Apologies if this is the wrong forum for this topic, and I hope it's not repeating what's already well covered. I couldn't find much relevant help from a Search.
I would like to make a State of Charge meter for the unsealed lead acid batteries on my sailing boat. These are 300Ah total, 12V. They are charged by the boat's engine when it runs (occasionally) at up to 30A and more often by a solar panel which can achieve up to 2A. Discharge loads vary a lot, from 0.1 to about 10A. The purpose of the meter is to ensure that the batteries do not get discharged too deeply, and that the engine is not too long long when recharging.
I plan to use a Hall effect current sensor http://www.ampsense.com/AMP-55N pdf.pdf on the battery lead and an ADC input across the battery, both supplying data to a Picaxe (BASIC programmable version of a PIC) http://www.rev-ed.co.uk/picaxe/to do the sums.
I aim to determine state of charge by coulomb counting in and out of the battery. This seems to be more complex than I expected. From research on the web, I have found out about Peukert's law, Coulombic efficiency and self discharge.
My sources have not all been consistent but it seems that Peukert's law applies only during discharge, while Coulombic efficiency relates to charging. Have I got that right?
I expected that internal resistance would be significant but it doesn't seem to feature in the sources I found. Is it covered by Peukert and efficiency?
Is it reasonable to aim for 5% accuracy determining SOC over the range 40 to 100%?
Is Coulomb counting the best approach?
Thanks,
Derek
I would like to make a State of Charge meter for the unsealed lead acid batteries on my sailing boat. These are 300Ah total, 12V. They are charged by the boat's engine when it runs (occasionally) at up to 30A and more often by a solar panel which can achieve up to 2A. Discharge loads vary a lot, from 0.1 to about 10A. The purpose of the meter is to ensure that the batteries do not get discharged too deeply, and that the engine is not too long long when recharging.
I plan to use a Hall effect current sensor http://www.ampsense.com/AMP-55N pdf.pdf on the battery lead and an ADC input across the battery, both supplying data to a Picaxe (BASIC programmable version of a PIC) http://www.rev-ed.co.uk/picaxe/to do the sums.
I aim to determine state of charge by coulomb counting in and out of the battery. This seems to be more complex than I expected. From research on the web, I have found out about Peukert's law, Coulombic efficiency and self discharge.
My sources have not all been consistent but it seems that Peukert's law applies only during discharge, while Coulombic efficiency relates to charging. Have I got that right?
I expected that internal resistance would be significant but it doesn't seem to feature in the sources I found. Is it covered by Peukert and efficiency?
Is it reasonable to aim for 5% accuracy determining SOC over the range 40 to 100%?
Is Coulomb counting the best approach?
Thanks,
Derek