Dexcom Power Source

I am starting a new discussion thread about how to power the Dexcom receiver when there is no electrical outlet available.

I am thinking about situations such as back country travel, Hurricaine Isabel (when we were without electricity for a week) and similar situations.

I spoke to Dexcom technical support and to the Dexcom trainer. They said that people had asked them about transformers for use in other countries. However they said that they had not heard a question about a situation when NO ELECTRICITY was available for more than 5 days.

Basically Dexcom does not know. They said that I should call Radio Shack. I asked for the number of watts that it draws so that I could specify this when looking at chargers. They referred me to page 127 of the manual but this does not have the wattage for the receiver. I looked all through the manual.

I was calling at 4:15 on Friday afternoon (Eastern Time) so the upper level supervisor had already left for the day.

Thanks for starting a separate discussion!

I am almost positive that the output (into the Dexcom) will be less than two watts. That value is already about double the maximum power which “smart” charges try to push into AA NiMH batteries, and AA batteries are much, much larger; almost certainly capable of handling a lot more power than Dexcom’s tiny battery.

So start from there, and then add plenty of extra “headroom” for loss in your AC inverter. (Maybe 6 watts, == .5 Amps, of “wasted energy” from a 12v auto battery. Turns on the indicator light, fires up the electronics, and so on.). The Dexcom charger itself has more power loss, while it’s doing the exact opposite job (AC back into the DC you started from, but at different voltage and with “smart” electronics tresting the battery from time to time.) So expect right around 10-20 watts of total power from your original 12V battery source. That’s a really tiny load, shouldn’t be a problem. If you’re away for more than 10 days, you should run the car (radio and other accessories OFF) at moderate RPM’s to stoke the battery back up.

As I mentioned earlier, the important !!! is not the load; it’s whether than Dexcom charger can accept cruddy AC from a cheap inverter and still convert it into a nice, stable DC current into the Dexcom. In AC power from the wall, the voltage goes up and down smoothly, it’s an exact sine wave. But inverters which to try create AC from DC power sources don’t have actual generators with moving parts; they just modify the DC power electronically. They usually send a ragged signal, with choppiness. These distortions in the pattern happen with each cycle- 60 times per second, and because they’re not random “noise”, they can be described mathematically. It’s called “total harmonic distortion”.

If Dexcom can’t say whether the charger and battery can handle “modified sine wave” as input to the charger (without shortening battery life or hurting the electronics inside the Dexc), then I’d pay extra to get a “pure sine wave” inverter. And it’s a lot of extra money, you will not find a good one for less than about $100. (“Modified Sine Wave”, for comparison, can be purchased for only $20.)

DO NOT BUY a “pure sine wave inverter” which doesn’t state it’s maximum “total harmonic distortion” among it’s specifications. (That figure should be there, right along with the “peak watts” and “continuous watts” numbers.) If they don’t give you the number then it’s probably garbage, pushing out tons of distortion, but still claiming to be a “pure sine wave” inverter for marketing purposes.
(Unless you’ve got some fancy equipment, it’s really hard to measure harmonic distortion- except in high-end audio, where you can hear it with your ears. So these liars think they’ll get away with false advertising, and they nearly always do so successfully.)

The most widely respected Internet-Selling Inverter among Solar Power people who need medical-quality, ultra-clean Inverters is probably “Don Rowe”. If I were shopping today, I’d get this one:

$90 with free shipping. They’ve got another one (with less maximum power) for $20 less, and you don’t need anywhere near 180 watts – but the cheaper one doesn’t state it’s maximum total harmonic distortion in the specifications. This one states “less than 3%”, and that’s an excellent figure.

Radio Shack? Absolutely not! They don’t sell an inverter of this type (not even ONE). Everything they’ve got in on the Internet is cheap “modified sine wave” garbage, and the prices are way too high for the stuff they are selling. Yikes! I wonder, WTF was that Dexcom person “thinking”?

Thanks so much, that is a good resource. The only inconvenience is that it looks as if you either have to use your car or a large deep cycle battery to power the pure sine wave inverters. I do happen to have a large deep cycle battery which is an alternate power source for my electric chicken fence. If push came to shove, using the battery for the Dexcom would trump the keeping the chicken fence electrified. Do you know if there is a less bulky alternative for battery power?

Both the Dexcom trainer and the Dexcom tech support said to call Radio Shack, but I think that they really did not know. I don’t usually patronize Radio Shack because I can usually get better, more specific electronic items elsewhere.

sweet, you’ve got the picture exactly-- except for two things:

First, at home for a multi-day power outage, you can connect BOTH the inverter and the fence connector to the same battery. You’ll just need to use a “Y” adapters at your battery terminals.

And of course, because the power drain is so small (15 watts for only 2 hours every 2nd day), you can get by with a MUCH smaller battery on trips taken without a car. You can even use one of the 12v battery packs which contain a bunch of AA rechargeable batteries (10 batteries in the NiMH versions, 8 for the NiCad ones). I’d strongly recommend the NiMH over the NiCad, because you can fully charge it before you go without discharging it first. (That’s the famous “memory” problem which NiCad batteries all suffer from.)

