Date:         Fri, 9 Jul 2010 18:29:41 -0700
Reply-To:     "Mike \"Rocket J Squirrel\"" <camping.elliott@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Mike \"Rocket J Squirrel\"" <camping.elliott@GMAIL.COM>
Subject:      Re: 12 Volt Appliances: Correct Formula to Figure Amps Consumed?
Comments: To: neil n <musomuso@GMAIL.COM>
In-Reply-To:  <AANLkTim5VAZQ6UOrcV3Vli0MWxT6oD1NmX6czoc_AYJT@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hey Neil,

Ohm's Law tells us that current = power/volts. So an appliance that
consumes 12 W at 12 volts will draw 1 amp. You're not doing anything
wrong, Ohm's Law is the law. And don't you forget it.

But the manufacturer's specifications may have been written before the
product was done, or by an idiot. Unless your measuring equipment is way
out of spec, what you measure is going to be the final word.

Yeah, .45 amps is .45 amp-hours per hour. So after ten hours, you will
have used 4.5 amp-hours. That ain't a big deal. Run that thing for 48
hours and you've used 22 a-h. That could be a big deal depending on size
of battery, etc.

--
Rocky J Squirrel
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR



neil n wrote:
> Hi all.
>
> Viewing this:  http://tinyurl.com/23utmeo in the store, I wondered how
> many amps it would use. On the back it says: 12 Watts, 12 Volts. Only
> vaguely recalled Ohm's Law at that moment, didn't obviously know the
> resistance of the unit, so couldn't calculate amps used. Bought it
> anyway.
>
> At home checked current draw. Low -  0.45 amps. High - 0.6x amps
>
> But entering 12 volts and 12 watts here,
> http://www.the12volt.com/ohm/page2.asp shows 1 Amp. Here:
> http://www.csgnetwork.com/ohmslaw2.html  0.58 amps. They both *appear*
> to use the same formula though the latter gives closer to what I
> measured on high speed, hence the makers rating I assume.
>
> What am I missing or doing wrong? Or more to the point, what formula
> should I memorize?
>
> Looks were deceiving. Had it been over 1 amp draw, I likely wouldn't
> have purchased it thus saving time. As it turns out, for my needs,
> 0.45 amps/hour over a few nights use, shouldn't draw down my group 42
> aux. battery too far.
>
> Thanks!
>
> Neil.
>
>
> --
> Neil Nicholson '81 VanaJetta 2.0 "Jaco"
>
> http://tubaneil.googlepages.com/
>
> http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines