12 Volt or 24 Volt?

[native pepper]

Kappy, if you connect 4 x 3.2v cells positive to negative, you end up with 12.8v and the amperage of each cell, which is called a serial connection and is a combination of the voltage, but not amps. So 4 x 100 amp cells connected in series gives you the combined voltage, but only 100amp output. If you connect the 4 cells positive to positive and negative to negative, you get the combination of amperage and not voltage, this is called a parallel connection. So you would end up with 3.2v and 400amp output.

To get bigger voltage means connecting more cells in series and to get bigger amps, means connecting the cells in parallel. That's the only way I can work it out, all the maths in the world won't help me, just simple practical things you can see is the way I go and with batteries/cells connections, you can see what how things are connected and go from there. CCA is for starting things, when choosing your batteries, forget CCA and think deep cycle amperage and with lifepo4, you can think big in you usage. Unlike lead acid where you will be lucky to get 35-50% of the batteries capacity for use before your voltage drops beyond use and lessen their life. With lifepo4, you will get 80% without any problems and at much higher voltages, compared to lead acid. We got or lifepo4 cells, chargers and equalisers much cheaper than retail, because we buy in a group. This reduces the cost dramatically now we have what we believe is the best lifepo4 charge system around, as we had built dedicated lifepo5 charge controllers and along with the equalisers we use, it's just plug in and that's it. I'm sure there would be other group buyers around and if not start one.

[T1 Terry]

you are basically starting again Kappy, lithium lithium lithium.
You dont need to change the panels but need a regulator to suit

So I need a different controller from the Steca I already have?

Says its a 12/24 volt.
I have to admit I'm a little nervy at what I see is the cost of lithium compared to good quality AGM's.

I can get quality AGM with an unconditional replacement warranty for 12 months with a further 2 years for under $1000.

Still am confused about what lithium to jump at,
https://www.ev-power.eu/en/By-Brand-Man ... param=calb
I stumbled across these, I think Dapope has this type.???????

All the others I see start at over a grand each.

Still need to digest as much info as possible.

Had the batteries tested by another independent today and 3 are toast one passed.

Maybe CCA his not applicable for house batteries but it makes sense to me when they failed overnight with really little draw.

400Ah of AGM will give you 200Ah useable down to the recommended 50% state of charge and this will still deliver 12v at a load no more than 20 amps. If you count each time you take the battery down to 50% SOC as one day, the AGM battery will last for approx. 700 days or 700 cycles as the manufacturer calls it. This relies on the battery returning to 100% state of charge after each 50% discharge cycle, if you don't then you won't see the 700 cycles and still have 12v at a 20amp load. The price? Batteries direct http://www.batteriesdirect.com.au/shop/ ... vAodE7oDiw have them for $363 per 100Ah plus freight, so $1452 or $7.26 per Ah @ 12v for the 200Ah useable
Lithium can be taken down to 0% SOC without harm, this is not zero voltage but 100% of the advertised capacity, therefore to have the same useable 200Ah and still have 12v plus available only requires a 200Ah lithium battery. Rough price at the moment is $1.80 per Ah @ 3.2v, it requires 4 x 3.2v in series to build a 12v battery so 4 x $1.80 = $7.20 per Ah @ 12v for the same 200Ah useable.... cheaper not more expensive.
If you are happy to get the same 700 cycles you don't need anything else, if you want the 7,000 cycles then you need to spend $$ on battery strapping and condition charging and a battery management system to make what you have now work with the lithium batteries.
In your case changing from 24v back to 12v means the solar regulator must be changed and the mains charger, maybe the DC to DC charger as well depending on the type.

T1 Terry
Edit to fix me typing

[jon_d]

Hi Kappy,

This must be driving you crazy! may I try and explain. (these are my learnings)

You know a 12 volt car battery, it has 6 red filler caps. Each cap is a small battery of about 2 volts. Each of those red caps is known as a cell. When you join them up, they make 12 volts. 2+2+2+2+2+2=12


So, lithiums are the same. Except they dont have caps because each battery is a single cell.

The trick is, instead of being 2 volts, they are 3 volts.

So, now, when everyone talks about 4 cells, they are talking about joining 4 cells (batteries) of 3 volts together. 3+3+3+3=12.

When they do join them up, its known as a "pack"


Lets talk about capacity.

Martin said he has 8 cells. What that means is he has two 12 volt packs joined together. The + terminals are joined and the - terminals are joined.

That means, the pack voltage doesn't change, but the capacity is doubled.

ie: Martin has 8 x 100amp cells. This equals 2 packs (3+3+3+3) making 100amps + another pack (3+3+3+3) making 100 amps equalling 200amps total. at 12 volts.



Lets talk the difference between AGM vs Lithium capacity.

In very simple terms, if you use a AGM battery set of 600 amp/hour, and it meets your needs.

Then you only need a 300 amp hour Lithium pack. ( ie 1/2 the AGM capacity.)

This is because the Lithium chemistry can handle the bigger load.

