Had to Lower My Solar Float Voltage-Update

[BFL13]

Updated 9 July

Just a note for folks in a similar situation.

My usual procedure in a normal summer here with my set-up with the Eco-Worthy controller (adjustable Absorb and adjustable Float ) is to set Vabs at 14.8 and then, since it immediately goes to Float (no time at Vabs) I set the Float as high as it will go, which is 14.5 so it stays there till dark.

Somewhere not long before dark the batts are at "true full" by baseline SG, which I can tell because the Trimetric reads 15AH "over" (into positive)and this corresponds to baseline SG. Supper and evening usage of the big draws via inverter (microwave etc) keeps the batts from going on too long at the high voltages, losing positive plate and water.

Well not this year! We are having fabulously good weather, thanks to some giant squids off Peru or whatever it is, so now the batts are getting to baseline SG mid- afternoon and IMO spending too long at high voltage before dark.

So the new drill while this lasts, is to lower the Float voltage to 13.8 once the Trimetric says we are at 10AH over, which is about 3:30 pm these days. I will keep track and adjust as required of course.

The EP Solar controller I had before had a fixed charging profile of getting to 14.6, stay there for two hours, then drop to 13.8 till dark. That would be perfect right now, but with this controller, I will have to do manual resetting of the Float till the weather gets back to normal. Put it back to 14.5 in the morning then to 13.8 mid afternoon.

Lesson is---keep an eye on things and adjust as required. Solar is not a set and forget system.

[BoonHauler]

BLF, how big is your battery bank?

[landyacht318]

There are so many affecting variables, the broad brush approach has to be implemented at some point.

I try and think of it as a surfboard with 5 removable fins, and one can significantly change how the board rides by different fin combinations. What might work good on one day and one particular wave, might just feel wrong when conditions change.

With So many different fin options, one forgets to just go surfing. Analysis paralysis is real. A broad brush might not further the science, but it does help one to remain sane.

If it costs a battery a few dozen cycles overall, it is worth it?

Some days I say absolutely, other days I can't care one whit.


Now, to go design my next surfboard, how many fin boxes will I incorporate and What Cant angle and Tow in angles will i use. How will they react with bottom contours keeping in mind my advancing years, and the overall outline, displacement and the ridiculous number of greedy self important surfers now sharing the lineups.

A million variables, all with the potential for analysis paralysis, and no objective way to keep score.

At least batteries have a Hydrometer, and an Ammeter for objective analysis.

[BFL13]

Thanks, so I must be seeing a smaller version of that. (your good work on that screwy 31 reporting did not go to waste!) It's back to the idea you can't fine-tune the solar, so just broad-brush it.

On today's SOC, it is confirmed not as far up as yesterday by seeing more battery amps still being accepted even after the drop to 13.2. Yesterday it was about half and amp but today the Tri is showing 2.4 amps to the battery at 13.2v.

So this is like a mini-absorption stage at the moment till the battery gets to full. As long as it gets there before the big amp draws start from suppertime on, it will work out.

[landyacht318]

The screwy 31 required a lot more time at higher ABS voltages with an even higher finishing stage, when depleted to 50%, compared to when it was recharged from 75%.

Also a higher initial amp rate ( ~25 to 40 amps) from a grid powered charger required lower Vabs for less duration, compared to the low and slow 200 watts of solar on a good sunny day.

I kind of came to the conclusion that any specific Vabs and duration that achieved full SG by 3PM, was only valid for that specific initial depletion level, and every other depletion level, was a compromise using those same Solar controller settings.

But the Screwy 31 was a petulant battery. I am interested in figuring out what a new T-1275 requires in my usage, whenever I get around to acquiring one.

[BFL13]

Today was a little different, so this needs more watching.

I checked SG when battery voltage passed through 14 and it was not up to "full SG" like it was very close to being yesterday. So waited until it went from Bulk to Float and SG was just a titch less than baseline SG. Say 1.280 instead of 1.285 for size.

Trimetric says minus 2.4AH so that fits. (it should be up to plus 10 or so at full SG) Apparently, it could do with a little time at Vabs today and not be down to Float already.

