Custom built solar charger

[hellosailor]

"To suggest that " conventional " charging schemes have been obsoleted is nonsense. The LA battery is the same and is charged the same as it always was, IUI or IUU "

Okay, Dave. Since conventional chargers simply applied one of several fixed voltages and allowed the amperage to float as it might, and the new MPPT chargers are selectively changing the charging voltage in response to battery condition, maybe you don't see any change in the charging paradigm but the folks who make them do.

The party who explained this to me, along with the change from pure DC to pulsed DC (or PWM or whatever you prefer to call the output from MPPT chargers) was a lead engineer at one of the top battery manufacturers in the US, I take him at his word when he said "we don't do it that way anymore" refering to the old 3-stage chargers.

And while MPPT may have nothing to do with the battery side of a charger, the plain fact is that MPPT chargers DO take special consideration of the environment that they will be used in, not just how they connect to the solar panels, so in point of fact they DO charge the batteries differently. Maybe not the cheap stuff from China that calls itself MPPT, but the brand name stuff does a lot more than just match the power point of the panels.

Conventional charging IS obsoleted in the context of solar chargers, even if it is still good enough for cheap dumb boxes that are running off cheap shore power, or internally regulatred alternators. And even those dumb AC charger boxes are getting hard to find, some of the new ones won't even allow charging if you've pulled the battery down to 10V.

Could be everyone was lying to me and you're the only one who knows the truth, but the folks who are actively working in the industry are singing a different song.

[Paul Elliott]

Originally Posted by hellosailor

[...] The party who explained this to me, along with the change from pure DC to pulsed DC (or PWM or whatever you prefer to call the output from MPPT chargers) [...]

Just to avoid any confusion, there are chargers that are based on pulsed DC (PWM or similar), and this is not the same as MPPT.

PWM control the average charging current, and when the pulse is "on", the panel is effectively directly connected to the batteries.

MPPT uses switching technology to perform a voltage/current conversion where the panel voltage is *not* equal to the battery voltage. MPPT switching-regulator technology may use PWM in the regulator circuitry, but this is *not* the same as the simple PWM solar controllers.

[catakate]

Originally Posted by hellosailor

Since conventional chargers simply applied one of several fixed voltages and allowed the amperage to float as it might, and the new MPPT chargers are selectively changing the charging voltage in response to battery condition, maybe you don't see any change in the charging paradigm but the folks who make them do.

It makes perfect sense to me to keep the voltage just high enough for the amps to charge the battery, this way more amps can be harvested and transfered into the battery. This is not complicated or expensive to build.

[hellosailor]

"Just to avoid any confusion,"
Good idea, Paul. But the point here is not whether MPPT is PWM or vice versa, the point is that "DC is dead" compared to pulsed DC of any type. Apparently pulsed DC causes less boiling (microbubbles, not gross boiling) in the electrolyte, which in turn allows more current to be pushed through the electrolyte and into the plates. So that charging with "pure" DC can be 10-20% clower than charging with any type of pulsed DC.

[Paul Elliott]

Originally Posted by hellosailor

the point is that "DC is dead" compared to pulsed DC of any type.

OK, good point. I still see simple controllers that brag about using PWM instead of linear regulation. PWM in that context is a perfectly good way to perform the regulation, but it is definitely a different animal than what you have brought up.

Thus the potential confusion.

[goboatingnow]

Originally Posted by hellosailor

"To suggest that " conventional " charging schemes have been obsoleted is nonsense. The LA battery is the same and is charged the same as it always was, IUI or IUU "

Okay, Dave. Since conventional chargers simply applied one of several fixed voltages and allowed the amperage to float as it might, and the new MPPT chargers are selectively changing the charging voltage in response to battery condition, maybe you don't see any change in the charging paradigm but the folks who make them do.

The party who explained this to me, along with the change from pure DC to pulsed DC (or PWM or whatever you prefer to call the output from MPPT chargers) was a lead engineer at one of the top battery manufacturers in the US, I take him at his word when he said "we don't do it that way anymore" refering to the old 3-stage chargers.

And while MPPT may have nothing to do with the battery side of a charger, the plain fact is that MPPT chargers DO take special consideration of the environment that they will be used in, not just how they connect to the solar panels, so in point of fact they DO charge the batteries differently. Maybe not the cheap stuff from China that calls itself MPPT, but the brand name stuff does a lot more than just match the power point of the panels.

Conventional charging IS obsoleted in the context of solar chargers, even if it is still good enough for cheap dumb boxes that are running off cheap shore power, or internally regulatred alternators. And even those dumb AC charger boxes are getting hard to find, some of the new ones won't even allow charging if you've pulled the battery down to 10V.

Could be everyone was lying to me and you're the only one who knows the truth, but the folks who are actively working in the industry are singing a different song.

