting 5 monitors in it. I wouldn't worry about regulating the voltage unless when your charging its exceeding say 15.5. But if thats the case you most likely have a problem with your charging system. Running a line directly from the battery won't make a difference, the alternator is hooked up to the battery, you will see the same voltage at the battery teminal when your alternator is charging that you will see on any 12 volt line in your car.

 

The voltage regulator blew out in my dad's probe at highway speed. The alternator puts out over 16 Volts when they are running at high speed and the regulator cuts it down to 12. Anyway.. It fried all the dash lights. The stereo, the ECU, and other expensive equipment was protected because most of them employ an internal voltage regulator. Don't risk frying your screen.. It's a $2 part, 3 pin connections, so it's not hard to hook up either... Nothing to loose.