Whether you’re flying electric power or nitro, electricity is an integral part of the RC hobby. Every RC aircraft (and even cars and boats) has an electrical system that’s powered by batteries. What’s more, the battery’s health is vital to your model, since without power, you have no control. If that happens on the ground, it’s not a big deal, but if you lose power in the air, you’re in trouble.

Every modeler needs some way to monitor their model’s power system to make sure that batteries are charged properly, circuits are not overdrawing the available power etc. To fill this need, RC Electronics has developed the Watts Up Wattmeter.

The meter with a few adapters I've made up

A bit smaller than a pack of cigarettes, the Watts Up meter is compact and sturdy. It comes with unterminated wire ends, so that you can use whichever connector type suits your needs. For my applications, I chose to use Anderson Power Poles (also known by some as Sermos connectors) because I use this type of connector in my Ham Radio pursuits. The Power Pole has been adopted by many Ham Radio organizations as the standard connector, and I have a TON of them. Also, I will be using the Watts Up with my Ham Radio stuff as well, so this made sense for me. To connect the meter to my vairous equipment, I’ve made several sets of adapters. Moving from one application to another is as simple as grabbing the right adapters and hooking up the meter inline between the power source and the device you’re trying to measure. You are cautioned in the manual to be aware that the meter act just like a straight wire, so you don’t want to short-circuit the leads of the meter, since doing so will effectively short out any power source it’s connected to.

I’ve found the meter handy to carry with me to the field to do things as ordinary as checking the charge states of batteries, which I do quite a lot. The meter can also be placed in-line with a LiPo or other battery charger to monitor the amount of charge put back into a battery, should your charger not be capable of this. This is a neat thing for me, since I charge a lot of my smaller LiPo packs (2s 7.4v receiver packs and such) on a charger without this capability, and it’s nice to see what I’ve taken out.

The Watt’s Up wattmeter measures three things directly: current, voltage, and time. From these three measurements, the software is able to calculate things like peak current (Amps), peak power (Watts), power (Watts), energy (Watt-hours) and charge (Amp-hours). These measurements can be used to give you, insight as to the condition of your equipment.

Having recently finished a new nitro helicopter in which I’ve installed several high-powered, fast digital servos, I was concerned with the amount of current I was pulling through my heli’s regulator. I know that the reg can provide up to 6 Amps of current, but I was unable to find the current draw specs for any of my servos. It wouldn’t do me a whole lot of good to burn out my regulator in mid-air and crash. I am plenty capable of crashing all by myself, without mechanical problems helping.

The Watts Up measuring current draw at rest

So, I connected my Watts Up meter in between my receiver and my receiver’s battery pack to measure total drain on the system. As you can see in the picture, at rest my electronics draw a total of 0.19-0.20 Amps (or 190 – 200 milliamps). Fairly conservative in my estimation. At that rate of consumption, my receiver pack would last over 9 hours! Unfortunately (and obviously), when the servos are moving, they draw considerably more current. Next step in my test was to get all the servos moving simultaneously. Servos draw the most current when they’re in transit. What this means is that when the servo arm is not moving, it raws very little current. When you move the stick and cause the servo arm to move, it draws a lot more, until it gets to where you told it to go, at which point it again draws very little. To measure the total draw I’m likely to see in a flight, I had to get all the servos moving at once. As I started stirring both sticks on my radio, I got a reading of 2.88 Amps. I don’t think I’m going to be flying my heli like that anytime soon, but it’s nice to know that under somewhat normal conditions, I’m drawing only about half the current that my regulator can provide.

One thing that can be very bad is to stall a servo. Sometimes crash damage can prevent a servo from reacing it’s destination and the servo will keep drawing more and more current until something gives. Usually what gives is the regulator or some wiring. I’ve been told that a JR 8717 can draw up to 4 amps when stalled. My regulator could thus handle one stalled servo, but not two. It would likely catch fire and make for a crappy day. I did put a little pressure on the servos to the point that they started buzzing, but I didn’t test to destruction. The results were encouraging. I would recommend that anyone with an RC aircraft perform such a test on their model, if only to give a little peace of mind that your power system is up to the task.

An auxiliary battery can be attached here to measure down to 0v

The unit is capable of measuring voltages down to 0 volts, but if you need to go that low, you will need to connect an external power source to the meter. To facilitate this, the manufacturer has built in a standard (Futaba type) connector into which you can plug a standard receiver pack. When powered thusly, the Watts Up does not meaure the voltage supplied by the auxiliary pack, but uses it to power it’s circuirty only. The measurements are taken at the main leads only.

One of the primary (and most useful I think) abilities of the Watts Up wattmeter is measuring battery pack voltages. I’ve been to the field many times and have wanted to verify that I had indeed charged a battery pack. Sure, I could have used a pocket voltmeter, but since I have the Watts Up, I can quickly plug the battery in and see…well… what’s up. I don’t have to worry about making sure I get the pointy probes inserted into the right contacts to avoid shorting a pack, and I don’t have to fiddle with knobs and dials to make sure I’m on the right function and range. Don’t get me wrong, I have a VOM too, but it’s not as covenient as the Watts Up.

I even use it to make sure I'm grabbing a charged pack

Another place I find myself using this little device is the area where I keep my batteries. I have several batteries that look alike and it’s easy to get them confused. I know I should be a little more conscientious about how I track my batteries, but sometimes I just slack off. Whenever I grab some packs to go flying, I check them to make sure that they are charged. I didn’t always do this, which led to me discharging one of my big 6s 5000 mAh packs down to 2.5v per cell. Luckily it was an Air Thunder and I was able to revive it, but you can’t be too careful. Esapecially with a battery that costs as much or more than a .50 size engine.

When I first recieved my unit, I had just completed the build of my GWS Slow Stick. The plane is great, but like most imported hobby products, the instructions left a little to be desired. In the interest of trying to figure out how long my battery pack would last, I wired up the Watts Up between the Slow Stick’s battery and ESC. Then, making sure the aircraft was secured, I spun up the motor to see what the current draw would be. I didn’t write down those numbers, but let’s just say that the measurements provided me with the necessary information to calculate my projected flight time to within 30 seconds. I flew slightly over the projected time and the ESC’s low battery cutout…. well… cutout.

I do not recommend doing this with any power system that’s expected to draw more than 50A of current. The unit is rated at 50 Amps continuous and 100 Amps surge current. In my experience, exceeding such design specifications tends to let the magic smoke out of things. This will also prevent me from using this meter to perform a similar test on my Trex 600E, which can very easily exceed 50A. Not only that, but it’d be more dangerous and I like to keep all my body parts in their OEM locations.

All in all I’ll say that I’ve not even begun to scratch the surface of what this little device can do. It’s provided with a very comprehensive instruction manual, that’s also available for download from RC Electronics. I’m glad I decided to pick one of thse up and am very happy wth the device’s performance and utility and I’m looking forward to finding out all the rest of the applications I can use it for. I will add that I think it’s a bit on the expensive side, especially when compared to your basic multimeter, but it’s not prohibitively so, especially when you consider all it can do.

The Watts Up wattmeter is available directly from RC Electronics at http://www.rc-electronics-usa.com as well as several other online distributors. It’s currently selling for $59.95 USD. A full description with specifications and a downloadable instruction manual is also available from the RC Electronics website.

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