Jun 20 2016

What’s in a watt?

When you turn on a light in your house, the light goes on. That’s simple. But when you turn on a light in your Airstream while on battery power, it may seem like you’re suddenly expected to have an advanced degree in electrical engineering.

That’s because managing power is one of the biggest challenges new owners face when they start roaming away from reliable campground electricity. Volts, amps, watts, and strange jargon quickly become part of daily conversation.

As Airstreamer said to me the other day: “I don’t know what any of it means, and yet I’m expected to know just to operate my trailer.”

Discussing electrical systems in an RV can be endlessly complicated, but let’s just keep it simple for now.

AC and DC—Your Airstream has two electrical systems, one for 120 volt AC power (just like the power in your house) and one for 12 volt DC power (from the battery).

Think of volts as a measure of pressure, like water pressure in a pipe. The higher the volts, the more pressure. North America uses 120 volts for ordinary outlets, and Europe uses 240 volts.

The 120 volt system in your Airstream is functional when the trailer or motorhome is plugged in. It powers the air conditioner, microwave, television, standard electrical outlets, and the refrigerator (when running in electric mode). It also goes to the power converter, which turns some of that 120 volt AC power into 12 volt DC power. This is used to recharge the battery.

When the Airstream isn’t plugged in, those circuits are off—in most cases. Why “most cases”? Because some Airstreams have generators which can produce 120 volts, and some Airstreams have inverters.

An inverter takes 12 volt power from the batteries and turns it into 120 volt power (the exact opposite of what the converter does). Because this will drain the batteries pretty quickly, inverters are usually wired only to a few things like TV and microwave, just so you can use them while you’re boondocking. You can’t run the air conditioner through an inverter because it draws too much power.

So how do we know much power something consumes? That’s where “amps” and “watts” come in. Every household appliance has a label printed on it somewhere that shows how much power it uses. For example, take a look at the power adapter for your laptop converter, or the charger for your tablet computer. In very fine print it will say something like this: “Input 100-240v~ 1.5A 50-60Hz Output 20v 4.25A max.”

That means this device can accept a range of voltage from 100 to 240 volts of alternating current (AC) at frequency of 50 to 60 Hertz. In other words, it can be used on both North American 120-volt and European 240-volt electricity. That’s nice to know in case we decide to use it in Europe, but we are really interested in the amount of that power it consumes.

This part tells us the rest: “~1.5A”. That means the laptop power adapter requires up to 1.5 amps. Let’s go back to the water pipe analogy. If 120 volts is the pressure, 1.5 amps is analogous to the diameter of the pipe. More amps means a bigger pipe, which of course can carry more water.

The total amount of energy consumed by this device is the product of the pressure and the diameter of the imaginary pipe. This device consumes 120 volts X 1.5 amps, which comes out to 180 watts. That’s the number we were looking for.

(By the way, if you’re wondering about the “Output” numbers, you can do the same math. This adapter puts out 20 volt power for your laptop at a maximum of 4.25 amps, which is 85 watts. The difference between 180 watts input and 85 watts output is lost mostly as heat. That’s why the adapter gets warm when you’re using it.)

From light bulbs you know that a higher wattage bulb is usually brighter. That’s because it’s using more power. Watts tell us the total electrical consumption of anything, and we can use watts to compare different devices.

So why do we talk about 30-amp or 50-amp power cords? That’s the maximum your power cord is rated to carry on a continuous basis. A 30-amp power cord is really a 3,600 watt cord (120 volts X 30 amps) and we could refer to it that way but it’s standard to talk about it in terms of amps.

“Aha,” you’re thinking, “so a 50-amp power cord is really a 6,000 watt (120 X 50) cord?” No, because there’s a trick. 50-amp power in North America is supplied at 240 volts. So it’s really a 12,000 watt cord. I know, it’s not fair, but that’s the way it is. Now you know why the 50-amp cord is so much heavier: there’s a lot of copper in it to carry all that power. A smaller cord would melt!

That means an Airstream with a 50-amp connection has more than three times the power available to it compared to a 30-amp connection. Even if you’ve got dual air conditioners, you’ve got plenty of extra juice. Those air conditioners will pull up to about 4,800 watts at full tilt, leaving you with 7,200 watts for everything else. Our example laptop at a mere 180 watts is hardly even noticeable in the overall scheme of things.

Once in a while you may need to plug the Airstream into a regular household outlet, which generally provides just 15 amps at 120 volts (which is 1,800 watts). This is fine for keeping the Airstream charged and powering low-wattage AC appliances, like portable fans and laptop computers. But it’s a very bad idea to run the air conditioner on 15-amp power. It might seem to work, but long term it’s likely to damage the air conditioner’s compressor or cause overheating or even melting at the plug.

Now let’s look at the other power system in your Airstream. The 12 volt DC system is driven by the batteries, and it is responsible for powering everything else in the Airstream, including lights, water pump, furnace, “cigarette lighter” 12 volt outlets and USB outlets, fans, refrigerator (when running in gas mode), propane leak detector, stereo/DVD player, breakaway switch, etc.

