User avatar
TonyWilliams
Posts: 10090
Joined: Sat Feb 19, 2011 1:48 am
Location: San Diego
Contact: Website

Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 11:45 am

Has anybody figured a way to accurately measure battery drain? I want to be able to know exactly the changes in energy consumption with given changes over a closed course. Speed, tire pressure, lowered suspension, front air dam, reducing weight, and many other logical modifications to improve to range of the car.

A way to hack into the Nissan software might be easy for some, but I don't have that level of expertise. A simpler way might be a simple interface between the battery and the motor to measure and data-log amps.

User avatar
davewill
Posts: 5045
Joined: Thu Mar 17, 2011 6:04 pm
Location: San Diego, CA, US

Re: Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 3:55 pm

If I understand your purpose, you don't need a precise objective measurement, just one that is consistent enough for quantifying the relative differences between runs (i.e. lowering 1 inch improved efficiency x.x% over stock). I would suggest that the car's miles per kwh number should be up to the task. While it would be nice to have another significant digit in the measurement, this should be sufficient over a decent sized course.
2014 Rav4 EV, Blizzard Pearl White
2011 LEAF SL w/QC, Blue Ocean, returned at end of lease

GroundLoop
Posts: 1725
Joined: Mon Sep 13, 2010 9:31 pm

Re: Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 4:11 pm

Remember that the drive system is controlled for 'power', so you would also need to record voltage along with amps.

(This information is on the EV CAN bus.)

User avatar
TonyWilliams
Posts: 10090
Joined: Sat Feb 19, 2011 1:48 am
Location: San Diego
Contact: Website

Re: Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 4:50 pm

davewill wrote:If I understand your purpose, you don't need a precise objective measurement, just one that is consistent enough for quantifying the relative differences between runs (i.e. lowering 1 inch improved efficiency x.x% over stock). I would suggest that the car's miles per kwh number should be up to the task. While it would be nice to have another significant digit in the measurement, this should be sufficient over a decent sized course.



The difference between 3.9 mpk and 4.0 is 2.5 percent, but it may be as much as almost double that, or as little as almost zero, depending on how that number is actually presented.

That is a far greater tolerance than I was hoping for.

User avatar
TonyWilliams
Posts: 10090
Joined: Sat Feb 19, 2011 1:48 am
Location: San Diego
Contact: Website

Re: Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 4:53 pm

GroundLoop wrote:Remember that the drive system is controlled for 'power', so you would also need to record voltage along with amps.

(This information is on the EV CAN bus.)


How can we get this CAN bus info?

GroundLoop
Posts: 1725
Joined: Mon Sep 13, 2010 9:31 pm

Re: Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 5:06 pm

TonyWilliams wrote:
GroundLoop wrote:Remember that the drive system is controlled for 'power', so you would also need to record voltage along with amps.

(This information is on the EV CAN bus.)


How can we get this CAN bus info?


There are two separate CAN busses brought out to the Data Link Connector.
The BCM CAN bus is on pins 14 & 6.
This bus connects the BCM, VCM, and Dash.

The EV Bus is on pins 12 & 13. This carries communication between the TCU, VCM, HVBAT, and OBC.

Note that VCM is on both, and bridges some messages.

(The main Nav computer is connected to the TCU by USB, not CAN)

User avatar
gbarry42
Posts: 888
Joined: Mon Jan 10, 2011 5:48 pm
Delivery Date: 06 May 2011
Location: Moonlight Beach

Re: Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 5:14 pm

So, there's your answer. Let us know when you have it done ;)

What I want to know, though, is whose MPK have we chosen to believe? After all I've read, I don't believe hardly anything I see. Certainly not Carwings.
And there goes the first capacity bar! At 24,000 mi on 9/9/2013.
Second bar at 30,500 mi on 2/7/2015.

User avatar
davewill
Posts: 5045
Joined: Thu Mar 17, 2011 6:04 pm
Location: San Diego, CA, US

Re: Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 5:27 pm

TonyWilliams wrote:The difference between 3.9 mpk and 4.0 is 2.5 percent, but it may be as much as almost double that, or as little as almost zero, depending on how that number is actually presented.

That is a far greater tolerance than I was hoping for.
Whoops. I should have done the math before spouting off. Yeah, that would be a bit coarse. As far as CAN bus stuff, wasn't turbo2ltr the guy doing that work...Yup, here's the big thread:
viewtopic.php?f=8&t=2794

He seems to have something in progress, I'd PM him and see if he is able/interested in assisting your effort.
Last edited by davewill on Sat May 28, 2011 5:35 pm, edited 1 time in total.
2014 Rav4 EV, Blizzard Pearl White
2011 LEAF SL w/QC, Blue Ocean, returned at end of lease

User avatar
davewill
Posts: 5045
Joined: Thu Mar 17, 2011 6:04 pm
Location: San Diego, CA, US

Re: Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 5:34 pm

gbarry42 wrote:So, there's your answer. Let us know when you have it done ;)

What I want to know, though, is whose MPK have we chosen to believe? After all I've read, I don't believe hardly anything I see. Certainly not Carwings.
Well if you only want to know if you're doing better or worse than the day before, I think you can use the car's numbers. If you want an accurate measure, the only way I know is to measure wall output while recharging and divide it into the miles traveled since last charge...which would be a highly awkward for this kind of testing, but for a commuter should be pretty good.
2014 Rav4 EV, Blizzard Pearl White
2011 LEAF SL w/QC, Blue Ocean, returned at end of lease

User avatar
TonyWilliams
Posts: 10090
Joined: Sat Feb 19, 2011 1:48 am
Location: San Diego
Contact: Website

Re: Accurately Measuring Battery Amperage Draw

Sat May 28, 2011 11:47 pm

davewill wrote: If you want an accurate measure, the only way I know is to measure wall output while recharging and divide it into the miles traveled since last charge...which would be a highly awkward for this kind of testing, but for a commuter should be pretty good.



Too awkward.

Return to “Engineering”