'Float' voltage under varying DC loads

[landyacht318]

This post is an observation, and observation which bucks the 'this wors like this, and that works like that' mentality which pervades online forums. Empiracle data trumping theory.

I can spin a dial on my dashboard, which controls the voltage my Alternator is told to seek/hold, just like I can spin a dial on my Meanwell power supply to do the same thing.

With the MEanwell, and a Northstar AGM group 27, I would notice that if I held even slightly less than its prescribed float voltage while still running loads, the battery would discharge slightly, indicated by an ammeter when I would goose the voltage back up into the mid 14's.
The Bigger the load, the more it would discharge the battery, even held at the prescribed float voltage. So while the battery prescribes 13.6v at 77f float voltage, I would have to keep the voltage slightly higher than this to prevent my ammeter from flickering in the - amperage region, and the high the DC loads I was running, the higher the 'float' voltage I would need to hold to prevent slightly discharging of the battery.
Obviously lower battery temperatures would also increase the voltage required too to prevent dicharge.

Recently I drove cross country, and once my dashboard Ammeter (with a resolution of 0.2 amps) would indicate 0.4 amps or less into the battery I would lower the voltage from mid 14's to the 13.6v range.

now at 13.6 or 13.7v the Ammeter during the daytime would mostly read 0.0, but sometimes 0.2 or - 0.2amp, during the day basically hovering in the 0.0 amps into or out of the battery.

But come nighttime with the battery chock full after driving all day, holding mid 14's until amps taper to 0.5% or less of capacity, with the additional ~15 amps of headlights Load and perhaps 5-8 amps of blower motor, if I held it at 13.7v, the ammeter would read -0.2 to -0.4 amps indicating the battery was being discharged despite being held at voltages over those what the battery recommends at float voltages, even accounting for less than 77f battery temperature.

Now, I can simply twist the voltage dial up, and get that negative amperage leaving battery to neutral, and of course would do so.

The voltage at which negative amperage turned to 0.0, was no less than 13.9v, at night, when the headlamps were on, and the colder the outside temperature, as my battery is not really soaked in engine heat, the more voltage required.

Now My dashboard ammeter is just the Bayite hall effect 100 amp sensor, and is susceptible to interference on the rather long 3 wire ribbon cable from sensor to the display gauge itself, but I also have a shunted Digital ammeter which I can not safely observe from drivers seat.

Since I had a passenger who could read the shunted ammeter reading for me while I was driving, I discovered it basically agreed with the dashboard ammeter. That at night with the additional 15 amps of headlight load, I had to increase the voltage to prevent the fully charged battery from discharging slightly as I drove. Basically the highest load I will employ engine off overnight when plugged in is 10 amps, and 13.7v is generally enough to prevent eh ammeter from ever going into the neagtive, but driving at night, with teh 12.2 amps my engine requries to run, plus the 15 amps of headlights and 5 to 8 amps of Hvac blower motor, I basically have to approach 14v to prevent the battery from discharging.

Theory says, and whatI basically expected was that any charging source that would hold the battery above its fully charged resting voltage, would prevent the batttery from discharging, but this is not the case. And the recommended float voltage is also apparently not enough to prevent the battery from discharging, when there is a fairly significant load on the DC electrical system.

I do not understand why this is, but I trust the measurement devices and these observations, and these observations disagrees with what one often reads on forums such as these.

I think many converters, doing their float or storage modes, while the owners are above using as much DC electricity as they want, are blissfully unaware that their batteries are likely discharging at a very slight rate, instead of being kept chock full by the converter as its mareting will loudly proclaim.

Whether this makes any measurable difference in battery longevity is of course argueable, but it does make me glad I do not have an Fixed voltage charging source, and can simply twist a dial instead, further cementing my seething contempt for automatic charging sources, and the ignorance often displayed by those that repeat the marketing mumbo jumbo of automatic charging sources but have no tools to measure actual variables, or the aptitude to question them if they did.

[MEXICOWANDERER]

That alternator draws about five amperes of field current. Most of Frank's regs slumped <.05 from 1% to 99% field draw.

You have one sense lead connected to the highest possible circuit voltage potential the second connected to in intermediate bias sense point. There will be a differential. Temporarily connect a bridge of 10AWG from alternator output stud and battery + and see this differential radically decrease. Disconnect from battery and connect to ignition 2 circuit and see a base voltage increase. Of course this is just playing around. To answer your question.

There isn't a need for ultra-precise voltage regulation for load. Merely to have a meter agree with voltage seen at the battery.

