# How to design a circuit checking if 12V car battery is charging?

I have a small solar power charging module and load balancer, that takes input from a solar panel, has connectors for a car battery (12V) and output terminals.

These things are pretty common on thing like RVs, caravans, camper vans, etc.

The module however, has no digital readout displays. Attaching a couple of those to the terminals of the charger / power manager is trivial, but I was wondering how I can have an LED light up, when the car battery is charging, i.e. current is flowing in to the battery. And have no LED light up, when current is being drawn from the battery.

The Voltage / Amperage meters I use, just shows the absolute values, they don't display for instance a negative amp value to signify direction.

So, how / what would be the simplest circuit to display current direction, in to the battery (battery is being charged) and if current is drawn from the battery (battery is discharging)?

Obviously, the circuit should draw as little current as possible itself.

Edit

Couldn't I simply use a comparator, like an LM319, and use the batteries wire that connects its terminal to the power management unit as resistor? I.e. having the non-inverting input going to the battery terminal, and the inverting input to the power management box.

• Can you provide more information about your current meter. It would be very unusual for a DC current meter not to provide an indication of the direction of the current it is measuring. – Barry Jul 23 '16 at 0:59
• How much current? Charge current? Discharge current? – Dwayne Reid Jul 23 '16 at 2:05
• Get a DC current clamp meter, clamp the output of the solar panel or regulator - bingo! Result! – winny Jul 23 '16 at 8:17
• @Barry: I don't want to link to ebay pages, because it's discouraged here, but it's basically a 5€ V/A digital meter. It displays voltage and current, but the current doesn't go negative when the current changes direction. If the current would be displayed as negative when the batter is - say - discharging, that would be fine, but the meter displays positive current no matter the direction. – polemon Jul 23 '16 at 13:21
• ACS712 + comparator. – mkeith Aug 27 '16 at 3:05