Battery S.O.C.

[shonky]

Hi, all.

Can anyone tell me if there's a mathematical correlation between the number of amps going into the battery and it's state of charge?

[kiwipaul]

Yes there is but it's beyond human computation.
It requires the complete history of the battery both in charge & discharge cycles.
try http://www.smartgauge.co.uk/
but it is expensive and (IMO) not proven but I'd suggest it would work.

[BruceS]

In a word ... no!
For a particular battery ... yes.
Obviously it would depend on AHr of the battery involved.
Simply 50AHr into a 100AHr battery wouldn't be the same % as if it was going into a 60AHr battery.
State of charge (SOC) is really an expression of a percentage of charge.
There are various types.brands of SOC meters.
My Victron uses SOC in any way you want it to express it.
EG.... If you have AGM batteries and it's OK with them/you to 'flatten' them down to 50% of their stated capacity, then with the victron you would set the 50% usage to be 0 (Zero) and fully charged to be 100%.
So you can see now the % of charge is not SOC anymore.
BUT .... by reading the SOC meter and religiously ensuring you never go below Zero you should never hurt the battery by 'flattening' it too much.
That also means that the 100AHr battery you bought will now only allow you 50AHr before the alarm goes off (when set).
As the battery ages you will need to reduce the 0 level (raise it?) to compensate the reduction of 'holding capacity'.
A disclaimer : all this from an uneducated mug!!
Hi Bruce!!

[shonky]

Hi, all.

Bruce S. - as one to another, thanks for your input. Might just keep on using the genny if at 4pm the PL40 is showing a shortfall of more than 20 amp hours.
BTB we're currently at the Dam Fine Rally - having a great time but might tie a label on the Jaylec 20amp charger renaming it "Six Pack" It's had a lot of use recently.

[BruceS]

Definately advise you to 'top up' with genny rather than allow your batteries going too low.
Can you tell us roughly what voltage you have in your house batteries before sunrise or very shortly after?
Does your fridge/freezer run off your house batteries or on gas over night?
Maybe they should rename it "Damn Cloudy Rally" ??
Maybe grab a 40A charger? Is your genny under loaded with the 20A one?

[shonky]

Hi, all.

Bruce S. - At dawn the battery voltage is about 12.5, and the fridge is a Dometic 90 compressor model, drawing about 1.8 at night, but up to 4amps during the day, with the Imac probably on around 5 hrs daily. There's a 40amp cheap charger running through the PL40, and a Projecta 25amp going straight to the main battery terminals. Works well. Oh, yes, 4*125 AGM's.
There's no problem with the charging setup, just had too much coffee, not good for an inquiring mind.

[T1 Terry]

A lead acid battery roughly uses 10% more than the calculated amps the equipment connected uses for every time you exceed a multiple of 5 amps per 100Ah capacity. If you use 5 amps then only 5 Ah worth of energy was reduced from the battery, 10 amps and you reduced the capacity by 5.5Ah, 20 amps and you reduced the capacity by 4 x 10% of 5 amps plus the 20 amps every hr you continue to discharge it, 20 amps from a 100Ah battery for 1 hr continuous will use 22Ah of the capacity the battery had.
What capacity did you have to start with:
If it was a 100Ah battery fully charged via a generator or solar but still in use while charging, the battery will have no more capacity than 95Ah and it would need to have reached 14.4v and stayed there for 4 hrs. When it reaches 14.4v the rough figure is 75% charged or 75Ah per 100Ah capacity.....
Now to put it back, if you used 50% of the available capacity you will need to put between 10% and 20% more back in to get it back to the same point, if you took 50ah out you will need to put up to 70ah back to reach the point you started from..... these are all rough drawn in the sand figures, but you will be reasonably close to the target with them...... now you know why we say lithium batteries are so easy to work with, exactly what you took out no matter what the rate up to 100 amps per 100Ah capacity is all you took out and all you need to put back, and it will take it as fast as you can put it in all the way up to 95%, any thing less than 20% of the capacity in amps, 20 amps per 100Ah capacity, and it will take it all up to 99% full, easy to calculate how long it will take to reach fully charged eh
Bet you need another cup of coffee now

[shonky]

Hi, all.

T.I.Terry - does the same battery draw apply to AGMs?

[T1 Terry]

Hi, all.

T.I.Terry - does the same battery draw apply to AGMs?

Flooded cell, AGM and Gel are all just lead acid batteries, the AGM and Gel technology require lower charging voltages and some restriction on max charging current (amps) particularly the gel type, as there is no way of replacing the lost electrolyte in an agm or removing the bubbles from the gel in a gel electrolyte battery. The technology itself is rather inefficient, but up till around 20 yrs ago it was the best of a bad batch. The Edison battery is by far the best battery for long life, but only around 60% efficient, the flow cell battery is more efficient than the lead acid battery, but weight is an issue. Power to weight LiPo is about the best there is at the moment, but the fact they can burst into flames if over charged, dragged flat, charged too fast or discharged too fast makes them too dangerous for high capacity use.

LiFeP04 is the only stable chemistry around at the moment that is both energy efficient with a very small inefficiency, too small to measure in a house battery situation as it's in the 0.0... of 1% when use within its designed operating range. As far as the weight issue, it comes in second to LiPo but the safety factor makes it the better choice.
Tesla use a combination of lithium, cobalt and aluminium in its car cells and plan to use the same for one of the Tesla Powerwall batteries, I'm assuming the 7kW everyday use pack, and the other will be a combination of lithium, manganese and cobalt... but there is still confusion as to which chemistry will be for rapid cycling and which will be for long term storage and back up power use. The point here is, all these battery packs are liquid cooled/heated to keep the cell temperature stable, that just about eliminated them for RV use as the cooling/heating system would add more weight, complexity and take up more room.
There is nothing on the 10 yr out horizon that could come to the retail market that will be better than the LiFeP04 chemistry for RV power use so there is little point in waiting for the latest and greatest while still using 19th century technology

[native pepper]

There is nothing on the 10 yr out horizon that could come to the retail market that will be better than the LiFeP04 chemistry for RV power use so there is little point in waiting for the latest and greatest while still using 19th century technology

Was talking to some people last week and they say the next technology may likely be, lithium graphene. There is a company in Sth Aus who are experimenting with it at the moment and working with the graphene makers there. My techo friends reckon because of it's amazing conductivity and strength, it may turn out to be the best thing yet.