Custom built solar charger

[sailinglegend]

Originally Posted by catakate

...1. Just how much higher then the battery's voltage should it be?

2. Absorption Voltage ....

3. There are quite a few ways for determining when the Absorption should end....

1. It should be whatever gets the most amps going into the battery - depending on the Panel power and the battery SOC.

2. My Balmar alternator regulator has a Boost and Absorption voltage that are different. So it gets to 14.4 volts and can stay there for x minutes - or until the current into the batteries is starting to fall, and then it goes down by 0.2v - below the gassing voltage - for the rest of the absorption time which can then be set quite long without fear of excessive gassing.

3. On my Victron shorepower absorption time is 5 times the time to get to Boost voltage. This can be changed. It has to be an intelligent combination of many factors. If the charge current that the controller can supply falls too low when the array power is still high that is a good indication that the batteries can't accept any more charge, rate of change of current, sudden high current demands which must be extra boat loads which then disappear, rise and fall in battery voltage. The Smartguage Battery Monitor can very accurately calculate when the battery is fully charged, just by measuring battery voltage 1100 times a second! All you need is very clever software.

All these settings need to be able to be set for each boat/battery setup.

[goboatingnow]

Originally Posted by 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.

PWM charging , ( ie proper PWM, not solar PWM ) hasn't taken over because there are little quantifiable gains , greater design challenges and often prohibitions from battery manufacturers. In today's electronics cheap or dear is often set by marketing departments not the price of the components.

Mppt isn't PWM chargers. Which mppt controllers are using PWM charging. Often they do so because you have switched mode conversion anyway and its cheap to pulse charge. , but I don't think any of the consumer mppt units are going anything other then 2-3 stage DC charging.

Apple do not allow replaceable batteries , because of Li technology. Firstly the battery lasts long " enough" secondly Li charging means the battery needs to tightly coupled to the electronics. This is a trend in all Li products. Its nothing to do with the issue of changing batteries ( seen am apple mouse, trackpad etc recently !)

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.

A charger can only use current and voltage , you can monitor that as well, equally the science of LA charging is well documented. You can determine enough to know if you are looking at 2-stage , 3-stage , pulse , absorption cutoffs , safety timers etc. sure you can't read the code, but you can see the method the device is using to charge the battery , after that who cares.

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.

There are many methods to implement constant voltage and constant current systems, some may step , others may be continuous analog, often the " step" you saw is that the regulator is digitally controlled by a micro and the voltage is set in preset steps rather then an analog constant current. At the end of the day , its just CC charging

In practice battery resistance sets voltages not charger circuits. But what you describe is again just a variant of CC CV charging , what you described is also a function of simple mppt design where the charging voltage control is used to regulate the input to the mppt so as to move the panel operating point. ( ie simply letting max current flow would drag the controller away from the panel Vmp ) , so in mppt design , you must control current through every part of the charging process so that so have the ability to actually load the panel correctly to achieve Vmp. This is because some low cost mppt implementations don't have true DC DC converter isolation between the input mppt process and the charging process

Again there no magic. The charge method is a function of the mppt design but its just 2stage charging

[/QUOTE]

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.

[/QUOTE]


The costs of toroids today from China is cheaper then I was buying them from the UK 30 years ago. The change over has nothing to do with transformers

Today switched mode is popular because its far more thermally efficient ( and hence more efficient ) , lower weight and more controllable. Modern ICs means the considerable circuits needed to support good SMPS can be easily design in as opposed to numerous discrete components otherwise needed. SMPS is simply a technically better way , especially in high powered designs., that's why it's prevalent. This has nothing to do with pure DC or pulsed DC charging , the output of most SMPS is smoothed to DC, proper high power pulse DC charging of big LA banks is quite uncommon and not something in see regularly.

But the MPPT market? Catering to folks who have probably already spent a thousand dollars on solar panels and anothousand 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>

Sure , there is lots of snake oil in the mppt market. How many users actually validate that the controller actually does Vmp tracking, how many actually verify charge controller performance. But then again this is true in many areas , so what , I'd retort.