Ah the days when Oropeza was around -- call Orlando and a fresh product would appear. The 911 regulators used laser cut voltage divider networks. I saw many units with a .01 max slump. I have a pair of one of his last works, a Delco SI series of "one-wire" regulator that excites at 40-70 alternator RPM, 100-amp MOSFET and FET driver. Laser cut voltage divider. No more. The exotics stopped being produced. Sad.

Even the Megawatt and the Meanwell power supplies have load droop. My 10 amp 60 volt and my Lambda adjustable power supplies have zero droop. Such is life.

[BFL13]

Not quite the same thing as the OP's, but I did note when on solar and had Float at 13.2 in the summer at 77F, it would not handle any loads. I had to move it up to 13.6. I figured that is why converters stay at 13.6 if the RV is being used and only drop to 13.2 in storage.

[landyacht318]

The Ammeter on my dashboard, while it can display volts or amps or toggle between the two, is not used for voltage. it displays ONLY amperage.

When I first got it the volts displayed were off by 0.2, high or low I can;t remember but I would not have used it anyway, for displaying voltage.

I have two other Voltmeters, 3 wire voltmeters, with one of the wires being the positive voltage sense lead, and these are connected right to the batteries terminals themselves.

Well one of those 3 wire voltmeters is not hooked to any battery as I have no battery in my engine compartment anymore.

The Transpo540HD voltage regulator is not wired ideally. I have it taking power from the alternator output stud instad of the battery (+) itself, but the negative effects of this are only that once the wire heats up from high amperage and or engine heat the potentiometer needs a little twiddling to keep voltage on target.

I stand by my assertion that to completely prevent any discharge of a battery at float voltage range,when larger loads are on the DC system, that higher voltages are required.

This is likely more of a factor with lower resistance AGM batteries than higher resistance flooded, but I cannot easily perform experiments on Flooded at the moment to test that statement.

[MrWizard]

your meter is alternator voltage and amps
or battery voltage and amps
i mean where is it physically attached to the circuits

the loads you mention are attached to the vehicle wiring
after the battery, some after the ignition switch

the alternator feeds the battery , which then feeds the loads

the increased voltage drop created by the increased loads means the 'applied' voltage must be increased

the battery is a 'power source' located 'electrically' closer to the loads than the alternator

the 13.6v is not high enough with the night driving loads

nice observations

nothing i would worry about though
even an 0.4a for 8 hours of driving, would only be a net loss of 3.2 amphrs from the battery

[pnichols]

MEXICOWANDERER wrote:
Designing systems, I chose to operate the charging system by sourcing alternator voltage sensing right at the alternator. And meter voltage sensing at the exact same point. Reason: An open in the charging line would lead to load dump but not to uncontrolled voltage at the alternator.

Hmmm ... it seems like no matter what you did at the alternator to keep it's voltage from going off the charts with an open line ... you should also have implemented a voltage sensing negative feedback closed loop, terminated at the load, so as to ensure that whatever/whoever controlled the alternator could set exactly what voltage they/it wanted to wind up on the load's terminals.

For instance - barring an open line - I think the OP is trying to precisely control voltage fed to his batteries ... albeit not via the ultimate of voltage sensing right at the batteries' terminals. (?)

[MEXICOWANDERER]

In an ideal circuit voltage will be equal at all points.

The IASF voltage regulator Landy is using "A" is both source point power to the alternator field -and- voltage sense.

Designing systems, I chose to operate the charging system by sourcing alternator voltage sensing right at the alternator. And meter voltage sensing at the exact same point. Reason: An open in the charging line would lead to load dump but not to uncontrolled voltage at the alternator.

I presented Frank Oropeza of Transpo a question of voltage slump (droop) in 1983. He really took it to heart and incorporated FET transistors to minimize vf

I suspect the phenomenon is a clash between sensing and meter source points.

[pnichols]

landyacht318 wrote:
I think many converters, doing their float or storage modes, while the owners are above using as much DC electricity as they want, are blissfully unaware that their batteries are likely discharging at a very slight rate, instead of being kept chock full by the converter as its mareting will loudly proclaim.

I have never spent the additional money to replace our Class C's stock Parallax 45 amp fixed voltage converter. I wanted dry acid batteries instead of liquid acid for a variety of reasons, so alternatively I spent the money for a retrofit to 230 AH of 12V AGM deep cycle coach batteries that get along well with the converter.

I have a +/- 0.1 amp resolution ammeter mounted on the cab dash (with it's shunt installed in the negative lead of the 230 AH AGM coach battery bank).

