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From: Bob F <bobnospam@gmail.com>
Newsgroups: alt.home.repair,rec.autos.tech
Subject: Re: Solar car battery charger
Date: Mon, 18 Nov 2024 07:45:05 -0800
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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.
> 
> 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>
> 
> 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.
> 
> The specs on that RV pump are 12VDC, 4.65Amps, 8.0 Amps maximum.
> 
> 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).
> 
> All I need now is the solar panel setup. But I know nothing about solar.
> 
> I'm sure I need a panel and some way to control the battery charging.
> 
> What kind of panel do you think I need?
> And does it need some kind of control module to charge a car battery?

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.

Black polyethylene water pipe could make an excellent water heating coil.