Electrical System


Like just about everything else in my Overlander, both the 120 vac & 12 vdc electrical systems were completely original with the exception of a new outlet in the kitchen when we first started camping.  Although I have no formal training in either electricity or electronics, I have hobbied with both since I was a little kid, and am quite comfortable working with both.  You may not be.

But if you are, and are looking for a little insight into what makes a vintage Airstream tick electrically, there are a few observations worth sharing.  Although I have tried to keep the “glaze factor” down, my tendency is to drift into the minutia, so feel free to email me for clarification if I should lose you in useless detail.

The Wiring

Solid aluminum wiring was all the rage in the late sixties because it was cheaper & lighter than copper.  What aluminum wiring lacked in conductivity as compared to copper could easily be made up in increasing the wire’s diameter.  When sized & installed by a properly trained individual, it works great.  Unfortunately, if the correct connectors are not used, problems can occur.

In a nutshell, different metals expand & contract at different rates when the temperature changes.  If a wire is connected to terminals made of metal with a different expansion/contraction rate, after several temperature changes, the connection will loosen up.  After that happens, arcing at the connection can occur.  Either the heat from the arcing or the arc itself can prove to be a fire hazard.

It is my understanding that a flood of improperly installed aluminum wiring forced National Electrical Code changes banning the use of solid aluminum wire in residential applications.  Stranded aluminum wire, commonly used in high current applications, is still allowed.  Seems like I heard that solid aluminum wire is still used in mobile homes.

Both my Airstream, and my house use aluminum wiring for 120 vac circuits.  My Airstream was in a great shape.  My house, however, had several instances of improper connections.  If your Airstream has aluminum wire, it would behoove you to check each outlet & breaker to make sure it is rated for aluminum wire and that the wiring’s screws are tight.  Most home improvement stores sell special outlets & switches rated “Cu/Al” or “CO/AL” (copper/aluminum) wire.  For what its worth, I have heard that the terminals are made of zinc.

Copper wire is used for the 12 volt circuits in my Overlander.  I have a feeling the Factory would have used aluminum if they could, but did not for two reasons.  12 volt circuits have to be able to carry a lot of current since the voltage is so low.  10 gauge wire is the largest solid wire gauge I have seen available, and that may not be big enough.  But aluminum wire was probably not used because its lower conductivity would result in an intolerable voltage drop (dim lights, slow motors).

Update:  My Airstream was built at the Ohio plant.  I found out the other day that a friend of mine’s two ’67 Airstreams built at the California are wired differently.  In both of his Airstreams, the copper wire carries 120 vac, and aluminum wire carries 12 vdc.  For the reason outlined in the paragraph above, I think a boo boo occurred at the factory.  But I did want to pass the info on.

The Univolt

I like the Univolt.  But I also appear to like doing things the hard way like lighting pilot lights & winding clocks.  Sure, the modern day power converters do a fine job of powering 12 volt circuits & keeping the battery properly charged.  But I enjoy having a “say” as to when & how much my battery is charged.  Everything nowadays is computerized to do its job.  Computerized control is great…while it is working.  New boards always seem to cost at least $100 if they are still available.  Now that you realize I am eccentric and cheap,  here are a few observations on the Univolt:

Univolts do not regulate the voltage they deliver. They were designed to output one single voltage with as much current as available. A Univolt is amazingly simple: A big transformer to step down the voltage, diodes to convert AC to DC, and capacitors to tune the circuit.

If you were to study power supply theory, you would find the Univolt’s circuit listed as a ferro-resonant transformer.  I believe this particular design was chosen because its output terminals will continue to deliver full current, with no adverse affect to the transformer, even if they are shorted together.   While I have a schematic for those that are truly interested, ferro-resonant basically means there is a capacitor hung off a tap on the output windings to tune the circuit.

Some people appear to think that a battery must be present for the circuit to be properly tuned.  This is incorrect.  The battery serves to filter, and smooth the Univolt’s output, but is not required for operation.  However, your 12 volt lights will be dim, and your radio will have a lot of static in the absence of filtering & smoothing.  During the refurb, and now in the winter, I keep a bank of old electrolytic capacitors out of my toy box wired up to act as a “battery simulator”.  The capacitors do all the filtering & smoothing, and allow me to keep the battery in plain view in my Shop so I don’t forget to check it every so often.

Speaking of battery charging

My '67 owner's manual says that the Univolt has a 100% shut off and that it is impossible to overcharge the battery. I will give Airstream the benefit of the doubt, and assume that some Univolts had a circuit breaker which would trip to effect "100% shutoff". A Univolt has no "smarts" to it.  It could care less if your battery is boiling, simmering, or even there.  It's job is to supply roughly 13.5 vdc with as much current as it can muster.  I put it that way because, the voltage will drop as the load on the Univolt increases.  If you are actively camping and have a bunch of lights & fan motors going, the voltage difference between the battery & the Univolt will be small. In fact, the battery may even help the Univolt out if you have A LOT of stuff on.

