8

I have a digital camera (Panasonic DMC-FT1) and will be going multi-day hiking with it soon. I'm looking to build a solar charger for it using something like this and strap it to my pack. Does anyone have any experience doing something like this, or any pitfalls in general that I may fall into (ie will my battery explode if I do xyz) ? There will be plenty of sun on my trip.

Battery markings:

  • Model: DMW-BCF10E
  • 3.6V 940mAh 3.4Wh Li-ion

Charger markings:

  • Model: DE-A60A
  • Input: 110-240V~50/60Hz 0.2A
  • Output: 4.2V 0.65A
endolith
  • 28,494
  • 23
  • 117
  • 181
jeremy
  • 5,055
  • 5
  • 33
  • 32

4 Answers4

6

You'd probably be better off taking a bigger spare battery.

But if you really want to charge using solar energy, you have to understand that there isn't much. If you have a 3cm^2 solar panel and go on the basis of 15% efficiency for the solar cell (which is pretty good), then plug that into the solar energy per square meter on Earth, which is from 1,413 to 1,321 W/m^2, which gives you about 59mW. Your battery is 3.4Wh, so it will take over 2 days to recharge it, nevermind that the sun is only around for a fraction of that or conversion efficiency.

Working backwards with those numbers, if one wants to charge a 3.4Wh cell within 4 hours, they would need a (3.4Wh)/(4h)/((1321W/m^2)*0.15)=43cm^2 solar cell.

tyblu
  • 8,167
  • 6
  • 40
  • 70
Thomas O
  • 31,546
  • 57
  • 182
  • 320
  • sparkfun sells a 5.2W solar panel: http://www.sparkfun.com/products/9241 , wouldn't this (ideally) need to be in the sun for <1h to fully charge the battery ? – jeremy Jan 02 '11 at 13:06
  • now that I re-read your post, a 3x3cm cell is tiny! I am willing to carry a much larger one if it means my battery will always still working (buying a new battery is expensive and much less fun) – jeremy Jan 02 '11 at 13:12
  • I obviously made some mistakes in my original calculations. Could someone point out these ones in particular? I think I made an error in converting cm^2 to m^2. – Thomas O Jan 02 '11 at 13:14
  • @ThomasO, Nowadays I find myself trusting Google and brackets more than my head! You can type in `(3.4 W hour)/(4 hour)/((1321 W/m^2)*0.15) in cm^2` to get the conversion. – tyblu Jan 02 '11 at 13:20
  • @penjuin, Fancy panel! It is 400cm^2, so I'd say yes, go for it! `(180 mm)*(220 mm)*(1321 W/m^2)*0.15=7.8W`, disclosing an efficiency of `5.2/7.8=66%`. There is, however, the small issue that I have zero experience with solar ;) – tyblu Jan 02 '11 at 13:27
  • @tyblu, 66% efficiency is *very* high for solar. The typical range is 15% to 40%, and you only get 40% with really expensive cells. – Thomas O Jan 03 '11 at 15:33
  • @ThomasO, That is the efficiency of the regulator, not the cell. Take a peek at the previous calculation: it has `*0.15` at the end. – tyblu Jan 03 '11 at 22:44
3

I have read that Lithium Polymer batteries can, in fact, be dangerous. I think they are actually a fire-hazard when overcharged. You're also not supposed to "trickle-charge" Li-Po batteries. They require a pretty specific charge cycle characteristic from what I understand. Basically, what I'm saying is I don't think you want to DIY when it comes to Li-Po battery charging.

I used them once before, on an academic high-altitude ballooning project, and we were required to charge them in a metal enclosure because of the fire hazard, even though we were using a commercial charger.

Also on a somewhat unrelated note, I believe they are also pretty sensitive to being discharged to lower than 3V, and will not recharge if you take them down too low.

vicatcu
  • 22,499
  • 13
  • 79
  • 155
1

good app note here if you want to build your own http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1037,C1078,C1089,P89360

0

Just in case could matter to someone, I've been recently experimenting with LIFEPO4 used batteries charging over a 2*50W solar panel and, realized that they weren't as dangerous as LIPO batteries, I connected four of them in series (3.7V*4) and those to a big lead acid battery in parallel. This one would provide enough stability during the charging process AND overcharge protection, limiting roughly at 15V peak.

As for LIPO batteries I've been thinking to experiment with a portable 12V/10W solar panel. The idea behind could be pretty much the same, using a simple 7815 or 7915 for limiting the voltage at 15V. According to specs, 10W panel would provide 1A peak, about 0.5C of commercial stick batteries (those normally found on laptops). This latter could be the solution for portable (backpack) application for many of us.

Nick Alexeev
  • 37,739
  • 17
  • 97
  • 230
Michele Romanini
  • 1
  • Your proposal for simple charging of LiPo using an eg 7815 is fatally bad. The voltage is actually too low (15/4 = 3.75V/cell which will provide far far from a full charge). BUT, increase that to closer to the 4.2V/cellneded for full charge and leave them tricklecharging and they will die in short order. Vchg MUST be removed once current falls to say 10% of Imax. – Russell McMahon Feb 27 '14 at 09:37