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Main => Main Forum => Topic started by: wallyhooker on April 06, 2005, 11:48:37 am

Title: 300ma too much for 12v coindoor bulbs?
Post by: wallyhooker on April 06, 2005, 11:48:37 am

Hi!

I promise I searched the forum before asking this question.  :)

I wired up two #194 automotive bulbs to a 12v 300ma wall wart for my coin door.  The wall wart gets very warm.  Not so hot that you can't grab it, but definitely warmer than normal.  Is this safe?  Am I doing something wrong?   Will a lower (maybe 100ma) rated power supply run cooler?

I know I can use my 'puters power supply, but I have the coindoor and marquee lights on a separate switch, so they can be lit, even when the computer is off.

If I really have to, I have a spare computer power supply that i wired the mainboard green wire and a groundwire together so it's always on.  But is that going to be any safer?  (and it takes up a lot more room, and has it's own fan that adds noise)

tia
Wally

Title: Re: 300ma too much for 12v coindoor bulbs?
Post by: MonitorGuru on April 06, 2005, 12:18:24 pm

Wrong way...

Title: Re: 300ma too much for 12v coindoor bulbs?
Post by: Ken Layton on April 06, 2005, 12:20:08 pm

Holy crap! What are trying to do, burn down your house?
A single 194 lamp draws 270 ma. Since you have two of them paralleled you're drawing 540 ma from a power source that can only put out 300ma. No wonder it's getting hot! You need a bigger power source. Normally for safety purposes you should take what your load is (540ma) and double it. That's the size you should buy. For modern purposes that would mean that you need a power source capable of at least a 1 ampere output (or 1,000 ma).

The only wall wart that Radio Shaft has close to what you need is # 273-1668 (around $23) and leave the selector switch on it at "13.5 volts".

Title: Re: 300ma too much for 12v coindoor bulbs?
Post by: wallyhooker on April 06, 2005, 12:39:50 pm

thanks for the detailed answers!  You guys rock.

Good thing I unplugged it!  I knew something wasn't right.

I'll get the correct power supply.  (or maybe go with l.e.d.'s. What amps do 12v led's typically draw?)

thanks!
Wally

Title: Re: 300ma too much for 12v coindoor bulbs?
Post by: gl.tter on April 06, 2005, 12:59:53 pm

Not sure about 12V in particular, but LEDs generally draw between 10-40ma (depends on the colours etc).

Title: Re: 300ma too much for 12v coindoor bulbs?
Post by: gw71mgb on April 06, 2005, 04:39:34 pm

So, while we're on the subject...

When I'm using one of the on-line calculators to determine my resistor values for the LEDs I'm using, do I use the typical current draw or the peak?  I'm assuming typical?

-gary

Title: Re: 300ma too much for 12v coindoor bulbs?
Post by: MrSaLTy on April 06, 2005, 06:29:09 pm

Yes typical.... this is usually 20ma for most leds.