solar lead acid battery controller

hi rene

surely! i try to post a schematic, as soon as i have a good circuit.

bye

walti

[snip]

Can we get a sample each then ?

Rene

what research have you done so far?

martin

hi martin

i tried to find a good ic or a circuit in the net or from books, libraries etc. i also asked some friends. i did not found a good thing so far. so i think, i must design a schematic.

as i wrote, i have some ideas how to do that.

do you also have an idea or a hint?

please tell me. thank you.

walti, dipl. electr. eng. eth, zuerich, switzerland

[...]

For a lead acid, this is basically a voltage regulator with a bit of funny back lash added. When the charging current it flowing, you allow the battery voltage to rise a bit above the "float" voltage and then drop back down to float.

--------- D1

------! LM317 !--+--+/\\/\\/---+-->!-------battery --------- ! ! ! ! / \\ ! ! \\ / ! ! / \\ ! ! \\ / ! ! ! ! ! ! ! \\! ! ! ! !------- ! ! /! PNP +------+-- ! \\ / \\ / ! V --- D2 ! GND

D1 and D2 are the same sort of diode but very different sizes.

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hi herbert

thank you very much for your posting!!

Why not? ###the idea is to charge the battery directly from the solar cells and simply to switch off when the battery is full.

This implies that you will be inserting some series sensing device and reverse polarity protection which tends to reduce efficiency of the system.

###that"s right. but the sensing device needs only some mVs with an opamp current sensor. if a mos-fet is used as a series element, the voltage drop should be less than 0.5V @ 10A (ok, @30A we have 1.5V, that is too much. but then a schottky diode with 0.4V is better)

Why is this necessary? You aren't going to be sitting in front of the display all day just to see what is going on.

Why do you need this complexity? (See reply above)

###you are absolutely right, i also don"t see a need for such a display, but my chief wants so!!

With all this "fruit" you want to include there is no way it can be simply nor canit be cost effective - (that is a relative term by the way, so it depends on a number of factors).

###i also think so. the highest costs will result from the display and the gas gauge.

For a domestic installation the main aim of a controller for alternative power systems is that it should be simple yet reliable, does not introduce losses in the charge or discharge paths, and requires minimal or no maintenance. Provided that the correct batteries are specified, the correct gauge of wiring is used, and the whole thing is installed by a knowledgable person, there is hardly a need for visual displays at all. Perhaps a simple voltmeter which can be manually switched either across the battery or the supply source is all that is needed to estimate the charging status. Similarly an ammeter which can be switched in series with either the charge or discharge leads, and can also be bypassed completely, is probably all that is required to monitor what is happening regarding charge and discharge currents. Any reverse polarity protection is best incorporated into the devices being powered. Standard fuses and circuit breakers are all you need to protect against overload currents.

###for my own use, i would do it like you write, but i develop this controller for megasol inc.

and the company says what they want to have..

Probably one of the most reliable and and cost effective methods for wind, solar, hydro systems etc, is the shunt controller. It simply connects directly across the battery supply and monitors the battery voltage. When the voltage reaches a preset maximum any surplus charge is dumped into a dummy load.

### yes, you are absolutely right. as i wrote above, i must work with the simple on/off system, which does not make a fine regulation, but simply disconnects the solar cells from the battery if the voltage is too high.

Once you have an effective controller the best way to determine if the batteries are in good order is to observe normal maintenance practices such as regularly checking electrolyte level and SG. You can't really avoid doing these things anyway so you soon know when something is wrong. ###yes, we must say the clients of megasol inc. to do so! please write me: what means "SG"?

###so i thank you very much you for your advice and your good ideas! as i see, you are an expert in this materia, and i would be glad to discuss with you further more on this intersting topic!

with kind regards

walter nussbaum, dipl. electr. eng. eth, zuerich, switzerland

hi ban

thank you for your posting!!

Siemens makes some charge controllers for 12 or 24V batteries, which can be switched to gel-type. 17V is certainly a strange number, I hope you do not apply it to a 12V nominal battery, especially with 30A charge current.

### no, no! this is a special battery with 17V nominal voltage. and 30A is the peak load current.

The Siemens controllers have a display with a SOC (state of charge) percentage, with some self-learning algorithm, you can also connect a temp sensor, but the acid weight is not done, I doubt it will be of much use anyway. ### perhaps the soc will do the job, i will look at the data sheet. thanks for the hint!

ciao, tanti saluti alla bella italia

walti

hi martin

thank you for your posting.

i tried the links:

the article about lead acid batteries from panasonic is very good. thanks!

linear technology has only Li-ion batterys, unfortunately.

maxim: i have a friend working there. he said they also only have ics for li-ion or ni-cd.

bye

walti

Why not?