Dave

[goboatingnow]

Originally Posted by sailinglegend

1. It should be whatever gets the most amps going into the battery - depending on the Panel power and the battery SOC.

2. My Balmar alternator regulator has a Boost and Absorption voltage that are different. So it gets to 14.4 volts and can stay there for x minutes - or until the current into the batteries is starting to fall, and then it goes down by 0.2v - below the gassing voltage - for the rest of the absorption time which can then be set quite long without fear of excessive gassing.

3. On my Victron shorepower absorption time is 5 times the time to get to Boost voltage. This can be changed. It has to be an intelligent combination of many factors. If the charge current that the controller can supply falls too low when the array power is still high that is a good indication that the batteries can't accept any more charge, rate of change of current, sudden high current demands which must be extra boat loads which then disappear, rise and fall in battery voltage. The Smartguage Battery Monitor can very accurately calculate when the battery is fully charged, just by measuring battery voltage 1100 times a second! All you need is very clever software.

All these settings need to be able to be set for each boat/battery setup.

Bit of a misunderstanding of electronics here.

The internal resistance of the battery during charging determines in effect the terminal voltage. The battery typically being a far smaller equivalent input resistance then the output resistance of the charger.

So usually in bulk mode the charger cannot determine terminal voltage , it just supplies as much current as it can consistent with its power. The terminal voltage is " set" buy the battery. In effect the charger is in current limit

At a certain point the current will drop so that the charger no longer is in current limit, the terminal voltage will rise as a result of the charging process, under at a certain point , the charger must begin voltage regulation otherwise an undesirable characteristic of LA will rear its head. The charger does voltage regulation by increasing its output resistance which limits currents and hence controls voltage. Hence the charger transitions from current limit mode ( a sort of CC ) to constant voltage regulation , ( with a current limit usually )

At this point determining absorption end point is quite complex , most chargers merely sense current flowing from the charger and once this drops to a preset value then absorption mode is ended ( ie the charger increases the output resistance and current falls and the battery chemistry reduces to a float voltage ) some chargers , especially with digital control systems, run " safety " timers that protect against inadvertently staying in absorption mode too long. System loads while charging are the main reason absorption mode gets extended

Some chargers , like many cheap PWM solar regulators , just stay in absorption mode permanently.

You can also do change in current over time ( di/dt) and optionally dv/dt ( often used in nicd , NiMh, Li etc) to determine battery status ( or more correctly to infer such status )

What smart gauge go is learn the dynamic voltage model of an LA battery. Voltage does correspond to SOC in a LA even under charge and load , but is a complex non linear relationship.

Dave

[hellosailor]

Not so simple:

"1. ... lowering the Voltage means more Amps into the battery for same panel Power." Lowering the voltage does not automatically raise the amperage, it just means more of the wattage MAY be converted into amperage, assuming the controller is set up to do that.

"Just how much higher then the battery's voltage should it be?"
I was told that's not a simple answer. It will depend on battery chemistry, and more importantly on internal temperature, so some assumptions are to be made and a manufacturer is more likely to give you a number that is intended to "do no harm" than to give you a real spec on that.

"2. Absorption Voltage should be best found in battery's specs."
Another number designed to prevent you from doing harm. If you could monitor the internal temperature (and for sealed batteries, the pressure) then you could push the limits more.

Remember, a stored energy device like a battery is bascially a bomb. Push too much energy too quickly, and it explodes as the "containment" fails. That's part of the reason battery makers don't want to confuse the end-users with too many technical details, they want to protect themselves from more battery explosions. "More" because there are literally thousands every year anyhow, just using conventional chargers in conventional automotive installations.

[catakate]

Originally Posted by hellosailor

Lowering the voltage does not automatically raise the amperage, it just means more of the wattage MAY be converted into amperage, assuming the controller is set up to do that.

Good thing you brought that up!
How each and every good info will be put in practice is beyond the scope of this thread but every suggestion is welcomed. My goal this far is to put together a draft with all known techneecs for maximizing the charging efficiency.