OpAmps for Solar charge / battery use power monitor

[cg6]

Hi All,

This is my first foray into analogue circuits so I would appreciate somebody commenting on my plan.

I'm building a power monitor for my solar + battery camping kit. I would like to monitor current from the solar panel to the battery, current from the battery to load and voltage at the battery.

Analogue data capture will be via a PIC with 5V VDD as the voltage reference. The LP2950 has tight enough tolerances for my needs. I'll calibrate results in the digital realm.

I've selected the LM324 op-amp because it is designed for single supply and is linear down to 0V. I'm expecting close to a 25:1 gain on the voltage across the shunts.

Thanks,
Chris

[Seekonk]

Solar panel note says it includes charger.  That will likely be PWM and will be a full current no current signal.  As it is you will get next to useless information on current from panel as it currently is.   Add a 1K resistor in series with a 100uf capacitor to form an averaging filter.  The resistor values for the voltage amplifier will have to be at least ten times greater than they are now so it doesn't place a load on the averaging circuit.

[cg6]

Thanks for the PWM tip.

So the RC will be across the shunt and I'll measure between the resistor and capacitor?

Also the op amp comes in a quad package so I can setup a voltage follower to reduce load - or is it recommended to use higher resistor values anyway?

[Seekonk]

A buffer will just add noise and drift.  Shame to have that micro and not include a power point charger.