State Of Charge (SOC) Chart for AGM Batteries

madaboutled · Guru

State Of Charge (SOC) Chart for AGM Batteries

Cruising Cruze · Guru

Hi Steve

I've got this hanging in the van

Cheers John

-- Edited by Cruising Cruze on Tuesday 16th of June 2015 11:44:41 PM

madaboutled · Guru

That's sort of what I had in mind for SOC but also another to show at what point it's OK to charge/use devices whilst charging the batteries from the panels.

Ondabeach · Senior Member

John, your colour chart is a good idea mate, but you need to move your yellow and red bands up 4 places with yellow (getting low) starting at 70% and red (critical) starting at 50%. Taking your batts below 50% will dramatically shorten their life. Really, if you're going to have a chart, 100% down to 0% of usable power should be on your chart, where you have 100% down to the 50% mark.

12v mobile phone chargers are going to draw less than 1 amp form your battery, so you could charge your phone pretty much any time as they will typically accept anywhere from 9v to 18v as an input. A tablet is going to use maybe 2 or 3 amps and laptops up to maybe 10amps for a big one.

If you're charging from solar, then the power going in is 'clean' or 'smooth' so even sensitive electronics can be used when charging. Most modern equipment is fairly tolerant of 'noisy' power that you get from some older generators.

-- Edited by Ondabeach on Friday 19th of June 2015 12:36:59 PM

-- Edited by Ondabeach on Friday 19th of June 2015 01:15:37 PM

Peter_n_Margaret · Guru

madaboutled wrote:
That's sort of what I had in mind for SOC but also another to show at what point it's OK to charge/use devices whilst charging the batteries from the panels.

While the battery is being charged (or discharged) it is not possible to establish its voltage or its state of charge. It must be at "rest" for some time to do that.

Also, power used while the battery is being charged comes direct from the charge source without going in and out of the battery.

There is no problem taking AGMs well below 50% from time to time. That is what they are designed to do.

Take a look at the Fullriver web site. There is lots of good (factual) information available on charge/discharge life cycles that can be expected.

Cheers,

Peter

Phil C · Guru

When I first started caravanning I was astounded that a 110AH battery would only be useful if not discharged lower than 50% of its full capacity. One tends to think in terms of what a battery will deliver and for how long till "flat". These fancy new batteries (AGM etc are well past my technical use by date). I now have a better understanding of these critters.

The chart is a fine idea, but it relies on us reading something and not being 100% sure if its charging or discharging. From what Peter says ( and I agree with him) that can never be determined unless its at night and everything is off.. The modern chargers condition the battery when fully charged (another thing I needed to understand) so if my panel tells me its charging one moment, then discharging I have no need to be concerned.

Im not sure about this or if one has been invented but a voltage alarm say set at the 50% voltage mark to sound a buzzer or such would be ideal. It would be interesting to see what others think about that one.

Cheers.

Baz421 · Guru

A good thread and some good info but I thinks the theory and practice collide from time to time. I'll give an example.

Its 0900 the suns up and your battery voltage is 13.8V and solar is cracking along and charging 20A.

What is the SOC of your battery???? Any ideas??? Well this info doesn't tell you. All it says is your batteries are being charged.

It's now 1200 and sun is still good and battery voltage is 13.8V and charging 20A.

What is the SOC of your battery???? Any ideas??? Well this info doesn't tell you. All it says is your batteries are being charged.

It's now 1500 and suns up and your battery voltage is 13.8V and solar is cracking along and charging 20A.

What is the SOC of your battery???? Any ideas??? Well this info doesn't tell you. All it says is your batteries are being charged.

THE QUESTIONS ABOVE ARE REAL TIME QUESTIONS.

So when do you plug in the laptop/phone/wizbangs to charge them.

IMHO it comes down to knowing your batteries ie if I draw down to 12V the night before I need to put back 200ah the next day. So 10 hours of sunshine will do this IF and it is really an IF I get 10 hours of sun to give 20A ALL DAY.

Will this happen, probably not.

BUT HERE'S THE PRACTICAL SIDE

I can probably plug in my accessories to charge and the charging current may increase to 23A,,, ie the panels supply the load and charge the batteries at 20A.

Not so simple,,, many factors involved,,, theorists will be all over me here.

I would charge my accessories as soon as the charging hit the 20A (for example) and see how the charging goes for the day and the Amps delivered for any time during the day.

NOW THE OPPOSITE.

If the charging current was say 10A on a winter's day I know (again from experience) I will never be able to generate 200ah during that day. I would therefore not charge accessories but give the batteries the best chance to recover.

