Building a Windspeed Meter for an RV

For years I have been wanting to put together something portable to measure windspeed while we’re out camping. I finally have all the pieces, and as a recent outing proves, it was a successful project.

Since this is something of interest to folks who are interested in the weather, I’ll share the details of how it was built here.

Let’s start by stating the problem:
Portable windspeed measurement systems tend to be hyperexpensive and somewhat fragile. They are not something that you’d just permanently mount to your RV and use. Fixed locations like houses and sturdy spots like sailboat masts, sure. Not an RV.
Unless you’re a closet millionaire who can afford to break a $300 anemometer head on the first low branch.
You could use marine-grade stuff, but … wow. Well, it costs … like marine stuff!!! (I had a sailboat once, and did you ever notice that two words that are never used together in a positive manner  are ‘inexpensive’ and ‘marine…’) I mean, Davis Instruments’ stuff is beautiful, but truth is, just as in sports cars, beauty costs.
There’s also the problem of where and how to put up a tall enough pole to get an acceptably accurate reading with the anemometer. You’re always going to have stuff in the way, no matter where you go. I choose to accept a reasonable degree of inaccuracy. If I wanted perfection, I’d pull out the handheld pitot tube.
Meanwhile there are lots of times and places where I’ve been out camping and was thinking, Gee, I wonder how hard the wind is blowing. You don’t need beauty, you need practicality, affordability, and robust construction.

So here’s how I solved it. Parts list:

  • Pole-mount anemometer
  • 12V 2-pin waterproof connector
  • 1″ stainless hose clamps
  • Package of “broom clips”
  • Aircraft hardware: 2 #10 roundhead screws and self-lock nuts
  • 3/4″ PVC (at least 10′, cut into manageable pieces)
  • 3/4″ PVC unions (as many as you need)
  • Folger’s coffee container

The most expensive part of the measurement system is the anemometer, and I found one on Amazon. Do a search for “Pole Mount Anemometer, by Windspeed Vortex,” and you’ll be directed to the least expensive (about $75) reliable anemometer on the web. Part of their secret for keeping the cost down is to use a bicycle speedometer. The display isn’t huge but watch-sized is enough to do the job. It also records peak and average speeds – a bonus. I’ll throw in a link to a photo here and hope the link lasts a while….

Windspeed Vortex Anemometer

The anemometer comes with bare-wire to bare-wire connections so you can build your own system, or use parts of it as replacement parts in another system. So we have to have a connector. We need one anyway, since it all has to knock down. I used two-pin 12V connectors because they’re positive, waterproof, and good for about a thousand connect-disconnect cycles before they fail. And when it fails, out comes the soldering iron and I put a new set on. Ah, the beauty of off-the-shelf stuff. Here’s a photo from the web of the connector that seems to work (at least as of this writing.)

2-pin weatherproof plug

Well, why not spade lugs, you ask? Spade lugs and such are clunky and tend to be hit-and-miss if disconnected and reconnected a lot. The signal levels we’re dealing with here will be affected by corrosion. So the automotive 2-pin is the best bet. A little bit of soldering, heatshrink tube, and Bob’s your uncle.

So now we have the starting point; we just have to figure out a mount that knocks down for transport, and (just as important) a way to ‘transport everything without it getting busted or otherwise screwed up,’ to use an old television engineering term.

Let’s work out the mounting pole: The best poles are anodized antenna masts, but they’re expensive and will have electrolysis corrosion troubles if connected with anything but compatible metals. Next would be EMT conduit, because it’s strong and light, plus you could just add length (well, height) by adding a coupling. But I can imagine what it’d look like when I pull it out of the closet after its last use by salt water… Hmmm, no. So PVC pipe has to be the next best thing, even though it’s a bit ‘flexy.’ We’ll work around that.

The wire and connectors have to go through the pipe to keep them out of the wind. They therefore must fit through the PVC pipe, and as luck would have it, they’re about 1/2″ across. This means they fit perfectly through 3/4″ Schedule 40 PVC and its connectors. Plus the PVC is available anywhere if I find I need to add a length.

I bought a standard 10′ length at the hardware store and had them cut it into 3′, 4″ (equal) pieces. I got a couple of unions so that I wouldn’t have to glue anything and I could knock it down into reasonable-length pieces. Get the longest length unions you can, so that there’s more structural integrity. Here’s a photo of what you’ll need (once again hoping the web-photo is fairly permanent).

PVC Unions; the longer the better

Once we have the mast taken care of, a knockdown mount for the anemometer is simple. A couple of stainless 1″ worm-drive hose clamps do the trick. Feed the cable down through the PVC and tighten down the clamps. Running the cable through the inside of the pipe instead of the outside keeps it from slapping and banging in the wind. Here’s a look at how the head goes together.

Anemometer secured, ready to go up

So the next thing is how to clip it to the trailer’s ladder. I got some “broom clips” during that same trip to the hardware store and a bit of ‘aircraft hardware’ (self-locking) to hold the clips back-to-back so that I can snap the clip over the ladder and then push the pole into the clip. Here’s a photo.

Here's the clip, assembled and ready to go

The best thing to do is get a clip pair as high up as possible to prevent the anemometer head from swaying in the wind. When the head sways because of the pipe flexing, the gyroscopic action of the head will be counter to the sway; this slows the rotation, and you won’t get an accurate speed. I found this out after the first use. The photo here shows my first try, before I moved the upper clip up above the top union.

How the pole clips to the ladder

I bet you’re waiting for me to get around to the Folger’s container. It was the only thing around that had about the right amount of volume and was about the right size to keep the sending head from getting damaged. I cut a slit in the lid to allow the mounting post to stick out, but keep everything inside and organized. Here’s a shot of how it looks, all packed up and ready to go. Sorry about the fuzzy shot; sun was going down…

Packed up and ready to go

One note: Coil the cable up in under-over fashion, not around-and-around. The conductors are about 36 gauge and could be broken by this kind of improper handling. The cable does a good job of protecting the conductors, but it’s not made to be coiled and uncoiled a lot, so if you coil it up around-and-around style, like over your hand, you force the conductors to flex and twist excessively – and eventually they will break from this kind of handling.

Hope you enjoyed this; I’m enjoying using my windspeed meter!

Feel free to use the comment field to ask questions.

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