Flooded lead acid solar charging voltage

[sailorboy1]

All last year I had my solar controller set to 14.4V for absorption because that is what the manufacturer spec sheet said to do. I have the controller programed to 1 hour at absorption before going into float. This worked well far as I could tell. But it always seemed to me that the voltage under a 5 amp load and 95% SOC of 12.4V seemed lower than it should be (batteries seemed that way to when they were new).

Last week I decided to change the absorption to 14.6V and the batteries have to stay at that for 1 hour before the controller goes into float. Boy what a difference this appears to have made. Even though according to the controller history the system doesn't always go into float and that overall the daily amp-hours into the battery are about the same, I can tell from the voltage that the batteries are really charged a lot better than before. Now at a 5 amp draw and 95% SOC the voltage is about 12.5+V. I noticed today that at 14.6V the batteries were still accepting 6 amps, which is about 1.5% of the 20Hour capacity.

I only post this as a note that it may be worth while to vary your charge voltages a little to see how this effects your batteries (and I'm not saying jack up the voltage really high and boil them out all the time).

I'm also not saying to obsess over the stupid cheap pieces of lead with acid in them that rule your boat life.

[FlyingCloud1937]

The stupid pieces of lead don't rule the boat.

The need for electrons when not plugged into shore is what rules the boat.

That dumb lead is the key to life aboard when not plugged in. So it makes sense to design and maintain your electron storing, distribution, and producing system as efficiently as it can be.

It also make sense to manage the charge and discharge profile to be as efficient as possible. This will increase battery life and lower overall costs.

Not to mention make life aboard as good as it can get.

QUIT thinking they are just dumb worthless pieces of lead, and start thinking of them as you would your partner or wife, and treat the same

You will then have a happy life.

Lloyd

Originally Posted by sailorboy1

All last year I had my solar controller set to 14.4V for absorption because that is what the manufacturer spec sheet said to do. I have the controller programed to 1 hour at absorption before going into float. This worked well far as I could tell. But it always seemed to me that the voltage under a 5 amp load and 95% SOC of 12.4V seemed lower than it should be (batteries seemed that way to when they were new).

Last week I decided to change the absorption to 14.6V and the batteries have to stay at that for 1 hour before the controller goes into float. Boy what a difference this appears to have made. Even though according to the controller history the system doesn't always go into float and that overall the daily amp-hours into the battery are about the same, I can tell from the voltage that the batteries are really charged a lot better than before. Now at a 5 amp draw and 95% SOC the voltage is about 12.5+V. I noticed today that at 14.6V the batteries were still accepting 6 amps, which is about 1.5% of the 20Hour capacity.

I only post this as a note that it may be worth while to vary your charge voltages a little to see how this effects your batteries (and I'm not saying jack up the voltage really high and boil them out all the time).

I'm also not saying to obsess over the stupid cheap pieces of lead with acid in them that rule your boat life.

[sailorboy1]

Originally Posted by FlyingCloud1937

QUIT thinking they are just dumb worthless pieces of lead, and start thinking of them as you would your partner or wife, and treat the same

never said they were worthless, but you may need relationship help

[Ex-Calif]

Originally Posted by sailorboy1

never said they were worthless, but you may need relationship help

My wife left me and took the batteries from the boat. Sure am gonna miss those batteries.

You know you are in trouble when your battery bank "unfriends" you on facebook...

[colemj]

The only important manufacturer spec to follow is that from your battery manufacturer, not the solar controller.

Trojan recommends 14.8V absorption voltage for their FLA's. One hour at absorption seems kind of short to me unless those batteries are rarely discharged much.

Mark

[noelex 77]

I would normally recommend following the battery manufacturers advice (don't forget the temperature compensation) but 14.4v is on the low side and 1hr absorption time is short.

Is it possible to increase the absorption time on your controller?