However, there is such a thing as "SG Lag" and even at Float the AH counter should gain some like it did yesterday, so I will check SG again later and see if it got up any.

I wonder if being at 13.2 for so long yesterday slowed it down somehow, so it needs more effort to get to baseline SG than it did with the 14.5v float previously. Or it might be that the cycle was a little deeper today where a few more AH got used. Or both.

I believe there is some sort of line you cross when going deeper that it takes more effort to get back up than if you start shallow. IE it is not a linear effort. ISTR that was one of the things that came out of the Screwy 31 study? Not too clear on that.

Anyway, this has to run a few more days before general conclusions can be made, so I will not adjust the plan yet.

I should have known this would not be so easy to get right the first time.

[BFL13]

JiminDenver wrote:
I'm going to miss pointing the panels east in the morning. Float by 9 am and the solar covers everything but the biggest loads for the rest of the day. Then again 3 250w flat should cover what one 230w did tracking. The two 245w tracking saw 23-26a as soon as the sun burned off the frost on the panels, I'll miss that at 6 am. The three 250w's tracking could almost run the A/C at sun up but I'd probably use the 470w stove top to cook breakfast instead.

So with a inexpensive solar set up you are doing what people with expensive generators and fancy converters have been trying to accomplish for years. The ability to force feed the bank until it doesn't need a long tedious float stage. Pretty sweet as long as it isn't damaging the battery somehow.

It is just that daily AH usage is so low in the summer despite microwave, kettle, and toaster besides the usual TV, etc that the solar can keep up easily.

Anyway, I have time to go out and twirl the panel every so often instead of being stuck with my head in the laptop trying to program my fancy kabillion dollar solar controller so it will at least do something! (Tee hee)

[MEXICOWANDERER]

Herb Tarlick rules the roost. Grid grain enhancers like silver have no effect on performance only on strength but hey, it's a free country. You might want to check out recommended float values at 40c and 0c - they are a heck of a lot more significant than four tenths of a volt.

[JiminDenver]

I'm going to miss pointing the panels east in the morning. Float by 9 am and the solar covers everything but the biggest loads for the rest of the day. Then again 3 250w flat should cover what one 230w did tracking. The two 245w tracking saw 23-26a as soon as the sun burned off the frost on the panels, I'll miss that at 6 am. The three 250w's tracking could almost run the A/C at sun up but I'd probably use the 470w stove top to cook breakfast instead.

So with a inexpensive solar set up you are doing what people with expensive generators and fancy converters have been trying to accomplish for years. The ability to force feed the bank until it doesn't need a long tedious float stage. Pretty sweet as long as it isn't damaging the battery somehow.

[BFL13]

Not sure how to force it into Float except by resetting the Vabs below the current voltage during Bulk.

I was at the controller when it went from Bulk showing 14.7v, 13.6a to Float (set at 13.2) and on the display, voltage slowly died down while amps were 0.00 for a while. Once the battery voltage faded down to 13.2, amps started again, showing the solar amps to run loads and on the Trimetric, which shows only battery, it showed part of an amp.

You could see the Trimetric part of an amp move up and down a bit as (I think) the controller maintained the 13.2 and the green "charging" light flickered sometimes when amps went part of an amp negative a little at times. You could see this more when turning the laptop on and off while the controller and battery took a moment to adjust themselves, then it went back to plus half an amp or so.

I will leave it as is with Float at 13.2 while this weather lasts. I really don't need any solar once the batts are full. I could use the solar to run loads for the rest of the day and not draw down the batts so much before next morning, but with so much solar coming due next morning, that is just not necessary. The batts will still be full mid-day.

With no solar for the second half of the day, all it would mean is the shallow cycles would be not quite as shallow. Who cares?

Actually I will still have the panel aimed East for the morning and South for mid-day, but if it stays sunny after that I will just leave it South and omit the usual twirl to West. Not that I am lazy or anything! 🙂

[JiminDenver]

Why wouldn't the voltage come up if the battery was full? What was the banks voltage when you thought it was full? When the controller did finally go to float did the amps drop to near nothing? At that point the battery would be controlling the acceptance rate and if it was full, it should have accepted very little.