I hope this simple explanation helps, but each application is different so IMHO the sooner you get the "feel" of what's happening the better.

We have 480W of solar panels and previously 400ah (now 480ah) of battery capacity as our choice and often we have an "excess" of solar capacity, so we charge whatever needs it,,,, laptops/cameras/phones etc etc.

Good luck all and if in doubt keep records of what's happening, how you think your batteries are, and how quickly they discharge when you load them up, ESPECIALLY after sunset. You will get the hang of it I'm sure.

Cheers Baz.

I just ducked my head so theorists can "av a go".

Phil C · Guru

Love this thread...

Baz, I just thought about it. If we are discharging no more than 50% that means with a 100AH times two combo, 8 hours at 10 amps would just about top them up. Not shooting you down in flames or anything BUT I forgot the 50% thing and thought it important.

Cheers

madaboutled · Guru

Phil C wrote:

Im not sure about this or if one has been invented but a voltage alarm say set at the 50% voltage mark to sound a buzzer or such would be ideal. It would be interesting to see what others think about that one.

Cheers.

Phil, I have a Battery Monitor who's Red LED will light up IF the battery gets to 12.00 Volt, I've simply tapped into that circuit sending it to a Change Over Relay which will then cut off the power to preserve the batteries. Once battery level is above 12.00 Volt the Replay will switch back. I also have a heavy duty power supply that supplies 12v power when on Mains Power. Again I use a relay to detect power from the power supply to switch off using the batteries to give them a rest and allows the solar panels to bring the batteries up to full charge. It's more or less a set and forget system, but educating the missus when she can charge her laptop or other "must have's" when we're not on mains power is a constant battle.....

Baz421 · Guru

madaboutled wrote:
Phil C wrote:

Im not sure about this or if one has been invented but a voltage alarm say set at the 50% voltage mark to sound a buzzer or such would be ideal. It would be interesting to see what others think about that one.

Cheers.
Phil, I have a Battery Monitor who's Red LED will light up IF the battery gets to 12.00 Volt, I've simply tapped into that circuit sending it to a Change Over Relay which will then cut off the power to preserve the batteries. Once battery level is above 12.00 Volt the Replay will switch back. I also have a heavy duty power supply that supplies 12v power when on Mains Power. Again I use a relay to detect power from the power supply to switch off using the batteries to give them a rest and allows the solar panels to bring the batteries up to full charge. It's more or less a set and forget system, but educating the missus when she can charge her laptop or other "must have's" when we're not on mains power is a constant battle.....

Sounds like a great idea to me,,, set and forget works for me.

Phil C · Guru

Baz421 wrote:
madaboutled wrote:
Phil C wrote:

Im not sure about this or if one has been invented but a voltage alarm say set at the 50% voltage mark to sound a buzzer or such would be ideal. It would be interesting to see what others think about that one.

Cheers.
Phil, I have a Battery Monitor who's Red LED will light up IF the battery gets to 12.00 Volt, I've simply tapped into that circuit sending it to a Change Over Relay which will then cut off the power to preserve the batteries. Once battery level is above 12.00 Volt the Replay will switch back. I also have a heavy duty power supply that supplies 12v power when on Mains Power. Again I use a relay to detect power from the power supply to switch off using the batteries to give them a rest and allows the solar panels to bring the batteries up to full charge. It's more or less a set and forget system, but educating the missus when she can charge her laptop or other "must have's" when we're not on mains power is a constant battle.....
Sounds like a great idea to me,,, set and forget works for me.

Thanks for that, do you have any circuits or commercial info for me please, it is something I would like to investigate further.

Cheers

madaboutled · Guru

Phil C wrote:

Thanks for that, do you have any circuits or commercial info for me please, it is something I would like to investigate further.

Cheers

It's simple enough, the battery monitor I have is a Rotronics AM12R, but can't buy them anymore. The relays are just standard 12v Auto 30Amp 5 Pin Changeover relays. You could use any monitor that has different colour LED's for different statuses then just tap into the circuit for the LED corresponding to the voltage level required to cut because the switch mechanism on the relay's can be triggered by very low voltage.

I've attached a very basic wiring diagram of my set up.... might be of use

exa41 · Guru

My solar regulator shows state of charge and also cuts off power to protect the batteries at a programmable voltage, plus current in and out of the batteries.

Muzzlehatch · Senior Member

@Baz421 " theory and practice collide from time to time "

" In theory there is no difference between theory and practice but in practice there is". That is absolutely true when it comes to Solar Systems - more Art than Science.

Depending on the time of year and the weather you can go from having n embarrassing plentitude of power, to struggling to keep the batteries charged with a minimal load. Good call on your observations !!