Battery charge/discharge testing with USB 6009 DAQ

[BWag]

I would like to use a USB 6009 to monitor battery voltages during charging and discharging at specified rates.  I use a grounded  power supply (with multiple channels) where I can program current limits as the current source, and use solid state switches to reverse polarity on the battery for charging and discharging.  Also, I am currently using a DVM with a serial connection to record battery voltages.  To automate multiple channels of battery testing I would like to use the A/D channels on the 6009.

Since I am switching the ground of the power supply to alternating terminals of the battery, I was wondering if the differential A/D measurement mode with the two 100k resistors to ground is the appropriate connection mode to use?  I am measuring cell voltages of nominally 1V and charge/discharge currents of tens to a few hundred mA.

Thanks!

[johnsold]

When you say multiple channels, are you referring to separate cells or a battery such as a 9 V battery with several cells connected in series?

If you have independent cells, then a differential connection should be correct. If you are measuring series connected cells, then you still want a differential connection to the DAQ but you must also be certain to stay within the common mode range of the DAQ input.  On the USB-6009 that range is +/-10 V from GND.

I have used the USB-6009 to monitor discharge of multiple independent cells. The test ran for a month or two without any problems.

Make sure you set the power saving options in the OS to not let the computer sleep and to not shut down the USB port.

Lynn

[BWag]

Hi Lynn,

Sorry - I am referring to running multiple single cells  - one each per A/D channel.    I was just worried about shorting the batteries through the ground connections when I switch the ground of my power supply to the high side of the battery for discharge.

Thanks

Brent

[johnsold]

If you look at page 16 of the USB-6008/6009 User Guide and Specifications, you will see what the input circuitry looks like. Each input has ~127000 ohms in series and about 144000 ohms equiivalent to ground. So you should not have any problem with switching the cell polarity.

This is the way I would connect this. R1 - R8 are the input resistors internal to the USB-6009. 

Lynn