Remember, the rough equation is 1/2 AGM equals the same usable capacity in Lithiums




In summary:

4 cells are needed to make a 12 volt pack.

packs can be joined together to increase capacity.

When determining the equivalent usable capacity between AGM and lithiums, just divide the AGM capacity by 2. (ie 1/2)


Hope that helps. Apologies if it sounds like it's dumbing it down.

jd

[dapope]

Nearly right Jon.
I have 4 pairs of 200ah cells joined to make the 400ah at 12v
So two cells are connected pos to pos neg to neg then connected in series neg to pos to the next pair and so on. Still only 4 cells

[Boblebago]

Hi Kappy

A picture is worth a thousand words.
I have 400 amps at 12 volt, 16 x 100 amp 3 volt cells.
4 x 4 cells connected in parallel 4 x 100 = 400 amp @ 3 volts then these 4 connected in series = 400 amp @ 12 volt.

Regards Geoff

[jon_d]

From the picture, there a four groups of cells.

Yellow, Red, Blue, Green. Each group is 3 volts. (3+3+3+3=12) This makes a pack.

The purple line shows the current flow in the pack. (with the plusses and minusses showing how the batteries are connected)


Each group has four batteries in it connected in parrallel. (eg 100amps + 100 amps + 100 amps + 100 amps = 400 amps)


My previous description may have been confusing by saying the packs are paralleled and not the groups. They are paralleled at the groups to make management easier.

[Kappy]

Hi Kappy

A picture is worth a thousand words.
I have 400 amps at 12 volt, 16 x 100 amp 3 volt cells.
4 x 4 cells connected in parallel 4 x 100 = 400 amp @ 3 volts then these 4 connected in series = 400 amp @ 12 volt.

Regards Geoff

Thanks Geoff, Jon.

Yes A picture makes a difference.

I think I inherited a poor system, to makes thing worse I think this stuff has been confusing me.

http://www.ebay.com/itm/Pro-Power-12V-1 ... 2058138817

Now I see the battery people are talking about things are a lot clearer.

Discovered this as an example

https://www.ev-power.eu/Sinopoly-40Ah-3 ... .html#tab2

I guess maybe I need to work out what I need to power and go from there.

The plan is to be self sufficient as possible.

I see a good Lithium system is affordable.

[jon_d]

Kappy,
glad the fog is clearing a little!

You're on the correct path which is to understand your requirements first. I think using Martin's set up as a baseline would be a good start for you. (Similar bus size, both talking about free camping, both have A/C's etc.)


With the designs, if you are going lithium's, there are some that can do it themselves and understand the shortcoming of their system. AND then manage it accordingly.

There are some who have built a fully managed systems using different approaches and technologies. Terry is one and has been tested in the field for a few years now.


Honestly speaking, given that it sounds that things are confusing you and electrics is not your strong point; may be the best solution to talk to Terry about a installation. (for me, when it comes time, I'll probably do my own)

[T1 Terry]

To add a bit more to the differences between lead acid (flooded cell, AGM, Gel) and LYP or LFP (the type of lithium chemistry we use as it is the safest). With lead acid you can't add another battery part way through the cycle life of the original battery pack without shortening the cycle life of the new battery, the older batteries will let the new battery do all the work until it is in the same condition as the rest of them, then they will sort of share the load again.
With the LYP cells, where you may have 4 cells in parallel to build 400Ah @ 3.2v, even after a few yrs you can add another cell or 2 to increase the capacity to 50Ah or 600Ah if you were using 100Ah cells. Each parallel group must have an equal number of new cells added but that is the only restriction, the new cells will work along with the older cells and all share the load. Added to this, if one cell dies it can be removed and a new one added in its place, no need to replace the whole battery pack, just the crook cell.
Having said that, it is not simply a case of dropping the right number of cells into the spot where the lead acid batteries were if you want the extended cycle life. There is a complex building and conditioning sequence that is required to turn electric vehicle cells into house battery cells, otherwise the cycle life will be similar to that of electric vehicle cells. I won't go into the process here, secret squirrel stuff as someone once said, but really it's a proprietary secret thing that we don't want to hand over to the opposition, cost way too much to learn to just give it away to them, let them spend the yrs and $$ learning.
2yr to 3 yrs will tell the story, LYP cells are tough but not bullet proof, treated wrong and they either have their death cycle accelerated or they are immediately murdered, there is blog http://www.technomadia.com/lithium/ where an American couple fitted lithium cells up and it tracks their gradual death cycle, now at some where around the 60% capacity I think after 5 yrs and that was not continuous use, so a loss of 40% capacity in 5 yrs, yet the battery packs built using the T1 Lithium conditioning process still have close to full capacity after the same 5 yrs, well 5 1/2 yrs now and many 24/7 use as they live full time off grid.

There is more to setting up lithium house batteries than first meets the eye, some are about to find that out the hard way

T1 Terry

[triptracks]

There is more to setting up lithium house batteries than first meets the eye, some are about to find that out the hard way

Agree. And, unfortunately, they will give Lithium a bad name in the process and the doomsayers will be out in full force.