Li-ion Power-Pack charger Solar

Rsadeika · 2011-08-09 03:23

I am considering creating a small remote data logging station using the li-ion power pack as the power source. What I would like to do is have a solar cell(panel) attached to the station to be the input power for li-ion charger. Does Parallax have a matching solar panel for something like that, and they do not, will Parallax be selling something, soon? The docs mention that li-ion pack input requirements should be +5 - +12VDC @ 1amp. Since the solar panels are rated at a (w), I am not sure as to how figure out the amperage output for the solar panel.

Thanks

Ray

kwinn · 2011-08-09 06:30

The current output of the solar panel would be the rated watts divided by it's rated voltage. Do keep in mind that the watt rating is usually for when the panel is in full sunlight so the actual power output will normally be less than that.

Matt Gilliland · 2011-08-09 08:00

Hi Ray -

The input power requirement for charging the Lion pack is a minimum of 5 volts. (It can be anything up to 12 vdc.). And the output voltage of the power pack is a nominal 7.2 vdc (at full charge it's 8.2 vdc).

So, how can a 5v source charge a 7.2v device? Simple: When in charging mode, the two 3.6 volt Lion cells are each charged individually. When the charging source is removed, the cells are connected in series automatically - download the Product Doc for more insight on this.

Our 30 watt solar Panel Kit has a nominal output of 6 volts with a maximum current of 5 amps, hence the 6 volt x 5 amp = 30 watt rating. This Panel can be the charging source (that's one of the first circuits that I put together myself). In fact, the Product Doc (for the Lion, in Fig 7) has an application note describing this exact circuit.

-Matt

Tracy Allen · 2011-08-09 09:34

Ray, what do you mean by small, in terms of average current consumption. While the solar charger is great, I don't know if there is a way for it to automatically switch from charging mode to powering your logger. Is that right, Matt?

Franklin · 2011-08-09 09:53

http://www.adafruit.com/products/390&zenid=190964565445de4dba44935efaf709fd Take a look at this.

Rsadeika · 2011-08-09 09:58

By small, I mean not having to put up a six foot by six foot solar panel, and then have a storage shed to house everything. I made a general assumption that when you have the solar panel plugged into the charger everything would continue to run, something along the lines of how a laptop works. Now, if that is not the case, and you have to plug, unplug the solar panel, physically be out there to look at the charger to see if needs to be charged, then that is a big problem. To bad the charger does not have a mechanism on the board so the microprocessor could check to see what the charge level of the batteries are. Since the setup I am thinking about, will have an xbee on board, at least then you could have the xbee send a message when the charger would have to be plugged in. But all this is starting to look like my idea will not work, not with the materials that Parallax has to offer.

Tracy Allen · 2011-08-09 10:34

I'd wait for a reply from Matt before reaching that conclusion.. It may be that you can draw off power at 3.6 to 4.1 V at the same time that the batteries are charging. Matt would know. If your logger uses the Propeller, that would be enough to run it. But not a BASIC Stamp. As Matt said, when not charging the batteries are connected in series to deliver 7.2V.

I asked about the power requirements of your remote logger, because 30 watts might be overkill. Maybe you need to run other stuff from that power source too?

Rsadeika · 2011-08-09 11:55

I noticed Parallax sells a 6v 1w solar panel, but can not tell if it can be placed outside as is. What I am thinking about is using the Gadget Gangster USB PP board, temperature and humidity sensor(s), and xbee to start out with. Then maybe add a wind direction, and rain/snow accumulator with other things added even later.

I really want to test out the xbee, since the above described setup will be approximately 100 to a 150 feet away from the house, and the base unit will be in the basement.

Matt Gilliland · 2011-08-09 17:14

Hi guys -

I noticed Parallax sells a 6v 1w solar panel, but can not tell if it can be placed outside as is.

Yes, it can. It is completely sealed.

It may be that you can draw off power at 3.6 to 4.1 V at the same time that the batteries are charging.

Short answer is no. (Besides, as Tracy says, it wouldn't run any 5 volt circuits)

And yes, the 30 watt solar panel is more than the charger requires.

However, I wasn't awake enough earlier when I posted my first reply - I thought (but apparently didn't type!) the answer to the question).

The Lion can be easily configured as a Un-interruptable Power Supply (UPS). That's the circuit that I was referring to in the Applications area of the Product Doc above.

Therefore, circuit operation would be as follows: When the Sun is shining, power is delivered to your circuit (by the Sun) while charging the cells as well. When the Sun no longer shines, power is then delivered to your circuit via the Lion cells.

I noticed Parallax sells a 6v 1w solar panel

Yes we do. However, by itself, it does not have enough amperage to operate the Lion Pack. You could connect several of these in parallel however, to get to the 1 amp minimum.

-Matt

Matt Gilliland · 2011-08-09 17:15

Oh, yeah. The 30 watt solar panel measures 16" x 24" x 3/8" thick, when fully assembled.
-Matt

Matt Gilliland · 2011-08-09 17:23

Hi Ray - one more thing...

I made a general assumption that when you have the solar panel plugged into the charger everything would continue to run, something along the lines of how a laptop works.

Yes, this is true. The only thing you really need to add is a couple of diodes and a capacitor (which essentially turns the Lion into a UPS), as outlined above. We purposely didn't include these simple components on the PCB, because their values would vary, depending on the application.

-Matt

Li-ion Power-Pack charger Solar

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