What sensors and instruments are needed to measure battery level and fuel capacity?

[mcchea]

Hello all, I am a senior engineering student converting a gas powered golf cart to a electric/gas hybrid. One of our requirements requires us to measure and display the battery (lead-acid) level and fuel capacity on LabVIEW. Currently, all we have is a NI-6008 USB DAQ and LabVIEW software. What sensors and instruments would we need to measure these parameters? All replies are appreciated!

[NIquist]

Well, the 6008 measures voltage so you probably want sensors with voltage outputs.  Other than that it's really up to you.  There are so many ways to do this it's hard to narrow it down without knowing your preferences.  Fluid levels are currently measured using resistive elements (with and without floats), optical detectors, sonic detectors, etc.  Making these choices is what Engineering is all about.

EDIT:  You can probably rule out the resistives and floats in the battery acid. 

[SnowMule]

Easiest way is going to be a voltage divider to an input on the DAQ.  A fully-charged 12V SLA is 12.9, discharged typically 11.4,  that 1.5v span can give you a pretty good estimation of 100%-0% charge.

Better way is a charge controller type setup that measures capacity in amp-hours.  Can also measure current out of the battery and integrate that area to give you power delivery, then gauge based off that number.

Lots of ways to do that.  Figure out what you need, what you have, and make a system work to give you the numbers you want at an acceptable cost.

[johnsold]

You have received some good advice.

With lead-acid batteries the open circuit voltage gives you a pretty good indication of the state of charge.  Of course while the cart is running you cannot measure the open circuit voltage.  Something along the lines of SnowMule's suggestions are probably best.

Lynn