# Camera for Hood-Mounted Mirror

NOTE: This post is something I wrote back in May 2015, and was published on the Escapees HDT Forum.  Here it is with a few minor updates.  Still my most-used electronic driving aid!

After adding a Volvo hood-mounted mirror, I still wasn’t quite happy with how well I could see my front right corner. I feel like I have really good coverage down the side with the normal and wide angle mirrors, the over-the-window mirror, and now the hood mirror.

# Grandma’s Toaster

That failure was disappointing.  I remember an old toaster in my grandmother’s kitchen that they got not long after they were married.  It had a battle scar from falling off of the top of the curved refrigerator where it lived when not in use.  But it was regularly in use for more than half a century–that kitchen cranked out some of the best breakfasts on the planet.

# Water Misters, Part 2: How Much Money Can I Save?

The water misters can make the air conditioner perform better, but does it make sense to use them?  Of course, if you’re in a campground with unmetered water and electricity, there are no immediate savings other than comfort.

Electricity is one of the bigger costs in operating an RV park though, so we all pay in some form or another. The park doesn’t get it for free, and the cost is ultimately passed on to the consumer, so everything we can do to reduce our own usage benefits the community at large.

# Calculating Air Conditioner Costs

If we make a few assumptions about air conditioner usage, we can estimate the cost of running one for an hour.

For now, let’s take 12 amps as the average load running at 120VAC, and assume a power factor of one.  Running the air conditioner one hour consumes 1.44kWh, and a national average residential electricity price of $0.129/kWh gives us a cost of about$0.19 per hour.  If the air conditioner runs about 1/4 of the time through the summer, it costs about $33/month to run. Now let’s consider the scenario using the misters. They reduce the power needed to run the air conditioner by about 10% in my testing, or about$0.02 per hour.  But if the air conditioner was previously able to keep up, it will also run less.  How much is heavily dependent on the weather, but it could easily be a 25% reduction.  That’s over $10 per month, per air conditioner. But let’s also consider the water usage. If we set it up so the misters only operate when the air conditioner is on, and that we use 0.5gal/h of water, we’d use 3 gallons a day. At the national average price of water, that’s less than half a cent–a negligible amount. So far, it looks like the misters make sense as far as utility costs. The campground benefits (in most cases) from your using them. What if we’re not grid-connected? # Misting While Boondocking Here’s where it gets more complicated. Most RVers probably only run air conditioners with their generators running when they don’t have hookups. With a limited water supply, you’re particularly conscious of its use, but you may also want to cool the RV quickly after a day away from it. Let’s look at the previous math slightly differently. Instead of$0.129/kWh, let’s assume we have a generator that uses 0.5gal/h of diesel at idle, and 1.0gal/h with both air conditioners running.  If we only consider running the generator with both air conditioners on, each one is using 0.5gal/h.  At about $3/gal for diesel, that’s$1.50/h.

