Thursday, May 28, 2009

12V Measurements & DMOC Parameters

Shane and I measured the 12V power consumption to determine if the 12V supply (DC/DC converter) is correctly sized (it's rated for 22A).  One thing of note right away is that with the car turned off, we're still drawing 0.3A... probably the cRIO and the SOC display, which right now are on all the time.  That should get fixed, the car should operate reliably using just the ignition key.

Off: 0.3 A
On: 2.5 A
Wipers: 8 A
Turn signal: 5.2 A
Hazard: 0.5 A
Brake: 0.4 A
Running: 1.7 A
Reverse: 3.1 A
Headlight: 9.6 A
High Beam: 11 A
Fog Lights: 4.9 A

You can see the big difference the LED bulbs made: compare the LED brake lights or hazard lights to the incandescent backup lights.  The 5A from the turn signal must be an anomalous reading, or there's something funny going on with the blinker circut, we'll have to investigate further.

The results are we should be fine during daytime driving: we draw about 4A, with the display possibly bumping that to about 8A.  We'll have more issues doing nighttime drives in the rain, where our draw is close to 20A between wipers and headlights.  Worst case would be driving on a rainy night and breaking down on a deserted road (nevermind all the other issues related to this scenario), after trying to backup to the last exit without success you leave it in reverse and rest your foot on the brake, with the high beams and fog lights on, you turn the hazard lights on and crank the radio up to drown out the sound of the the wipers and the pouring rain while you wait for help to arrive.  35A.

We also discussed how the "frankenstein" switch might be replaced by a smaller switch, to open up more room in the back.  The only high current connection through it is the charger (~10A now, hopefully 30A someday), the primary issue is few switches are rated to break 30A DC (since you could get a self-sustaining arc in the switch), though hitting the E-stop would correctly break the circuit using the contactors, and actually, breaking the HV connection to the BMS will cause the contactors to open anyway.

We also looked at the DMOC parameters, trying to figure out what led to the interesting motor torque curve mentioned last week.  We didn't come to any conclusions, but will keep looking into it, there are tons of undocumented params.

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