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RC Electronics Watt's Up Meter - a Quick Look

The compact "Watt's Up" multi-function test meter from RC Electronics packs a lot of functionality in a small and rugged package. Here's an update to the December 2004 review.

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Introduction


Voltage Range/ Resolution:0-60V* / 0.01V
Current Range/ Resolution:0-100A / 0.01A
Power Range/ Resolution:0-6500W / 0.1W
Capacity Range/ Resolution:0-65Ah / 1mAh
Energy Range/ Resolution:0-6500 Watt-hours / 0.1Wh
Dimensions:3.1 x 1.7 x 0.8 inches (7.9 x 4.3 x 2 cm) plus wiring
Weight:2.5 ounces (71g)
Current required to run meter:<7ma
Price:$59.95 US
Manufacturer:RC Electronics
Available From:The Manufacturer and
US Dealers
International Dealers
*Measurements from 0 to 4V require use of auxiliary battery of 4-60V

For anyone who’s been flying electric models for long, or newcomers who want to learn more about their power systems and the effects of changes to the many variables in those electric power systems (prop, gear ratio, battery voltage, motor wind, etc.), a means to measure the voltage and current in the power circuit is essential to knowing what’s going on.

A Little History

Back at the dawn of time (well, 20 years ago) the only way to do this was to have at least two pieces of test equipment set up – one to measure the voltage where you wanted to measure it and another to measure current. Since the currents involved were often in the tens of Amperes, ordinary multimeters were not capable enough. Some of us resorted to buying panel current meters and using them, but they had fairly high resistance shunts in them and noticeably affected the results you were trying to measure. There was also available for a time a 0.01 ohm shunt with test probe sockets attached that you could put in the circuit, and then read the voltage across it with an inexpensive voltmeter. But either way you had to have two different meters and test leads to manage along with the actual power system to be tested. It was clumsy and messy and even dangerous what with spinning props around all that loose wire!

Then some years ago (I don’t recall when) Astro Flight came up with a nifty little inline digital meter that could show either volts or amps on a big LCD display. You put it in the circuit like an amp meter (in series with the rest of the components). What it displayed was determined by the position of a little slide switch on the front. The meter was good for the voltages and currents we were likely see in most power systems and was a huge step forward. Instead of test leads and meters to set up, all you had to do was put this little gadget (equipped with compatible connectors) in the power circuit, then use the switch to choose what you were reading – volts or amps.

A few years later Doug Ingraham and Bob Boucher came up with a breakthrough piece of equipment which could show, at the same time, both voltage AND current. It was just as simple to use as the original Volt/Amp meter – just plug it into the system. Since it measured both volts and amps at the same time, some internal calculations also allowed it to display total energy (in ampere-hours) and instantaneous power (Watts, which are volts times amps) as well as the real-time current and voltage. This was the Astro Flight "Super Whatt Meter" – a single tool to give you lots of information about what was going on in your power system, all at once. The first one was designed to handle currents and voltages commonly in use at the time.

After the Whatt Meter had been out for awhile came the huge growth in park flyers and indoor models. The Whatt Meter’s 1/10 amp and 1/10 volt resolutions were a little coarse for measuring those power systems, so a new version, the Micro Meter, was introduced. It had a much more limited current capability (only 15A or so) but resolution to two decimal places on both current and voltage, making it better suited to looking at small power systems. It was also very useful for looking at other things such as servo current draw or the load on the BEC circuit of a speed control. We active electric flyers had to have these tools and we all wondered how in the world we ever got along without them. Well, I sure did, anyway.

Recently several companies have introduced multi-function test meters with different or added features, compared to Astro Flight's originals. A new US company called RC Electronics introduced their product late in 2004. They followed a long tradition of using “punny” names for electric power-related products by dubbing their meter model WU100, or “Watt’s Up”. But beyond the name is a pretty serious piece of test equipment.

What follows is an updated version of the review first posted on December 19, 2004. This update reflects the current version of the meter's software (Version 2.0 as of June, 2005).

Overview

The Watt’s Up is designed to be able to resolve to 0.01V and 0.01A across its entire operating range. In the Watt’s Up’s case, this operating range is 0-60V, with readings from zero to about 4V requiring a separate battery to be plugged in (more on that in a bit). The current range is 0-100A, with a continuous (meaning you could run it all day at this level) current rating of 50A. For motor and ESC testing purposes, it is usable all the way to 100A. There is extensive guidance in the manual for how to properly deal with these high currents.