If we’re operating the misters effectively enough to reduce runtime by 25%, we reduce the hourly cost from $1.50 to$1.13.  That’s $0.38/hour. Looking just at that part of the equation, the misters can pay for themselves really quickly. The savings would pay for the misters in a couple of weeks running 2 air conditioners for 3 hours a day. But we’re using water from our fresh water tanks, which has a much higher cost, especially in terms of convenience, than a municipal or campground supply. If it’s 3 gallons a day, in the same two weeks we’ve used 42 gallons each of water and diesel. You quickly arrive at a situation where the answer is it depends. In my case, if the tanks were all full at the start, neither one is limiting. Staying longer than two weeks, fuel and holding tanks would become the limiting factor before fresh water. I’d run the misters. How about you? Next time I post on this subject, I’ll cover setting it up to run efficiently. It’ll be triggered by the air conditioner’s compressor running, so the nozzles don’t run when the air conditioner doesn’t. # Lithium Batteries and Upgrading the 12V DC Power System Last fall, I wrote about installing a PC power supply to power the remaining 12V DC loads in my RV, but that’s getting replaced with a DC-DC converter. The power supply did the job it was supposed to, without fail. But there are a few drawbacks with it: • The power supply converts AC power from the inverter to 12V DC. That means the inverter is on, and there’s an extra conversion that wastes energy. • Under load, the 12V output from the power supply is lower than I’d like. At the source, it drops to about 11V, and my rig’s 12V wiring is mediocre at best. Vent fans, water pumps, etc. all run a little slow. • The power supply doesn’t respond well to sudden load increases. This is most evident with the stereo system. # Great Plate Disaster of 2017 One of those age-old questions of seasoned RVers–not necessarily old ones–is what kinds of plates and other dishes to travel with. I can’t count how many times someone has asked how I pack glass dishes, and I’ve always had a simple answer: I don’t. They just sit in the cabinet where they always do, with nothing in between them. # Power Adapters 101: What power adapter is safe to use? Just about every RVer has a few power adapters, often referred to as “dogbones,” to make sure that they can connect to whatever power is available to them–this post will go over which power adapter types are safe to use, and which ones you might want to carry. ## Circuit Protection The job of a circuit breaker or fuse is to protect the downstream wiring from overloading and short circuits. Any wire configuration has a current rating, and a circuit breaker typically protects that wire. Keeping that in mind, when we adapt an RV with a 50-amp plug (NEMA 14-50P) to either a 30-amp or 15-amp receptacle, the circuit breaker at the source will shut off power the wire’s limit is reached. At worst, under one of these configurations, we experience a nuisance pedestal breaker trip: • 50-amp RV cord plugged into 30-amp, 20-amp, or 15-amp receptacle • 30-amp RV cord plugged into 20-amp or 15-amp receptacle For any of these configurations, you can find a UL-listed power adapter, and operate your RV safely. But the other way doesn’t work. Let’s say you have something you want to power with a normal 15-amp plug. That includes a patio light, a heated hose, space heater or a string of flamingo awning lights. Now suppose you don’t have a 15-amp receptacle on the pedestal, or that you have something else plugged in. Can you adapt down from a 50-amp or 30-amp receptacle on the pedestal to one for your 15-amp appliance? NO. If there was a problem with the appliance, or its cord, you could easily melt it before the breaker is overloaded enough to trip. Note that in any of these situations, and even when plugging your RV directly into a pedestal, a receptacle in poor condition is still a hazard. A loose connection can easily generate enough heat to melt your plug or start a fire without tripping a breaker. If a plug goes in with little resistance, the receptacle probably needs replaced. ## Power Adapters that are Safe to Use All of these power adapters will have a smaller, lower amperage plug (male blades) on one end, and a larger/higher-amperage receptacle (female terminals). Look for UL-listed versions of these adapters, preferably with rigid grab handles. ### 50-amp RV plugged into 30-amp source Power adapter has 50-amp female receptacle (NEMA 14-50R) and 30-amp male plug (NEMA TT-30P) ## Products from Amazon.com • Price:$13.99
• Price: $9.00 Was:$24.78

### 50-amp RV plugged into 15-amp source

Power adapter has 50-amp female receptacle (NEMA 14-50R) and 15-amp male plug (NEMA 5-15P)

## Products from Amazon.com

• Price: $19.01 • Price:$20.89
Was: $22.89 ### 30-amp RV plugged into 15-amp source Power adapter has 30-amp female receptacle (NEMA TT-30R) and 15-amp male plug (NEMA 5-15P) ## Products from Amazon.com • Price:$8.15
• Price: $8.92 Was:$12.99

I’d advise avoiding this last type, just because of the mechanical strain it will create in most situations:

• Price: $5.65 Was:$6.99

These adapters allow for the connection of a smaller cord to a larger source.  The cord in this situation could be overloaded without a breaker tripping, which is a safety hazard. These devices cannot be UL-listed.

### 30-amp RV plugged into 50-amp source

Power adapter has 30-amp female receptacle (NEMA TT-30R) and 50-amp male plug (NEMA 14-50R)  DO NOT USE!

## Products from Amazon.com

• Price: $9.07 Was:$24.78

### 15-amp RV/device plugged into 30-amp source

Power adapter has 15-amp female receptacle (NEMA 5-15R) and 30-amp male plug (NEMA TT-30R)  DO NOT USE!

## Products from Amazon.com

• Price: $4.88 Was:$7.59

### Any combination of 15-amp and 30-amp receptacles plugged into 50-amp source

Power adapter shown has 15-amp female receptacle (NEMA 5-15R) and 30-amp female receptacle (NEMA TT-30R) that are split from a 50-amp (NEMA 14-50P) plug.  If you look closely, the handle for unplugging is a thin rubber strap that hooks on to the sides–that style isn’t very easy to unplug, and they’ll break, usually long before the plug itself needs retired.  DO NOT USE!

