Measure DC output from 12V Battery

[aolima]

Hi,

I'm building a solar-powered remote data collection system and would like to use the NI system (cDAQ9135) to also track battery voltage state of the 12V car batteries I'm using.

I have a 9215 and a 9205 module available but they only read +-10V so I was wondering if there is an easy way for me to still use them for my system.

I've though about trying to lower the voltage with a buck converter but not sure if that will also allow the voltage to fluctuate with battery charge state (from ~12-14V).

[santo_13]

If you just need to monitor, you can create a potential divider using resistors to scale it down within 10V.

[crossrulz]

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@santo_13 wrote:

If you just need to monitor, you can create a potential divider using resistors to scale it down within 10V.

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My thoughts exactly.  Two 1MOhm resistors to do a divider to half the voltage should do the trick.  If a more professional setting, I would also look at a simple op-amp to buffer the divider from the DAQ.

[Henrik_Volkers]

I would go with two 100k resistors without buffer. Use identical resistors and if you can couple them thermally.  

I don't assume you want to go with SMD resistors otherwise the Vishay CDMA resistor array is a nice and affordable  solution.

For DC that is fine, otherwise you would need to consider a impedance match with an additional variable capacitor (in it's simplest way)

Use a second channel without divider , apply a  voltage (9V batterie) to both and calculate the ratio (do a calibration).