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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 11-29-2012
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Do I Need A Solar Charge Controller?

I get asked this question quite often and the answer is almost always a resounding, yes. There are always caveats to everything however..

In the video below I have two group 27 batteries, in parallel, consisting of 160 Ah's at the 20 hour rate. The batteries were recently equalized, specific gravity checked and tested. They are in excellent health for their age. Once equalized and fully charged they were left in float mode over night. Room temp in my shop was about 72F..

As you will see in the video below the current accepted or needed to maintain 14.4V is just 0.2A.

TWO TENTHS OF ONE AMP AT 100% FULL TO MAINTAIN 14.4 VOLTS !!!!!

Two tenths of an amp is all these batteries will take when full at 14.4V without over shooting 14.4V. They will remain taking this 0.02A for days or weeks at a time. With an accurate enough charger or power supply that can deliver mA current levels they will accept 0.02 - 0.08A continuously at 13.6V or float voltage. Most switch-mode chargers don't have the accuracy to do this so they "pulse" on and off when they get to currents below 0.2A or so. For older feroresonant chargers they begin pulsing on and off at much higher currents to maintain a voltage..

This "acceptance rate" is a far cry from the misguided and mostly incorrect information spread around the net that a "full battery will take 2% of its capacity". This information likely stems from resetting battery monitors when a bank is taking less than 2% of "C". It does not mean the battery is 100% full at 2% of capacity it just means that this is a "good enough" spot on a boat to call "full" for resetting a battery monitor.

There is also lots of information out there suggesting that a solar panel of 10% of capacity does not need a charge controller? yes, in many cases where batteries are used or cycled daily or even sometimes every third or fourth day this "unregulated charging" can work and can be a sort of "truth".

Conversely when batteries are left to sit for weeks at a time on a solar panel with no regulation it can become a dangerous situation to battery health and quickly becomes an "untruth"... With many boats they often sit for days or multiple weeks between use with all loads turned OFF. In these situations the batteries can still get to 100% full even with just a 10% of "C" panel. When they eventually get to "full" they will have the voltage pushed well beyond where it should be.

Having charged hundreds & hundreds of batteries and watched the "accepted current" at varying voltages these comments always made me cringe. The other day the question came up again and I decided to use my bench top power supply to illustrate this.

A diminutive 10W solar panel can produce about 0.59 -0.6A in good sun. 12V nominal panels have voltages from 16V to 18+V. So even with a small panel if the bank is left on charge for multiple days or weeks at a time, with no loads, as is the case with many boats, you can over charge your batteries if you are not careful. It has happened to a number of my customers most recently a bass boat owner whom I installed a fish finder for. He toasted a very expensive AGM battery....

While that difference from 0.2A, what the battery is willing to accept at 14.4V, to 0.59A, what a 10W panel is capable of, may not sound like much the difference between what the batteries actually need at FLOAT, 0.02A to 0.08A, can be quite a dramatic increase.

Remember a 10W panel can produce, about 0.6A, and this is actually a 637% increase in current from a float current of 0.08A that the batteries "accept" to maintain 13.6V. Unregulated, when the batteries approach full, will cause the voltage to rise and the electrolyte to boil off.

The general guidelines are usually stated that a panel of 10% of capacity or less would not need a controller. 10% of 160Ah would be a 16W panel but a 16W panel could produce nearly 1A of charge current even more than a 10W panel.


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 !!!!!!

Beyond just the potential to over charge your batteries, if left on charge long enough, a small panel like this won't recharge your batteries very quickly, but when it does, and does not have a controller, you could run a risk of over charge.

Something to think about anyway and if you do run unregulated please be careful.


I made a video seeing is this is much easier to see than to explain..

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Last edited by Maine Sail; 11-29-2012 at 01:24 PM.
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Old 11-29-2012
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Re: Do I Need A Solar Charge Controller?

Great information! Your posts are the definitive word!
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Old 11-30-2012
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Re: Do I Need A Solar Charge Controller?

What's the right number? 0.2 amps or 0.02 amps. Thanks.
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Re: Do I Need A Solar Charge Controller?

Quote:
Originally Posted by sstuller View Post
What's the right number? 0.2 amps or 0.02 amps. Thanks.
For this bank at "float" voltage 0.02A.


0.2A pushes the voltage to 14.4V which is too high for long term charging..
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Re: Do I Need A Solar Charge Controller?

SStuler,

I should have been more clear. A voltage regulated controller that limits the voltage would be best then you don't need to worry about the unregulated current...
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Re: Do I Need A Solar Charge Controller?

Does anyone make a charger controller that will take input from:
Solar, an unregulated alternator, a wind generator, and an AC-powered 12v power supply?

It seems that all the various bits of a standard 120v charger, a solar charge controller, a wind charger controller, and an alternator regulator are about 90% redundant of each other. How many four-stage multi-chemistry charging circuits do you need on a boat with two batteries?

I want to run one "supply line" from my external inputs and then one charge controller per bank. As I add more sources of juice (solar in 2013, wind later), I'd just wire them into the supply line and let the charge controllers do their thing.

Does anyone sell parts for this sort of setup? I've seen scholarly work(pdf) on driving MPPT controllers via AC/DC power supplies, but I want to buy something, not write a paper on it.
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Re: Do I Need A Solar Charge Controller?

Quote:
Originally Posted by eko_eko View Post
Does anyone make a charger controller that will take input from:
Solar, an unregulated alternator, a wind generator, and an AC-powered 12v power supply?
No they don't. I do know Sterling Power is working on one...

Quote:
Originally Posted by eko_eko View Post
It seems that all the various bits of a standard 120v charger, a solar charge controller, a wind charger controller, and an alternator regulator are about 90% redundant of each other. How many four-stage multi-chemistry charging circuits do you need on a boat with two batteries?
Some solar controllers can be used as wind controllers but they often do neither as well as standa alone units and are often big and expensive. Wind often needs a "dump zone" which solar does not..

Quote:
Originally Posted by eko_eko View Post
I want to run one "supply line" from my external inputs and then one charge controller per bank. As I add more sources of juice (solar in 2013, wind later), I'd just wire them into the supply line and let the charge controllers do their thing.
No need for one charge controller per bank. You will be better off to run all charge sources, wind, solar, alt & battery charger direct to the house bank then use a combining relay (ACR or VSR) or a battery to battery charger (B2B) such as an Echo Charger to top up the start/reserve battery bank.

The problem one wire for all sources is that each wire will be sized for the least voltage drop for the source supplying it. The alt may have 1/0 wire but the solar panels may have 10GA and wind perhaps 6GA and the battery charger possibly 4GA.. You then need to have over current protection for each wire at the "source" / battery or where it steps down. It is usually much easier to use a buss bar to collect all the charge sources close to the battery because the battery charger, alt, solar and wind often take different paths to get to the batteries.. You cna then fuse each wire at this location..

Quote:
Originally Posted by eko_eko View Post
Does anyone sell parts for this sort of setup? I've seen scholarly work(pdf) on driving MPPT controllers via AC/DC power supplies, but I want to buy something, not write a paper on it.
The problem with this is that in order for it to work it gets quite complicated and these units will be pricey. You also may not get all the features and control options you want or expect in a stand alone regulator, controller, wind controller or charger.

It would be nice if someone could build a Balmar MC 614/Outback MPPT/Sterling ProCharge Ultra and put them all together but it would not likely come out as good as the separates would and would still cost a lot of money to do so.....
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Last edited by Maine Sail; 12-03-2012 at 08:49 AM.
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