Need extended battery life -- 15 hours+

[+user13371]

I usually put NiMH rechargeable batteries in my SporTrak Pro. I get about 9-10 hours on a charge, and always have a charged set ready to swap when needed.

 

However, I now have a need for much longer battery life. I've started using the GPS on my bicycle, and I analyze track logs after a ride for performance evaluation. For an accurate track log and maximum and average speeds, the power has to stay on for the whole ride (even during stops). A day-long trip might be 150-200 miles, so I need the GPS to run on batteries for at least 15 hours and maybe more.

 

Has anyone experimented with lithium camera batteries? Any idea how much life I might get out of a pair? I expect most geocachers and casual users wouldn't bother with lithium cells, because these batteries wouldn't be cost effective for routine use. But if anyone has tried them, please let me know how well they worked for you.

 

My alternative might be to build a battery pack of higher capacity, and attach it to the external power connector. That would be clumsy for hiking or any handheld use, but not really a problem on the bike -- but it still seems inelegant.

 

Suggestions please?

 

---

LDR.

[+mrp]

I remember seeing (though I can't seem to find) a cool custom setup where a guy had taken a standard 2 C-cell bicycle headlight assembly and outfitted it with a pfranc connector so that he could power his etrex with it. He had it set up so that when the batteries in the headlight got low (or the headlight got switched on), it would revert to the batteries inside the eTrex (vista?).

 

I don't know how easy it is to get bare-wire connectors for the SportTrak like, but if push comes to shove you can sacrifice an external power cable. It might be worth looking into.

 

-- Mitch

[+Jamie Z]

LDR,

 

I've considered the same thing, as I have my Meridian mounted on my bike, and I'd like to be able to keep it powered full-time. About the only thing I could come up with is to buy a bottle-cage battery and power the GPS using that. I'm not an electrician, but I suspect the voltages would be different, so you'd have to rig some sort of adapter or something, but that's the easy part.

 

You might also consider a yellow eTrex. The battery life for that unit is somewhere longer than 15 hours.

 

I'm leaving on an extended trip in about a week. My compromise for powering my GPS is just to carry several sets of batteries and only use the GPS when I need it, as I'm not so concerned about my track.. and I can get my speed and distance data from the cyclometer.

 

Not that this will help you, but here's my handlebar setup, with my headlight to the right of the GPS.

 

 

Jamie

[+EScout]

The most simple thing to do is make a battery pack with 2 D cells and use a power cable. Cut off the cig plug and get some molex connectors. That way you can attach the battery pack or cig plug depending on whether you are bicycle or car mobile. The D cells should last 3 or 4 times longer than AAs. Get 2 alkaline Ds at 99cents Only store for 99 cents.

[freeside]

This may be a little too much solution for the problem, but one guy developed an onboard power solution using a Dynohub in parallel with a 6v nicad rechargeable. Elegant, though D cells are probably more practical.

[+jonboy]

I have used Lithium AA batteries and was amazed how long they lasted, about four caching days with the GPS on most of the time. I usually use NiMh and have to switch them. I was in the woods and had forgotten to change batteries on the NiMh, so I put in the lithium I always have in my pack. They have a shelf life of years, if unused, so I just leave a pack in my ditty bag, for either the GPS or the flashlight, plus they are not affected as much by the cold. I still will use rechargeables because of the environmental effect of throwing away batteries on a regular basis, but I was very impressed.

[Team Sidewinder]

I use the lithium batteries and they last long enough to justify the extra cost for me. No real data to prove how much longer but it is enough that I can tell. I also got a solar port from Brunton to run my gps on if I need but the sun needs to be shining and it was a little spendy at $80 from REI but I never need to worry about batteries if the sun is up. Also use the Solar port to run my cell phone if it gets too low.

sidewinder

 

LOST AND FOUND DEPT.

[+Sissy-n-CR]

I was curious about the lithium batteries, so I went on a search.