A unique feature of the Watt’s Up meter, one that I like a great deal, is its ability to capture and display both the highest current and the lowest voltage between power cycles of the meter. This is intended to let you see the peak “hot off the charger” current draw of a power system and also the lowest voltage a battery sags to before you throttle down or the low voltage cutoff feature of a speed control kicks in, for example.

In the 2.0 version of the Watt’s Up, the peak current, minimum voltage, along with peak Watts, Ampere-hours and cumulative Watt-hours are all displayed in the lower left hand corner of the display. The display in that corner, which the maker calls the "Data Queue", rotates through those five items, changing every two seconds. In the other three positions real-time Amps, Volts and Watts are displayed continuously. Well, to be precisely correct the “real time” values are really the averages over the display refresh period, which is 400 milliseconds or 4/10 of a second.

The "Data Queue" is a real improvement over the two alternating displays of the first version which showed A, V, Ah and W alternating with peak A, min V, Wh and W every three seconds (this is visible in some of the pictures of the green meter below).

Note that the limit values are not averaged. Since the unit samples the data every millisecond, the peaks shown on the display are virtually instantaneous peaks that you might not even see with the display refresh time.

For some of the power system testing I do, these peak values are information I very much want to have. Having the Watt's Up meter capture them saves me having to try and remember the values during a test until I can shut things down and write them down (or rerunning tests until I manage to remember the data long enough to write it down). This is truly a useful feature.

Physically the Watt’s Up is quite a bit smaller than the Astro Flight or Medusa Research meters (the other ones I have) – it’s actually almost the same size as the original Astro Flight Volt/Amp meter. The very robust case comes in three colors: a sort of matte black called “onyx”, a translucent blue called “electric blue” and a bright translucent green called “kryptonite”. The meter that was the subject of review in December 2004 was a green one. It was easy to see through the case to a very neat board layout and construction. One look says this is a well-made little unit. It is kind of hard to read the “source” and “load” markings molded into the case, though. Pictures of the black one on the maker's web site show them much more clearly. I finally decided to use a Sharpie® marker to make the markings easier to see.

My Version 2 unit is the "electric blue" color, as you can see in the pictures above. For this one a silver Sharpie® did a good job at making the markings more readable.

Very robust 14 gage, four-inch long high-strand-count silicone covered wiring emerges from each end of the case. Adjacent to the source-side wiring is a little socket into which a standard servo-type connector can be plugged – this is where the auxiliary power is connected. The socket has a slot for the polarizing tab of a Futaba-J type plug. Of course a JR/Hitec type plug will also fit – you just have to be aware of the polarity – with the negative lead furthest away from the main wires. Nothing bad will happen if you plug your external battery in the wrong way: the meter just won’t power up. The external battery, by the way, can be anywhere from 4 to 60V. I’ve been using an older two-cell Kokam 1020 mAh LiPoly battery as the external power on mine. In the manual they suggest that you could wire up a little 9V transistor radio battery as an external power source – a good suggestion. You could also use a regular radio receiver battery, but how many of us even have receiver batteries lying around that are still good anymore? I don’t. (By the way, the external power source on the new versions of the Astro Flight meters may be any voltage from 4.5 to the meter’s maximum as well.)

Version 2 of the Watt's Up has an odd quirk: If you connect an external power source and have nothing connected to either of the main inputs, it will read a very small voltage. I asked the manufacturer about this and they assured me that when anything is connected to either input a correct voltage value is shown. This is what my own experiments have shown as well.

No power connectors are supplied with the Watt’s Up. This means you’ll need to obtain and install your favorite connectors on it. But it also means that you aren't paying for and don’t have to remove or make jumpers for connectors as you would if the meter came with a connector type you didn’t use. I put Anderson Powerpoles on my Watt’s Up as they are the standard in all my larger power systems. One of the advantages of Powerpoles, by the way, is their gender-less design. This makes it easy to turn the meter around as one would do to, say, put it between a battery charger and the battery being charged. Unlike the just-released versions of the Astro meters, which have a limited capability to read current “backwards”, the Watt’s Up is like the older Astros and the Medusa meter in reading current only from the “source” side to the “load” side. Voltages, of course, will read with a battery attached at either end.

This uni-directional operation is simple to set up (as long as you have the right jumpers if you're favorite connectors are polarized) and you always have the meter's full capability available for a measurement. One very subjective thing I like about the Watt's up is having the source on the left and the load on the right while the display is right side up. Somehow it just seems more intuitive than the other way around.

