Differential input burned chip.

[LittleJoe]

I'm attempting to use a PCI-6031E and Labview Signal Express to monitor a large battery pack as it's charging.  The battery consists of quite a few 7.2V Ni-MH batteries in series.  I have a differential input across each battery in the pack.  When I connected just the first 16 batteries and attempted a trial run I could smell something wrong and immediatly unplugged the device.  I probed each differential input and no channel had more than 7.7V across it.  My PCI-6031E has a few small chips burnt beneath the metal sheilding.  I don't understand why these chipped burned since it should be able to handle a 10V input.  Please help me understand what I did wrong,

-Little Joe

[LittleJoe]

Is the problem that there was less than 10V differential but there is far more than 10V potential across say, pin 1 and pin 16 since the cells in the batteries are connected in series?  Does it have something to do with DC coupling?

[Bueller]

Hi little Joe,

When batteries are connected in series the voltage on the terminal of the setup will be the sum of all the voltages of the batteries in between.

Probably, you were reading 7.2 V * ( number os connected batteries).

Hope this will answer your questions, and I'm sorry that your DAQ is burnt.

Best regards,

Faris Alhorr

AE NIC

[Mcdan]

Little Joe,

From the manual from your device, take a look at the "Analog Input" section.  There you'll see that the "maximum working voltage" is spec'd to be +/- 11 V of GND.  I believe this is the range of voltages you can attach to the input and expect to get reliable readings.  The over-voltage protection on this device is spec'd to be +/- 25 V when the device is powered on, and +/- 15 V when powered off.  I believe that using voltages greater than this results in risk of damaging these devices.  It sounds like this is what happened when the devices was hooked up to many batteries were attached in series.

For more information on how to make high-voltage measurements, please have a look at this link.

Hope this helps,

Dan