solar minty lives !!

[ransomhall]

gwolverine - this is a test project to see how big a solar panel and battery would need to be to power a real time remote environmental monitoring station. The feds are cutting a long standing monitoring program in my area. See http://waterdata.usgs.gov/usa/nwis/uv?04294500 for an example. Those of us who rely on the data need to come up with an affordable alternative for the stations that are being removed and attempt to get funding locally. I think DIYers like myself can do it better and cheaper, but I need a working proof of concept to convince anybody else. I use GHI's boards because the feature to price ratio is outstanding! I'm a .NET developer at my day job, so am able to quickly dive into NETMF and crank out a very serviceable solution to the above problem with minimal effort.

[ransomhall]

mambo - I like this setup because you can swap out batteries quickly. Anything that provides 3-4V is usually trivial to add a JST connector to, so I can quickly hack together a bunch of options from the variety of battery holders I already have. My suggestion would be start scrounging LiPo/LiIon batteries from any old cell phones or other nonfunctional gadgets you (or friends and family) are about to recycle. In a short time I've managed to get my hands on a bunch. For their size, they are very "power dense". On a cautionary note, I have needed to add a protection circuit where necessary. That's the trade-off with these - they are picky about how they like to be (dis)charged. Those you find here and on other similar sites generally come with built-in protection, but are relatively expensive. I'm saving up for the 6600 mAh beast sold here!

[scottinnh]

OK, I do not understand something about this setup (about the Lion charger really).

The Lion charger has 2 outputs: battery, and load.
Assume a device is connected to load (an Arduino or something).

Let's suppose the DC input port is getting zero power (it's nighttime).
Does then the charger board intelligently switch to drawing power from the battery port (until such time as there is power coming into DC in, ie sunrise)?
In other words, a completely maintenance free power source (at least until winter <grin>)


thanks!

[ransomhall]

Yes, it augments input with battery power if input < load. So if input = 0,then it's all coming from the battery. I've unplugged a solar panel with a load drawing roughly 150 mA at 5V and the switch to battery power did not cause any power blip, thanks in part to that huge capacitor on the charger. I'm not 100% sure if the opposite is true, that is, any extra power the load does not need goes to charging the battery. I believe the answer is yes, but I'm not sure at what threshold. i.e. how much leftover do you need to charge.

[adafruit]

it prioritizes the load over battery charging - this is the most efficient method to act
there is a good discussion of it in the datasheet

[scottinnh]

Ah. the product description here doesn't explicitly mention this feature, that power input will automatically switch to source against the battery.
Damn. I would have put this board in on my last order had I understood that.

I read the datasheet best I could, and I thought "prioritized" must mean that "load" port gets 100% of DC IN when needed.
But that's not the whole store... if DC in shuts down, power source will automatically switch to the battery.
That's pretty sweet! It's a charger -and- a power supply.

[scottinnh]

Using this battery charger and solar panel -

Will this charge say the 3.7V 6600mAh Lion?

Is charge time proportional to the battery size? (Meaning 3.7v 2700mAh takes just over twice as long to charge as the 1300mAh)

[adafruit]

yes, it will just take longer (its a very big battery!)

[ransomhall]

Assuming you're using the 6V 2W panel you can get max 300mA. So that's 22 hours to charge the 6600mAh beast in bright sun. From the online research I've done for solar power, most take 20% off theoretical max power to get a rough estimate of real charge time. That puts it at 26-27 hours, which you could only pull off continuously in an Alaskan summer! Credit to adafruit for doing the math in another post.

[ransomhall]

Thanks to this nice tutorial http://ladyada.net/make/solarlogger/ I've done a substantial upgrade! Now I can monitor and save the following data:

Voltage: Panel, Battery, Load
Current: Panel and soon battery (waiting on parts)
Temperature: battery, in case it gets too hot.

[adafruit]

you might want to use the temperature montioring built into the lipo charger?

[ransomhall]

Yes, I did see the blurb on replacing the resistor. I've got a thermistor lying around here somewhere... It would be nice to correlate charging amperage with chip temp, to be a little more scientific than "it's warm to the touch" when charging from USB. The chip does not seem to heat up much when charging from the panel. It does noticeably when charging from USB. I may pony up for a beefier 6V panel, as that LiPo takes a lo-oo-ong time to charge. Temperature monitoring would become essential at that point. I had a DS18B20 already hooked up to measure ambient temp, so just taped it down to the battery as a stopgap.

Plenty of tinkering left to do. Next version will include serving up the data on my local network using one of the new WiFi Xbees

[sandman1962]

my two versions:one using an ipod touch retail container, and another using stacked altoids can (big battery)


solar charger by Sandman1962, on Flickr


solar charger 2 by Sandman1962, on Flickr


solar charger 3 by Sandman1962, on Flickr

[ransomhall]

Nice! I mangled a tin trying to do cutouts like that. I'll probably go with laser cut acrylic once I'm done with the monitoring project so I can trick out the container a bit. That big 6.6A LiPo rocks! I'm still testing how long I can run various gadgets with it.

[ransomhall]

I finally stopped playing around with all the parts (monitoring setup earlier in thread) and wrapped up the 6V 3.7W panel, Minty, and solar lipo charger in a nice fluorescent blue acrylic housing. Along with a 6600 mAh battery, I can now charge the heck out of USB powered gadgets. See http://www.ransomhall.com/Pages/solbooster.aspx for more details of this build. I am going to create an Instructable for this and enter it in the Epilog laser cutter contest. I'll post links when that is ready. In the meantime, the enclosure design file is available at my showcase on Ponoko: http://www.ponoko.com/design-your-own/products/sol-booster-6376.



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