Changing battery in the middle of a track?

marlar · March 27, 2011, 23:38:43

Hi Menion,

I am soon going to Turkey where I want to walk on the famous Lycian Way. A typical hike will take a full day, so I bring a spare battery.

Now I wonder, what happens if I have to power down the phone to change the battery? Can I then resume the recording with Locus afterwards, or will I end up with to tracks?

Martin

berkley · March 28, 2011, 07:36:24

Hi Martin,

why don't you try that thing out and see what happens? I'm pretty sure, that if you (in case of an "accidental" reboot) start Locus again and tap the Rec-Button, there whill be a kind of question: "It exists a old unfinished track. Do you want to continue recording this track?"

Just an off-topic question: Do you take a solar-powered battery charger on your trip?

Cheers, berkley

Menion · March 28, 2011, 10:08:04

yes, try first.It's easier then asking

marlar · March 28, 2011, 10:36:15

You are right of course. I wrote this just before midnight and I must have been tired! It didn't occur to me that I could simply turn the phone on and off to see what happened :oops: I thought about actually going out, changing batteries etc.

I tried it now and I Locus handled it fine. Thumbs up!

Re. solar power, I do have a solar charger but I will probably leave it at home to save weight. I will bring two spare batteries so that should be adequate for a day hike.

Menion · March 28, 2011, 10:55:32

hmm if you want to use some whole day recording I can suggest few things that I want also try by myself when weather will be better to some longer trips

1. use bluetooth GPS! It increase phone battery life a lot!
2. if you don't need track recording, to record every cca 20m, try to set "Time between gps locations" in settings to longer value.When you use internal GPS, this turn off gps for that time, then enable, record point and then disable again. But try it before trip to know how it works and even if this works fine! I didn't tested it by myself yet ...
3. my DHD have terrible display that can consume whole battery after cca 4 hours when on on full bright. I think on DZ it's similar,so count with that ...

marlar · March 28, 2011, 11:01:10

Good suggestions menion! I do have a bluetooth GPS but I don't want to carry it. I have 3 batteries :-)

But setting time beween GPS points sound like an obvious way to get a little more juice from the batteries. And since it is in walking speed, that should not be a problem at all.

Menion · March 28, 2011, 11:41:27

yes, question is only if gps will wait until some fine accuracy location is received or if this will just take first not so good location. It's system function that do this so it need to be tested

svartbjorn · March 29, 2011, 09:46:26

I have done a lot of testing with different sestting of "Time between GPS locations" = TBL. With screen off, I get the following (HTC Desire):
- TBL = 0: battery usage 14 %-points per hour
- TBL = 60: battery usage 8 %-points per hour
- TBL = 120: battery usage 4 %-points per hour

So the TBL setting makes a huge difference. When walking, sampling every 2 minutes should be more than enough. Locus once again is outstanding having this great feature!

Regarding solar panels: heads up! I have checked out the solar panel market for a long time. There is a lot of crap out there, so be very careful if you consider buying anything. I am a computer hardware designer, so I know quite a bit about hardware technology. The spec for a panel is something you may get close to only under the very best conditions: bright sun light and sun light perpendicular to the panel. If you walk with a solar panel on your backpack, you will face the sun at all kind of angles, and the charging current will drop dramatically. And if it on top of that is a cloudy day, the charging current quickly drops to 1/10 of spec. So all these small, neat, compact solar panels you can find on the market, are pretty much useless. I have done some mathematics on this. To have a solar panel make sense under practical conditions, it really need to be large. That means space and weight. After considering solar panels for a long time, I finally concluded this is not a good solution. The solution I found, was to use an external USB-based battery with two standard USB output ports, and it can be charged with a standard mini-USB cable. That means you can use the same charger for your phone as for your battery, just different cables (mini USB/micro USB). Here again, there is a lot of crap out there, so be careful. After a lot of searching, I bought this one:
http://www.portablepowersupplies.co.uk/ ... remium.htm
This battery (5 Ah) can fully charge your battery twice. Size and weight is about the same as a HTC Desire. You can get much larger batteries (even 21 Ah), but as usual it a compromise of price, weight and size.

marlar · March 29, 2011, 10:09:13

Interesting post, svartbjorn. I agree that 2 mins sampling should be enough for most walking.