• Price: $54.99 # Differences between RV Plugs and Common Household Plugs Perhaps the most confused RV plug is the 30-amp TT-30, which looks very similar to the common 3-wire clothes dryer plug (10-30) which was installed in homes built prior to 1994. The two plugs are physically different in the center pin, but more importantly, they’re wired differently. The dryer plug supplies 240V, with a ground-neutral bond. This bonding means that the ground–which is designed to be a safety feature–is also current-carrying, which negates that function under certain conditions. The National Electric Code prohibited that practice in new home construction beginning in 1994, and a 4-wire plug has been used since then. If having an electrician install a 30-amp service for an RV, make sure that it’s a TT-30 configuration, and that it’s properly wired to supply 120V with separate ground and neutral. Which brings us to another plug, the RV 50-amp plug, which is a NEMA 14-50. This plug is commonly found on electric ranges, and is similar to–but different from–the typical dryer, which uses a NEMA 14-30. The 30-amp dryer plug has an L-shaped neutral, whereas the 50-amp RV plug has a straight blade. While not common, it would be safe to plug a 50-amp RV into a 30-amp 4-wire dryer receptacle, but not a 30-amp RV into a 50-amp range receptacle. ## Is there a way to plug a 30-amp RV into a 50-amp pedestal? Yes, but it’s not a product that you can just go out and buy. Do do it safely, you’d need a short cord sized for 50-amp service into a subpanel with a 30-amp breaker. If enough of you are interested, we might build one up to show the process. # Ok. Enough already! I’m a new RVer–what power adapter should I carry with me? Each of these adapters have a rigid, molded grab handle, and have the plug at the proper orientation so that the cord and plug aren’t strained when hanging. Identify which type of RV you have based on the plug images below. If you have a 50-amp RV, it should have a plug like this: In that case, you can plug in anywhere (50-amp, 30-amp, and 15-amp receptacles) with these two adapters: ## Products from Amazon.com • Price:$9.00
Was: $24.78 • Price:$19.01

If you have a 30-amp RV, your plug will look like this:

And you’d just need this one power adapter:

• Price: $8.92 Was:$12.99

# Using Water Misters to Save Electricity and Keep Cool

It’s that time of year again–temperatures are rising and the non-fulltimers are out in force. Depending on where you’re camping, that may mean managing your power use on a limited hook-up, listening to the air conditioner run non-stop, and possibly still being hot inside in the afternoon sun. We can improve on that with a few misters.

At first glance, you might think I’m about to talk about swamp coolers, solar shades, or misters on the patio.  Not quite…

# Electrical Myths, Part 2: Showing Heater Current doesn’t go up when Supply Voltage Drops

Last time, we talked rather abstractly about why a space heater doesn’t draw more power when supply voltage drops.  This time, we’re going to talk about it with a real space heater, current and voltage measurements, and a short, poorly produced video (I made it, so I can say so).  More pictures and fewer formulas this time!
Continue reading Electrical Myths, Part 2: Showing Heater Current doesn’t go up when Supply Voltage Drops

# Electrical Myths, Part 1: My Space Heater’s Plug Gets Hot

Since it’s still winter time, let’s start with one dealing with space heaters:

My RV’s wiring isn’t big enough to handle a space heater.  If I plug one in, the heater’s plug gets hot.  I should blame the campground, then open the box and hose it down to cool it off.

Ok, that might be a little much.  But let’s start with the most basic of principles in circuit protection.  Circuit breakers protect wires run in your RV, and in the campground supply.  That circuit breaker has a rating in amps, and its most basic job is to kill power if the load on the circuit exceeds what the wire can safely handle.

That’s why the wires on your 50-amp RV’s shore power cord are bigger than on a 30-amp RV.  It’s also why the wires are the same size on a small 30-amp travel trailer as they are on a larger 30-amp motorhome.  The breaker can’t allow more than the wire can safely handle, so if you need more power, you have to step up to heavier gauge (smaller AWG size number) wire.