Hi, your fundementally mixing up mppt with battery charging , which it has nothing to do with mppt is a technique to extract maximum power from a solar panel ( or other power source ) that has a non linear response. Battery charging algorithms are separate and may vary from simple to modestly complex.

Mppt " chargers" is a meaningless phrase.

LA batteries can be charged with PWM , but its actually not a recommended approach by most companies. IUU or IUI is the normal 3 stage process applied and its the same as it always was.

The problem with listening to the industry is they complicate explanations to convince people f their " white mans magic"

People get mixed up with PWM solar regulators and mppt and switch mode power conversion

PWM regulators , often called " bang bang" controllers , simply modulate the solar panels output and hence battery charging by connecting and disconnecting the panel to the battery , its a very very crude technique , used because its cheap and works because PVs are essentially current sources. It can cause panels to be grossly inefficient.

Mppt is a method of extracting the maximum rated power from the panel under a particular illumination, and is neccessary because PV output is not linear , that is, the watt output is maximum for a particular voltage at a particular illumination. ( ie Vmp)

The solar mppt controller then takes that power and simply implements a standard 2 or three stage battery charger , just like your AC charger ( in practice only really 2 stages are neccessary )


LA batteries are best charged as they always were.

1. A bulk phase , constant current , upto the batteries rated max charge ( if the source is powerful enough )

2. Upon reaching the batteries specified absorption voltage , switching to constant voltage , again charging at maximum battery acceptance rate ( in absorption) , again assuming the source has sufficient power.

Terminating absorption on a number of factors , usually either fixed % or absolute i , di/dt , or a combination of (i) , di/dt and a fail safe timer.

Nobodies found anything better.

Dave

[goboatingnow]

Originally Posted by hellosailor

"Just to avoid any confusion,"
Good idea, Paul. But the point here is not whether MPPT is PWM or vice versa, the point is that "DC is dead" compared to pulsed DC of any type. Apparently pulsed DC causes less boiling (microbubbles, not gross boiling) in the electrolyte, which in turn allows more current to be pushed through the electrolyte and into the plates. So that charging with "pure" DC can be 10-20% clower than charging with any type of pulsed DC.

Sorry absolutely not, many LA battery manufactures do not recommend pulse charging, pulse charging of LA batteries is as old as the hills and not that effective.

Dave

[hellosailor]

Paul-
Actually, the Delco (GM) alternators in the 70's all used PWM to charge car batteries. Delco didn't say much about it but they used to be real good about answering the phone. The "Delcotrons" from that period actually used PWM with only the frequency of the pulses being modulated, form something like 100 Hz to 20kHz in frequency. In their case, they did this partly in order to reduce the number of wires in the alternator harness. The Delcotron would turn off, look at the battery voltage that was present on the output lead, and then depending on that, turn back on again. If the battery was low, it would do this very rapidly. If the battery was charged, it would delay the next turn-on cycle. And the alternator output was consistently 14.3-14.4 volts, as opposed to the wider ranges (13.8-14.4) still being used by a lot of other makers. Their logic was that by eliminating the voltage sense wire, they could save gobs of money for GM. Whether that was supposed to have any other advantages, I don't know. The fellow who explained it to me was only explaining how it worked, and why the sense wire was "missing".

Dave, you may be confusing the pulse charging supposedly used to break up sulfating, with other PWM schemes. As I said, at least five years ago one of the major battery manufacturers was not only recommending PWM but they had already gone over to it in their charging designs.

[sailinglegend]

Originally Posted by hellosailor

....the plain fact is that MPPT chargers DO take special consideration of the environment that they will be used in, not just how they connect to the solar panels, so in point of fact they DO charge the batteries differently......

Interesting stuff... so what happens if the battery charging voltage takes a very long time to reach the "absorption voltage"? Could this get the battery up to more, or less, than the 80% SOC that is normally associated with reaching the absorption voltage. If it does either then does the controller still hold the batteries at this voltage for the programmed 2-3 hours before dropping to float? Would this then overcharge, or undercharge the batteries? I suppose the cheap MPPT controllers don't take any of this into account!

[hellosailor]

"so what happens if"

That's where things change from one vendor to the next. The only way to know what logic a particular vendor is using, is to ask them. If they are using a chipset that has a default set of options, you may be able to tell from the chipset. If it is some entrepeneur from a basement in Shenzen...good luck asking, even if you ask in Mandarin.

Some vendors won't discuss these things at all and claim the logic they use is proprietary. Some offer you programming options.

