Battery monitor

Thingiverse While I was working with CAN scanning, I accidentally drained my car battery to the point where I could not  crank the engine. I decided to do a little research on the battery capacity.

I found on Amazon a little LCD module which shows the battery capacity in percentages. Capacity is calculated by measurement of  input voltage. I did a quick check and here is the result:

12.65v – 85%
12.55v – 80%
12.45v  – 69%
12.35v  – 63%
these percentages slightly off from various sources, but for me it is  important to see the trend of overnight discharge level. The “dark current”  100mA in my car is draining  the battery.
To take measurements in a convenient way, I designed and 3D-printed a simple enclosure for this monitor and OBD-II male connector from Sparkfun store. The OBD-II port provides battery power, which is always on, important for this purpose. Location of the connector also perfect for monitoring.
Design of enclosure shared on Thingiverse.
The monitor consumes 5mA, but after removing LED backlight, it drops to 0.22mA.  Because of such a low consumption,  this monitor can stay connected for a long time without any harm to the battery.
Initial observations:
After 24 hours of inactivity monitor shows 80% of full capacity. Turning ACC without engine on will drain battery to the 50% level in 10 minutes. But this is under load and maybe it is not an actual capacity value, because monitor calibrated for the open circuit mode (without load).
Nice article about dark current here.
Recently, I left my car for 15 days with a fully charged battery. After 15 days, the battery monitor shows 81%, which is no bad at all.

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s