Re: Solar car battery charger

On 11/18/2024 8:21 PM, Xeno wrote:

On 19/11/2024 8:32 am, AMuzi wrote:

On 11/18/2024 9:45 AM, Bob F wrote:

On 11/3/2024 8:58 PM, Charlie wrote:

I have a project I've been wanting to create for years which is a solar spa
where the entire setup runs off the grid completely. No 120VAC is desired.
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I already have an RV pump which pumps water from the spa back to the spa
(after running it through a long black hose of probably hundreds of feet).
<https://www.amazon.com/dp/B0DF7B1VYD>
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I tested that pump today on an old battery and it seems to be working.
a. It pulls water out of the spa via a garden hose on the pump input.
b. And it puts it back via a garden hose on the pump output into the spa.
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The specs on that RV pump are 12VDC, 4.65Amps, 8.0 Amps maximum.
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I have three spare car batteries (which probably aren't in the greatest of
shape as they're old batteries which friends discarded & gave to me).
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All I need now is the solar panel setup. But I know nothing about solar.
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I'm sure I need a panel and some way to control the battery charging.
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What kind of panel do you think I need?
And does it need some kind of control module to charge a car battery?

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You might not need a pump. If the heat collection coil is placed low relative to the top of the spa with the water from the spa taken out at the bottom and the water going back to the spa going in near the top, the hot water from the heat coil will rise to flow back just from the heated water rising into the spa. The more heat it collects, the more water flow it will have.
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Black polyethylene water pipe could make an excellent water heating coil.

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+1
Very much like a Model T Ford water system
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The Model T system is known as a *thermo-siphon*. The *fill point* is at the top of the radiator which is also the highest point in the system. All points lower in the system are sealed.
 A low point in a spa, the water surface in the spa itself, will not be sealed. That means, in order for it to work as a siphon, thermo or otherwise, you will need a means of bleeding the air from the pipes on the roof. Then you will likely have another problem, the circulation will be slow if not pump assisted so the water in the roof pipes is likely to boil creating a gas barrier (steam) which will prevent the thermo-siphon effect from working.
 I have a solar hot water system on my roof which takes water from the tank at ground level and sends it around the solar collector on the roof then back to the tank. It has a small pump at the tank just for circulation, the thermo-siphon effect being insufficient to provide adequate water flow. The circulation pump only consumes a few watts of power @ 230 Volts.
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Obviously a convection circulation system requires the heated water to go up from the heat source. Hot water weighs less than cold water /volume so it rises.