On Fri, 15 Nov 2024 20:39:11 -0700, Charlie wrote:

> Do you think this 10 Watt (claimed) solar panel can charge a car
> battery?
> https://www.amazon.com/dp/B0DG5J98YH
>
> It (says it) supports 12 volts.
>
> The goal is a DIY science project but it has to work to do the job.

I doubt it. It says it has a switch for 6, 9, or 12 volts which makes me
think it has adjustable voltage regulator similar to

https://www.sparkfun.com/products/527

to be compatible with AAs, Ds, or whatever the game camera uses, A charged
car battery is around 12.6V and the charging circuit is 14-14.5.

https://www.amazon.com/dp/B07N2PR267/

is designed to maintain car batteries and has some overcharge circuitry
but doesn't limit out at 12 V. It's similar to the plug in battery
maintainers that I use to keep the bike batteries healthy over the winter.

Now for the bad news. How many watt-hours is your science project going to
require, In other words how many watts does it require, and how long are
you going to run it per day? Then consider the solar panel. The 10W
rating assumes full sunlight. Even on a sunny day in southern AZ, unless
you have a tracker, if you graphed the output you'd get a nice curve
maxxing out when the panel is perpendicular to the sun, building up in the
morning and declining in the afternoon. You won't see full output on
overcast days and obviously nothing at night.

https://www.radarsign.com/

Those are popular here and are on trailers so they can move them to
different locations, The trailer has a battery pack and a small solar
panel, I'd guess around 30W. It's been cloudy and rainy for the last few
days so the one I passed on my way home was barely functioning. If the
weather forecast is correct it will be dead pretty soon.

They work well in the summer but with shorter, darker days they struggle.
That's solar power in a nutshell. Without knowing further details of your
project my guess is you won't be happy.

On Sun, 17 Nov 2024 08:42:22 -0700, Charlie wrote:

> I'm trying to size the solar panel, where you're helping a lot, as I
> just realized only when I did the math above that I may need something
> like a 50 Watt panel for the smaller pump to run it real time.
>
> But don't I need a smaller panel if it's running off the battery?

There is no magic. The battery is a storage device. If you take 250 watt-
hours out, you need to put 250 watt-hours in, or more like 300 for
inefficiencies. You have to figure out how many hours of dependable sun
light you have, allowing for overcast days.

Think of a battery like a checking account. It doesn't matter when you
deposit money or when the checks clear as long as there is as much or more
going in than out. Erring on the high side is better. Say you have three
or four overcast days where you're not putting much in. That will
discharge the battery.

Car batteries are designed mostly for cranking amps and do not like being
deeply discharged and recharged. RV or 'deep-cycle' batteries are designed
for that use.

https://en.wikipedia.org/wiki/Deep-cycle_battery

RV batteries are a compromise:

https://www.interstatebatteries.com/recreation-vehicles/rv-batteries/deep-
cycle

The gold standard for solar systems are golf cart or forklift batteries.
They are heavy, expensive, and what you find locally may be 6V so you need
two.

I'm leaving out lithium ion batteries, given your shoestring budget.