You might want to check your water levels if the amps dropped dramatically as soon as it hit float. If the amps didn't drop your battery wasn't full and you need to check your meter.

You could set the absorb set point to a lower voltage and see how it goes. Maybe try leaving as it is and dropping the set point once the meter says the bank is full. Force it into float and see if the amps taper quickly.

[BFL13]

Getting to full SG before "controller Bulk" ends is a new one on me.

(If it is correct what I think I saw where full SG happened an hour before the controller reached 14.8, the set Vabs, and went to Float)

That means from the battery's point of view, "Absorption" ended when the SG stopped rising at whatever voltage that was, and from then on it was in "Overcharge" until the controller's "Bulk" was over.

Can't figure out when the battery went from "Bulk" to "Absorption" as there was no defining moment. The Vector charger does its Absorption with the battery voltage rising from 14 to 14.8, but with amps tapering. So you can tell when it goes from Bulk to Absorption by when the amps start to taper.

Here, the amps did not really taper except for the business where the controller output in watts was a fixed amount, so as battery voltage rose, amps fell.

That is just normal buck converter activity, not to be confused with the "battery acceptance" tapering. Might be a bit of that in there too, but also you have all that heat loss at the high SOC where you can have more amps but the battery is not absorbing them.

Not sure the usual charging stage names mean much in this case, or else I am not understanding what I think I saw?

[JeepCB]

MEXICOWANDERER wrote:


Or are these manufacturers too stupid to figure out how to use a shunt to tell when correct amperage is present?

None of the charger folks have talked to a genuine battery design engineer.

Where DID they get the people who come up with these Laurel & Hardy grade "smart" chargers?

Mex and everyone,
I humbly ask the following; With the level of knowledge you guys all posses, why don't you guys put your heads together and create the charger you want and need and we can buy the right one? I believe it would be easy for you.

Build a few and see what happens? Could be another income? I would buy one, and I'm sure many others would too!

Respectfully,
Billy

[pnichols]

I'm going with Lifeline's original published recommend float voltage of 13.2 volts instead of unrecorded phone calls with Lifeline that myself and others made.

Based on that approach, I figure that a 0.4 volt difference (13.2 V versus 13.6 V) up to a 0.6 volt difference (13.2 V versus 13.8 V) - all at 77 degrees F - can indeed be significant enough between AGM battery brands to possibly cause more or less H2O evaporation over the years with certain AGM batteries on certain float maintenance programs.

For lack of a better way to say it ... there MUST be some construction and/or material type and/or material purity and/or chemistry differences between AGM battery brands that gives rise to the various recommended float voltages I see in print.

After all, "for years" 13.2 volts was the accepted float voltage for wet cell LA batteries. Why do the various AGM battery brands now have float specs differing from this and differing among themselves ... unless there's some engineering reason for the differences?

[MEXICOWANDERER]

And THAT Is my point EXACTLY.

Eliminating a same chemistry battery because of a point two volts difference in float recommendation is NUTS!

That ppint two volts diffetential gets eaten alive feet-first with a seven degree plus or minus temperature change. What'cha going to do at 90F or 50F? Most of ypu fllks shluld be aware enough by now to have figured this out for yourselves.

[pnichols]

Mex wrote:
At

What

TEMPERATURE

Are

These

Guys

Rating

Their

Float

Voltage

?

Assuming can get one in trouble ... sometimes. But this time I'll bet with 99.9999993% certainty that it won't get me in trouble: When a battery spec sheet says float at 13.2 volts at 77 degrees F ... what is safe to assume is that what's being specified is the temperature of the air in which the battery is sitting.

The air temperature around the battery is the only thing a battery user knows about, cares about, can measure, or can control.

What the battery designer cares about and takes care of is inside-to-outside and outside-to-inside heat transfer rates inherent in his/her design such that at 77 degrees outside air temperature in which the battery is sitting - the internals of the battery reach no than higher than X degrees at Y specified external applied float voltage.

(Boy was that a mouthful just to say that air around the battery temperature is the name of the game. All In My Humble 99.9999993% Opinion, of course.)