Solar float mode: Necessary?

[Snowman9000]

As a practical matter, is float mode necessary with solar charging? As an alternative, the controller would simply stop charging when the battery was full. The next day the process would repeat.

Floating was developed to maintain batteries over weeks and months of continuous charging. Solar charging is not continuous, and the cycle restarts each (sunny) day.

I wonder if solar float mode is "because we can and the customer thinks they need it", rather than because it produces any real benefit.

Couldn't the extra watts put in at float voltage be instead put in at absorption voltage? Amps would be low; charge pulses would be short. Is there float in an automotive alternator charge?

[MEXICOWANDERER]

We Are Borg. Floating Is Futile.

HyGrometer: Moisture content

Two keys to the left, please.

Solar float means you had enough energy to fully recharge the battery bank. It is near Nirvana but not easy to achieve.

[azrving]

Harvey51 wrote:
I look forward to 20 years from now when charging will be controlled by a computer with inputs from a hygrometer built in to each battery, a clock, camera watching the clouds, weather report and perhaps brain implants in those who are thinking of using energy. When short of electric energy we will turn the darn thing off.

Total control is easy. They already have implantable chips.

[MEXICOWANDERER]

THE DAY AFTER CHRISTMAS

[Harvey51]

I look forward to 20 years from now when charging will be controlled by a computer with inputs from a hygrometer built in to each battery, a clock, camera watching the clouds, weather report and perhaps brain implants in those who are thinking of using energy. When short of electric energy we will turn the darn thing off.

[Ed_Gee]

Float charge is beneficial to a battery. Period. I do not understand why anyone would want to disable that portion of a charge controller function. It's not like you're paying for the sunlight that maintains the float charge. Disabling float charge would be analogous to turning off your house water at the city street connection everytime you did not need to turn on a faucet inside your home.

[BFL13]

smkettner wrote:
BFL.... how do you determine 'full' when battery is under some random load?
Must be unattended for proper use of RV. (IMHO)

Probably need a battery monitor connected to the controller.

This is the reason I frequently bring up what a benefit it is to have a controller with a variable absorption time. Still if the mark is missed it is better to remain in float vs off.

I got that now, you meant float is better than off while there is any sun at all.

I determine "full" by comparing my AH counter with my hydrometer reading "Baseline SG" . Once in a long while for the SG part as a cross-check of the AH counter. The AH counter needs a reset every so often--do it when at full by SG reading. there is no set and forget for all summer--you have to adapt to the weather.

Last summer we discussed how my batts were losing water in the long days at Vabs, so I had to drop to Float, trying 13.2v at first, but this was too low for also running loads so I made it 13.6v.

Which was noted as being what converters do too while camping on grid--do 13.6 instead of 13.2.

EDIT- BTW, I am reverting to "lurker status." Thanks everybody for all the help with my questions on how to keep the RV working right!

[time2roll]

BFL.... how do you determine 'full' when battery is under some random load?
Must be unattended for proper use of RV. (IMHO)

Probably need a battery monitor connected to the controller.

This is the reason I frequently bring up what a benefit it is to have a controller with a variable absorption time. Still if the mark is missed it is better to remain in float vs off.

[mlts22]

What might be ideal, as the SoC nears 100%, would be a desulfating mode, similar to my Battery Minders, which pulses a small charge, as opposed to a constant current. This is useful for keeping the batteries from boiling, and is helps keeps the battery plates usable.

[Snowman9000]

OK, I was taking artistic license. 🙂

[Almot]

Snowman9000 wrote:
As BFL is mentioning, is float mode stealing valuable electrons, preventing you from getting as fully charged as possible from solar?

I think what he said was that Float mode might not get you to Full on some days (after it had switched to Float at 90%), because it's getting dark soon. In other words, on some days it's better to extend the Bulk and/or Absorption longer because Float is too slow charging. Float mode can't "steal" anything, charging is charging.

[BFL13]

There is some confusion in scenarios here. I am saying you first need to get to "full" before you drop to "float" --unless there is enough daylight left that you will still get to "full" at float before dark.

If you will not get to "full" before dark at float, stay at Vabs longer so that you will get to "full"

Some days you can't get to full even if you stay at Vabs till dark. Some days you can't even get to Vabs before dark.

You have to play each day as it comes, with the object of getting the batts to full each day, or as high as they can get short of full.

[Almot]

BFL13 wrote:
IE it is more important to get to full than drop to float at 90% and never reach full that day.

It is all situational. Each "user" needs to keep an eye on what his situation is at the time and place and adapt. Having a Float option on the controller lets you adapt to more situations.

Yes, getting 100% is most important, and yes, it's situational. The more functionality and features controller has - the easier to make it work in one's particular situation.

My controller drops to Float only when the current drops to pre-determined adjustable value. Still not perfect, as there are often some loads running. But better than toys that have only one setpoint (that can be set as either Bulk or Float), so you have to be there and adjust it higher or lower or turn it on and off; or - all fixed setpoints, i.e. you can't adjust anything.

[Snowman9000]

So let's think about the algorithm at full charge w/o float. It could be like a battery charger. The battery is full, the charging stops. It should not be pushing unnecessary current at 14.4v and boiling the battery. The best way to view it would be that you take the charging profile of a 3 stage charge, lop off the right hand tail (float), and just stop at the end of absorption. I think some of you are imagining a 14.4v float. I'm imagining an actual or virtual stop.

It could either flat out stop the charge while remaining ready to provide current as needed, or it could idle with virtually no current, at 14.4v. I think the latter is the most common of the no float controllers.

As BFL is mentioning, is float mode stealing valuable electrons, preventing you from getting as fully charged as possible from solar? Of course, just lopping off the float would do the same. So if the battery is not truly charged 100%, why float? Why not keep absorbing, at a low current? This might be a sidetrack from the question of, is float necessary. This is more about the programming of absorption. ie Don't start float (or stop charging) until the battery has done X amount of absorption. So maybe two different issues.

[time2roll]

BFL13 wrote:

smkettner wrote:
IMO float is good in all conditions. Most alternators drop voltage with time based on heat or are controlled by the main ECM.

Does "all conditions" include when you will be doing an "incomplete recharge" by dropping to float, when you could have reached "full" before dark if you had stayed at Vabs?

??? Float is best when fully charged. Float is also good when battery has somehow not fully charged.

The alternative (see OP) is not more Absorption but rather to just turn the solar power off. Yes IMO float is better than off in ALL conditions.

Yes it is best to get the battery 100% before float and that does require a very good controller to adjust depending on conditions.