A battery is charged by applying a DC voltage to the battery that is higher than the voltage the battery currently has. The higher the voltage difference, the greater the charge rate will be. I believe a fully charged battery will read 12.9 vdc on a volt meter.

Charging a battery is an electro-chemical reaction. As the battery charges, tiny bubbles of hydrogen gas & water vapor form on the plates, and eventually bubble off. These bubbles eventually escape from even sealed batteries. The higher the charge voltage, the more bubbles that are formed. It is this bubbling that is commonly referred to as boiling although it does not occur the same way as water boiling in a tea kettle.

But, with no lights or anything but the Univolt on, the battery will be subjected to the maximum voltage the Univolt can deliver. It will attempt to charge. After a while, the water will bubble off.

My Univolt is conveniently located under the bathroom sink.  While reinstalling it during the refurb, I took the opportunity install a simple, external ON/OFF switch.  When camping on shore power, I leave the Univolt off unless an electric motor is running, or a lot of lights are on.  Between this switch, and the original analog battery minder, I have yet to boil a battery.

Power Quality

Just because a campground has a 30 amp receptacle for you to plug into does not necessarily mean you will get power your Airstream is happy with.  A lot of trailers at the campground all running their air conditioners, may affect the line voltage.  Ideally, you would like to measure 120 vac on your voltmeter once you plug up.  After letting your air conditioner run for half a minute or so, the voltage will probably drop a volt or two.  As long as the voltage stays at or above 115 vac, you’re in Schaefer City.  Be careful about running the microwave though.  I have heard of people continuing to run the air at voltages as low as 110 vac.  Not me.  RV Air conditioners are too expensive to repair when damaged by low voltage.

Also, if you have to use an extension cord to plug your Airstream into shore power, make sure its wiring gauge is 10 gauge or lower.  Lower gauge means thicker wire.  The wiring gauge should be stamped on the outer insulation.  If it is not, it is a cheap extension cable & should not be trusted.  I only point this out because I once saw a vendor selling an extension cord with 30 amp fittings, but the wire gauge was 12 gauge, which is only rated for 20 amps.  Using the wrong gauge can result in an unwelcome voltage drop.

Light Bulbs

My '67 Overlander requires two certain light bulbs, an 1141F, and an 1176, which proved impossible to find locally. All the big, on-line companies sold one, but not the other.

I found a "Mom & Pop" place in Missouri called AMT Electrical who sold me both bulbs for a ridiculously low price. We're talking 16 to 18 cents a piece.   I ordered a total of 40 light bulbs which were UPSed to my door for a grand total of $10.36.

Their website does not list prices, but they do have a 1-800 number. Rosemary was quite helpful.

BTW, the 1141F, a frosted version of the common 1141, is now designated as 1141IF. The version sold to me by AMT Electrical looks different than I was expecting, but works just fine in my Overlander.

12 volt Circuit Breakers

In 1967, Airstream used three, 12 volt, 20 amp, self-resetting circuit breakers to limit current flowing through the 12 volt DC circuits.  Additionally, there is one, 25 amp breaker in the belly which keeps an eye on the charge wire’s current.

Coincidental with replacing a bad light switch, I had one of these breakers bite the dust. Kinda cool how simple the breakers are. The autopsy showed the device has nothing more than a bimetallic strip with [apparently] a certain amount of electrical resistance. When too much current is drawn, the strip pops the circuit open. When cool, it closes.

In my case, the contacts had fused, and melted away from the strip. The point source heating around the damaged contacts made the breaker work in an interesting way.

Luckily, with minor modification, the breakers being sold nowadays are physically quite similar to what I had. At $3 a pop, I replaced all three breakers.

Light Switches

Everything went fine on our first couple of camping trips.  But then the kitchen sink light switch failed in the every-bulb-ON position.  Although I could see the original switch had been made by Leviton, they now no longer make it.  Much time was spent on the Internet, and at local lighting vendors to no avail.  Although 3-position switches are still being made, none could be found that had the shaft length needed for my light fixture.  So, at over $15/switch plus S&H, I ordered two from an Airstream dealer.

The previous owner must have used the kitchen sink light a lot because the insulation on the light bulb sockets’ wires was dark & hardened.  I was able to find new socket center contact wiring at a local auto parts house.

A couple more camping trips later, the second switch was installed in the bedroom fixture when that switch failed.  Interestingly, the sockets’ wires did not need replacing in this fixture.

A couple more trips later…

Since I could see where this was going, I broke down ordered three switches, and replaced the rest before they could fail.  The bath fixture, judging by the wire caps used, appeared to have been replaced before.  But, to be on the safe side, it was also replaced.  My motto is now, “Replace your light switches every 38 years whether you need to or not…”