By running most things on the 12 volt system, most power consuming appliances in the Airstream can be used anytime, which is convenient for roadside stops and overnights without hookups. Since the 12 volt battery is kept topped up by the 120 volt power converter, it will never run out of power as long as the trailer is plugged in. Only when the trailer is unplugged will appliances be working solely on battery power, and with a little conservation, battery power can last for days.

You might be wondering why we don’t have 120 volt batteries so that everything can use the same voltage. The reason is simple: 120 volt batteries would be extremely heavy and expensive. It’s much more practical to use a 12 volt battery, charger, and appliances—much like your car does. It’s also easier to design solar panels and generators that produce 12 volt power.

In the end, it doesn’t make much difference to most appliances. A light, whether running on 12 volts or 120 volts, will produce about the same amount of illumination for a given wattage. In other words, a 12 volt light that consumes 1 amp is about the same as a 120 volt light that consumes 0.1 amp. Both consume a total of 12 watts and both will be about the same brightness.

So a watt is a watt, whether that power is supplied at 120 volts, 240 volts or 12 volts. If you ever get confused about comparing power from your solar panels, generator, or the needs of various appliances, figure the watts (remember, volts X amps = watts) and you’ll have a fair comparison.

Rich Luhr is the author of Airstream Life’s (Nearly) Complete Guide to Airstream Maintenance, available at the Airstream Life Store. There’s a lot more about Airstream electrical systems, including maintenance tips, in this 220-page book.

May 23 2016

Fixing mysterious electrical problems

The worst problem you can have with any vehicle is not a total failure. It’s an intermittent failure. Those little quirks that crop up but can’t be reliably reproduced can drive you batty, especially when you haul the Airstream into the dealership and they come back to you with a note: “No problem found,” or “Unable to reproduce customer complaint.”

Of these, the most common are electrical problems. Flickering LED lights, problems with the refrigerator or electric brake actuator (if your trailer has disc brakes), short battery life, and dim lights can all be symptoms of one common problem: bad electrical grounds.

In 12 volt DC wiring systems, every device (light, water pump, fan, furnace, etc.) has a 12v+ (positive) and 12v- (negative) connection. The negative connection goes to “ground” (or “earth”) in British English) to complete the circuit. Generally, all of the ground connections in a travel trailer or car end up being attached to the metal frame of the vehicle.

When the ground connectors get corroded or loose, all kinds of strange problems can occur. Electricity wants to find a path, so if the ground is poor, the current may run in unexpected ways, even backwards through a circuit. This can cause appliances to fail, work incorrectly, or intermittently.

Late model Airstreams usually have one or two external grounding points that provide the main electrical path to the frame. On vintage Airstreams the ground may be inside. Once located, these grounds can be easily checked. On a late model Airstream one is usually toward the front, possibly beneath the A-frame where the propane tanks sit. Look for a thick bare copper wire that is bolted to the frame or to a propane gas line with a small copper clamp. The location may vary—on some trailers it is located near the front curbside stabilizer jack.

If this wire looks corroded or exceptionally dirty, unscrew the clamp that holds it in place and clean up the clamp and wire with sandpaper or wire brush. The copper should be shiny where the wire makes contact with the clamp, for a good electrical connection. Don’t paint it!

There may be a second ground wire located inside the rear bumper compartment, which can be serviced in the same way. After cleaning, you can coat the area with dielectric grease (or pure silicone grease) to reduce future corrosion.

Checking the grounds is not just a good diagnostic step, it’s good maintenance that might help you avoid mysterious electrical symptoms later. Since it’s easy to do with just a screwdriver and sandpaper, considering doing this procedure once a year.

May 09 2016

Digital Voltage Monitor

Should you care about the power that comes into your Airstream from the campground?

Absolutely. YES.

Even newer campgrounds can have problems with their electrical power. Outlets may be mis-wired or damaged in a way that can be hazardous to your health—and the health of your Airstream.

Especially on a hot and humid day, when everyone in the campground is running their air conditioner, you’ll need to know that voltage is high enough to avoid burning out your A/C compressor.

The best way to know you’re getting good power is to use a digital AC voltage monitor. Outside Interests recommends one of the best: the Prime Products monitor, available at the Airstream Life Store. It constantly displays voltage so you’ll know if the power is sagging, and it checks for common mis-wiring conditions:

Reversed polarity (which can cause a very dangerous “hot skin” condition
Open neutral
Open ground

It’s simple to use: just plug it into any available outlet in your Airstream while you’re connected an electrical hookup, and observe the lights on the display. You’ll always know at a glance that you’re getting good power.

This voltage monitor is something every Airstream should carry at all times, and is available from the Airstream Life Store. When you order from Airstream Life you’ll also receive Rich Luhr’s short instructional booklet, How To Avoid Electrical Problems At The Campground.

