Battery Charging Question

[Maine Sail]

I am a degreed Electronic Engineer (radar,sonar,comm) and that is my interpretation of this issue. I taught electronics (including solar) at Butte college for many years. Chief

I am a marine electrician and the guy that gets to replace the cooked batteries because people read and believed what they heard on the internet........

Did you watch the video? Many of the batteries in my shop right now only need hundredths of an amp to maintain a float voltage. Any more than that and the voltage begins to climb to gassing levels. That is real world battery acceptance when the batteries are full.

Over charging won't happen over-night with small panels, or even in a week, but when left unattended for weeks or months it can happen and does happen. People forget and things happen. People also read on the internet that a panel of 10% of Ah capacity or less can not over charge a battery. This "truth" becomes and non-truth if left unattended for long periods with no loads. It is true in the short term or when the batteries are being actively used.

When I show up and see a controller-less panel and a battery at nearly 15V and nearly bone dry well, I generally suggest a new battery and to add a controller. Simple controllers cost less than a new battery....

I have had about half a dozen or so banks/batteries cooked by unregulated solar panels and all of them were in the +/-10% of Ah capacity range and all of them left to sit with no loads for extended periods..

 

[Chief RA]

Maine Sail: My objective is to assist not argue the merits. You would not want to hear my qualifications! Chief

 

[Maine Sail]

Maine Sail: My objective is to assist not argue the merits. You would not want to hear my qualifications! Chief

Your qualifications nor mine are really relevant.. I work in the real world and see real fried batteries due to unregulated solar panels. For years we heard from all sorts of "qualified" people about how a locked prop causes less drag than a spinning one....

I will stand by real world observations that a 12W panel can eventually raise the voltage of a group 24 battery to a point where it can damage the battery. Are you suggesting this can't happen?

I will also stand by my statement that any panel worth having, that can actually do anything in a reasonable time frame, should have a controller, if it is to be left unattended.

 

[Ward H]

Interesting. FWIW, The 6 watt and 12 watt Ganz flex panels being offered by Jamestown distributors have a fuse and diode installed in the 10 leads. The diodes are to prevent the battery from draining back through the panel at night., so the tech info says. That is why I considered one of the panels.

Main and Brian especially explained the need for a controller in a way I understood.

So my current plan (Pun intended) is to buy the Senasun controller and 12 watt panel.

More than I was planning to spend so I may wait a few weeks to see how the battery holds up charge wise, under the OB charging only.

 

[Chief RA]

I can't believe all this! Can't anyone calculate that the battery will be charging at 1/400th of it's total amp/hours?!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I quit, you guys can't be helped! Chief

 

[Maine Sail]

I can't believe all this! Can't anyone calculate that the battery will be charging at 1/400th of it's total amp/hours?!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I quit, you guys can't be helped! Chief

1/400th of an 80Ah bank is .2A. A 12 watt panel is capable of more than double that in good conditions. Even if we figured .5A this is 1/160th of the Ah capacity....


When fully charged....

1/800th of the Ah capacity of the 160Ah bank in the video pushes it to 14.4V.....

1/266th of the Ah capacity of the 160Ah bank in the video pushes it to 14.9V.....

1/160th of the Ah capacity of the 160Ah bank in the video pushes it to 15.2V.....


On my bench today is a 7 year old, well cared for, 125Ah deep cycle group 31 12V battery.

When fully charged...

1/1250 of the Ah capacity pushes it to 14.4V

1/625 of the Ah capacity pushes it to 14.7V

1/312 of the Ah capacity pushes it to 15.0V

 

[FourPoints]

with a quality MPPT controller, a 12w panel will output in excess of .75A in good sun. It will in theory output up to 1A, but that's peak, and won't do that for long as it will drop output as it heats up from the sun.

I use .75A/hr as my assumed recharge rate with my Ganz 12w + GV4 controller, and find that it seems to often exceed that in good weather, although my calculations are pretty rough since I don't have a battery monitor or ammeter.

Given the fact I am at (temperature compensated) float stage on the controller 85% of the time I get down to the boat, it is blatantly clear that the controller is absolutely necessary, or I would certainly have fried my batteries by now.

 

[Maine Sail]

with a quality MPPT controller, a 12w panel will output in excess of .75A in good sun. It will in theory output up to 1A, but that's peak, and won't do that for long as it will drop output as it heats up from the sun.

I use .75A/hr as my assumed recharge rate with my Ganz 12w + GV4 controller, and find that it seems to often exceed that in good weather, although my calculations are pretty rough since I don't have a battery monitor or ammeter.

Given the fact I am at (temperature compensated) float stage on the controller 85% of the time I get down to the boat, it is blatantly clear that the controller is absolutely necessary, or I would certainly have fried my batteries by now.

12W Solar panel vs. a 220Ah AGM bank and a 125 Ah deep cycle group 31 flooded battery..