A good guide to check if the absorption time is right is to look at the battery return amps (this is the current actually going into the batteries. So production -load) just before the transition between absorption and float. A figure of 2% of the AHr capacity is often used (so 10A for a 500 AHr bank). However I feel this is a bit high and around 1.5% is better.
If the absorption cycle is ending when more current is still entering the batteries the absorption duration is too short. You need to monitor a few typical cycles.

I think a longer absorption time would produce the same effect and stay within the battery manufacturers recommendations.

Many more lead acid batteries die from undercharging and if keep the water up there is not much damage from overcharging, so I think what you are doing is reasonable, but an absorption of say 14.5 v for 2 hrs may be a better solution.

Don't forget to check the voltage at the actual batteries with a multimeter that is accurate. Many of the controllers do not have an accurate voltage measurement and there is no allowance for voltage drop in the wiring between the controller and batteries. Even 0.1v does make a difference to charge current the batteries will accept, so these factors can be significant.

It is the genuine voltage at the batteries not the voltage on display at the controller that is important.

[sailorboy1]

At the 14.4V I was normally seeing less than 1.5% going into the batteries and that was when the voltage first got to the 14.4 so I was figuring that the batteries were pretty well charge. And I have the controller programmed to compensate for the actual voltage at the battery.

But like I said the increase to 14.6V seems to have really made a positive difference.

[Maine Sail]

Originally Posted by sailorboy1

At the 14.4V I was normally seeing less than 1.5% going into the batteries and that was when the voltage first got to the 14.4 so I was figuring that the batteries were pretty well charge. And I have the controller programmed to compensate for the actual voltage at the battery.

But like I said the increase to 14.6V seems to have really made a positive difference.

This could more likely be due to your limited availability of charge current from solar mixed with system loads.. With a low current source like solar the bank may not even get to 14.4V until it is in the high 90% SOC range. 1 hour may be enough, but often not.

Best to double check your net accepted current with the alt...... Turn off solar & loads, fire up alt and measure current and voltage. Current should be less than 1.5% and voltage should be 14.4V +....

Using solar to determine net accepted current can be very deceiving.

How do you program for voltage drop compenasation at the batteries without dedicated voltage sensing? If you have it set for 14.4V when the batteries get full the terminal voltage at the batts should still be pretty close to 14.4V.. When the controller is moving a lot of current then there will still be voltage drop. You can't program around voltage drop by adjusting voltage settings, you'd need dedicated voltage sensing leads that don't carry any current in order to do that, and most controllers simply don't offer this, so the largest wires you can fit from the controller to the batts is the only resonable option.

[sailorboy1]

I have found that the voltage at the batteries with the solar doesn't get even get to 14.4V till the SOC is around close to 100% and amp-hr by the battery monitor are pretty much 0. By that time the acceptance has gone from around 15 amps to just about 5 amps.

I watched the alternator when the engine was running and at the same SOC and voltage the acceptance was pretty much the same as what the solar would put in if sunny and no shading. So the acceptance suggests the same battery condition (I'm going to have to increase the alternator settings now).

I compensated the voltage by measuring the difference between the battery and what the controller was putting out and programing that into the solar controller, which then adds that to the program. So a 14.6V absorption setpoint becomes 14.7V at the controller. I have a 6awg wire from the controller to the batteries, not much drop there and if there are no loads running the solar and battery voltage become the same.

I'm not looking for any fix, just making the observation that the new higher voltage is resulting in a much better charge to the batteries. I noticed that at 14.6V yesterday with the solar that the batteries were still accepting 6-7 amps instead of 2-3amps at the old 14.4V setting.

Time will tell.

[Maine Sail]

Originally Posted by sailorboy1

I have found that the voltage at the batteries with the solar doesn't get even get to 14.4V till the SOC is around close to 100% and amp-hr by the battery monitor are pretty much 0. By that time the acceptance has gone from around 15 amps to just about 5 amps.