NOTE: If you’re planning to use the Watt's Up at anywhere near the peak 100A capability, choose your connectors with care and also be sure to do a very good job installing them. At currents like that even a little bit of extra resistance means a bunch of extra heat. Remember heat losses are proportional to the square of the current – doubling the current across a resistance causes four times the power to be dissipated as heat.

I made up a pair of Powerpole-to-mini-Deans adapters to suit using this meter with my smaller stuff. I also made up a little JR servo-to-mini-Deans jumper (which is visible plugged into the auxiliary power input in many of the pictures) so I could use batteries like that Kokam as the external power supply. By the way, checking chargers’ outputs is one of the applications where the external power feature comes in handy. Chargers don’t put out any current when the battery is not yet being charged, so you can use the external power to get the meter going and ready before even plugging in the destination battery. Using external power also allows the preservation of the peak readings after the battery involved in the test (whether it’s the “source” or the “load”) is disconnected.

In use

Once equipped with connectors and an lead for the desired external power source, putting the Watts’ Up to use is about as straightforward as can be: put it in the circuit where you want to take the measurement, making sure the polarity and the current flow direction are correct. As soon as 4V or more is supplied to either end of the main leads or the auxiliary power input the meter boots up and is ready for use. The calibrations are fixed at the factory, so there is no self-calibration process run when the meter is first powered up. Note that when powered through the auxiliary input, the unit will display (almost) zero volts until there is a voltage present on the main leads. Then, proceed to do your test.

The maximum current and minimum voltage readings (as well as the peak Watts, cumulative Watt-hours and Ampere-hours values) are maintained as long as power is applied. As I mentioned before, preserving these readings until you can write them down is another use of the auxiliary power input capability. You must power down the unit completely to reset these values.

My first uses of the Watt’s Up were in conjunction with the CamLight Systems PD-12V battery discharger (review here), and the meter’s maximum current and minimum voltage readings captured the initial stage 1 current and the voltage at which the transition to stage 2 discharge occurred very nicely. The real-time readings update quickly, which makes catching them clearly in a picture a little tricky as you can see here.

I also did a little comparing with other meters I have. I did this by hooking three of them up in series (easily done with Powerpole connectors) and then comparing their current and voltage readings. Please be aware that I have NO WAY to tell which one is most accurate – that is, which one is closest to the true values – as I have no laboratory-grade equipment. Also, because of losses in the wire and connectors (four pairs of them) between the meters as well as within the meters themselves, and the small amount of power each meter needs to run its own circuitry and display, each of them connected this way is measuring slightly different actual conditions.

That said, what follows is an interesting series of comparative pictures. In these pictures are shown my early production Astro Flight Super Whatt Meter that has been in use in my shop for many years. Connected to it is the Watt’s Up, and connected to that is my recently acquired Medusa Research Power Analyzer Plus. All three meters have their factory lengths of wire in place, and in the case of the Astro Flight meter there are also short jumpers going from the factory-installed Astro Zero Loss connectors to Anderson Powerpoles. The other two have Powerpoles I soldered onto the factory leads.

The first picture shows the three meters connected to a partially-charged 10-cell pack of Sanyo 3000CR NiCds. No current is flowing except that needed to run the meters themselves. The second shows the battery (connected directly to the Astro Flight meter) being discharged through the CamLight PD-12V at about 9 1/2 Amps shortly after the discharge was started. The discharger is connected to the load end of the Medusa meter. It is interesting to see where the meters agree and where they disagree. Note again that I have no way of knowing which of the various numbers displayed is actually correct. Also note that while the Medusa meter displays voltage to two decimal places, it really only resolves to one, like my old Astro Flight meter.

The third picture shows the situation after the discharge was completed – that 3000 mAh pack was fairly depleted when I started since it delivered only about 1/3 of its rated capacity. Note how closely all three meters agree on what that discharged capacity was. They’re all within 2% of each other. The fourth picture shows the situation after the second stage of the discharge was completed. Note the peak current of 9.87A and minimum voltage of 6.30V shown in the fourth picture. This picture, by the way, documents that I had the CamLight discharger incorrectly set for 7 cells and was using it on a 10 cell pack, hence the overly low cutoff voltage which was exactly right for 7 cells.

