Current logger for battery systems

[perky]

it looks as though I can cut the trace between the 4.7uF capacitor and OUT+, then solder a wire wire to the capacitor pad to power the LTC4150 independent of voltages on IN and OUT.  Then I'll just connect the solar cell to IN, and it should do the coulomb counting.  So, that's what I plan to do.  I hope it works.

Note the common mode sense spec for the LTC4150, it's VDD +/- 60mV. So this is going to be tricky if you use a separate supply.
Mark.

Edit: You might be able to fudge it, you'd probably need an opamp powered by your other supply set to generate the same voltage as OUT (see above post for why OUT not IN), and use the output of that as your power source.

[WhiteHare]

Thanks, Perky!  I think I'll hold off on this and try one of the easier methods first.

Happy 2017.

[WhiteHare]

Edit: You might be able to fudge it, you'd probably need an opamp powered by your other supply set to generate the same voltage as OUT (see above post for why OUT not IN), and use the output of that as your power source.

Do you think that an MCP6S21 would do the business for what you have in mind? (http://www.digikey.com/product-detail/en/microchip-technology/MCP6S21-I-P/MCP6S21-I-P-ND/562453)
Starting yesterday I started to use an MCP6S22 to better measure the self discharge rate on a capacitor without having the act of measurement itself drain the capacitor excessively.  While doing so it occurred to me that the same chip might (?)  fit the bill for what you had in mind.  In essence, the chip has a high impedance input pin, and then on an output pin it creates the same voltage, but sourced from a different power supply.  In the case of measuring the capacitor voltage, I attach my oscilloscope probe to the output pin of the chip, and as a result there's much less impact on the voltage of the capacitor under test than if I were to hook the oscilloscope probe directly to the capacitor.

[perky]

OTT I think. You just need a low input impedance unity gain opamp configured as a buffer, you don't need SPI or programmable gain.
Mark.

[WhiteHare]

It defaults to 1x gain on Channel 0, so I haven't actually been using the SPI or programmability aspects.

[perky]

Ah, OK. In that case it may well do the job