My batteries are specified to be floated in the 13.5-13.8 volt range - a perfect match for the stock converter. Since AGM batteries have such a low internal intrinsic resistance, when they're around 50% discharged they also charge good enough - at a 10 to 15 amp rate - from this same 13.5-13.8 volt fixed voltage converter. If I need to charge the AGMs quicker than through the converter, I first just idle the V10 with it's 130 amp alternator for awhile so as to temporarily pump current at up to a 70 amp rate into them (per the dash ammeter I installed -> the E450's stock alternator is capable of this at engine idle speed).

Whenever a converter - or other charger - is attached to your RV battery bank and current is being drawn from that 12 volt converter/battery system ... what you may be seeing is the current being primarily drawn from the source with the lowest internal resistance. This is usually going to be the batteries themselves instead of the converter or charger. As soon as the load is removed, the higher resistance (and voltage) source - usually the converter or charger - will resume providing current into the now somewhat depleted battery bank.

Source voltage setting, source amperage capacity, and cable size are not the only parameters to be concerned with .. internal resistance of sources and loads can often be just as important in a system.

However, some of the above is just my opinionated guess as to what may be happening in your situation. 😉

[MEXICOWANDERER]

This is a THIS WORKS LIKE THIS posting.

It's not argumentative. In fact this post tries to explain why electro-chemical energy storage fascinated me fifty years ago to the point that I pretty much dedicated my career to studying it. At the expense of omitting my classical rude and snide asides I will shed some light on the subject if I can.

Attempting to translate characteristics of optimum led acid battery operation and lifespan is not easy. The is a multiplex of factors involved and a majority of consumers read the first two words of an analysis then toss the sheaf of papers over their shoulder. And actually I agree whole-heartedly with them. The theory should remain firmly in the realm of designers and manufacturers.

The main problem is a barrier

The barrier exists between battery design and manufacture and battery charger designers and developers. There isn't free and fast flowing communications.

Over the years I have worked with some of the "biggies" on both sides of the aisle. What I discovered was TOP TIER battery manufacturers understand their products. But battery charging and maintenance design and control are outside of their realm.

The kingdoms of battery charging and maintenance seldom if ever perform comprehensive tests on actual batteries. Many manufacturers assume a protocol of FOLLOW THE ROTE and tweak here and there which gains nothing but gives exclusivity in advertising therefore gives their Herb Tarlek types goose bumps.

The consumer, tired of batteries and chargers in general, snap "How much does the goddamned thing cost?" He is not presented with cycle life data (95% of battery manufacturers do not conduct them and 99.9% of battery manufacturers do not experiment with different charging algorithms and protocols.

When @#$%^&! "Pulse Charging" became the ultimate Herb Tarlek buzzword several years ago, I tried to explain that it wasn't the frequency that offered any gain but it was the added kWh offered to the battery. Faint words lost in the fog.

Battery manufacturers should entertain studies like your post, but they don't. It is a net loser except in the emergency power supply field. If their product offers competitive lifespan, why spend money?

Another favorite term of mine is to counter the belief that electricity and chemistry and stable platforms in which to base electrical theory. They are not. A battery is reactive in several facets one of which is temperature. The second is construction techiques. The third is alloys.

Many general attributes gain be gained by proper study but again there is no tangible market for expense and complexity of design and marketing of advanced charging techniques.

For instance "Float". Many chargers hold a steady state temperature compensated voltage and this is a mistake. Simply raising voltage steady state is an error. Increasing voltage for a set time in frequency measured in several days or weeks is also an error. On a flooded battery voltage on float can be raised two tenths of a volt every six hours and remain for ten minutes. This measurably improves unintentional sulfate contamination which is measured in PPM on active battery plate area.

The distributor whom I leased property from used to wander over at coffee time and ask "What are we working on today?" But not when I was building alternators of conducting alternator research. I had tossed him a bone going in, of inventory battery charging maintenance that proved to be startling in his bottom line. Then there was the simple addition of evaporative cooling which dumped warehouse storage temperatures thirty degrees for summer. Specialty battery inventory reacts favorably to such babying and he saw his bottom line increase markedly.

Now

How can all of the above be translated into something that Joe Blow RV'er can use? Use cheaply and effortlessly?

Tall order.

It can't.
(to be continued...

[BFL13]

If the load reduces the charger voltage so it is not the higher voltage, then the battery will have the higher voltage and get drawn from.

Perhaps you are just adding charger voltage to give it enough to run the loads and still maintain battery voltage.

Might be some voltage "as seen" from different places going on too making them look different, so the battery gets drawn down.