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Old 27-10-2021, 08:54   #1
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Wintering batteries

I want to keep up charge of my 5 lead acid batteries, each 100 Ah, and parallel wired over an unattended period of 6 months, by means of a 50 W solar panel and a dedicated control panel. Without any other connections. Eventually before each battery a diode mounted, to overcome eventual voltage loss of unexpected battery failure. Any ideas? max voltage set to about 13,6 V. What do you think about this set up . And which controller would be ideal?
Thanks for your input.
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Old 27-10-2021, 13:41   #2
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Re: Wintering batteries

At a temperature of 80 degrees F. a lead acid battery will self-discharge at a rate of approximately 4% a week.
A battery with a 125-amp hour rating would self-discharge at a rate of approximately five amps per week, so you can just let your 50Watt panel run, unregulated.
It won’t even keep up with the self discharge of 5 x 100AH batteries.
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Old 27-10-2021, 13:54   #3
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Re: Wintering batteries

i wouldn't run any solar panel without a controller. Here's why:


Solar Systems: Selection, Installation & Controllers by Maine Sail SUPERB

http://www.pbase.com/mainecruising/solar_panel

Do I Need a Controller for Solar?

http://forums.catalina.sailboatowner...d.php?t=144557


I had my 400ah house bank connected to a small 11 watt solar panel with a $22 solar controller from June 20 to August 5, 2016 when I was away from my boat due to a move. Things were fine when I returned.


An unregulated panel will introduce too high a voltage to any battery.
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Old 27-10-2021, 16:02   #4
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Re: Wintering batteries

Quote:
Originally Posted by Stu Jackson View Post
i wouldn't run any solar panel without a controller.

An unregulated panel will introduce too high a voltage to any battery.
Actually it won't as long as the right size panel is selected.

You do understand it gets dark at night right? Even earlier in Winter. Plus in most places the angle of the Sun is much lower that time of year.

I had a 15 watt panel hooked up to my two 12 volt batteries that were in parallel for a couple years unregulated, and they were fine.

Later I bought a 65 watt panel, soldered on some 14 gauge wire and attached it to a cheap controller that held the voltage to a max of 14.4 volts. The batteries lasted 5 years, and one was a starter battery for the old diesel that was originally in my boat.

I still use unregulated panels when necessary and still have the 65 watt panel with the same 14 gauge wire charging my two 220 ah 6 volt Golf Cart batteries that are in series. Plus a few more panels on other PWM controllers.

But since the OP seems to want a controller, pretty much any of them will do even a cheap PWM set to around 13.2 volts Float.

https://www.amazon.com/Controller-Ba...62348230&psc=1
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Old 27-10-2021, 16:31   #5
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Re: Wintering batteries

I make sure mine are topped off with water, then fully charge. Disconnect hot side in mid November, reconnect mid April. They stay on the boat. The previous set of batteries lasted 8 years, and before that 10’years. Deep cycle lead acid, average winter temp 32F, with snow staying on ground typically mid January through early March.
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Old 27-10-2021, 16:39   #6
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Re: Wintering batteries

Quote:
Originally Posted by GordMay View Post
At a temperature of 80 degrees F. a lead acid battery will self-discharge at a rate of approximately 4% a week.
A battery with a 125-amp hour rating would self-discharge at a rate of approximately five amps per week, so you can just let your 50Watt panel run, unregulated.
It won’t even keep up with the self discharge of 5 x 100AH batteries.
You're smart, but I think you dropped a decimal. Check your math.


A 50W panel puts out about 20 Ah per day, or about 140 Ah/week in sunny weather. He will self-discharge about 25 Ah per week, but far less in the winter. An unregulated 50W panel would overcharge the batteries.

I think you were thinking of a 5W panel, which would charge about 14 Ah/week.


With a 50W panel you'll need a cheap controller. It's worth it.
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Old 27-10-2021, 16:40   #7
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Re: Wintering batteries

Thomm tends to have some interesting opinions. Not sure if I agree with this one.

Gord tends to be incredibly insightful, but I am not sure I agree with him on this one either. Using his 4% per week number and 500 Ah of batteries, you end up with 20 Ah per week, or 3 Ah per day, or 40Wh/day. Using the crude rule of thumb that says solar power puts out three times it's rated capacity per day, a 50 watt panel will put out 150 watts per day.