The next group of pictures shows the same battery, now on the “load” connection of the Medusa meter, with my trusty old Astro Flight 110D on the “source” connection of the Astro Flight meter, to recharge the battery. The first shows before the charge started, the second shortly after it began – with the 110D putting the maximum current it could into the pack. The third shows the charge completed.

Again, it is interesting to see where the meters agree and disagree, and in the latter group how they all disagree to some extent with the AF 110D’s built-in readout.

Conclusion

I have used the Watt's Up for much of my motor and charger testing over the past several months (though I have yet to push it close to its limits). It is a solid piece of equipment with some features to set it apart from the other units available to do the same job. Among these are the ability to capture the peak current and minimum voltage in a “session” and a very compact, rugged, and light form factor.

Also, the manual is extensive, yet easy to read. It includes lots of good basic electricity information that is handy for the newcomer to all of this electric stuff to have (and is a good refresher for us “old hands”). It also has quite a few application illustrations beyond those I’ve suggested here.

The Watt’s Up is small and light enough that it could be flown in many models, and used to capture peak current and power, and low voltage cutoff values in flight as well as on the test bench. It also has precision among the best of the currently available meters. And, for those who are interested in such things, it comes in three different colors…..It certainly is worthy of consideration if you’re in the market for a multi-function meter to test the power and control systems for or in your models.

Thread Tools
Dec 20, 2004, 02:57 PM
Motor Maniac
I just purchased this meter, but haven't had the opportunity to use it yet.

It is interesting to see Bernard's setup of all 3 meters in series. Seems that the Watt's Up and Astro seem to be in agreement to the precision of the measurements, but the Medusa seems to be a little higher on both amps and volts even though it is "downstream" in the setup. Someone with some lab quality equipment should do a side-by-side comparison of these products.
Dec 21, 2004, 12:59 AM
BEC
BEC
Registered User
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Thread OP
I had no idea what I would see when I set that up, but I agree with your conclusion that the Medusa seems to be "outvoted" - or at least my particular example is.

As for lab quality equipment and all that..... when I think about it, for our purposes, especially as close as they are, does it really matter which one is exactly "right" (if any)? Most of the other things we test - in particular propellers - are far less precisely defined than the margin of error in these meters. And really, even for things like setting low voltage cutoffs or discharging batteries, a tenth of a volt one way or the other is not really all that important. And a tenth of an amp is pretty much irrelevant in testing any power system.

Far more important, in my opinion, is repeatability and comparability so tests one does can be compared with one another with confidence. And I don't think you could go wrong with any of these units for that.
Dec 26, 2004, 09:40 PM
hty
hty
Registered User
Hi there,

If the accuracy of these 3 models is more or less the same, then which one is better in terms of features and user friendliness?

I am thinking of getting one of it and any recommandation is highly appreciate.
Dec 27, 2004, 08:18 AM
Registered User
RCISFUNREM's Avatar
I just wanted to mention that I was looking for a good Power Analyzer and after reading your review I decided to buy the “Watt’s up”. In your article you made the following statement:

“However, the limit values are not averaged. Since the unit samples the data every millisecond, the peaks shown on the display are virtually instantaneous peaks that you might not even see with the display refresh time. (By the way, the Medusa Research Power Analyzer Plus also calculates and displays watt-hours, alternating with ampere-hours on a three second cycle.) For some of the power system testing I do, these peak values are information I very much want to have. Having the Watt's Up meter capture them saves me having to try and remember the values during a test until I can shut things down and write them down (or rerunning tests until I manage to remember the data long enough to write it down)…”

Some features of the Medusa Research Power Analyzer were mentioned in the review, however; I feel that an important attribute of the Medusa Research Power Analyzer was left out. The fact that you don’t have to write anything down as it has a PC serial interface that allows you to log the data real time on your PC, had I known that at the time I might have spent the extra $10.00 and went with that system. Now that I have received the Watt's Up I am impressed with it small size and look forward to using it on some of my projects.
RCISFUNREM
Jan 04, 2005, 07:03 PM
BEC
BEC
Registered User
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Thread OP
hty,

Depending on what you want to do - any of them will serve you well. The Watt's Up is the most compact one and has the cleanest external power setup (compared to the Astro - the Medusa doesn't have an external power capability). I have a love/hate relationship with the peak values display because sometimes they're very good to have and sometimes they seem to be in the way (hiding the real-time data for half the time). The Watt's Up and the new version of the Astro Flight Whattmeter have very similar resolution up to their respective current and voltage limits. The Medusa meter is more like an older Whattmeter like mine in that it can only read volts to tenths (never mind it displays two digits after the decimal).