I have a solar panel which in fact works, but as you point out, I have been testing it in direct bright sunlight which the unit perpedicular to the sun. I don't think it is worth bringing it on my trip for the same reasons you mention. It justs add extre weight and will perhaps only give me a couple of hours more juice. Instead I have bought 2 spare batteries.

I also have a handful os these small chargers which works very well driven by a single AA cell: http://www.popgadget.net/images/emergen ... harger.jpg

I bought them for arund 3.5 USD and I use them for small presents :-)

svartbjorn · March 29, 2011, 15:31:45

I have looked a lot into those AA based chargers. I have some advanced equipment at home where I can measure exactly how much juice I get out of different types of AA's (batteries from different vendors have very different capacity). It is really bad. Be aware that a phone draws a certain amount of current, typically 450mA when charged from a USB data port and 850mA when connected to a AC powered USB port (defined as a power USB port, signalled by having the two data lines shorted). Now some mathematics: a two cell based AA charger has a battery voltage of 1.6 x 2 = 3.2V when fresh and not loaded. In the charger there is a step-up switching regulator. To be able to deliver 450mA @5V (USB voltage), the batteries have to deliver about 450/5*3.2/0.9 (90% efficiency) = 780mA. A one cell charger is even worse, since that poor battery now has to deliver 450/5*1.6/0.9 = 1.57A. I am designing a lot of switching regulators in my work, so I know all details about how this works. Delivering 1.56A for an AA battery implies that the voltage will drop significantly (internal battery resistance), causing the battery current to increase accordingly. The end result is that AA batteries are not suited for high loads for more than a short time . So if you carry AA batteries to charge your phone, you will need a lot of them. AA batteries are cheap, yes, and the chargers work, yes, but they are really bad in terms of stored power compared to LiIon batteries. With my lab equipment I tested AA batteries feeding a step-up regulator, which then charged my phone over USB. I monitored the input voltage (battery voltage) and output voltage (USB 5V) as well as current in and out. So I know exactly what these systems can deliver. I also calculated the weight and space needed for AA batteries versus LiIon batteries. Two different worlds! So if you need to carry power, forget AA based chargers unless you think it is ok to carry a *lot* of them. They are only suitable for an emergency situation, not at all as a portable power on a trip.

marlar · March 29, 2011, 15:55:59

I agree fully on the AA chargers. There are only meant as an emergency and I bought them because they were very cheap and actually does work. Sometimes getting just another bar on the batteri indicator can save your day!

What I have found is that NiCd batteries work better than normal Alkaline batteries because they are able to retain their voltage much better during the recharge cycle. But then they die, they die quickly ;-)

svartbjorn · March 29, 2011, 20:52:15

I hope you mean NiMH batteries? NiCd was 1st generation rechargable batteries. 2nd generation is NiMH, which about double the capacity for the same volume and weight. 3rd generation is LiIon and LiPol, which again double the capacity of NiMH. I though no one used NiCd any more. They suffer from the memory effect and bad capacity. Nothing is good with NiCd. Only disadvantage with NiMH is a noticeable self discharge, but they have no memory effect at all. LiIon has close to 0 self discharge, no memery effect, and very high capacity. Disadvantage is significantly reduced effect at low temperatures. LiIon batteries today also are available in versions that can deliver incredible large discharge currents. They are charged completely different from NiCd/NiMH, so a special LiIon/LiPol charger is required (a charging algorithm called "Constant I - constant V").

marlar · March 29, 2011, 21:01:45

Oops! Yes, I of course meant NiMH. I haven't had NiCd for years :-)

However, I do not agree on the memory effect of NiMH. After a number of recharging cycles, they start to loose capacity. But that is not what you mean with memory effect?

Oh - I think I know what you mean now. The problem that you have to fully discharge the cell before you recharge it? Yes, that is much better with NiMH. But in lot of instruction manuals, like for my electric tootbrush, they urge you to completely discharge it now and then.