Subject: Re: LeSharo Electrical problems
Given the propensity for problems in 12 volt auto systems and the power they
use, I often am amazed they work at all. But they seem to get along in spite
of their weaknesses...
To minimize radio, tv, etc noise - put a capacitor from the fuse lead ( or to
the 12 volt wire at the conenction near the appliance) to ground - they sell
them as replacements at most auto stores because most cars have/had them and
they break down with age. They "suck up" the radiated spikes of the spark
plug firing given off by the wires, etc.
If it doesn't go away, you might need new spark plug wires and a coil wire.
Cracks inside the wires cause internal sparks that "talk " to the radio, ECU,
etc.
now, about the 12 volt systems
...................................
For those who like such things - Basically it goes like this -
The equation is volts = current in amps x resistance -
it governs. period.
I've got 12 volts in the vehicle - that's all there is - I can use maybe
14-15 volts to charge the battery, but everything is pretty much designed
around 12 volts.
so --my AC needs 12 volts, my computer steps down 12 volts to get a relaible
voltage, my starter uses 12 volts, and so on. 12 volts.
so far, yeah, that's ok, we all know that - so now it gets good...
so we add a little corrosion, not much, just a little - maybe a couple of
ohms worth - and that ain't very much corrosion -
- a half ohm on the ends of the engine grounds,
-a half ohm on the AC mount,
-a half ohm on the battery terminal because it's not real tight or it's been
stripped or the like, and
-maybe the AC hot connector is just a bit loose or dirty for another half
ohm.
Now, I need 240 watts to run my AC -
watts = volts x amps
that's 20 amps at 12 volts
so I run my AC - and 20 amps goes from the battery to the AC and back to the
battery in a nice proper loop
But.....My 20 amps across the 2 ohms of poor connection takes - what -??? 40
volts? but I only had 12 to start with --
12 volts = 20 amps x ??? can't do it !!!
that leads to two important observations in understanding auto 12 volt
power--
first, if it is not 2 ohms but only 0.2 ohms (and that is a fine dusting in a
connection) I have to run my AC on 8 volts, not 12 volts --- because 4 volts
are taken by the bad connections- 0.2 ohms x 20 amps
but the AC wants 240 watts, not amps, so I now draw 30 amps to get the
watts at 8 volts, not 20 amps at 12 volts, but that takes even more volts out
of the 12, so I now have only 6 volts so it draws more - and it starves for
power, making the AC and the vehicle run like crud. The poor AC doesn't get
240 watts.
how much does it get as it struggles along?
so, second - the AC really will run with 2 ohms resistance - it does - and
that says that the amps are severely limited by the resistance because
-->you can't cheat the basic equation<---
so the resistance and the AC had to gang up and limit the amps to the AC
In other words - if I only have 12 volts, the amps are determined by the
resistance I present to the voltage - and if i have two ohms resitance, I can
only get 6 amps through.
To look at this yet another way - for an AC to draw 20 amps at 12 volts to
get its 240 watts, it had a resistance of 12/20 = 0.6 ohms ---which let 12
volts put 20 amps through.
The AC has 0.6 ohms resistance and it looks for 12 volts to do its job
efficiently - now what happens if I get 0.6 ohms resitance in my connector,
too?
You get 1.2 ohms resistance in the loop and 12 volts put on the loop - by
the basic math, that's 10 amps and only 120 watts used by the AC.
so the AC struggles along, weak.
You want some scary stuff - take a look at the starter and put 1/10 ohm of
resistance on the grimy engine ground when you hit the starter that draws up
to 120 amps.
smoke and fire....
the bright side of the big amps - the big amp draws tend to burn off the
light oxides in a blast of heat when the item is first turned on - but
carbon up or toast the stuff under bigger corrosion
weird stuff.....
hope it helps....