Battery State of Charge.

meetoo · Guru

Battery State of Charge.

rockylizard · Guru

Gday...

I can only speak for myself and my system.

My system has a solar controller which I believe to be what you are calling a Battery Management System.

The controller shows, let's say, at 7am 12.4V in the battery, it will show maybe 13V on the panels, and 0.00amps being fed from the solar panels to the battery. (sometimes those numbers will show bulk charge and e.g. 0.3amps trickling in to the battery)

9am - controller shows, let's say, bulk charge 13.8V battery, 20V on the panels and 7.8amps coming to the battery.

10am - controller shows, let's say, absorb charge 14.5V battery, 20V on the panels and 7amps coming to battery.

11.30am - controller shows, lets's say, float charge 13.4V battery, 20V on the panels and 0.00amps coming to battery.

I am told that means the battery is at full SOC at those readings. My battery stays at float 13.4V all day and only begins to drop when suns goes (eg to 12.8V) and gradually to 12.4V by the time I put my cute liddle head on my soft and snuggly pillow.

Now, to sit back and be told that is all wrong and my system is useless and the battery is near to dead. cry

Cheers - John

T1 Terry · Guru

If you want to test if they will take any more charge, raise the charging voltage to 14.4v and see if the amps drop back to 2 amps or less after 5 mins or so, if it remains higher than that they are still taking charge, the only reason they drop back to zero amps is because the charging voltage dropped. All lead acid batteries will take around 2 amps or so at 14.4v until absolutely full, then it will drop back to around 1 amp or so because that is the electrolysis in action turning the electrolyte into hydrogen and oxygen and a true AGM battery will recombine that back into water so there is minimal electrolyte loss.

This is different to testing the actual condition of the battery. That is done by going through the first stages of getting the battery fully charged, then a 60w light bulb for every 100 ah advertised capacity load on the battery. If it still reads 12.8v after 5mins the battery is in good condition, 12.6v shows still serviceable but getting tired, 12.4v says it is still going but lost at least half its usable capacity, 12.2v says its a door stop.

T1 Terry

Jaahn · Guru

meetoo wrote:
For those of you that do not have a battery management system, (probably most of you) and say that your batteries are fully charged by solar by lunch time, how do you tell and know for sure that the battery/ies are fully charged back up? Thanks.
Cheers, John.

Hi smile

You could do what Terry says but that seems a bit excessive every day biggrin

Like rockylizard you should have a decent solar charger which has a 3 stage charging system suitable for your batteries. Then when it shows the charge has gone through bulk - absorb - to float early in the day or well before sunset, you can be happy. Most have some lights even if they have no meter readings.

But if you have a meter you will soon get the hang of how the reading go over the day, like rocky does, and if you look occasionaly to see if is behaving as expected you can spot a problem when it happens, and fix it before the batteries are flattened.

Some cheap solar chargers have only one set voltage and are not recommended, or three step voltages which are not very good for batteries health. Who knows where they got them from. Adjustable settings are good and set to the battery manufactures specs. aww Or a menu of setting which will be OK.

Jaahn

PS sorry to disappoint you John, but I am not going to say that disbelief

rockylizard · Guru

T1 Terry wrote:
SNIP~~~

This is different to testing the actual condition of the battery. That is done by going through the first stages of getting the battery fully charged, then a 60w light bulb for every 100 ah advertised capacity load on the battery. If it still reads 12.8v after 5mins the battery is in good condition, 12.6v shows still serviceable but getting tired, 12.4v says it is still going but lost at least half its usable capacity, 12.2v says its a door stop.

T1 Terry

Gday...

I am a little confused, but that really is not unusual.

Given your example of 60W drawing power for 5 minutes seems to have an incredible drain on the battery you are using in the example.

Let's assume my battery is fully charged when the sun comes off the panel at 5pm+ ... reading 12.8V.

About 6pm, battery showing 12.7V, I put the TV on which draws 42w (about 3.5amps) and I watch TV for 2 hours. I also have LED lights on, 12V pump has been used for various amounts of time, laptop used for about 2 hours.

When I check it at 8pm before tucking me cute liddle head onto that warm snuggly pillow, the battery is showing 12.6V.

So, given I draw about 50V for over two hours and still have 12.6V does that mean my charging system, and the battery condition, is going OK?

Cheers - John

meetoo · Guru

rockylizard wrote:
Gday...
I can only speak for myself and my system.
My system has a solar controller which I believe to be what you are calling a Battery Management System.

I read the replies so far with interest, thanks.

Rockylizard, what I was referring to as a Battery Management System was something like a Victron BMV700 or similar which does show actual SOC.

Cheers, John.

T1 Terry · Guru

rockylizard wrote:
T1 Terry wrote:
SNIP~~~

This is different to testing the actual condition of the battery. That is done by going through the first stages of getting the battery fully charged, then a 60w light bulb for every 100 ah advertised capacity load on the battery. If it still reads 12.8v after 5mins the battery is in good condition, 12.6v shows still serviceable but getting tired, 12.4v says it is still going but lost at least half its usable capacity, 12.2v says its a door stop.