 

RadioShack sells a pair of Engergizer L91 Lithium batteries for about $9 a pair. According to the Energizer web site -HERE- The L91's are rated at 2900 mAh.

 

If you have high capicity NiMH which are probably rated at about 1800 mAh, then they might get you to your 15 hours.

 

I'm no electronics whiz, but the NiMH are pushing 1.2v x 1.8Ah that should be 2.16Wh. Compare that to 1.5v for the lithium x 2.9Ah should get you 4.35Wh. Right at double the power.

 

But of course, I don't know how these units deal with the differing voltages, but I would think a particular load would draw the same amount of power to operate. If so, higher voltages mean less amperages. Therefore, your amp hours get streched even further.

 

I'm sure an engineer will come along and set me straight.

 

That being said, it would be more cost effective to kludge a portable power supply.

 

I was thinking about a four AA cell battery holder that RadioShack sells. You'd have to modify it so you'd have two pair a AA's in parallel. Then sacrifice a "spare" battery holder for the SporTrak and have a power connector coming out of it to the modified battery pack.

 

An advatage to this is, you can change pairs of batteries at a time thereby not removing power to the unit. Change out one pair and then the other and the unit will have power the whole time. Plus, double the normal capacity of just two batteries. If you use a AA battery pack you can use the NiMH batteries that you already have.

 

CR

 

 

[This message was edited by Sissy-n-CR on May 27, 2003 at 05:44 PM.]

[+Sissy-n-CR]

Just did some more poking around. Energizer claims it's regular Alkalide batteries in AA have around 2850mAh. I'm not so sure that a GPS unit is considered a high power device.

 

It might not be an advantage to go with Lithium over Alkalide in this application. It you're not concerned about weight, low or high temperatures, or anything out of the ordinary other than longevity, I'd use alkalide over lithium. Or at least do some test runs first.

 

CR

 

[peter]

quote:

---

Originally posted by Sissy-n-CR:

Just did some more poking around. Energizer claims it's regular Alkalide batteries in AA have around 2850mAh. I'm not so sure that a GPS unit is considered a high power device.

---

 

For these purposes a GPSR is at least medium power. The alkalines get their 2850 mA-hr rating at a very low current drain of about 20 mA. At typical GPSR drains of ~150 mA, the capacity drops to about 2000 mA-hr while the lithium cells will still be putting out almost their full 2800 mA-hr capacity. Also the lithiums will maintain their voltage over almost their entire life while the alkalines will slowly drop in voltage until they go below 1.0 V. GPSRs have internal regulation and draw less current at higher voltages so this further favors the lithium cells. I'd expect the lithium cells to offer at least 50% more life than alkalines in GPSR applications, and about twice the life of current NiMH cells.

 

However, I use my eMap in much the way LDR described and just swap out NiMH cells at occasional stops (even a traffic light is enough). I haven't noticed this having any bad effect on the tracklog or any of the trip data (moving average speed, max. speed, distance, etc.). But I haven't used a SporTrack much so maybe it's different in this regard.

[Leemann]

Try batteries america get a bettery pack

7ahr 12 vdc with case charger ect will power gps for a long time. I say no to molex for power connectors and use Anderson powerpoles

best investment.

 

Hope this helps

Lee

 

Captain gps needs batteries got any?. Hows the Enterprise

sposed to navigate way out here with out em?

[+user13371]

quote:

---

Peter remarked:

...I use my eMap ... just swap out NiMH cells at occasional stops (even a traffic light is enough). I haven't noticed this having any bad effect on the tracklog or any of the trip data (moving average speed, max. speed, distance, etc.). But I haven't used a SporTrack much so maybe it's different in this regard.

---

 

The most common way for me to foul up my track log is to turn the unit off (to save battery power) at an extended stop, and forget to power it up again when I get going again. That's just me, that's not the SporTrak's fault.

 

But you are also correct that the SporTrak differs from the eTrex in a couple of ways.

 

First, the SporTrak resets "max" and "average" speed to zero if you power off the unit. Don't know why -- I'd prefer they were like the trip odometer and only reset when you intentionally give the reset command. Maybe Magellan will fix this on the next firmware update.