Once inside your RV, at the main power distribution panel, the wiring coming in splits out to power a number of devices–things like air conditioners, battery chargers/converters, refrigerators, dishwashers, and all of the household-type receptacles.  The wires feeding those things aren’t as big as what’s coming in from the campground pedestal, and are protected by circuit breakers, with smaller ratings, in the distribution box.

For a typical branch circuit, that means either a 15 or 20-amp circuit breaker.  Again, that sets the wire size going to each outlet.  The standard receptacle in your RV is a 15-amp receptacle.  Each receptacle is rated for 15 amps too–think about that for a minute.  With say 10 places to plug something in, any of them individually able to fully utilize that capacity, how do we not overload the wiring?  The circuit breaker serves as protection against that, though some planning is useful to prevent nuisance trips.

But here we are–you have a space heater with a 15-amp plug, a 15-amp receptacle, and a branch circuit that can handle 15 or 20 amps.  So we plug the heater in, and turn it on.  After a little while, the plug is quite hot (a little warm is normal, but here, it’s almost too hot to touch).

# Why is the plug getting hot?

Now let’s dig into why that might be.  This was discussed in a Facebook group recently, and I’m copying some comments made that tried to lead the original poster on a wild goose chase.  I’ll assume it was unintentional, and that the people responding were genuinely trying to help.  Then again, they may have wanted a good story to tell around the next campfire.

## The problem may be the wiring in your RV being under sized for the current draw or the connectors to the outlet you were using (many RV manufacturers cut corners).

Let’s think about this for a minute.  The wire and receptacles are pretty standard–you’re not going to find a standard outlet rated for less than 15 amps, and they’re not made to accept wire smaller than 14 AWG.  It’s easy enough to figure out if the right side wire was run though–Romex-type cable is color-coded, so all you have to do is look at the outer wire jacket at the breaker box or an outlet.  Expect it to be white, which is what it should be.  So long as nothing is damaged, you should be able to plug any appliance into a 15-amp outlet and be perfectly safe, worst case tripping a breaker.

RV manufacturers love to cut corners, but when there’s a regulatory body that requires a certain specification, they generally oblige.  It’s technically a possibility that something wasn’t done right, but it’s far more likely that something is operating in a degraded state.

## The problem is with your shore power. Many campgrounds operate at an under volt condition because they have poor and old and over utilized electrical distribution system (lower voltage causes larger amp draw and more heat in the wiring and connectors.)

We’re talking about a space heater, so the above statement is wrong every way to Sunday.  Just flat-out no-truth wrong. So it’s time for an electrical lesson.

###### What is a space heater, electrically speaking?

While most have some sort of fractional-hp fan motor, for all practical purposes the heater is simply a big resistor.  On a typical space heater, that resistor has a resistance value somewhere between 10 and 15 ohms.  It doesn’t matter whether it’s oil filled, infrared, ceramic, or wire-wound.   Nor does it matter whether it’s a \$10 heater from Wal-Mart or the built-in “fireplace.”  They all produce exactly the same amount of heat.

In terms of energy consumption, there’s no free lunch.  The heater is inside your RV, so all of the heat it generates is in the RV.  All of the energy it gets out of the wall outlet is turned into heat–you’ll see some even advertise 100% efficiency.  So again, more expensive doesn’t mean better.  You may get other features, like oscillation, or a remote, or an anti-tipover switch, but you’re not getting any more heat.

So it’s a big resistor.  What does that tell us?  At the most basic level, we’re dealing with Ohm’s Law, and the power equation.  First is Ohm’s Law:

$V=IR$

This says that the voltage is current times resistance.  With a little algebra, it can be rewritten as

$I=\frac{V}{R}$

Right away, this shows us that for a fixed resistance appliance, like our heater, when voltage drops, current drops.

###### What about heat generated in the wiring and connectors?

Now we’ll introduce a second equation, relating power, current, and voltage:

$P=IV$

As applied to our heater, we know that current and voltage go up or down together, so we can see that if voltage drops, power drops as well.

But this is more easily understood rewritten slightly.  To see the relationship between voltage and power more explicitly, we can substitute the Ohm’s Law relationship for I in the power equation:

$P=IV=(\frac{V}{R})(V)=\frac{V^2}{R}$

That lets us easily see what happens to the heater’s power as voltage rises or falls–a 10% increase in voltage results in a 21% increase in power; a 10% drop in voltage results in a 19% drop in power output.

