Offhand, that seems to be a reasonable approach.I am trying to light up several LED lights (LED signs for advertising purposes) when the car is turned off and the LEDs is going to cut off itself after the battery capacity is lower then maybe 70%. I am not sure how much current the LEDs is going to draw, but probably going to be .2 to 5A. I am thinking to use a small microcontroller to control the cutoff threshold and PWM to control the LEDs
I would use a separate battery to power the LED display. After all, you want it to be lit for as long as possible, right?So do you think discharging directly from the automobile battery will do me good in a long run? Or should i use a rechargeable battery to operate the LEDs when the car is turned off, and charge up the rechargeable when the car is turned on.
I am also dealing with a discharged car battery (due to Summer holidays it was left unused for some weeks...) and can tell you that, if you can access the battery elements, best way to know exactly charge condition is to measure electrolyte density. Reason for this is that, as in my case, if one element is bad (or different than the rest), you can't tell from total voltage. Yes, you would find voltage is lower than expected but wouldn't know the exact cause.The only way i know how to do this is to measure the battery output voltage[from 12.7v(100% capacity) to 11.8v(almost dead)]. Is it the only way to measure battery capacity? And does the voltage drop vary from different batteries?
Thanks in advance
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by Luke James
by Rushi Patel
by Luke James