"a very long time " If time is a consideration, that's something that each vendor would have to reply on. I've seen specs for some cheap stuff that basically just turn charging on/off and don't even attempt three-stage. And one company that proudly sells a "5 stage" charger with the fifth stage being "off". Honest. More is better, right? <G>

[goboatingnow]

Originally Posted by hellosailor

"Just to avoid any confusion,"
Good idea, Paul. But the point here is not whether MPPT is PWM or vice versa, the point is that "DC is dead" compared to pulsed DC of any type. Apparently pulsed DC causes less boiling (microbubbles, not gross boiling) in the electrolyte, which in turn allows more current to be pushed through the electrolyte and into the plates. So that charging with "pure" DC can be 10-20% clower than charging with any type of pulsed DC.

Heres a paper from 1998 http://www.ipenz.org.nz/ipenz/public...2wilkinson.PDF

Its a positive paper extoling the benefits of pulse charging. Funnily pulse charging has not taken over the world of charging, as in practice the benefits are hard to quantity and good quality pulse charger is relatively complex.


This has of course nothing to do with PWM solar regulators that are just bang bang controllers.

Dave

[goboatingnow]

The only way to know what logic a particular vendor is using, is to ask them.

a voltage/current data logger or scope will easily identify what algorithm a company actually uses as opposed to whats written in the lie sheet. Youd be surprised at the reality.

IN general, transition from bulk to absorption is done by voltage limit, trasnsistion from absorption to OFF , or float is a little more difficult and there are various techniques, varying from current set point, rate of change of current and run-out timer. often chargers use a combination.

None of this is technical rocket science and its all there to be read on the "net" if you like ploughing through tech papers, data sheets etc,

Dave

[goboatingnow]

....the plain fact is that MPPT chargers DO take special consideration of the environment that they will be used in, not just how they connect to the solar panels, so in point of fact they DO charge the batteries differently......

Just how do they charge the batteries differently , Im all ears, seriously I am.

How is the front end charging algorithm any different for any three stage ( or 2 stage ) charger. ( leaving aside a tech talk about proper pulse charging of LA)

Dave

[hellosailor]

Dave-
1- Why pwm charging hasn't taken over the world: I suspect because battery chargers fall into two markets. The main one, which is based on "CHEAP" with no other criteria. Batteries are way above the comfort level of most consumers, they can't even figure out which end goes up in a remote control. Witness Apple, who make many friends by requiring them to replace a phone instead of changing the battery in it.
And the second market, where performance counts and price is not a criteria, but that's the tail which will never wag the dog. And that's where MPPT is for now.

2-A data logger or scope will NOT tell you the algorithm really being used, until you have made many traces and analyzed much data. Sure, you can see the conditions at which point something changed, but that doesn't tell you the why of it, or show you how the entire logic table is populated. And these days, a chip with a logic table in it is what, two cents? five? Who's going to spend the day analyzing it?
The only reason I know what one system was actually doing, was because I set up the monitors and took notes on a day while I was there doing other things. Giving me enough information to ask "WTF?" but not enough to figure out the whole program.

3-"How is the front end charging algorithm any different for any three stage ( or 2 stage ) charger." From watching dual voltmeters and ammeters and noting the readings every 15 minutes for about four hours, I saw that the charging VOLTAGE to the batteries was being ramped up about 1/10th of a volt every time I turned around, while the amperage was coming slightly down. There is no 3-stage charger that continuously adjusts the voltage and amperage during the bulk charge phase, is there?
AFAIK every 3-stage charger is applying one set voltage during each stage, and any variation in that voltage is simply the result of something being saturated. Whether that's an analog charger or a digital one, whether the "control" is from regulation or from battery condition, the design of a 3-stage charger, even a "smart" one, is not going to keep changing the charging voltage suring each stage. That's different.
Do all MPPTs do this? I don't know, you'd have to ask them.

Whether a charger is going to use "pure" DC, or chopped DC, is partly going to be intentional and partly just the result of what design is cheap. Transformers, rectifiers, a cheap 3-pin regulator chip and some bootstrap transistors were the cheap way to build a charger 20 years ago. Today? The price of the iron and copper in the transformer makes them unaffordable, and those expensive IC-controlled chargers using logic tables become cheaper, way cheaper, so a whole range of options is there. Either by default or intent.

But the MPPT market? Catering to folks who have probably already spent a thousand dollars on solar panels and another thousand on batteries and interested in spending more as needed to max out their performance? In Bill Gate's immortal words "Hardware is cheap" and sloppy programming even cheaper.<G>

[catakate]

Thanking all of you for useful info / experience/ thoughts expressed here I'll summarize:

1. Charging efficiency by Voltage control. As anyone should know, P=U*I, lowering the Voltage means more Amps into the battery for same panel Power. Just how much higher then the battery's voltage should it be?

2. Absorption Voltage should be best found in battery's specs.

3. There are quite a few ways for determining when the Absorption should end. Except for the timer method which is obvious, can anyone propose some values for these?