T1 Terry
Gday...
I am a little confused, but that really is not unusual.
Given your example of 60W drawing power for 5 minutes seems to have an incredible drain on the battery you are using in the example.
Let's assume my battery is fully charged when the sun comes off the panel at 5pm+ ... reading 12.8V.
About 6pm, battery showing 12.7V, I put the TV on which draws 42w (about 3.5amps) and I watch TV for 2 hours. I also have LED lights on, 12V pump has been used for various amounts of time, laptop used for about 2 hours.
When I check it at 8pm before tucking me cute liddle head onto that warm snuggly pillow, the battery is showing 12.6V.
So, given I draw about 50V for over two hours and still have 12.6V does that mean my charging system, and the battery condition, is going OK?
Cheers - John

If the voltage is 12.8v when the solar is no longer really adding anything but by 6pm they have dropped to 12.7v, the battery didn't reach 100%. A fully charged battery should be able to hold 12.8v with a 60w draw for only 5 mins, 60w divided by 12.8v = 4.7 amps divided by 60 to converter Ah into Amp mins = 0.078ah per min x 5 = 0.39ah drawn from the battery over the 5 min period ... 0.0039% of the 100Ah battery capacity or 4/5ths of bugger all wink

T1 Terry

Jaahn · Guru

meetoo wrote:
rockylizard wrote:
Gday...
I can only speak for myself and my system.
My system has a solar controller which I believe to be what you are calling a Battery Management System.
I read the replies so far with interest, thanks.
Rockylizard, what I was referring to as a Battery Management System was something like a Victron BMV700 or similar which does show actual SOC.
Cheers, John.

Hi meetoo smile

I think you are confused in the uses of the BVM700. Victron makes several solar controllers/regulators which may be called a battery management system. However as I understand it the BMV700 is only an add-on unit to fit to their controllers and give a more complete view of all the battery parameters including the state of charge. It does this by meaasuring what goes in and what goes out, with an allowance for losses. If you had one of those or similar you would know if the batteries were fully charged straight up. They need to be correctly setup initially to be accurate, reading their instructions.

Rocky, if your battery is not fully charged then the absorb time is not long enough. But I am not saying it is not fully charged. disbelief Perhaps you could edit the mistake in your post (50V> 50W) to avoid confusion to readers.

Jaahn

-- Edited by Jaahn on Friday 15th of June 2018 07:16:39 PM

rockylizard · Guru

Gday...

OOPS ... thanks Jaahn - silly me ... yeah 50W not 50V

However, it all seems to be a little academic by the sounds of it. cry

From what Terry says, my battery is never at 100% SOC, so my solar system and battery etc I have been using for the past six years is no good.

cheers - John

meetoo · Guru

Jaahn wrote:
meetoo wrote:
rockylizard wrote:
Gday...
I can only speak for myself and my system.
My system has a solar controller which I believe to be what you are calling a Battery Management System.
I read the replies so far with interest, thanks.
Rockylizard, what I was referring to as a Battery Management System was something like a Victron BMV700 or similar which does show actual SOC.
Cheers, John.
Hi meetoo
I think you are confused in the uses of the BVM700. Victron makes several solar controllers/regulators which may be called a battery management system. However as I understand it the BMV700 is only an add-on unit to fit to their controllers and give a more complete view of all the battery parameters including the state of charge. It does this by meaasuring what goes in and what goes out, with an allowance for losses. If you had one of those or similar you would know if the batteries were fully charged straight up. They need to be correctly setup initially to be accurate, reading their instructions.
Jaahn

-- Edited by Jaahn on Friday 15th of June 2018 07:16:39 PM

Hi Jaahn. smile Thanks for your replies. No I am not confused in the uses of The BMV700, and it is also for use with other than Victron controllers.

You are correct in saying that if I had one I would know if the batteries were charged up; as that is one of their main functions.

However, my post only asked how some folks without one of these systems determined when their batteries are fully charged.

Cheers, John.

-- Edited by meetoo on Friday 15th of June 2018 11:03:13 PM

Warren-Pat_01 · Guru

John (meetoo), have a read of www.energymatters.com.au/components/battery-voltage-discharge/

I guess by a lot of vans these days, my system is relatively simple. We saw a couple at Mt Isa about three years ago with a "flash" camper trailer - it had an $8,000 battery system in it & it was almost totally destroyed! They had smashed an Anderson plug on the Plenty highway & in the dust didn't see the smoke pouring out of the cabinet. One battery "looked ok" but it showed signs of smoke damage!

I do not have a huge load - TV occasionally, a couple - may be three LED lights on at once. When on power, the SETEC system works well - yes it is the "smarter" variety (proven one night when communicating with Tony-Bev). I only have one fixed panel on the roof (55w) but carry up to 100w in portable panels if we are "going bush". The battery in the van is 100Ah. Living in north Qld has its benefits sometimes - lots of sun!

I keep an eye on the voltage a few times a night (matter of pushing a button on a VM installed on top of the wardrobe). I also carry a 8A smart charger with me (for the car as well as the van) & I use that to "condition" the battery(ies) occasionally.

Batteries are too expensive to be throwing them away by neglect. The previous owners of the Eagle camper we bought only looked at the battery when they were preparing to go away & the SETEC charger installed in that van was only a 5A trickle charger. The battery, when we bought the van was STUFFED! The terminal voltage was approx. 3v, however I managed to get about 12 months out of it before I replaced it.

I carry a printed copy of the voltages shown in the Energy Matters website with me for reference.

swamp · Senior Member

Hi
Meetoo
The easiest way to tell is either a SOC meter of just at what point in time it takes to get to the float stage plus 2 hrs .