Solar car battery charger

Discussion:

(too old to reply)

Charlie

2024-11-04 04:58:11 UTC

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?

rbowman

2024-11-04 07:00:37 UTC

Permalink

Post by Charlie
What kind of panel do you think I need?
And does it need some kind of control module to charge a car battery?

You can cheap out and skip the control module if you keep an eye on the
voltage. A little overcharging probably won't hurt not the greatest
batteries. Just check the electrolyte levels and keep them up. Put a
blocking diode in series with the panel.

https://www.homemade-circuits.com/how-to-make-solar-battery-charger/

Some cheap circuits if you know anything about electronics. Solar panels
have a nice feature. They are current sources. Short them out and the
voltage goes to zero and the current limits to the short circuit current.
Obviously you want a blocking diode since shorting a lead acid battery
usually is a little dramatic.

Charlie

2024-11-16 03:39:11 UTC

Permalink

Post by rbowman

Post by Charlie
What kind of panel do you think I need?
And does it need some kind of control module to charge a car battery?

You can cheap out and skip the control module if you keep an eye on the
voltage. A little overcharging probably won't hurt not the greatest
batteries. Just check the electrolyte levels and keep them up. Put a
blocking diode in series with the panel.
https://www.homemade-circuits.com/how-to-make-solar-battery-charger/
Some cheap circuits if you know anything about electronics. Solar panels
have a nice feature. They are current sources. Short them out and the
voltage goes to zero and the current limits to the short circuit current.
Obviously you want a blocking diode since shorting a lead acid battery
usually is a little dramatic.

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.

rbowman

2024-11-16 05:00:59 UTC

Permalink

Post by Charlie
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.

Charlie

2024-11-17 15:42:22 UTC

Permalink

Post by rbowman

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

I've seen those simple potentiometer diagrams which show how to use that
LM137 as an adjustable power supply. My goal is to build a solar-powered
spa heater that slowly (or quickly - it doesn't matter the speed) pumps
water in the summer from the spa (which is roughly about four feet cubed)
through a few hundred feet of black hose back to the (now warmer) spa.

I'm thinking of three major components might be needed to accomplish that.
1. 12VDC water-transfer pump (of some sort - I have an RV pump now)
2. 12VDC car battery (I have three old ones - which will work for now)
3. Black garden hose (I have a few hundred feet of Continental Rubber hose)
4. Some way of charging the battery using sunlight as the source

My first problem is how to figure out what solar wattage I'll need.

Post by rbowman
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.

Oooh. I like it!
The Amazon description says it's a SUNER POWER 10W 12V Solar Battery
Charger (Bulk, Absorption, Float) Maintainer, Built-in Smart MPPT Max Power
Point Tracking Charge Controller, Adjustable Mount Bracket, Waterproof 10
Watt Solar Panel Kits for Car Automotive Boat Marine RV Trailer with a
floating charge voltage of 13.8VDC & an optimal-charge current of 0.56Amps
with a trickle-charge current of 0.2Amps & an overcharge-protection voltage
of 14.4VDC.

The connector type they show is what my RV pump uses. What's it called?
They called it an "SAE harness" in the picture on the Amazon listing.
https://www.amazon.com/dp/B07N2PR267/

I need to get one with alligator clamps to connect to the battery.
So I need to know the name.

In their diagram, the red is the female & the black is the male.
But on my pump, the red is the male and the black is the female.

Do you know what name to look up to get it with alligator clamps?
And what is the overcharge-protection voltage anyway?

Is that the highest that it will go before it limits its cutoff voltage?

Post by rbowman
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?

Dunno. My friend dropped off a second RV pump for me to try.
1st RV pump: https://www.amazon.com/dp/B0DF7B1VYD (4.6Amps, 8Amps max)
2nd RV pump: https://www.amazon.com/dp/B0CBLYJX63 (9Amps, 18Amps max)

That makes the 1st pump about 55 Watts & the 2nd about double that.
The old "Interstate Batteries, All Seasons" battery sticker on the top says
MT26, 625CCA, 655CA & RC85.

Do you think that car battery (let's assume if it was new) could run the
smaller pump for about five hours during the hottest part of the day?

Using 50 Watts and 100 Watts for simpler math, I think that means the
battery needs five times that in watt hours, or 250 to 500 Watt hours.

Does my quick calculation above sound about right?

Post by rbowman
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.

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?

Unfortunately both battery & panel have to work together during the day but
the battery can be charged all day while the pump only needs to run during
the late morning and early afternoon to get the hottest sunlight, right?

Post by rbowman
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.

Thanks for helping me run the calculations.

Do you think the car battery can run the motor long enough for the hottest
parts of the day? And do you think maybe a similar-sized 30 Watt solar
panel can charge it back if that solar panel charges for the entire day?

rbowman

2024-11-17 20:03:42 UTC

Permalink

Post by Charlie
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.

Scott Dorsey

2024-11-18 08:37:52 UTC

Permalink

Sure. The question is how fast it can charge.

Figure a cell that gives you 10W in full Arixona sun gives you about 1W on the
average in upstate New York given cloudy conditions and the sun often being
lower on the horizon. Figure nine hours a day of sun in December in New York.
How many amp-hours do you need?
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Carlos E.R.

2024-11-17 22:13:40 UTC

Permalink

Post by Charlie
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 don't need a battery: just run the pump directly from the solar
panel. If the solar panel doesn't generate electricity, it means there
is no sun, so no heating the water either.

You may need a voltage limiter, perhaps.

--
Cheers, Carlos.

Bob F

2024-11-18 15:45:05 UTC

Permalink

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.

AMuzi

2024-11-18 21:32:58 UTC

Permalink

Post by Bob F

Post by Charlie
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.

+1
Very much like a Model T Ford water system

--
Andrew Muzi
***@yellowjersey.org
Open every day since 1 April, 1971

Xeno

2024-11-19 04:21:00 UTC

Permalink

Post by AMuzi

Post by Bob F

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.

+1
Very much like a Model T Ford water system

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.

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

Bob F

2024-11-19 17:43:30 UTC

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.

+1
Very much like a Model T Ford water system

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

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.