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

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

> Thanks for the clarification on the inverter. Unless it's quite large,
> the best way of using it is to have a seperate 120VAC outlet fed by the
> inverter and a switch to energize it "as needed". Make sure to install a
> pilot light near the switch so you don't leave it on accidentially.

I was planning on that.  Also, I think I'll put an indicator in the same
location I'm planning on putting the instruments for power monitoring.

> I like a light bulb for testing purposes in addition to a DVM. A tiny
> strand of wire or other leakage will show "power" with the DVM, yet
> won't supply enough current to actually DO anything. A good heavy
> lightbulb needs more than leakage to light it. My original suggestion
> was to use the light bulb in SERIES with your system to avoid blowing
> fuses; a direct short would only cause the bulb to glow at full
> brilliance.

That makes sense.  Do you like light bulbs better than test lamps?  

> No doubt your fridge should be connected to that receptacle near it if
> it's to work on 120VAC.

Yeah.  I think I'm going to switch it over to 12V, since that will be
native power while on the road.

> I personally prefer a relay for isolation because it has almost no
> voltage drop. A diode always has a few tenths of a volt drop across it,
> making a bad situation worse. It's very hard to charge your trailer
> battery to any degree from the tow vehicle unless you wire the
> connection with #4 welding cable and a forklift-type connector. My
> eMeter shows only a few amps of charge current when the vehicle is
> running, due to the 35' or so of #10 wire between the batteries. Maybe
> it'd do more if the battery was nearly dead, but I doubt it. 

I'm using #8 wire, and I noticed when I picked up the trailer, the
battery condition was "Fair" on the meter the PO installed in the
bathroom (!!).  When I stopped the first night, it was "Good" and has
remained so.  I'll check to see how many volts it has on it with the
DMM.  Anyway, I think I am charging it.  I'm also looking for a
higher-output alternator since the combination of the trailer, my in-car
goodies (cell phone, laptop w/ inverter, GPS), lights, and wipers was
problematic on the trip home from acquiring the Globetrotter.

> The relay that I use looks like a Ford starter relay ("solenoid") that's rated
> for continous use. The coil is connected to the ACC feed on the truck, so is
> closed only when the engine is running.

Where did you get this?  The other thing I like about relays (I don't
know if I mentioned it, but my original idea was to use relays for
battery isolation) is that they don't have the heat issues that the
isolators have.  We had to place my isolator in a vent on top of the
"wing" (that's fender to us colonials) so that it had sufficient air
flow.

> That transformer thing is crude, at best. You're right that you
> shouldn't need a switch for "battery/Shore" power, it should be
> automatic. Both my A/S and my Avion simply have the entire 12VDC system
> connected to the battery. The converter/charger is also connected
> directly to the battery. I do have a 50-amp fuse and Master Disconnect
> Switch in the main battery lead for disaster isolation. This is quite
> important, and not always incorporated in the older trailers. Remember
> that a regular ol' 12-volt battery is capable of several hundred amps of
> current for plenty long enough to melt every wire in your trailer, and
> you do need to protect that main wiring that's ahead of your branch
> circuit fuses/breakers.

I, too, am a strong believer in fuses and breakers.  I got this from
replacing the wiring harness (after a disaster) in my '65 Land Rover
:-).

> BTW: I got a "file not found" on your "modified wiring diagram".

Sorry about that.  Here's the corrected URL: 
http://www.thelen.org/airstream/ASWiring-mod.pdf 

(I actually pasted that into my browser to check it--QA is a good thing
:-).

8<
> > This trailer has only 12V lights.  My guess (still haven't tested the
> > sockets) is that they are 12VAC when on shore power, and 12VDC when
> > battery power is correctly applied.

I have now tested the lights while on shore power, and they are, indeed,
12VDC.

8<
> > I have come up with a new schematic for what I want.  It's at
> > http://www.thelen.org/ASWiring-mod.pdf

Correction:  http://http://www.thelen.org/airstream/ASWiring-mod.pdf

> > It shows a charger, tow vehicle, and solar setup connected to the
> > battery as well as an inverter.  Since most everything is 12V, that
> > gives me all I need for hookup, tow charging, and solar charging, and
> > leaves me the outlets when I'm boondocking.  I don't expect to need them
> > much, but it would be nice to have them occasionally.  I think that that
> > will make it so that I don't even have a switch to thow when hooking up.
8<

Thanks for all your help, and I would appreciate any feedback on the
diagram listed above.

C