Power Consumption vs. Time

[terry.kane]

Does anyone have or know of data available regarding the typical current draw of an EV motor through "typical driving scenarios"?

I'd love to see data sets, for instance, that plot current vs time (@ 2 sec. intervals) for:
1) a sample 5 mile trip around town, with several stops (like running errands) </= 35 MPH
2) a sample commute of (say) 15 miles on secondary roads </= 45 MPH
3) a sample commute of 15 miles with 2 miles to the expressway, then 11 miles at highway speeds, then 2 miles to the destination

I'm interested in developing statistics for current like AVERAGE, RMS, MAX at peak acceleration, steady state at various speeds, etc.  I am brewing a concept in my head regarding using a lower capacity battery supplemented with Super Caps (like the Micron PowerPaks).  I'd love to do some homework on predicting the minimum acceptable battery pack capacity if it's only asked to provide RMS current or below, with the SC's providing the surge demand.

http://nilar.com/be/__media/pageID_33/langID_1/24V9Ah_spec.pdf
http://www.microntn.com/PowerPak.html

[jack.hojnar]

Terry -

I know nothing about everything you just asked, but I do own a Zap and I am willing to help you secure your data in any fashion.

I drive the car everywhere (has 7 12v bats and get up to 45 mph).

So ... if you need testers, count me in and let me know what you need.

jack

[terry.kane]

Hi Jack,

That's great!  I appreciate your offer.  I believe there is a simple device that can be had - a data-logging ammeter.  I will look into it.  Installing it should be as simple as putting one of your motor leads through a "ring" and turning on the device.  The device will record instantaneous current and time data and save it in on-board memory.  The data would be downloadable using a USB port.  Combined with a simple driving diary & data on your vehicle, we should be able to produce a very clear picture of the power consumption profile of your (or any) EV.  I'll let you know as I learn more.  Any help from others on how to find this instrument and how much it might cost would be greatly appreciated!

Regards,

-Terry

[tom.gralewicz]

I picked up one of these:

http://www.sparkfun.com/commerce/product_info.php?products_id=8627

And plan on logging Volts, Amps, and possibly a few other parameters.

[terry.kane]

Tom,

Have you hooked up your data logger yet?  How will you send a "current" signal to the unit?  Does your ammeter have an output you can interface with the logger?

-TK

[tom.gralewicz]

My application is a little different:  I have another microprocessor monitoring each battery system (main pack and 12V) sending data to a screen on the dash board.  This recorder board will be logging the data stream.

For what you want to do you can monitor Volts and/or Amps with out too much work.

The board logs voltages between 0 and 3.3V.  To monitor pack voltage use a voltage divider (2 resistors in series) with a ratio of Pack max Voltage to 3.3V.  Connect the smaller resistor to the logger.  You need to scale the output when read the file to get actual volts (the board will store a number - between 0 and 1023)

Amps are a little more difficult:
In most cars you are using a shunt to monitor current that outputs 0 to 50mv (0 to 0.05V)  if you read that on a 0 to 3.3V scale at 10 bits you get values from 0 to 16, not very accurate. 

The 2 easiest ways to get more accuracy:
Change the ADC reference voltage - this could result in some noise problems.
Add an op-amp (1 small chip) and amplify the 0.05V to 3.3V

It depends how much you want to record and how much electronics you want to do.

[ted.lowe]

At last month's meeting i presented quite a bit of detail about measuring current and voltage (thus power) and this month's meeting i'll be presenting part 1.1, which will show a cool off the shelf device for this purpose.  Albeit, it will only do 50v and 90 amps, but it shouldn't be too hard to scale it to EV sized (EV X-Prize project:-).  Check out the Feb. newsletter for more details.