Sunday, January 27, 2008

DC-DC Overcurrent Malfunction

It's good to get the extra transmissions out of my garage. I guess it's poetic justice that the guy who bought my side shifter from the original car is going to give it to Jeff at Rothsport systems for a rebuild, the same guy who didn't work on it for 2 1/2 months when I gave it to him.... The buyer of the tail shifter transmission is also in the process of doing an electric vehicle conversion, so he asked a bunch of questions about my project.

I've been noticing that my auxiliary battery seems to drop in voltage significantly as I commute to work. After some experimentation today, I found that under a moderate load of 8 amps or so, the DC-DC eventually stops working and fails to charge the 12V battery. I was misled a few times because when I turn off the key for awhile and turn it back on, the DC-DC starts working again for about 30 seconds before stopping.

At light loads the DC-DC keeps working, so I can charge the 12V battery if I just turn on the key (to close the DC-DC relay), but don't turn on any accessories or start driving (thereby pulling current from the motor controller). For the moment, I charge the main pack at work and turn on the key for about an hour before I have to drive home to recharge the 12V battery.

Here are some current values I measured coming from the 12V battery (without the DC-DC in operation) from various accessory loads:

  • key off - 10 mA
  • key on (motor controller idle) - 700 mA
  • parking brake flashing light - pulses of 300 mA
  • parking lights - 3.7 amps
  • parking lights and headlights - 9.4 amps
  • parking, headlights and fog lights - 17.3 amps
  • left and right turn signals - pulses of 3.3 amps
  • backup lights - 3.1 amps
  • parking, headlights and backup lights - 12.3 amps
  • brake lights - 3.3 amps
  • CD player - 1.0 amps
  • climate control fan (low) - 2.8 amps
  • climate control fan (med) - 4.5 amps
  • climate control fan (high) - 6.7 amps
  • defroster (hair dryer) relay - 200 mA
As you might suspect, I'm irked by the DC-DC still not working, but it's probably my own doing given the modifications I made to the controller. I guess it's back to taking the thing apart and adding an increasing load to see when it fails. Argh.

1 comment:

Frank said...

I'm not sure what you DC/DC is designed for, but mine started out life as an RV auxiliary power supply.

So I came up with a clever scheme (yet to be implemented) that would use the Zivan's "all done charging" output to flip a DPDT relay over from the traction pack to 120 VAC from the charge cord. I.e. when the traction pack is done charging it tops up the auxiliary battery.