I noticed a tiny electronic device located in the receiver compartment of several experienced fliers that used a bar of green LEDs to indicate remaining battery life. It was a thin circuit board perhaps 3/4" wide by 2" long. There were perhaps 10 LEDs aligned in a row. The number of lit LEDs indicated remaining battery capacity.

Anybody know what these are called and who sells them?

Tom

You mean this thing:



It is a Hobbico VoltWatch Receiver Battery Monitor and they sell for around $11 at most hobby stores that are Great Planes distributors.

Check product number LXMZ56 on the Tower website.

That's it!! Thanks Maverick. For $11, it looks like a good investment.

Tom (CptCrunch)

It is a good idea to check receiver voltage after charging and before flying for the first time each day, then again after a few flights.

The VoltWatch although being a good idea and relatively inexpensive does have a downside you need to be aware of.

Firstly it takes up one channel on your receiver. Probably not a big deal in your first few planes, but it could be a problem for later planes where you need every channel you can get.

Also you need to buy one for each plane you have. At $11 it sounds inexpensive, but add this up over a few planes and it starts to become an issue.

I personally use a Hobbico Digital Voltmeter MkII that I can plug into the charge socket on any of my planes and get a read-out of the receiver voltage under load. The voltmeter has a switch to load up the battery to simulate servo use.

I can use my voltmeter on any plane and it is only a one-off cost.

I also use Ernst charge receptacles on all of my planes so that the charge jack is nicely mounted on the side of the fuselage and then checking the voltage or charging the plane is very simple and the wing does not need to be removed.

The Ernst charge receptacle is only about $2.50 and looks like this:



I highly recommend them.

Hope this helps!

I favor the VoltWatch over the loaded DMM/ESV technique. Significant current flows in the leads to the loaded ESV, causing some voltage drop across the leads and connectors. This can present pessimistic voltage readings. For example, the meter might read 4.7V while the voltage at the battery is actually 4.8.

I check my voltwatch immediately after a flight, before I turn off the receiver. This avoids the problem of battery recovery, where the battery voltage tends to gradually climb back up after the load is removed only to fall rapidly again once the load is reconnected (next flight!).

One note of caution on the voltwatch. I tested about 5 against a trusted Tektronix DMM. I found that they vary about 0.05 volt from unit to unit. It would be wise to test your VoltWatch before trusting your airplane to it. Same holds true for ESVs. These things are inexpensive and quailty control may not be the best.

Another benefit of the Voltwatch is that you can tell if you have a stuck or malfunction servo by moving the sticks and watching how the LEDs respond.

By the way, there are several other products similar to the voltwatch. One is a kit that was written up in Model Aviation a few years ago. Someone also makes a single LED version that changes color/blinks at the go/nogo voltage. They say it is so bright that you can see it while flying.

No matter what technique you use, judging battery capacity from voltage readings is a tricky business. You need to know the discharge characteristics of your particular battery pack and understand a little about electricity.

Good luck.
Jon

Surely this is a good thing! Leaves a little bit of reserve just in case.

I'm sold on the voltwatch unit, espesially on bigger heavier planes that suck up the battery juice faster. I always check the battery with load before flying and after 5 flights. I installed a Voltwatch under the canopy of my 60 size SeaFury. After the 2nd flight the Voltwatch had 2 green lights left so I went up again. After the 3d flight the last red light was the only one on! I parked the plane for the rest of the day when I saw that. It turned out I had a bad cell in my battery pack. As far as I'm concerned the Voltwatch save my plane. I never would have suspected that the battery pack would quit after only 3 flights, especially when it read good with a load before I started flying!

Where are most of you mounting your Volt Watch? Fatsky says his in under the canopy. I take it that it is in full view then all the time then on the ground.

AV* is right. With the Volt Watch mounted under my canopy it looks like part of the models controls and sits behind the pilot. It is easily visible through the clear platic canopy.

I appreciate all the people who took the time to respond to me question. I learned more than I thought I would.

Tom

I too am a big fan of the VoltWatch (and the several other similar devices), and put one on every flyable plane. I also include a "plane finder" which not only helps find planes that go down in the swamp, but also functions as a low voltage warning, giving me two indicators. On a high wing trainer, I put the Voltwatch just under the wing on the side opposite the exhaust. I like the idea of the VoltWatch under the canopy!

I have a question for those of you that have experience with the VoltWatch. What is the lowest light where you would fly? I noticed today after about 30 minutes of flying time, the Voltwatch was sitting with the third from the right light on, so I figured I'd call it a day. Obviously, you wouldn't fly with one of the three "low" lights on, but would you fly with the fourth from the right light on (the last ""safe" light)? In all cases, I'm talking about the state of the lightes with no servo activity.

Do they make a Volt Watch for 6 volt systems?

I fly until the second yellow (the one next to the red) comes on. This corresponds to a battery voltage of about 4.77 volts on my voltwatch, which should leave plenty of reserve.

Make sure you check the voltwatch after a flight (before turning off the switch). Once the switch is turned off the battery voltage will slowly start to creep back up and the next time you turn it on you will get a higher, misleading, voltage reading.

The Volt Watch is only for the 4 cell 4.8 Volt packs but there is a siiliar device that is selectable for either the 6 V. or the 4.8 V. battery packs. It is made by someone else and is a more expensive unit. I am not sure of the brand name. I have only seen the unit at my LHS.

Yah right. 1 LED. 8 functions "extremely easy to understand & interpret" How does one LED interpret eight functions with an accuracy of 4 decimal points? I'm not saying it can't do it, but I am saying it ain't going to be easy to interpret! I'll stick with my $10.00 Voltwatch with the easy to read bar graph display that's a third cheaper and does one thing well.

JNorton . . . The G2K's operation is a "no brainer". Although the LED has 4 operational states (or 5 if it has low fuel warning too) . . . the only thing you have to be concerned with is whether or not the LED is flashing steadily. It it's not, you've got a problem. It's that simplistic. The type of glowing status will tell you the general area of the problem. For example, if it's solid glowing solidly, you know it's a power prob. If it's flashing erratically, you know it's the switch harness. If it appears dark, you know it's an Rx prob. . . if it flashes once per second instead of the normal 6 pulses per sec . . you know your fuel is down to the warning level you preset . . etc. , etc. One of the Giant Scale pilots we sponsor was only 7 when she first started flying with G2K's onboard. She's now 11. It's saved her 100" scale Cub several times from one problem or another and she's never had any "interpretation" difficulties despite her age. But, if someone doesn't like it . . they've got 4 months to send it back for a 100% refund. Frankly, we've bought back a total of 3 units from 2 R/Cer's out of over 80,000 units in use in the past 3 years. Interpreting the G2K indications has never been an issue with anyone. " Accurate to 4 decimal points" simply means that if it is calibrated to trip (glow solidly) at 4.7777 volts on a 4.8 volt system . . . that's where it will trip every single time. All in all . . . the Gem 2000 is an ultra-simple yet extremely reliable safety product. BTW, I have no quarrels with what other products cost. Their mfg's know what they're worth. As the old saying goes . . you get what you pay for and you pay for what you get (as a rule).

Good Luck & Happy Landings,

Save your money and buy a real battery checker, i found that the voltwatch lies.

To check the batteries in my jet I use a fluke digital volt meter with a 12 volt car dome light bulb across the leads that draws 500mah.-I use a 5 cell 1700mah Sanyo nicad.My jet is now 17yrs old-so it works for me.I test for 7 secs.


Jackjet