Re: [DMCForum] Ohm's Law

["Walter Coe" <Whalt@xxxxxxx>]

> How many amps is the cigar lighter -supposed- to put out??

It is fused at 20 amps.  So according to Lucas, it should be
good for that.  Why waste a margin of error?  But seriously,
it is really a matter of duty cycle.

Realistically there should be no issues with pulling 5 amps
thru there continuously.  I have a small 12V refrigerator
that is fused at 8 amps.  Sometimes getting it to work is a
problem because the contacts get loose, continue to vibrate,
arc & build up carbon.

> but of
> course it blows the fuses in my cigar-lighter adapter
devices such as
> cell-phone chargers, and mini-disc player power supply.

Huh?  You say it is blowing the fuses IN your devices?  And
you mean devices as in plural?  Well, if you find that these
devices work in other cars then it would seem reasonable to
suspect the DeLorean.  I have an electronics background that
wraps around both sides quite a bit (not that I'm bragging,
of course :-)  There isn't much that a car can do to blow
such fuses.  The voltage from the alternator could be too
high, but you would probably notice that in the dash gauge.
But then maybe not if it were an intermittent spike.  Try
keeping a DVM hooked to the car that records peak voltage
and drive around that way while you blow a fuse.

The only other thing I can think of is that if the
connection were dirty then it might confuse the
filtering/regulating devices in your accessories causing the
fuse to blow.  I don't have enough electronics foreground to
say if this is likely, tho.  But I bet Gary could set us
straight. ;-)

> Do I have a short somewhere, or does it just need
attenuated?

If you have a short then you should have one in each
accessory that blows fuses.  Attenuated?  WTF is that?  I
think the only time you use impedance (attenuation?) on
things related to power supplies are on really high voltage
applications such as electric fences and secondary ignition
systems or in really simple situations where power & load
fluctuations are minimal.  But then I don't have the
foreground.  Maybe someone can enlighten me.

> Based on 13.5 volts and 4.5 amps DC measured at the
outlet,
> I figured I should put in a 50 ohm resistor.

You lost me.  What accessory is drawing 4.5 amps?  At 13.5
volts that is over 60 watts!  That can't be a cell phone
charger or a mini-disc player.  Is the 50 ohms to limit the
voltage drop across your accessory to 12 volts?  Bad idea.
If you want to do that then build a voltage regulator.
Radio Shack has little how-to's for that in their project
books.

> Now that I've publicly admitted I'm a dumbass feel free to
advise me.

You are in good company.  I swear that I am a bigger dumbass
than you. :-)

Walt    Tampa, Florida

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