Carrying a lead-acid battery on an airplane is definitely not an option. They make units which combine the battery pack with a “modified sine wave” inverter, in a single box; but as I explained above, you’d better get a more accurate “pure sine wave” inverter- so it has to be a separate box.

3% total harmonic distortion, BTW, is the generally accepted maximum for power on the Grid. Because they have multiple generators in different power plants being “tuned”, by phase-matching electronics, to work synchronously with each other, there are tiny distortions in the wave from your at-home wall sockets, too. 3% is really, really good for a hand-held converter.

Im actually surprised that Dexcom does not have some sort of 12volt adapter to charge their own device… Seeing they are using basically (one of the) Motorola style charge connectors… (please PLEASE do NOT try this on your own)… Being able to plug in a dexcom while you drive would be useful. But as an aside. does anyone know if the Dex will charge off its USB connector?.. This might be a viable (albeit slow) option if it can fully charge off the USB… Not sure since I tend to just plug it in for the requisite 3 hours to the wall.

I too am surprised there is no Dexcom supplied option for charging at least in a car, Sweetlady1’s situation is a little tougher. A solution for the car is to buy a cheap power inverter (12v dc to 110 ac) and plug into your vehicle’s 12 volt receptacle. Or, like in my wife’s car, there is a 110 receptacle in the vehicle (powered when car is running) so that works well (speaking from experience).

For Sweetlady1: there are products out there that contain a rechargeable battery along with a 12 volt and 110 volt receptacle built-in, used frequently at job sites. I believe Black and Decker and Ryobi make several models. Not sure on cost, weight, and how long they hold a charge, but if it’s used just to recharge the Dex, it should last awhile. Good luck

Rick actually brought up a possible issue with that… Can the Dexcom (handle) a modified sine wave inverter or does it need a true sine wave converter (which are a little more expensive, and a bit larger sized *usually)

Another option is if the Dex can use a 12 volt battery with a plug… I have one of those from B&D…

Wish Dexcomm would give a more definite batch of answers and not just the hand it off to Radio Shack because it still leaves a bit too much in the air…

I am wondering if we can source the “connectors” i.e. the USB cable we get from china… I would assume that the dexcom unit uses a 5volt charge similar to an ipod… I would assume that there is a li-ion battery that only requires a small amount of voltage… Why cant the USB cable charge this thing.

DEXCOM give us the pin outs for the DC voltage… Easy…

Then you can use any 12v to USB dongle in your car or on ANY battery… 110 is so over rated :wink:

This is only remotely related, but offered as a note of caution. A few months ago my family and I went up to Tahoe for a ski vacation for 4 days, and I forgot to bring my charger. I had three bars of battery power left, but I was worried about not having enough battery power for the full trip because I really like having the Dex for skiing…the Dex is very useful for skiing because it is difficult to fingerstick in low temperature environments, and it is convenient to just pull the Dex out of a pocket at the top of a run.

So to conserve power, I decided to use the Shutdown command at night (I don’t often get low sugars at night and was comfortable going without the Dex). I did it the first and second nights, but then on the third morning I couldn’t get my Dex to power up again. I tried everything. I called Customer Service and the rep had me stick a paperclip into the reset slot on the back but nothing happened. The rep told me that in some cases, when the Dex is put in Shutdown mode the receiver actually drains the battery! So then there is no juice left to start it back up!

This sort of ruined day 3 and 4 of the ski trip since I had to go by the old method of going to a warm spot on the slopes each time I wanted to fingerstick.

When I got home, I plugged the charger into the receiver and it started back up and I still had 2 bars of power! So the rep’s suggestion that the receiver had drained the battery was not true…for some reason the receiver wouldn’t power back up even with enough battery power left behind.

So my advice is…be careful using the Shutdown mode when you don’t have a charger handy…the receiver might not power up again.

This is very possibly true. The charger is rated at 5.0 volts, 3.0 amps, and it can handle both USA and EU power sources. And maybe the battery inside the Receiver is a widely used “industry standard” item.

Apple charges $107 to replace your iPod battery and ship it back. But with proper tools, (people sell “kits” for about 15 bucks), you can replace the $4.00 battery yourself. But you NEED the right tools, and good instructions, or you’ll probably break it.

The differences, however, are numerous: Dexcom sells a prescription-only, Class One Medical Device – anyone who goes into business “digging around inside” for fun, or profit, can find themselves in serious legal trouble VERY QUICKLY. (Bust your iPod, and you’ve only lost a few tunes.) Also, if the “smart charger” intelligence to reduce the voltage and then stop charging as the battery becomes full lies in the charger, your USB dongle could risk overcharging the battery. (Li-Ion and NiMH are easily damaged by overcharging; that’s why your toothbrushes and portable phones, among other things, are still being made with NiCad cells.)

There’s definitely “smart charger” computer control in there somewhere, and I’ll SWAG it to be within the charger. (And not the Dexcom, which doesn’t have room for such components… besides, CUI specializes in such stuff.) That’s why you can leave it plugged in all night without hurting it. “Smart Charger” integrated circuits cost only pennies-- the “ultra-fast” battery chargers you have at home cost about 10 bucks, and they’ve got 'em inside. But you need to have such protection! USB has to provide 5 volt power at all times, NEVER cutting back on the voltage, so it’s not “compatible” until you put another device in between.