 

Second, battery change on the SporTrak is a minor ordeal:

 

- take GPS out of mounting cradle,

- unscrew a tiny screw attached to a d-ring/lanyard,

- give lanyard a hard tug to pull batttery carrier out,

- remove batteries from carrier,

- install new batteries and re-assemble by reversing procedure above.

 

It's clumsy, but I guess it's waterproof Is the etrex really a lot easier?

 

Actually, all of the above is just a set minor annoyances I've learned to live with. Not a big enough deal that I would build a battery pack, but once in a while I probably WILL choose lithium batteries for a long ride just for the added convenience.

 

You said you'd expect these to offer at least 50% more life than alkalines in GPSR applications, and about twice the life of current NiMH cells. This turned out to be exactly right: I tested a pair of Energizer Lithium batteries the other day, and got over 20 hours continuous operation. It was more than I expected and will certainly be enough for my longest day-rides.

 

---

LDR.

[+zenrandom]

quote:

---

I'm sure an engineer will come along and set me straight.

 

---

 

Sounds like a close enough approximation to me. :-)

 

-zr

 

-----

If it ain't broke, I can *fix* that...

[+worldtraveler]

I always use AA lithiums in my Garmin V. A set of 4 usually lasts 30+ hours. My most recent set lasted 20+ hours, but I used the backlight a lot more than I normally do.

 

Walmart now sells packages of 8 AAs for ~$16.00 U.S. That works out to less than 27 cents per hour of use for me.

 

Worldtraveler

[+EScout]

What Leemann is describing is a great way to go for portable power. 7 AH 12V Gell cell batteries can be charged at home or in the car. You can charge your AAs, cell phone, or run items for a long time.

Regarding connectors, Anderson Power poles are great. I use them for radios, etc that use 12-13.8 V. However, I was describing a connector on the low voltage end (3V) and I use molex there so as not to be confused and plugged into 12v and fry the GPSr.

[+user13371]

quote:

---

Originally posted by EScout:

va great way to go for portable power. 7 AH 12V Gell cell batteries

---

 

Great -- so what do they cost, what do the weigh, and where do I get them?

 

---

LDR.

[Leemann]

Lee David like me try batteries america for aprox 65-70 bux 7 ah sealed lead acid (gel cell), case, charger and sig socket.

 

Battery itself is about 25 bux

 

Leemann Lee

 

Captain gps needs batteries got any?. Hows the Enterprise

sposed to navigate way out here with out em?

[pepperpot]

Your right, changing batteries on an etrex really is simple. Twist a clip, and remove cells, ....... thats it.

Buy a yellow etrex for $100 for your bike trips ...... great battery life.

 

Peppeprpot

 

Pepperpot is actually my dog, she's a miniature schnauzer that comes on all our cache hunts.

[AZcachemeister]

I'm not sure how may cells the SportTrack uses, but I have a MeriPlat that uses 2, and have rigged up an extended use system using a 6v gell cell from an old cycle lighting system. Yes, the 12v adapter works fine with only 6v input. The power cord is really the only 'problem' as it tends to get snagged on things. I suppose a 'water bottle battery' would work as well, assuming it was at least 6v. Then you wouldn't need the special nylon pouch I'm using, which came with the lighting system. You can also get 12v gelcells that are pretty small, I don't know what the endurance differences might be between 12v vs. 6v. These gel cells are available at Radio Shack and Batteries Plus, as well as several online retailers, Fry's electronics, also they are used as backup batteries in alarm systems. Good Luck!

 

[This message was edited by Azcachemeister on June 01, 2003 at 10:23 AM.]

[+EScout]

I get 12V 7AH gell cells for $15 new at the TRW hamradio/computer swap meet. (You can also get larger or smaller ones.) I rig up the wires to charge it from a car's cig socket (while car is running), or a 12V wall wart. With a cig socket mounted on top of the gell cell, you can use it for lots of things.