Knowledge Is Power: Why You Need A Wattmeter

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Written by Terry Dunn Electrics
As seen in the February 2021 issue of Model Aviation.
Electrics

a wattmeter is an invaluable tool for all electric fliers
A wattmeter is an invaluable tool for all electric fliers. It provides the data you need to tune and troubleshoot a model’s power system.

 

ALTHOUGH I’VE WRITTEN numerous articles and reviews for Model Aviation throughout the years, this is my maiden "Electrics" column. I was flattered when Greg Gimlick asked me to take the reins. I’ll do my best to keep this space entertaining and educational (in both directions!).

Some Things Never Change

I became involved with electric-powered RC models in the late 1990s. At that time, most power systems still used brushed motors and NiCd batteries. Achieving good performance from a model often required some tinkering and experimentation. In fact, that is what initially attracted me to electric power. Each new project was like a brainteaser. With a given setup, I might have changed the cell count of the battery, the propeller size, the gear ratio, or some combination of those things in a never-ending search for better performance.

We often pushed motors and batteries well beyond their advertised limits. More often than not, electric modelers of that era had to strike a balance between performance and equipment longevity. You could only push a motor or battery so hard before it overheated or self-destructed in some dramatic fashion. Because we worked within such narrow margins, having accurate data was vital to success. Our primary tool for obtaining that data was the Astro Flight Whattmeter.

The Whattmeter (aka wattmeter) is a handy device that is inserted between the battery and ESC. It displays the system’s voltage, current (amps), power (watts), and electric charge (milliamp-hours; mAh) on an LCD display. That’s all great information to help you better understand whether you still have some headroom for more power, or whether a meltdown is imminent! You can also place a wattmeter between your charger and battery to make sure the battery is accepting the expected amount of charge and reaching the proper voltage.

these wattmeters differ in age and cost but they work essentially the same way
These wattmeters differ in age and cost, but they work essentially the same way and provide nearly identical data. Brands from top to bottom are Astro Flight, Great Planes, and HTRC.

Much has changed in 20-plus years. Participating in electric-powered flight no longer demands a tinkerer’s mindset. Powerful and efficient brushless motors and LiPo batteries ensure that most electric-powered models have more than enough power right out of the box. Additionally, modern battery chargers now have built-in screens that display the information that we once relied on from a wattmeter. Despite all of those advancements, the wattmeter remains a vital tool for electric fliers.

Components for electric power systems are readily available from vendors around the globe, in a wide range of price points.

The quality of those components and the accuracy of their printed specifications can also vary. Sometimes it’s difficult to really know what to expect from the gear in front of you.

Did I install a 30-amp ESC for a system that actually pulls 40 amps? Can I use this motor with the largest recommended propeller and the maximum recommended battery voltage at the same time? Those are both common questions, and a wattmeter provides the answers.

Even off-the-shelf ARF models with factory power systems need to be checked from time to time. A wattmeter can immediately tell you the effect of using a battery with a different voltage or discharge rate. Perhaps you want to try a new propeller that looks more scalelike. Or maybe you just want to know whether that puffy LiPo can still deliver the juice that it used to. Landfills around the world are littered with burned-out LiPos, melted ESCs, and overheated motors because their owners (including I) committed to a change that pushed some component past the breaking point. The only way to truly understand how a power system is performing is to measure it with a wattmeter.

There’s no question that buying a wattmeter will save you money sooner or later. Preventing the destruction of just one ESC, battery, or motor is usually enough to recoup your investment. Trust me! It’s much better to have a wattmeter tell you that you’ve over-propped your motor than to wonder why your favorite model suddenly has a smoke trail!

Data on a Budget

I still have my original Astro Flight Whattmeter and use it regularly. Throughout the years, numerous hobby companies have released their own variations on the wattmeter theme. For example, I also have a Great Planes PowerMatch Power Meter. It is basically a wattmeter with a few extra features and a built-in battery balancer. I would trust a wattmeter from any well-known RC company for the purposes that I have previously described. Among the various wattmeters I have seen, there are minor differences, but they all function essentially the same way.

I recently saw reports from a few modelers who were using wattmeters that they purchased from Amazon at low prices. That got my attention because some of the RC equipment found on Amazon is, quite frankly, junk! My hunch was that these inexpensive wattmeters would be inaccurate and/or unreliable. Perhaps the only thing worse than no data at all is shoddy data.

I decided to buy one of these budget Amazon wattmeters and compare it with my trusted Astro Flight and Great Planes units. For approximately $15, I obtained a wattmeter from HTRC, a company based in China. It did not come with battery connectors, so I soldered on a set of Deans Ultra Plugs. The unit appeared to be well built. I could not find any obvious physical or cosmetic defects.

The one-page instruction sheet is typical for imported electronics. Some information is confusing because of poor translation. There are also contradictions. One section stated that the wattmeter can be powered by an auxiliary battery of at least 4.8 volts (up to 60 volts), yet a diagram indicated that the auxiliary battery must be at least 8 volts. A quick test revealed that the 8-volt value is correct.

In order to test the accuracy of the HTRC unit, I measured data from three different models with power systems ranging from approximately 40 watts to 800 watts. I then compared data collected with my Astro Flight and Great Planes units. I limited variables as much as I could by using the same battery for each model and topping off its charge between each test.

My results were encouraging. All of the data I collected with the three wattmeters differed by no more than 5%. That’s well within my margin of error when honing or troubleshooting power systems.

At this point, I have no reason to question results from the HTRC wattmeter. I can’t speak to other wattmeters offered on Amazon, but this one seems legitimate. My only gripe so far is that the LCD screen is difficult to read in sunlight. I’ll report back if my long-term testing reveals any other issues.

Get Smart

If you’re an electric flier without a wattmeter at your disposal, you’re now officially out of excuses. A tachometer is useful, and a servo driver is handy, but a wattmeter is essential if you want to understand, troubleshoot, and optimize your electric-powered models.

the screen on this wattmeter from htrc is somewhat difficult to read
The screen on this wattmeter from HTRC is somewhat difficult to read, but the author’s testing indicates that it provides accurate power system data.

SOURCES:

Astro Flight

(949) 855-9903

www.astroflight.com

Great Planes

www.greatplanes.com

HTRC

www.ht-rc.com

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