I watched the alternator when the engine was running and at the same SOC and voltage the acceptance was pretty much the same as what the solar would put in if sunny and no shading. So the acceptance suggests the same battery condition (I'm going to have to increase the alternator settings now).

I compensated the voltage by measuring the difference between the battery and what the controller was putting out and programing that into the solar controller, which then adds that to the program. So a 14.6V absorption setpoint becomes 14.7V at the controller. I have a 6awg wire from the controller to the batteries, not much drop there and if there are no loads running the solar and battery voltage become the same.

I'm not looking for any fix, just making the observation that the new higher voltage is resulting in a much better charge to the batteries. I noticed that at 14.6V yesterday with the solar that the batteries were still accepting 6-7 amps instead of 2-3amps at the old 14.4V setting.

Time will tell.

Voltage is your pressure and at 14.6V you will certainly get more current into the batteries. Higher charging voltages make pretty big improvements in most serviceable FLA batteries. How big is the bank? If set at 14.7V then the battery will too eventually get to 14.7V if the absorption time is long enough.

Don't count on the SOC and Ah counting by the battery monitor in terms of using it for any level of accuracy.. Just go by net accepted current, and voltage at that current, and you can much more easily determine when "full" is... Keeping Ah counters that accurate is extremely difficult and time consuming.

In odder to get them accurate these are the important ones:

*They need to know actual physical 20 hour capacity which is never the same as the factory rating for very long and is constantly changing. Many flooded batteries do not even achieve their full rating for 20-50 cycles...

*The need to know the Peukerts exponent which is also changing with age.

*They need to know the actual battery temp. Most monitors don't even have a temp sensor option just a guess range.

*You need to know your Coulombic efficiency, which is also constantly changing.


They are great informational tools, but not for pin point accuracy unless you really devote a lot of time to it....

[ranger58sb]

SB, don't know how big your bank is, but FWIW we charge at 14.8 bulk and then 4 hours of absorption also at 14.8. This per battery manufacturer's recommendation for each a bank of three Group 31s (and given what our charger will do).

-Chris

[sailorboy1]

My bank is 460Ah and it is getting fully charged. How do I know or what makes me think so; well the specific gravity says it is charged and when the sun goes down and the bank is 98% SOC with a 5 amp draw the voltage is still 12.6V.

I don't see any need to increase the time at absorption beyond the 1 hour (that is an hour after there is only 1.5% AH capacity even going into the batteries). I'm interested in charging the batteries, not becoming a battery waterboy.

The point of the thread was to tell others that maybe when charging with solar that a voltage higher than the manufacturer suggests is worth checking out.

[colemj]

Originally Posted by sailorboy1

The point of the thread was to tell others that maybe when charging with solar that a voltage higher than the manufacturer suggests is worth checking out.

For clarity, are you talking about the controller manufacturer or the battery manufacturer?

Mark

[sailorboy1]

Originally Posted by colemj

For clarity, are you talking about the controller manufacturer or the battery manufacturer?

Mark

The battery manufacturer, but the same thought applies to controller/regulators that have some set voltage profile standard. I found last year that the factory Flooded battery program for my regulator didn't really charge at higher enough voltage (I have a new one and now need to adjust it some also as it went into float the other when the battery still wasn't fully charged).

[ranger58sb]

Originally Posted by sailorboy1

My bank is 460Ah and it is getting fully charged. How do I know or what makes me think so; well the specific gravity says it is charged and when the sun goes down and the bank is 98% SOC with a 5 amp draw the voltage is still 12.6V.

I don't see any need to increase the time at absorption beyond the 1 hour (that is an hour after there is only 1.5% AH capacity even going into the batteries). I'm interested in charging the batteries, not becoming a battery waterboy.

The point of the thread was to tell others that maybe when charging with solar that a voltage higher than the manufacturer suggests is worth checking out.

Just offering another data point. Not debating or advocating for any specific course of action.

-Chris