Okay, but that’s power at the heater, not power (heat) in the wiring.  Power in the wiring, or in a connector, is governed by the same relationship.  But we don’t know right off what the voltage drop across the wire or connector is. We do, however, know the approximate current through the connector or wire, and how it changes as voltage changes.

Going back to the power equation and subsituting Ohm’s Law, this time for V, we get the following:

$P=IV=(I)(IcdotR)={I^2}{R}$

Like our heater, a wire or connection point has (for the most part) a fixed resistance.  If system voltage drops, let’s say by 10%, current through the heater drops by 10% as well.  But for our resistance in the wiring, power drops by 19%.

We could get into heat transfer, and a lot of other downstream effects that come into play if we wanted to estimate a temperature, but we now know a drop in pedestal voltage is not going to make things hotter!

## The problem is trying to run a space heater on a 30-amp hook-up.

Uhh. No.  Last time I checked, 15 is less than 30.  There’s absolutely nothing wrong with running a space heater, or even two of them, on a 30-amp hook-up.  What is a problem is trying to run a space heater along with other stuff, combining to use more than 30 amps.

But putting more stuff on that 30-amp hook-up isn’t going to make the plug at the heater hot.  Remember, heat at the plug is related to current flowing through it, and current flowing through it goes down as the pedestal voltage drops.  If you had a heater running, and added a toaster to the mix, the heater’s plug would actually be a little cooler, as the voltage to the heater would be a little lower.  Not enough to notice, mind you, but bigger loads in the RV won’t make the heater’s plug hotter.

## My heater is 1500W. P=IV, so if V goes down, I goes up.

Again, nope.  Remember, I and V are related by R, and in the case of a heater, R is fixed.  There are devices with regulated power output where this isn’t the case, but heaters are pretty simple devices.

## It’s hot because you didn’t have a surge protector.

I’m starting to sound like a broken record.  Nope.  Surge protectors will get their own discussion, but aren’t even remotely related to the problem at hand here.

# Ok, really.  Why is it getting hot?

First things first.  For the plug to be hot, there has to be more power being dissipated at plug than normal.  Recall the power equation:

$P=IV=\frac{V^2}{R}={I^2}{R}$

Normally, the voltage drop across the plug should be very close to zero–maybe a volt or so.  With it, and a normal heater drawing on the order of 10 amps, power at the plug is on the order of a watt.

For the power (heat) at the plug to go up, either current or voltage at the plug has to go up.  If pedestal voltage goes up, or the heater’s resistance goes down, current goes up.  Both are possible, but not too likely.

However, if resistance at the plug increases, so does the voltage drop across it.  The resistance is still very small compared to the heater’s resistance, so total current isn’t significantly changed.  Using the last form of the equation above, we can see that as R increases, so does power.

But why would R increase?  There are a couple of possible causes.  First, there could be fraying or a poor connection in the heater’s plug end.  It’s most likely a molded plug, and those rarely fail.  And the actual contacts are fixed pieces of metal, so unless there’s corrosion on the surface, they’re also probably not the problem.  To be sure, move the heater elsewhere and see if the same thing happens.

That brings us to the receptacle.  There are two current-carrying wires (commonly referred to as “hot” or “line” and “neutral”), and each one has two connection points at the receptacle: the connection meeting your heater’s plug, and the one on the back side connecting to the supply wiring.  The receptacle itself has spring-loaded terminals that maintain contact with your heater’s plug.  These could be worn, and not contacting with enough force.  On the back side, most RVs have insulation displacement connections, where the Romex cable is just clamped into the receptacle.  Either one could be the cause, but the solution is essentially the same–replace the receptacle.

# Enough!

This post has ended up about four times longer than I shoot for, but hopefully it makes sense. If you have questions, if you think I’ve erred somewhere, or if this doesn’t make sense, speak up!

Next time, I’ll include a demonstration where we monitor power to a heater, measuring voltage, current, and power, and tinker with the power supply.  I’ll be using my electrical meter, which can measure current inductively, and the line splitter that goes with it, so that I can probe voltage and current safely without exposing live wiring.

FYI — If you want to be notified when the next post goes up, there’s a box in the upper left that allows you to subscribe to the “newsletter”.  The only thing you’ll ever get is an e-mail notifying you when a new post is published.