RCISFUNREM,

The Medusa Power Analyzer Plus is $15 more.....but that's not much for the PC interface. If you have a Win2000 or later box (in your workroom) and don't mind the coarser resolution on voltage (nearest 0.1V rather than 0.01V) then it's a good choice. I am having communication failures with my Win 98SE box and my Medusa unit. They're working with me to help resolve what's going on (a good thing) but it's not yet settled. I need to get access to another, newer PC so I can isolate whether it's my individual meter or my computer that's the source of the difficulty.

I didn't mention the interface in the Watt's Up review as that's a distinct and unique feature. I was assuming that the regular Medusa Power Analyzer (not the Plus) would behave the same as my Plus when not connected to a computer.
Jan 06, 2005, 03:48 PM
Motor Maniac
I have finally used my Watt's Up meter a few times. I have some of the same feelings about the display as Bernard does. I guess I would prefer to have it display the normal numbers all the time, then have a small button/switch to hit to get the peak/min values to show up. Since the peak Amps/min Volts numbers are stored until you power down, there doesn't seem to be a downside to this approach other than the added cost in production.
Jan 06, 2005, 04:08 PM
BEC
BEC
Registered User
BEC's Avatar
Thread OP
Review is updated for version 2, which addresses the alternating display concern of V1 very nicely.
Last edited by BEC; Jun 28, 2005 at 01:56 PM.
Jun 28, 2005, 12:42 PM
What power line?
PoudreDerf's Avatar
Got one because "They" said I needed one. In the first ten seconds of use, I found a binding servo that I didn't know was in trouble. Now I use the thing more than I use my VOM. Yes, sometimes good things DO come in small packages.
Jun 29, 2005, 05:34 AM
Master
ChrisP's Avatar
Highly tempted, but the going price in Germany is $85 vs $60 in the USA
Jun 29, 2005, 04:58 PM
Outcast outlaw
I was working with an office buddy to design our own "el cheapo" volt / current meter. Then I saw this review, and couldn't pass it up. It's only 2.5 ounces, and has so many cool features for only $60 (our target retail price was around $50), I just couldn't stand to reinvent the wheel...

I ordered Kryptonite Green. I figure it'll be hard to misplace!

Thank you for posting this review!
Jul 13, 2005, 02:41 AM
Registered User
gmitano's Avatar
I have an AF Whatt Meter and am thinking about getting a clamp ammeter to avoid having to take inline measurements. What sorts of results could I expect, vs the meters in your review. I've seen both pro and con opinions on this forum and elsewhere with regard to clamp ammeters, but nothing really definitive. thx
Jul 13, 2005, 09:04 AM
Outcast outlaw
The biggest difference is that you can't FLY with a clamp meter. The clamp meter also won't tell you mAh used, watt-hours, peak watts, peak amps, or minimum voltage.

Testing on the bench will yeild different results for drawn amps than testing in the air, due to the fact that your airplane is being held back. The bench will show more amps than are actually drawn in-flight.

Finally, the clamp meter will be much more expensive than the $60 Watt's Up meter. Clamp meters usually measure AC amps only -- only the more expensive clamp meters can measure the DC amps.

Hope that helps!
Jul 14, 2005, 07:41 PM
BEC
BEC
Registered User
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Thread OP
My own anecdotal experience is that I've had lousy luck with that much-discussed $49 Sears clamp meter that claims to be able to measure DC current - but the results have never been all that close to what I get with any one of several inline meters (I now have even more of them than those shown all in series in pictures in the review). Others love the Sears meter. I don't and would be glad to give someone a good price on mine......

The point about not being able to put it in the airplane is fair as well, though I've not yet flown either the Watt's Up or the Emeter. That time may come.

gmitano: love the N9M in the avatar!
Jul 14, 2005, 10:51 PM
Registered User
gmitano's Avatar

N9M Chino Airport


Quote:
Originally Posted by BEC
My own anecdotal experience is that I've had lousy luck with that much-discussed $49 Sears clamp meter ...
Thx. Looks like I can save the clamp meter $s for an onboard systems monitor! Btw, I and my then 5yo son were able to see the N9M maiden at Chino Airport. That's one sweet little plane!
http://www.flightonline.mcmail.com/northrop.htm
http://www.planesoffame.org/airshow05-schedule.php


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