Airborne RC Battery Indicators

CHEAP INSURANCE OR FALSE SENSE OF SECURITY?

What a brilliant idea... a little electronic gauge that will tell you just how much charge is left in the battery which powers your receiver and servos.

Instead of guessing whether your battery has enough charge for one more flight, what if you could actually see how much capacity remains?

Even better, what if that gauge was able to be seen and read from a distance, so you could check now and then by doing a low-pass down the flight-line

Well that's the theory... what's the reality?

Perhaps the most common of these battery indicators is the smart little unit sold under a number of different brand-names and which consists of an array of bright LEDs, a switch to choose between 4.8V and 6.0V, and short lead to plug into your receiver.

When something like this is sold for under $4, I have to admit that I wasn't expecting too much, especially since other units carry a price of up to five times that amount.

Quality of construction

While the basic circuit-board is quite sound and reasonably well constructed, thanks to the use of subminiature surface-mounted components, the tiny switch on several of the units tested was intermittent - not good.

The units come with double-sided foam tape already affixed to the back surface making them easy to install on most models but difficult to remove once fitted.

The supplied lead is probably plenty-long enough for most installations and is fitted with a universal (JR/Hitec/Airtronics) connector that should fit any standard RC system.

How well does it work?

Obviously what you really want to know about this is whether it really can tell you how charged your batteries are.

I tested several units by applying a variable regulated voltage to the units and noting at what point the different LEDs illuminated.

Here's what I discovered...

So what does this mean?

Well it look as if the Hextronic/TowerPro battery indicator would be a fairly accurate indicator of most modern nicad or nickel-metal hydride battery packs.

What was a surprise however, is the fact that the low-green level for the 4.8V pack is still higher than the "nominal" voltage of 4.8V, whereas the low-green level for the 6V pack is actually well under 6V.

In practice, this may be a good thing, since a 5-cell pack has more reserve voltage headroom anyway so is less likely to produce a brownout or receiver reboot than a 4-cell one anyway.

The Verdict...

So are these things really worth the paltry amount the cost, or might they tempt you to have just one flight too many because you're still "in the green"?

Based on the sample tested, it would seem that the "RED" voltage is still fairly conservatively high making it unlikely they'll over-estimate your remaining capacity.

However, the most effective way to be sure you're not going to run your batteries flat is to use a modern charger/cycler to measure the remaining capacity once the red LEDs start to glow.

Experience indicates that most of my 40-sized models consume anything from 80-140mAH per flight so I was pleased to see that the red light on one of my models actually left me enough for two safe flights because there was in fact some 350mAH remaining in the pack.

On their own, these devices aren't a guarantee against running out of battery power but they are an excellent reminder and a warning against some other problem that might cause your batteries to dip unexpectedly.

And besides, they look kind of cool, especially if you mount them inside a model's cockpit so they're visible through the windows.

Apart from the flaky switches, the Hextronic/TowerPro voltage indicator gets a thumbs-up from RCModelReviews.com.