This implies that you will be insering some series sensing device and reverse polarity protection which tends to reduce efficiency of the system.

Why is this necessary? You aren't going to be sitting in front of the display all day just to see what is going on.

Why do you need this complexity? (See reply above)

With all this "fruit" you want to include there is no way it can be simply nor canit be cost effective - (that is a relative term by the way, so it depends on a number of factors).

For a domestic installation the main aim of a controller for alternative power systems is that it should be simple yet reliable, does not introduce losses in the charge or discharge paths, and requires minimal or no maintenance. Provided that the correct batteries are specified, the correct gauge of wiring is used, and the whole thing is installed by a knowledgable person, there is hardly a need for visual displays at all. Perhaps a simple voltmeter which can be manually switched either across the battery or the supply source is all that is needed to estimate the charging status. Similarly an ammeter which can be switched in series with either the charge or discharge leads, and can also be bypassed completely, is probably all that is required to monitor what is happening regarding charge and discharge currents. Any reverse polarity protection is best incorporated into the devices being powered. Standard fuses and circuit breakers are all you need to protect against overload currents.

Probably one of the most reliable and and cost effective methods for wind, solar, hydro systems etc, is the shunt controller. It simply connects directly across the battery supply and monitors the battery voltage. When the voltage reaches a preset maximum any surplus charge is dumped into a dummy load.

Once you have an effective controller the best way to determine if the batteries are in good order is to observe normal maintenance practices such as regularly checking electrolyte level and SG. You can't really avoid doing these things anyway so you soon know when something is wrong.

Siemens makes some charge controllers for 12 or 24V batteries, which can be switched to gel-type. 17V is certainly a strange number, I hope you do not apply it to a 12V nominal battery, especially with 30A charge current. The Siemens controllers have a display with a SOC (state of charge) percentage, with some self-learning algorithm, you can also connect a temp sensor, but the acid weight is not done, I doubt it will be of much use anyway.

--
ciao Ban
Bordighera, Italy

try looking at the battery manufacturers for example

and

There have been some very good posts here about battery charging over the years, so use google groups search facility. Also try

I think i saw some good app notes there, and of course maxim make a glut of IC's

martin

I remember now, TI/unitrode, such as

martin

hi martin

that´s a good device, the bq2031. perhaps i can use it. thanks!

walti

Given that you are doing the design based on a client specification then you have no choice. I therefore agree that you are bound to give him what he wants despite any recommendations as to the necessity of certain functions.

It did occur to me that modern deep cycle storage batteries using Absorbent Glass Mat (AGM) construction does make it impossible (and unneccessary) to check electrolyte levels and SG, so some other means of determining the battery condition may be desirable. I still don't think a great deal of assistance can be gained by having gas gauges and SoC readings even with AGM batteries. If all batteries in the string deteriorate at the same rate gauges will likely indicate this symptom but I think their readings will only tend to confirm what is already detectable using local knowledge of the system. If only one battery fails in the string, gauges are not really going to give any reliable indication of the problem. You still need to get down to basic checks on each battery in the string in order to find the culprit.

Good luck!

Ross Herbert

SNIP

hi herbert

yes, that's my problem: i'm bound on these specs.

that's interesting: so you will say that the charge of cells in a string can be different despite charging/loading current is the same?

thanks for your good advices?

i wish you a nice week!

walti

Solar charge controller doesn't have to be very quick or precise. If response time on the order of minutes is too slow, you've got way too much solar or way too little battery. Use a PIC (or other processor) with A/D. Use a PWM shunt (charge dump) regulator. PWM rate can be SLOW, SLOW...no problem with doing it in software.

For a domestic system, dump the excess energy into a big resistor in the water heater.

And the PIC can do all your integrating, storage, display. And it'll be cheaper than trying to do it analog. And easy to change in firmware when your beta test discovers it's all wrong. mike

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Well....since insolation varies many orders of magnitude over a 24 hour period, just how do you propose to make a solar pack that outputs "just a little more voltage than the battery"????

Problem with a buck switcher is that it is lossy ALL the time. The shunt switcher is lossy only when you have more solar energy than you can use.

Now, if you were advocating a higher voltage solar pack and a buck switcher that operates the solar pack at maximum power output for any level of light input, you might have a point... My research indicates you'd get more benefit from sun tracking than from peak power sensing. mike

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[...]

If you simply open the connection between the charger and the battery, there is no excess energy dumping needed.

If you make your solar pack such that it outputs a little more voltage than a charged battery, a very simple system will do. There is not much to be gained by adding a switcher. If you want to get the last bit of energy, a very simple bucker will do nicely.

The micropower PICs can work at low clock speeds over a wide voltage range. This means you can use a very bad regulator to run the PIC.

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kensmith@rahul.net   forging knowledge

I think I came to the same conclusion, once.