The OPs objective cries out for bottom line price solution. The 50 W panel is a good start. But a dirt cheap $20 PWM controller would round out the solution with no risk to his batteries.
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Old 27-10-2021, 16:52   #8
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Re: Wintering batteries

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Originally Posted by sailingharry View Post
Thomm tends to have some interesting opinions. Not sure if I agree with this one.

Gord tends to be incredibly insightful, but I am not sure I agree with him on this one either. Using his 4% per week number and 500 Ah of batteries, you end up with 20 Ah per week, or 3 Ah per day, or 40Wh/day. Using the crude rule of thumb that says solar power puts out three times it's rated capacity per day, a 50 watt panel will put out 150 watts per day.

The OPs objective cries out for bottom line price solution. The 50 W panel is a good start. But a dirt cheap $20 PWM controller would round out the solution with no risk to his batteries.
As I mentioned in my post except the controller I recommended was about $17.00.

Point being if you cannot do the math get the cheap controller.

These cheap PWM controller are fun to play with though. You can set the Float anywhere from like 13 volts up to 14.5 or so

Another thing to consider is the OP is talking Winter and in some places even this latitude the Sun quickly gets near below like 40 degrees as a noon high so with a Sunlight day that lasts only 9 hours or so of low Sunlight there isn't a lot to worry about with a small unregulated panel hooked up to five 100 ah batteries in parallel.
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Old 28-10-2021, 01:07   #9
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Re: Wintering batteries

Quote:
Originally Posted by thinwater View Post
You're smart, but I think you dropped a decimal. Check your math.

A 50W panel puts out about 20 Ah per day, or about 140 Ah/week in sunny weather. He will self-discharge about 25 Ah per week, but far less in the winter. An unregulated 50W panel would overcharge the batteries.

I think you were thinking of a 5W panel, which would charge about 14 Ah/week.

With a 50W panel you'll need a cheap controller. It's worth it.
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You're absolutely right and I'm wrong ...”
Thanks Thinwater, and also to Stu J. & sailingharry!
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Old 28-10-2021, 03:50   #10
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Re: Wintering batteries

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Originally Posted by Tetepare View Post
I make sure mine are topped off with water, then fully charge. Disconnect hot side in mid November, reconnect mid April. They stay on the boat. The previous set of batteries lasted 8 years, and before that 10’years. Deep cycle lead acid, average winter temp 32F, with snow staying on ground typically mid January through early March.
Totally agree.
I charge to 100%, top off with water & disconnect all wiring including any jumpers between batteries in the bank. They're usually around 70% SOC in the spring after sitting on the boat all winter up in Maine.
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Old 29-10-2021, 09:38   #11
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Re: Wintering batteries

Thanks for all your thoughts,
It all comes down to the self discharge of the 5 batteries of about 80 - 120 Ah/month, depending of age of the batteries, and location or avg temp. Therefore I calculate with 100 Ah/month. A Panel of 50 Wp, latt 38 degr North will result in 3 to 4 Amp during 5 hrs and have an efficiency of 30 % results in 5 Ah/day. Assuming 4 days p week are sunny. It will result in 20 Ah per week or 85 Ah per month. Adding the loss of a controller the 50 W panel which could be around 5 Ah, the recharge of the Solar could be 80 Ah. After february the days are getting longer and the solar amps will increase to about 100 Ah/month.
And I will surely install a controller, to be set at around 13,7 v taking into account the voltage loss of the diodes, which will be placed in the + lead from the battery.
The charge could be a factor two too high and to avoid any difficulties a 12 V timer could be installed to charge 2 weeks every month. Does this make sense?
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Old 29-10-2021, 09:48   #12
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Re: Wintering batteries

It's not the wattage it's the voltage. In one of the links to Maine Sail
s writeups, he mentions this, in bold (his bold, not mine):


REAL WORLD FACT:

Just 1.0A of current (same as a 15W solar panel) at 100% full on this 160Ah bank pushes the voltage beyond 15V !!!!!!


What is your entire bank worth compared to a $20 controller?


Your boat, your choice. But please: Don't say we didn't warn you.

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Old 29-10-2021, 10:00   #13
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Re: Wintering batteries

As I resume all your thoughts a continuous charging of a theoretical panel of 20 - 30 Wp could be the correct size. I doubt if a 20 to 30 Wp panel has not a worse efficiency of a 50 Wp panel?
I can use during my 4 months sailing In summer an additional 100Wp panel I will install a MPPT controller and gain also all advantages out of this set up. My sailing area is in the Eastern Med.
thanks again.
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