My Amp doubt

[Sunking]

Well I disagree with some of the POV with respect to charging Lithium batteries and Nickel Metal Halide. Lithium charging algorithm is quite simple employing Constant Current-Constant Voltage-Terminate. It is what is known as 2-stage. It can be even simplified to just Constant Current up to around 80% State of Charge voltage and terminate, which prolongs battery life. In contrast Lead Acid batteries require 3 and 4 stage charging algorithms.

Now with that said with respect to Renewable Energy Systems and Electric Vehicles a Battery Management System (BMS) must be used with Lithium which adds complication and thus expense. With Lead Acid technologies to make say a 12 volt 1000 Amp Hour battery takes 6 cells of 2 volts @ 1000 AH. Very few cells are involved and no automated monitoring of individual cells equalization is required. Lead Acid batteries are more forgiving to over charges, therefor manual equalization monitoring is easily accomplished on a weekly or monthly basis with a hydrometer and volt meter.

With Lithium to make a 12 volt 1000 AH string can require up to 8000 individual cells. This makes individual cells or group of cells impossible to monitoring equalization. So one needs a BMS to charge individual groups of cells to guarantee equalization and protect the investment. This is fairly expensive but available, but not feasible in RE systems. EV

[greenHouse]

To be more specific, since I'm sure some people haven't been properly scared off --

LiIon and similar technologies require some pretty fancy software and sensing. NiMH is another technology that requires something with smarts to charge.

The problem with some of these technologies is thermal runaway (can happen with most batteries) and a negative voltage response to charge when full.

You must monitor, in real time, the temperature of each cell. You =must= stop charging any cell that exceeds the manufacturer specified temperature (and it isn't all that hot -- in the 45 to 50 C range). You =must= immediately stop any bulk charge if the battery voltage =declines= in response to a fixed (or rising) charging current. If the vendor provides finishing charge details (typically fixed current for some length of time), the same rules apply.

If you don't do these things, in real time, the battery temperature can very rapidly rise. Then they can catch on fire, burst, leak, get ruined, make a mess of your back porch (got tied up at dinner once charging some batteries on the wrong charger -- even I don't have all the gear needed to charge every technology).

Companies have spent millions of dollars developing the proper chargers for these batteries. If you read the news, their ability to make mistakes and catch things on fire is well documented.

[Mike90250]

if the batteries have been used they likely have near or no life left, li-ion needs proper li-ion chargers, not a lead acid charger. making li-ion packs is not all that easy.

Ditto Charging Li-ion batteries needs a specific charger for the battery or it goes boom. Even with the right charger, batteries still sometimes go boom or flame. Just don't try.

[RifRaf]

if the batteries have been used they likely have near or no life left, li-ion needs proper li-ion chargers, not a lead acid charger. making li-ion packs is not all that easy.

[marcos]

Also, lithium-ion cells

There is another thing I would like to know:

I have 12 3.7v lithium-ion cells from 2 notebook battery packs. I wonder whether it would be a big problem to built from them, say, 6-pack of 22,2v and try to chrge it with my 24v (36Vmp) panel via my 24v 5amp regulator.

[RifRaf]

use a dc to dc adapter for the laptop, search for something lke 'truck laptop adapter 24v' i found a few switching models that should be far more efficient for you, 24v to 19v is alot easier than 24dc to mains AC and back to 19vdc. 12v to 19v is far easier to find as you just need a car laptop adapter, many more choices. as for the lights, change to a 24v globe or 2 x 12v in series so you can use both batteries. i use a 12vdc-20vdc adapter for a netbook, 40w max when charging,normally less than 20w and is 82% efficient, draws less then 2A @ 13V or so when not charging

[marcos]

Amazing

Amazing discussion here while I was absent!
The panel is 36Vmp 115W, and I have it now connected to 2x12v batteries. It sure is a linear charger, made by Xunzel, 12/24v 5amp. From what has been said here I suppose , on a sunny day, I am charging 24v system at 3-4 amps, right?
I thank you all for your comments and interest, and no worries - I indeed WAS able to understand it all, and it helped me to make a more accurate picture of my case.
The biggest thing I

[RifRaf]

here here

read the question slowly, try answer to assist the person, not to confuse with loads of stats that often appear wildly exaggerated

[john p]

This is what I think is the problem. And I think its the problem that occurs many times where a person asks a question,especially if its a very small system. ie one x100w solar panel, one cheap charge controler one battery ,and he wants to power either a few lights or is just trying to find a use for what he has.
example.. he asks about upgrading one component.. then the first thing that should be asked id "how much money are you willing to spend" ?

Its silly offering and giving all the advantages of some super dooper expensive part if he only says he wants to spend a few dollars.
I could give many examples of replies on forums where the person asking one simple question never gets an answer to his question but gets an explanation of everything else under the sun and hundreds of maths figures to explain it all.So the person asking the question goes away still not knowing anything about what he asked about..

Mabe we should all read more carefully what the person is asking, note the size of his system ,then give an answer that is economically achievable. and try to find out what percentage of loss in the system he is willing to sacrifice to keep costs down.
And try to put yourself in their shoes many dont understand the maths or even understand any electrical theory.

If a person is looking to buy a new refrigerator they just looking usually at its energy rating and if its big enough for their needs.. they not wanting the salesman to give pages of information on how the compressor works and all its design paramaters

[Sunking]

I'll bet "marcos" the OP, has a spinning head trying to follow you two

Mike you are right. All I was really trying to point out is using a 24 volt panel with a Linear CC, on a 12 volt battery is a huge waste.

[john p]

ok you all win in future i will assume like you have everyone that says a panel is 24 v I now know they mean 36v....
as for anything about the 2 batteries in parallel . i did read and amazingly understood it was a mistake..

[RifRaf]

i agree, the OP was asking about a very simple setup, sure the charger will have a fair percent of loss but why confuse the issue, what most people call a 24v panel is capable of 36v into the correct charger, and therefore the 2 batteries in series would be ok, if you read the post the charger was capable of 12 or 24v charging. the mistake about the batteries being connected in parallel was corrected in the second post minutes later!

[Mike90250]

I'll bet "marcos" the OP, has a spinning head trying to follow you two

[Sunking]

John read his post. 12 volt battery as in singular battery at 12 volts. Then he ask a theory question of 2 12 volt batteries in parallel to get 24 volts. Did you catch that 2 in parallel for 24 volts.

I am assuming when he says a 24 volt panel, he means a 24 volt panel for 24 volt battery systems which is actually 36 Vmp.

Now with that said if his panel Vmp is 24 volts, he can charge a 24 volt battery with a MPPT controller, but not with a Linear controller. That is a fact.

[john p]

sunking I think you missed the 2 main points
he says the panel is 24v I asked .. is that its real output?? if it is it wont charge 2x 12v batts in series..FACT,,,,, if it really puts out 36v then of course it coiuld be used to charge 2 x 12v batts in series
its way too expensive to use a MPPT charger on just one 115 panel.

im not calm today.. my experiment im doing for another forum is going very badly,, wasted now almost 2 work days . and $2000 worth of batteries just bought by supplies..

but my 2 points are valid on any day..