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 0.2A 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 often misguided and 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, in wattage, or 1.5% of capacity in amperage 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 voltage 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 in wattage, and can certainly over-charge with 1.5% of "C" in panel amperage. When they eventually get to "full" they will have the voltage pushed well beyond the safe zone or where it 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 on, as is the case with many boats, you can over charge your batteries if you are not careful.
It has happened to a few of my customers, most recently a bass boat owner whom I installed a fish finder for. He toasted a very expensive battery set....
The West Marine Advisor states: (The quote below is as of 8/11/2012 they will likely change that statement when they realize they were giving potentially destructive information.)
*West Advisor is suggesting that approx 25% in watts/Ah capacity is safe:cussing:
*They are also saying that unless you have two or more large panels connected to your batteries you will be safe without a controller
What is "large"? Who defines that?
While the difference from 0.2A, what the battery bank above 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 gas off. It can also cause positive plate erosion inside the battery.
The general guidelines are sometimes stated that a panel wattage of 10% of capacity "C" 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. Of course the "suggestions" for controller-less solar are all over the map so who is to know what to believe.
West Marine = 1.5% in current of the 20 hour rate
Calder = 0.5% in current of the 20 hour rate
Casey = 0.3% in current of the 20 hour rate
Everywhere you turn on the net there are formula's for controller-less solar. They rarely if ever agree.. Who are you to believe? West Marine? Calder? Casey? Norther Arizona Wind Sun etc. etc. etc.........?
These are but two more examples, from actual solar distributors:
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..
I made a video seeing is this is much easier to see than to explain..
EDIT July 16th 2013: I finally had the opportunity to set this up with a small 12W panel and two banks. Both banks were charged with regulated solar until full then the controller was removed. Panel was left flat, not angled towards the sun, just like it would be on a boat. This did not happen over night but the small 12W panel eventually brought both banks over 15V!!! This panel is 10% of the 125Ah bank in watts and only 5.5% of the 220Ah bank in wattage..
Bank #1 220Ah Lifeline AGM's
Bank #2 125 Ah Marine Maxx Group 31 Flooded Lead Acid
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 0.2A 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 often misguided and 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, in wattage, or 1.5% of capacity in amperage 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 voltage 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 in wattage, and can certainly over-charge with 1.5% of "C" in panel amperage. When they eventually get to "full" they will have the voltage pushed well beyond the safe zone or where it 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 on, as is the case with many boats, you can over charge your batteries if you are not careful.
It has happened to a few of my customers, most recently a bass boat owner whom I installed a fish finder for. He toasted a very expensive battery set....
The West Marine Advisor states: (The quote below is as of 8/11/2012 they will likely change that statement when they realize they were giving potentially destructive information.)
If we translate that advice to watts:West Marine Advisor said:
*West Advisor is suggesting that approx 25% in watts/Ah capacity is safe:cussing:
*They are also saying that unless you have two or more large panels connected to your batteries you will be safe without a controller
What is "large"? Who defines that?While the difference from 0.2A, what the battery bank above 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 gas off. It can also cause positive plate erosion inside the battery.
The general guidelines are sometimes stated that a panel wattage of 10% of capacity "C" 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. Of course the "suggestions" for controller-less solar are all over the map so who is to know what to believe.
West Marine = 1.5% in current of the 20 hour rate
Calder = 0.5% in current of the 20 hour rate
Casey = 0.3% in current of the 20 hour rate
Everywhere you turn on the net there are formula's for controller-less solar. They rarely if ever agree.. Who are you to believe? West Marine? Calder? Casey? Norther Arizona Wind Sun etc. etc. etc.........?
These are but two more examples, from actual solar distributors:
Not a single qualifier other than a panels of 15W or less don't need a controller......Sunshine Solar said:
Photonic Universe said:
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..
I made a video seeing is this is much easier to see than to explain..
EDIT July 16th 2013: I finally had the opportunity to set this up with a small 12W panel and two banks. Both banks were charged with regulated solar until full then the controller was removed. Panel was left flat, not angled towards the sun, just like it would be on a boat. This did not happen over night but the small 12W panel eventually brought both banks over 15V!!! This panel is 10% of the 125Ah bank in watts and only 5.5% of the 220Ah bank in wattage..
Bank #1 220Ah Lifeline AGM's
Bank #2 125 Ah Marine Maxx Group 31 Flooded Lead Acid