May 09 2016

The 7-way cable on an Airstream

Most people don’t think about the fat black cable that connects the Airstream to the tow vehicle—until something doesn’t work, like taillights or brakes.

It’s called either the “umbilical” or “7-way” cable, and keeping it in good condition is important because it’s the critical link for correct operation of trailer brakes, lights, and signals.

The 7-way, explained—

Dirty 7-Way plug — Don’t let your plug look like this

Since 1989 all Airstreams have used the same wiring arrangement. (Earlier trailers may have different wiring, but typically they have long since been rewired to fit modern tow vehicles.) Each location in the 7-way plug is dedicated to a specific signal. Two of them—the 12 volt positive and 12 volt negative—supply power to keep the battery charged while towing to prevent depleting the battery while using the electric brakes. The other pins carry signals to activate the clearance lights, turn signals, brake lights, and back-up lights (if the trailer is equipped with them).

Is your cable too long?

Take a look at the 7-way cable the next time your Airstream is hitched up. Does it drag on or very near the ground? It will wear away quickly if it touches the ground during ordinary towing. You can use a bungee cord to take up the slack. (Drooping to touch the ground only in a sharp turn is okay, since that contact with the ground will be very brief.)

The cable should have enough slack so that the tow vehicle can make very sharp right and left turns in a parking lot without pulling the cable taut. If your cable is too short, you can buy an extension cable or (better) have the entire cable replaced. On vintage Airstreams, old stiff cables are common, so replacement is a good idea anyway.

When hitching up…

…double-check that the plug is inserted fully each time. Often it feels like it is in all the way when it really isn’t. To be sure, kneel down and look at the connection from the side. There are little tabs on the plug and the lid of the receptacle on the tow vehicle, which lock the plug into place. If the plug isn’t inserted fully, you’ll be able to see it from the side much more easily than from the rear, and this will ensure it doesn’t come loose while towing and make sparks on the freeway.

Avoid corrosion

Corrosion is the major cause of problems for the 7-way plug. Just a little moisture over time will result in greenish or white corrosion on the connectors, and that will cause problems like inoperable lights or brakes.

Be sure to position the plug between trips so that the head of plug is hanging downward. That will help keep rainwater from settling in the plug. At various RV stores you can find a generic “7-way plug holder” that mounts to the A-frame, which gives you a place to lock the plug when it’s not in use.

Periodic maintenance…

…for the 7-way plug on the trailer is important. Periodically you should clean corrosion from the seven spade connectors. It’s difficult to do without the right tool, so we recommend a kit available in the Airstream Life Store which includes a burnishing tool (a special file designed for electronic use), a premium electrical contact cleaner, and instructions.

You can also use the same tools to clean the connectors in the tow vehicle’s 7-way outlet, if they need a little help. Plan to do this simple cleaning job at least once a year as preventative maintenance. With the right tools it takes just a few minutes.

With those simple checks and a bit of annual maintenance, you’ll have eliminated the most common causes of problems with trailer lights and brakes.

Apr 25 2016

Options for preserving your Airstream batteries during storage

Ed B. from Washington posed a question that might be on your mind, too—

“I’m wondering about replacing the factory converter/charger unit with a ‘smart charger’. Battery management seems to be my problem just now. When in storage, the batteries go down to zip or overcharge, both of which are hard on the batteries. We have no problems while underway.

I tried putting a small charger unit on the batteries while in storage, but the small constant draw seems to fool the charger in to delivering full charge all the time without activating a trickle delivery as it is designed to do. Is this why Airstream has not put ‘smart charging’ units in at the factory?”

The converter/charger that Airstream installs works very well for the vast majority of cases. It is perfectly adequate unless you (a) want integrated inverter capability; (b) switch to AGM or other type of batteries; (c) want a faster charge rate, or some bells & whistles; (d) add a lot more battery capacity.

Before you spend money on an upgrade, try a few other basic steps:

1. During short term storage, use the “Battery Disconnect” switch to cut off demands on the battery (except the propane leak detector).

2. During long term storage, disconnect the battery cables and put the trickle charger on. Make sure what you have is really a smart trickle charger designed specifically for storage of batteries and not simply a battery charger with a “float mode”. If the latter, then all you’ve done is replace your Airstream’s charger with another one that is doing exactly the same thing.

3. As an option, if your Airstream is stored outside, consider a solar panel and solar charge controller. A 100 watt panel would be plenty to keep your battery happy under average conditions.

4. Make sure you are maintaining the water level in the batteries during storage. Consider switching to AGM batteries. These will not “boil off” (lose water) during charging cycles so you don’t have to check the water level during storage, and they last longer.

5. If you have the ability to measure current draw on the battery while the trailer is stored and the Battery Disconnect is switch to “STORE”, do so. Parasitic draw may account for up to half an amp, but if it’s higher than that you have a voltage leak or device that isn’t working properly, and that will kill the battery pretty quickly.