Solar charging only on partially depleted Lead acid 12V battery.

[jack2964]

Can't find an appropriate place for this thread so I'll try here. Mods please move as fit.

I have a deep cycle EK brand thai made battery (12V lead-acid) which I use for my trolling motor on my boat. The batt is mounted inside a box with a 4 LED capacity indicator (Recharge-Half-Full)) and have never seen it go below 'Full'. Previously after each outing I put it straight on charge with a 'smart charger' and it takes about 12 hours plus to fully charge the batt but I have recently acquired an 18W solar charger with controller and I understand it only handles 'trickle' charging. My question is; say if the batt is partially drained e.g 3/4 capacity or less would the solar charger be capable of fully charging the batt. With the 'smart charger' I know it has both constant current and voltage modes and finally trickle charge to ensure batt longevity. So would the solar charger with just trickle mode suffice without compromising batt longevity? I am aware it would take few days of full on sun to fully recharge a partially depleted batt on solar cells.

[Crossy]

Your 18W panel will put about 1A into the battery in full sun, less if it's a bit cloudy.

What capacity (Ah) is the battery, most deep cycle batteries of 50Ah or more will take a 1A overcharge without damage, maybe a little gassing.

[gerry123]

with the solar panel you have is 17 watt ? but i would expect it is only pushing out about 3 amps

which would be as you say a trickle charge it should (depending on the controller) fully charge your battery to about 14 volts and then switch off automatically also some have the function of stopping feed back to the battery i suggest you use the internet to search the controller by name /brand there is a reasonably easy calculation with regard volts/amps/watts that with a little online research should give you all the correct gen

[RichCor]

Here are some 'pull quotes' from Yahoo Answers: Solar panel to charge a deep cycle battery?

Q. I have a 12 Volts, 125 AmpH deep cycle battery which I would like to charge using a solar panel. I am not looking for a trickle charge I actually need the solar to supplement and fully charge the battery from 50 percent or lower used state. What kind of 12V solar panel would I need for this job. I would like to charging to be completed in 24-48 hours if possible. I live in NorthEast of US with a south facing roof.

John W answered 3 years ago

Well, you'll need about 24 V to fast charge the batteries, you could probably get away with 15V for trickle charging or maybe 18 V. Lead Acid batteries are 50% efficient at charging and you're talking about trying to squeeze up to 1.5 kWh into the battery so if we assume that you want to do this during an 8 hour day, you would want 3 kWh / 8 h which is 375 W of 24 V panels. At the typical installed price of $10 per watt, that would be $3,750 of PV panels.

Can't do 24 hour charge cause the sun won't shine for 24 hours regardless of how nicely you ask it to.

You don't want to overcharge as that would just boil off hydrogen so you might want to wire up some FET's and zener diodes to cut off the charge when the battery reaches a certain voltage level.

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[jack2964]

My battery is rated at 65AH and like I mentioned earlier I've never seen it drop below the 'Full' LED indicator even after using it to inflate the boat and then hours on the lake.

And charge indicator on the solar charger/controller too shows 100% full after a trip on the water. I am a little doubtful on the accuracy of both these indicators but then this really isn't my concern.

What I am really after is since the solar charger hasn't the 'capabilites' (no constant I or V modes) of a smart charger would it then be detrimental to my battery if I depend solely on the solar charger alone?

btw, the solar cells is rated at 1A and controller is 10A.

[IMHO]

Solar chargers are designed to charge lead acid batteries, as that's what every solar system uses..... So I can't see what the problem is?

Do you have any brand/model info on the charger?

What leads you to believe it's not working right or not compat. with your lead acid battery?

[stubuzz]

There should be some lights on the charge controller. Mine starts to flash when it reaches its set cut off voltage-13.7, but at this voltage my battery never reaches 100% charged. I opened up the controller and tweaked the variable resistors. It now now cuts off at 14.1 and with such a low amperage, plus changing voltage from the sun/clouds, i haven't had any problems.

[Crossy]

To be quite honest, with such a big battery and such a small panel I wouldn't even bother with the controller.

Just use a 5A blocking diode between the panel and the battery (if the panel doesn't already have one), the overcharge rate won't even get the battery warm.

[jack2964]

Thanks for all the feedback guys.

Perhaps I haven't been clear enough what I am asking about.

Let me try again.

I did some reading up on lead-acid battery charging and chargers and the chemical reactions that go on during the charge/discharge cycles but I'd admit I do not fully grasp all I read.

With dedicated ac powered battery chargers a fixed sequence is programmed to ensure optimum charge by automatically switching between modes when the unit senses some threshold voltage/current. With solar chargers, I am unsure if they have these capabilities and if they don't then the correct charge process is not followed and batt life would be compromised?

[IMHO]

Thanks for all the feedback guys.

Perhaps I haven't been clear enough what I am asking about.

Let me try again.

I did some reading up on lead-acid battery charging and chargers and the chemical reactions that go on during the charge/discharge cycles but I'd admit I do not fully grasp all I read.

With dedicated ac powered battery chargers a fixed sequence is programmed to ensure optimum charge by automatically switching between modes when the unit senses some threshold voltage/current. With solar chargers, I am unsure if they have these capabilities and if they don't then the correct charge process is not followed and batt life would be compromised?

Again, if you can provide info on your solar charger, that might help.

Also again, I'm going to point out that the sole purpose of a solar charger is to charge lead acid batteries - so unless you have reason to believe it's junk or defective, there's no reason to suspect it's not doing a good job of maintaining battery health

[stubuzz]

Adding a diode will rob about 1v and a 20w panel will never charge a large storage battery. I have a mobile 80w array, and charge controller, that would not bring a 35ah battery over 75% full in 3 days of summer sun.

A cheap charge controller and 20w panel will not replace a dedicated 3-4 stage smart charger. The battery life will be compromised and sulfation will build up if it is not kept near 100% charged.

Here is some interesting reading.http://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html

http://www.batterystuff.com/kb/articles/solar-articles/solar-info.html

[Pacificperson]

Do some simple math. Your 12V battery is rated at 65 amp-hours. This is 780 watt-hours. At a rate of roughly 1.5 amps, your 18 watt solar panel will produce 108 watt-hours in six hours of full sun. It will take 7-8 sunny days to recharge you battery, if it is drained. At these rates of charge, you are not going to hurt your battery, but if you fish more than 2 or 3 times a month, you are going to need your original charger.

[jack2964]

I think I'll continue to use the 'smart charger' after each outing to fully recharge the batt overnight and then use the solar charger to maintain a full charge in between outings which can be many days or weeks apart.