Solar for keeping batteries topped off.

pianotuna wrote:
Hi westend,

Actually irreversible plate shedding happens on the positive plate for each and every cycle. The negative plate "loss" is replaced during the charging process.

If the negative plate is "hard" sulphated then high voltage may "blast" that material off the plate, but that is what we hope to avoid by charging at ideal voltages. The material may drop to the bottom of the battery.

Higher temperatures, increased specific gravity, and higher voltage all contribute to the speed of the reaction and increase positive plate shedding.

westend wrote:
There is also plate shedding where the negative plate of the battery looses material from the plate. This is an ongoing process as the battery ages. The electrolyte is causing the material to dissolve. Raising voltages causes this to happen faster. A short duration of higher voltages like the 14.5V delivered by a vehicle alternator after starting the motor is not going to harm the battery as it is trying to recover from the large draw that was but upon it to turn the starter.

Thanks Don, a senior moment on my part. I'll fix my post.

Thanks West and Don for your explanation of the chemical process. As an "average Joe user" that dry camps 95 percent of the time wth an old MH I just use a 40 amp B&D charger to recharge my 2 6v GC batteries then float the batteries for a couple of days with my Magnatec charger that charges at 13.2 v then disconnect until I go camping again. When ready to camp again I will float a couple of more days and repeat the process. I find that a few days charging with the Magnetec after the smart charger says full will add a few days of dry camping before batteries reach 50 percent SOC. For longer storage I recharge after a 5 percent drop. I always thought that shallower discharges would cause less plate shedding and that constant charging even at a low voltage causes a small amount of shedding. I guess there is a fine line between shedding and sulfation.

Hi westend,

Actually irreversible plate shedding happens on the positive plate for each and every cycle. The negative plate "loss" is replaced during the charging process.

If the negative plate is "hard" sulphated then high voltage may "blast" that material off the plate, but that is what we hope to avoid by charging at ideal voltages. The material may drop to the bottom of the battery.

Higher temperatures, increased specific gravity, and higher voltage all contribute to the speed of the reaction and increase positive plate shedding.

westend wrote:
There is also plate shedding where the negative plate of the battery looses material from the plate. This is an ongoing process as the battery ages. The electrolyte is causing the material to dissolve. Raising voltages causes this to happen faster. A short duration of higher voltages like the 14.5V delivered by a vehicle alternator after starting the motor is not going to harm the battery as it is trying to recover from the large draw that was but upon it to turn the starter.

Gjac wrote:

pianotuna wrote:
Keep the voltage as high as possible without reaching the gassing voltage. If you are getting one bubble per second you are at the gassing voltage.

That sounds like a good rule of thumb, but isn't the chemical reaction still taking place at lets say 13.2v without gassing and if so isn't there some plate loss?

At 13.2 V there should be no sulfate building on plate surfaces since that voltage is still returning sulfate back into the electrolyte. A bit higher voltage, as referenced in the previous post, allows that to happen more efficiently.
I'd say, in a broad sense, that any voltage above 12.8 V ******* sulfation onto plates but in some batteries that may be occurring around some plate surfaces. Not all are built the same. A float voltage, as Pianotuna states, just below an excessive gassing point, is probably desirable. FWIW, I have my float voltage on the solar controller set at 13.6 V for two GC2 6v's. In the Winter, that will rise to 13.8 V, observable. I live in Southern MN where temps are low during the Winter.

There is also plate shedding where the positive plate of the battery looses material from the plate. This is an ongoing process as the battery ages. The electrolyte is causing the material to dissolve. Raising voltages causes this to happen faster. A short duration of higher voltages like the 14.5V delivered by a vehicle alternator after starting the motor is not going to harm the battery as it is trying to recover from the large draw that was but upon it to turn the starter.

Charging the batteries continuously at that voltage in warm weather when the electrolyte is at full value is going to cause electrolyte to boil off and more plate shedding can occur. Charging at that higher voltage when electrolyte is at a lower specific gravity like when the battery has been discharged may be a good value, however.

A battery user should be aware that a lead acid battery does have a limited life. There is just so much material available in the battery and the chemical reaction, at some point, is going to stop. I'd like that to be as long in age as I can make it since buying batteries isn't one of my happy times. FWIW, I replaced my truck battery a couple of years ago. It was 10 yrs, one month old when that happened. I consider that extraordinary value since I made it work to power all the truck's electrical needs and the 2000 W (maximum of the two amplifiers) of sound system I have installed. I bought the same Motorcraft battery.

If I can get anywhere close to the truck's battery age of replacement with my RV batteries, I will consider the exercise of tweaking the solar controller and having temp compensation a good exercise.

pianotuna wrote:
Keep the voltage as high as possible without reaching the gassing voltage. If you are getting one bubble per second you are at the gassing voltage.

That sounds like a good rule of thumb, but isn't the chemical reaction still taking place at lets say 13.2v without gassing and if so isn't there some plate loss?

Keep the voltage as high as possible without reaching the gassing voltage. If you are getting one bubble per second you are at the gassing voltage.

westend wrote:

Sam Spade wrote:

Boon Docker wrote:
IMO temperature compensation is not really necessary.

I agree with that.

But regardless of the subject, it seems that there will always be "purists" in the crowd that insist that anything short of perfect is not acceptable. :)

I dunno'. The objective here is to keep charge into a electrochemical reaction, i.e. a battery. By controlling the rate of charge, you're controlling that chemical reaction. If the voltage is too high, electrolyte begins to boil off and plate shedding occurs. If it's too low, sulfation starts and can become hardened to limit the capacity. With a solar controller, it's a special situation since power is only available during the day.

I know my temp comp will swing about .5 V between seasons. There are more discussions about lesser converter voltage differences.

What voltage do you consider is too low that would cause sulfation?

westend wrote:

I know my temp comp will swing about .5 V between seasons. There are more discussions about lesser converter voltage differences.

I won't say directly what I think about those discussions but how about this:

Instead of paying 3X or more of the price of an perfectly adequate 3 stage converter to get one with all the bells and whistles.......how about spending 30 to 50 percent more to get AGM batteries instead.
They don't gas at all and sulphate very little unless you treat them REALLY bad.

I just think that the average Joe doesn't need all that fancy stuff and might indeed do more damage with it than good (converters with adjustable voltage).

JMHO, of course.

Sam Spade wrote:

Boon Docker wrote:
IMO temperature compensation is not really necessary.

I agree with that.

But regardless of the subject, it seems that there will always be "purists" in the crowd that insist that anything short of perfect is not acceptable. :)

I dunno'. The objective here is to keep charge into a electrochemical reaction, i.e. a battery. By controlling the rate of charge, you're controlling that chemical reaction. If the voltage is too high, electrolyte begins to boil off and plate shedding occurs. If it's too low, sulfation starts and can become hardened to limit the capacity. With a solar controller, it's a special situation since power is only available during the day.

I know my temp comp will swing about .5 V between seasons. There are more discussions about lesser converter voltage differences.

Boon Docker wrote:
IMO temperature compensation is not really necessary.

I agree with that.

But regardless of the subject, it seems that there will always be "purists" in the crowd that insist that anything short of perfect is not acceptable. :)