State of Charge Question

[Eric G]

I'm trying to make a chart on the state of charge of my vrla 12v7ah batteries They have a resting voltage of 13.25volts after being charged. 13.25 would be considered 100% soc.

What should be considered as 0% soc.??? the lowest value you should run the batteries down to without damage. I've googled it and not found a definative number. One site says 12.2 is zero another will say 11.5v and another 10.5v yet another will say 12.6 is 50%.

How or what does determine the lowest value.

Thanks
Eric

 

[fechter]

That's a tough question.

Measuring the voltage is not the best way to find the SOC. The voltage depends on temperature and the length of time the cells have been resting. The actual cell construction plays a part also.

10.5v is possibly a voltage under load. 10.5v after resting is a destroyed battery.

I figure if the resting voltage is 12.0 or less, it's completely discharged.

 

[Eric G]

Thanks Fechter !!! Seems I've been running down my batteries a little more than I thought.
The new 600watt Clyte and 25amp cont. does drain the batteries a little faster....

Looks like the next batts I buy will have a higher AH rating...

Eric

 

[fechter]

Lead batteries will be much happier if you don't run them all the way down. You could keep your present batteries and add another set in parallel to increase capacity.

With lead-acid, if you double the capacity, you will get more than twice the range due to decreased Peukert effect.

 

[safe]

Lead batteries will be much happier if you don't run them all the way down. You could keep your present batteries and add another set in parallel to increase capacity.

With lead-acid, if you double the capacity, you will get more than twice the range due to decreased Peukert effect.

I'm running (3) 12V 38Ah batteries and start at 13.1V and tend to stop riding at 12V after going a very fast 10-12 miles. After that point you could still ride a lot longer, but with less power... so it's less fun. Since most controllers cut off the power at 10V I'm stopping really early and that means that the batteries should last from 500 - 1000 charges. The rate at which your batteries deteriorate is directly related to the depth of discharge.

One idea I've had it to use a spare NiMh/NiCad/Lithium pack that you would switch on after the SLA batteries sag below 12V. That way you can extend the ride a little longer at full power. This will mean that I would be doing more damage to the battieries however.

The Peukert effect is very real. If you take it really easy and use less power as you ride it seems to magnify the range proportionally. So if you use half the peak power (peak current) you get something like two to three times the range. (you get free energy for being a miser)

 

[Eric G]

Hi Fechter & Safe
Thanks for the information,I've found it most helpful.