Author Topic: Solar cell battery charging  (Read 2178 times)

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Offline pomprockerTopic starter

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Solar cell battery charging
« on: January 05, 2009, 01:39:03 PM »
Is it feasible to charge your robots batteries with solar cells?

I mean I've seen the circuit, It would require solar cells in series, and a resister to control the current, and a diode to make sure the batteries don't discharge through the cells when its dark. Also was thinking of using an NPN transistor connected to an output pin on the MCU to switch charging mode on and off.


But would this work reasonably well, or are there some downfalls that I do not foresee?


Think WALL-E here...    ;)


Offline cosminprund

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Re: Solar cell battery charging
« Reply #1 on: January 06, 2009, 01:39:37 AM »
How do you compute "feasibility"? You can clearly charge batteries from solar panels, there are installations powerful enough to power a house off solar power. They of course cost an arm and two legs :D

Also there are solar powered cars that run off solar power only. You see them on the Discovery channel, by the looks they seem to be 100% custom design that are interesting only on a theoretical level.

Offline pomprockerTopic starter

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Re: Solar cell battery charging
« Reply #2 on: January 06, 2009, 11:03:01 AM »
feasible meaning, is the cost acceptable, is the size and amount of cells i would need to charge a 6v 2300 mah AA battery pack  a reasonable size to mount on the robot, could it charge in a couple hours versus an entire day...etc.etc
« Last Edit: January 06, 2009, 11:04:55 AM by pomprocker »

Offline want2learn

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Re: Solar cell battery charging
« Reply #3 on: January 06, 2009, 12:34:25 PM »
Another beam reply here.
You can charge your batteries from solar but is the entirety of your robots exterior surfaces going to be clad with solar cells?

One of my beambots was solar powered, it carried quite a weight of solar cells (around 25) and could either walk or charge it's batteries, but not both. This robot only had 3x 8mm geared pager motors and a couple of I.C.s and other components (you've seen how simple beam bots are) and 3.6v@1500mAh AAA batteries.

In my opinion I don't think its worth it with a uC based robot unless your robot can carry enough solar cells to power everything with power to spare (in indirect light).
The question that drives me hazy:

Am I, or the others crazy?

Offline pomprockerTopic starter

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Re: Solar cell battery charging
« Reply #4 on: January 06, 2009, 01:40:07 PM »
Well, I was thinking wall-e status, where it could catch some morning rays, and then stow away its cells, and carry-on its day.

Offline want2learn

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Re: Solar cell battery charging
« Reply #5 on: January 06, 2009, 04:45:16 PM »
The solar cells i used were about 35mm square. They provided about 3v @ around 25mA on a normal Scottish day (read as overcast).
With your battery specs id say you would need 2 or 3 in series and about 40-50 parallel, so between 80-150 solar cells (that matched mine) to charge your batteries to capacity in a couple of hours of morning sun. Maybe less depending what the morning sun is like where you are.
I'd say buy one cell (or sample if you can), measure its output in differing light conditions. Take the average and work from there.
Sorry i can't be of more help :(

P.S. The cells i got were an absolute bugger to solder to (mine had no flyleads), watch for this as a good joint took a bit of practice
The question that drives me hazy:

Am I, or the others crazy?

Offline paulstreats

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Re: Solar cell battery charging
« Reply #6 on: January 06, 2009, 05:53:14 PM »
It depends a lot on the solar cells.
If you cheap out on em then you get little power for the size. But you can spend big bucks for the latest technology and come up with something close to efficient.
Solar power has been around for a long while but because of lack of interest/costs/applications and stuff its still a very much emerging technology. Meaning that its probably possible its just that nobody has put in the money and the research to produce good enough cells just yet. So the likelyhood is that at the present time your lizard style robot will not happen. (lizard style aka... sunbathing during the day to build up energy then going out hunting at night)

Offline Gertlex

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Re: Solar cell battery charging
« Reply #7 on: January 07, 2009, 01:19:04 AM »
In a word – two, rather – probably infeasible.

A robot with a solar powered docking station (fast charging, somehow; not sure what's involved in fast charging in general...) might make more sense.

Also there are solar powered cars that run off solar power only. You see them on the Discovery channel, by the looks they seem to be 100% custom design that are interesting only on a theoretical level.

I'm so glad you realize the cars aren't practical and never will be :)
I

Offline Admin

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Re: Solar cell battery charging
« Reply #8 on: January 26, 2009, 04:09:58 AM »
Do the math . . . your solar cell probably gives out ~10mA, and your battery is probably ~2000mAh, no?

Doing the math, it will take 8.3 days to recharge your battery. Feasible, of course! :P

Offline pomprockerTopic starter

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Re: Solar cell battery charging
« Reply #9 on: January 26, 2009, 10:59:46 AM »
I've been meaning to brush up on my battery fundamentals....I guess I don't really know what math is involved

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Re: Solar cell battery charging
« Reply #10 on: January 26, 2009, 09:54:53 PM »
2000mAh/10mA = 200 hours = 8.3 days ;D

Just plug in your average charging rate and mAh of the battery.

Offline Soeren

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Re: Solar cell battery charging
« Reply #11 on: January 27, 2009, 09:55:28 AM »
Hi,

You mentioned a battery of "6v 2300 mah AA".

You have a charging loss of around 30..35%, so to charge in 2 hours you would need a charging current of ~1.7A  AND a fast charge dU/dt controller with timer and temperature control with thermo-sensors mounted on the cells as well) as I assume that we're talking about 4 NiMH cells.

Your voltage should then be at least 5.8V (assuming 4 cells) plus something to account for voltage drops (which will depend on your charge circuit topology).

Given that your 'bot can run for a day on less than 12W, it is quite clear that it won't be able to drag around a panel of more than 10W.


A charging station (solar or mains) that it returns and connects to when needed is a possible solution however, as I assume you'd want to keep it around your home, rather than let it just wander off to never return.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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