Date: Sat, 13 Jul 2019 14:12:41 -0400
Reply-To: David Beierl <dbeierl@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@GMAIL.COM>
Subject: Re: Finding a short
In-Reply-To: <BYAPR12MB36400B4351562693932C4AABBACD0@BYAPR12MB3640.namprd12.prod.outlook.com>
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Electrical stuff works like hydraulics, but with electrons instead of
hydraulic oil. It only works when there's a complete circuit, so that the
electrons can get back to the battery.
The specific laws are from Georg Simon Ohm: Volts = amps x ohms, and watts
= volts x amps. These can be rearranged/decomposed to amps = volts/ohms,
ohms = volts/amps, volts = watts/amps, amps = watts/volts, watts = amps^2 x
ohms, and watts = volts^2 / ohms.
Volts is pressure, measured between two points in a circuit. Hydraulic
analalogy would be psi.
Amp[ere]s is current flow through a circuit. One amp is a ridiculous
number of electrons per second. Hydraulic analogy gallons per minute.
Ohms is resistance to flow, causing a pressure drop.
One volt will cause a current of one ampere to flow through a resistance of
one ohm.
These laws apply when conditions are steady, which in DC circuits they
mostly are. It gets more complicated with AC circuits, or under transient
conditions; but you mostly don't need to be concerned with that in the
van. It also gets more complicated when chemistry is involved, like inside
a battery. I won't get into that now.
An open circuit (like opening a switch) makes everything stop. With no
flow, no work can be done.
A short circuit is a sneaky way for current to get back to the battery
without going through the load. Short circuits blow fuses and/or let the
magic smoke out of the wires.
A poor connection increases total resistance in the circuit and thus
reduces the overall power -- but some of that reduced power generates local
heating at the point of the problem, which can melt wire insulation, melt
sockets, cause false blowing of fuses, and such.
Yrs,
d
On Sat, Jul 13, 2019 at 1:03 PM David Boan <dboan@outlook.com> wrote:
> Dear Dennis, David and Alex;
>
> This was great. I have no idea what those laws are (I am a social
> scientist by profession, this is all new to me), but I look forward to
> learning more.
>
> In the meantime, I attached a 4 AWG cable from the ground of the accessory
> battery (which is under the back seat) through the rear panel and to the
> frame. Presto, problem solved. I still don't know why or how, but I will
> do some reading.
>
> Now, the complete accessory setup looks like this, I have the 4 awg ground
> to the chassis, a 6 AWG + cable to the accessory bus under the driver seat,
> plus a 6 AWG ground to the same bus. Jay Brown suggested I would need at
> least 6awg to that bus if I want to put headlights on it (which I have not
> done yet). I also have a small bus on the cabinet panel opposite the water
> tank and moving accessories in the back (water pump, plugs and rear lights)
> to that bus to eliminate some of the wires going forward.
>
> Thanks again. Come to Boise and I'll buy the beer.
>
> Dave B
> Boise
> ------------------------------
> *From:* David Beierl <dbeierl@gmail.com>
> *Sent:* Saturday, July 13, 2019 8:55 AM
> *To:* David Boan
> *Cc:* vanagonlist a; alex@mevay.org
> *Subject:* Re: Finding a short
>
> What Alex said. You have an open ground on the house battery. As soon as
> you connect a load to it the positive terminal floats at chassis ground
> level, and the negative battery terminal is now -12V to chassis.
>
> Yrs,
> d
>
> On Fri, Jul 12, 2019 at 2:03 PM David Boan <dboan@outlook.com> wrote:
>
> I am working on correcting a short in my accessory wiring, and while
> making progress I have hit a plateau. I thought someone might have
> experienced this and could save me much time searching ...
>
>
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