Re: [A/S] '64 Globetrotter 19' electricals

["Christopher H. Dow" <dow@xxxxxxxxxx>]

>  I made a test light many years ago, using a tail-light socket with a
> large alligator clip soldered to it. There's about 36" of test prod wire
> with a smaller clip on the end, and a turn signal bulb in the socket.
> The latter draws over 1 amp, much more than a typical "test light". I
> typically clip the socket to a ground someplace, test the connection by
> touching the lead to a known "hot" terminal, then clip it to the
> terminal under test. The light is bright enough to see from quite a ways
> away.

That makes sense.  I can see the benefit of having a light that draws
more curent than a typical test lamp.

> Leave your fridge so it can be powered by 120VAC or gas, don't change
> the heater to 12VDC or bother adding that heater. Here's why:
> 
> The 12VDC heater on a fridge will draw several amps, probably 10, maybe
> more. This makes it totally impractical to operate on 12VDC except when
> on the road, and it might not work well there either because of the long
> wiring. Besides, why load your vehicle's alternator? And, you don't want
> the load on your converter while connected to shore power, it's better
> off just using the 120VAC directly. If you feel you must run your fridge
> while travelling, use the gas.

The advice on gas is the same as a friend gave me, and it makes sense to
me.  I didn't realize the electric mode simply heated up an element.  I
guess I was thinking it had an electric compressor as well.

> I got that isolator relay from the local NAPA store. Dunno what it cost,
> but I'm sure it was less than a typical diode-style isolator. Also,
> you've proved my point about voltage drop in the latter, if it's getting
> hot, it's dropping voltage. No voltage drop = no heat; my relay doesn't
> get hot.

That makes a lot of sense to me.  The only thing I do like about the
diode system is that it won't charge the trailer when the main battery
needs it.  We plan to do some nighttime desert driving and the bright
aux lights (Hella Rallye 1000s) are a must for driving in the desert at
night, and we always seem to get to the camp site at night!  It's even
more important to see where you're going with the trailer in tow.

> Your diagram looks good. It does get a lot more complex in the details,
> but you have to start someplace.

I need to be more specific about colors and the 110VAC system in
general.

> Apparently, you're planning on doing it right, so I'd like to suggest
> you install an eMeter. They're sold under several different names
> ("Link" being one) by several different companies. Although the eMeter
> is a bit of overkill, it's really nice if you're into serious
> boondocking and are relying on your battery(s). The thing is a small
> computer that tracks the voltage, current, and amp-hours. The latter is
> tracked "out" and "in" from/to your battery. It also takes into account
> the rate of usage when calculating how much capacity is left: A 200 AH
> battery bank will not supply 200 amps for one hour, if you're drawing at
> that rate, the life will be quite short. OTOH:, if you're drawing 5 amps
> of current, you'll get close to the 40 hours of usage calculated. The
> eMeter takes this into account; I think it's called "Puekert's
> Equation".

Thank you for that bit of information.  I was starting to think about
what I needed to do for monitoring, and had no idea where to start.

> The eMeter requires a half-dozen or so light-guage wires between it and
> the battery. A 500-amp shunt is installed near the battery and all
> current goes through it. You can see my control panel at
> http://www.oldengine.org/members/jdunmyer/avion/sep01_07.jpg; I have a
> piece of 8-conductor 22 guage cable running from the meter to the
> batteries, a distance of about 25 feet. There's a DB-9 connector pair
> inline so I can easily remove the panel from the cabinet above the
> fridge.

That panel looks great.  I'll probably install something quite similar
on the outside of left-hand wardrobe.

C