My Amp doubt

[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

[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]

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]

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]

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.

[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.

[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.

[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]

Dereck,

Well ... that's true for trivial batteries and for systems designed not to reach 100% SOC, but it's not true -- and becomes very complicated, very fast -- for batteries that are useful and need to reach 100% SoC.

NiMH require thermal sensing at any useful level of complexity because the activation voltage for the chemical reaction decreases with temperature -- meaning, warmer cells charge faster. And without something that can monitor multiple zones within the pack, you could be frying some cells and not charging others, and have no clue at all which is which.

[john p]

Sunking ,care to tell us how you arrived at the figure of 8000 cells??With Lithium to make a 12 volt 1000 AH string can require up to 8000 individual cells.All the cells I have used are nominal 3.5v at 10ahr.
Thundersky also have a 12v 90ahr battery MODEL NO：TS-LP12V90AH My guess then you only need about 11 in parallel to get 1000 ahr??

[Sunking]

Dereck,

Well ... that's true for trivial batteries and for systems designed not to reach 100% SOC, but it's not true -- and becomes very complicated, very fast -- for batteries that are useful and need to reach 100% SoC.

How is it complicated? To go from 90% to 100% requires the second stage charge which is constant voltage until charge current decays (tapers) reaches 3 to 5% of initial charge current. No more complicated than the 2nd stage (absorption charge) of a 3-stage charger lead acid battery charger. It is the exact same algorithm and requires the exact same hard and software. All you are doing is eliminating one stage (3rd float stage) and some expense. Sounds simpler to me and I know is less expensive.

[Sunking]

Sunking ,care to tell us how you arrived at the figure of 8000 cells??With Lithium to make a 12 volt 1000 AH string can require up to 8000 individual cells.All the cells I have used are nominal 3.5v at 10ahr.

Simple John by using the same extremes you are. How many 3.6 volt 2 AH cells does it take to make a 12 volt @ 1000 AH?

It takes 4 - 3.6 volt cells to make a 12 volt @ 2 AH equivalent string right. You would need 500 strings to get 1000 AH.. or 4 x 500.

Oops, my bad, I made a mistake, used pencil and paper this time instead of protein computer It would take 2000 cells. None the less the point is the same, it takes a lot of fricking expensive cells which you had better protect with some form of BMS.

But the real main issue is price. For now Lead Acid will dominate the RE market until the economics go the other way.

[john p]

Sunking I wish you were in purchasing dept here . If I ask for 20 lead acid batteries here to experiment with I get only 10 if you were here could ask for 20 and get 80.

[Sunking]

Thundersky also have a 12v 90ahr battery MODEL NO：TS-LP12V90AH My guess then you only need about 11 in parallel to get 1000 ahr??

You are talking packs, not cells.

[greenHouse]

You are talking packs, not cells.

Not all Li-based batteries are small factor tubes. It's possible to built a Li-Ion cell as a plate that has a much higher capacity than a tube, then stack those plates into a single cell.

The Tesla is about 6,000 2AH 3.6 volt cells, but those are all small cells designed for laptops. Tesla went that route based on the safety experience with those cells, and the fact that they have become a commodity.