PSA: Duracell Powepix in your Avy Beacon

**macthady** · 12-13-2006, 07:19 PM

Hi Folks.

I did some analysis of this last night, and posted to the same thread on couliormag.com. I include the text of that post below.

In short, a new powerpix cell (the ones I bought) seemed to have an output voltage of 1.7V. This difference times 3 (since the three AAA's are in series), leads to total supply voltage of ~5.1V, which seems to freak out the tracker in receive mode. Further testing (see subsequent posts on the couloir forum) indicate the tracker works *downto* a very low voltage, but that it seems to have an upper limit that is exceeded by these batteries....at least when they're new. I basically verified this by jury-rigging to lower the voltage output of the powerPix batteries, and the unit started working.

I have no idea which other beacons may/may not be affected by these batteries. That depends quite a lot on the design of said beacons....

Text of my post is below.

Regards,
-Thad

OK, I just couldn't leave this one alone, as it represents a really fun problem to solve. So tonight I bought some powerpix batteries on my way home for work, and sat down with my $20 super-cheap radioshack multimeter to see if I could figure out what's going on. This is a very cursory analysis, but I think it points to the root of the problem...hopefully beacon manufacturers will be able to use it, if they haven't figured this out already.

Indeed my tracker (which is probably 3-4 years old) does not work in search mode with the powerpix batteries, but does with regular duracell alkaline batteries. With the powerpix batteries, the transceiver seems to be doing something, but I get a constant "55" flashing on the beacon, which never seems to change, no matter how close I am to the transmitting unit (an old Pieps).

My first assertion is that, excepting longevity tests, etc, there shouldn't be any reason either of these batteries would "look" different to the beacon. The chemistry of the battery should affect the discharge curve, self-discharge rate, lifetime, etc., but that wouldn't really explain a "works/doesn't work" kind of problem like this.

My tracker has 3 AAA batteries in it, which reverse-engineering with a DMM shows are wired in series, to provide a nominal power supply of 4.5Volts
to the beacon internals. When I put three alkaline batteries in my transceiver and turn it on, a voltmeter shows 4.3V across the series combo of batteries, and the beacon works fine. Note that the alkaline batteries are used (I've got some ski trips in on them), or they probably would read 4.5V.

When I put the [new] powerpix batteries in the beacon and turn it on, I get about 5.1V across the series stack of batteries. This is a pretty big difference....in my test 0.8V difference, but if both sets of batteries were new, it'd probably more like 0.6V (still significant).

This would lead one to believe that the tracker won't work with this higher voltage, and that this is what's causing the problem. To test this hypothesis, I wired a small resistor in series with the series-stack of batteries, to lower the voltage that the beacon "sees", by the voltage-drop across the resistor. By doing this, I can get the tracker to *mostly* work in search mode. I say mostly because the current draw actually fluctuates quite a bit during search mode, and so the voltage that the beacon sees moves around alot, causing search-mode to work/not-work on about a 1-second period. This makes complete sense with a rather large series resistor like this (on the order of 40-50ohms).

So the question is....why do these batteries have such a high output voltage(~1.7V/battery)? I'm no battery-expert, but reading about them on the internet, it sounds like they're designed to go into digital cameras, and designed specifically to deal with the high-current requirements of those cameras (probably from things like flash-bulbs). This means they're basically designed to deliver a high current, while not allowing their output voltage to drop as much as an alkaline battery. One side-effect of this is probably that they have a higher output voltage when there is *very little load* on them.

So what kinds of devices are *designed* to present very little load on their
power source? *Avalanche beacons*!!!

It looks to me like this avalanche beacon, which is designed to draw *very little* current, basically just doesn't tax these batteries enough to bring-down their output voltage to the nominal 1.5V range that a AAA is supposed
to be. Combine that with what appears to be a sensitivity to higher supply voltages, and the beacon doesn't work.

In my opinion, this raises a few questions....mostly about how sensitive any given beacon is to variations in power supply voltage, and how that compares to variation that can be had from the various batteries that are on the market. Better equipment and more time would be required to figure that one out.

Bottom line is I'll be using alkaline batteries in my beacon.

Hope this is at least interesting reading for someone:-)

-Thad

**mtnbikerskierchick** · 12-13-2006, 07:23 PM

Missed this the first time, but.... Dang! That's REALLY interesting! Thanks for sharing this tidbit of important information!!!

**Blurred** · 12-13-2006, 07:30 PM

Thanks for the heads up Chuck.

That being said-PAGING OGRE!!!

**pechelman** · 12-13-2006, 07:32 PM

macthady, thanks for cross posting that.
definitely interesting.
hope you stick around.

**macthady** · 12-14-2006, 01:34 PM

Got the following from bcaccess today:

Thad,

We are well aware of the issues associated with using rechargeable, etc, batteries in avalanche beacons. This is why on page 17 of the Tracker Owners Manual we state the following in the Technical Specifications:

“Batteries: Three AAA/LR03 alkaline batteries. Do not use rechargeable, lithium, Oxyride or any other non-alkaline battery.”

You are correct in your conclusion that the Powerpix batteries increase the voltage of the unit. This in turn increases the background noise level in the beacon. You will see this issue with all avalanche beacons, not just the Tracker.

If you would like to post my response on the internet chat rooms that you frequent I would appreciate it. I am getting this email quite often, it seems to be circulating out there in internet land.

Thanks and I hope you have a great holiday season with copious amounts of deep powder.

Steve Christie