Dexcom’s connectors are all 12-pin components. They’re made by Hirose Electric, the picture for part number “3240-12P-C” is a perfect match for the plugs (on the cables from the charger and the computer). “3260-12S3” is the “matching” Socket, although Hirose’s picture doesn’t seem exactly correct. Dexcom might be using something slightly different.

I have NO IDEA which signals are being carried by which pins, although you could sacrifice a charger to identify the ones being used for that function. (And heck, you’ll be needing the cut-off plug later anyway, right?)

YIKES, and thanks for describing this issue.

For me, nighttime lows are the primary purpose of wearing Dexcom in the first place. I only use “shutdown” for airport security inspection, and again at airplane take-off and landing times (i.e., those “please shut down your portable devices” moments.)

I’m pretty sure that Dexcom added the “shutdown” capability for exactly that purpose: aviation safety requirements, and not battery savings. I’m not surprised that the restart function, which is very slow and battery-intensive, fails when the battery is just slightly discharged, but that’s another key thing in your post: Be absolutely sure that you’ve got 3 bars before going to the airport, or you’d better announce that your medical thingy does radio every 5 minutes (and can’t be turned off). When you say that, expect a pat-down, supervised, individual security screen (in the cubicle, with multiple personnel present) as a follow-up to your announcement.

Allow at least 15 minutes of “extra” security check-in time for that, because the wait time for a TSA supervisor to get to your inspection station can be quite long at busy airports.

Those “Contractor’s battery pack/Inverter” devices are much more expensive than the “pure sine wave” inverter listed above, because they’re capable of vastly more power output.

Lucky-Dad, I’ll try to clarify/simplify my big post (the first one): As Jake replied, your wife’s on-board inverter is a “modified sine wave” cheapo, similar to the $15 light-socket plug-in devices. “Modified Sine Wave” input creates unstable DC output on most A/C powered battery chargers, and that harms battery life. When you’re recharging your cellphone, it’s not a problem-- cellphone batteries are very cheap, and easily replaced.

The Dexcom Receiver is not designed to allow for battery replacement, and costs $hundreds to replace. If the internal battery pack is sensitive to unstable charges voltages, then you might need to use a “pure sine wave” inverter. I don’t know for sure, but I wouldn’t risk it. The high-quality inverter is great to have around for other “sensitive” electronic devices, too.

What do you do in the cabin when your Seven re-starts and makes the buzzer noise that would awaken the dead? That would be disconcerting to hear.

As an aside, I’ve never had an issue with my Dexcom at security screen.

A timely topic, as I just took two flights today and type this trying to adjust to local time. I have both the Dexcom and Animas Ping, so I am broadcasting with two devices. No issue with security other than the alarm from either my clip-less Animas pump or the sensor in my arm. On the plane, I have never shut down either device, partially because the power ougtput is so low but mostly because I forget!

We had a major rain storm about a month ago. The wind and rain toppled lots of trees in the area including one across the street that took our power out. During heavy rains we need our sump pumps. So I reacted as fast as I could and purchased a small gasoline generator. The power was off for two and a half days. During that period I was able to run the sump pumps and my freezer plus some other small appliances ( like my beloved coffee grinder ;-)). Home Depot, Lowes and other similar stores sell these. However, in your case I still recommend solar panels for charging batteries when AC power is liable to be unavailable for some time. The solar panels come is all different sizes to match your needs. In addition to the charging panels a control unit which manages the charging and protects the batteries is a great idea. The site mentioned by Rickst29 is a really good source of these items.

That works… unless you’re unlucky enough to have the radio “wake up” WHILE you’re in one of the newer, better scanners, at a major airport.

For me, that happened at O’Hare, and the wait for the Supervisor to arrive from a far-away section of the terminal was very long.

No problem during the flight: 5 minutes after take-off (and for that matter, while you’re sitting in the flight’s waiting area, and sitting on the plane BEFORE the Stew announces “Prepare for take-off; Please turn off all portable electronic devices”) you definitely want to turn it back on again.

BTW, I always tell strangers in adjacent seats, AND at least one of the Stews, that I’m stuffed to the gills with insulin pumps and automatic bG monitor devices. For the neighbors, I slide them out of my pockets for a tiny bit of “show-and-tell”, warn them that they’ll probably be buzzing and screaming a few times, and ask them to be SURE that I’ve waked up if that happens.

They’re ALWAYS delighted that I’ve asked them to “back me up” on my medical device alarms. They usually also say, “Wow, that’s amazing, my {relative} should get one of those!”

I have noticed a new class of small portable solar chargers designed for cell phones, laptops and even for larger car and boat battery applications. Most all of the smaller units have USB outputs. Also I have purchased a New Trent external battery to extend use of my smart phone which can drain its battery within a day or so when using some applications. Google "solar power for laptops (cell phones)" for a range of options. A solar power device seems ideal for your problem.