Thursday, July 1, 2010

12 Volt Dilemma Sorted

Yesterday afternoon, I pointed a large box fan right into the trunk, set it on high and let it run for an hour. I wanted to find out if the fans on the DC to DC converters would turn off if they had enough fresh air. They get fresh air now, but this would be a lot more. The question was, are the fans running continuously because they aren't getting enough fresh air, or because the ambient air isn't cool enough to actually cool them. Well, after an hour, I turned off the hurricane directed at them and found the fans were still humming away. So, 100 °F is simply too warm to cool these devices properly.

Last night I let the car sit with the DC to DC converters on and the 12V SLI battery connected. In the morning, after 12 hours of idle time, I found they had consumed 600 W/hours. To recap, without the SLI battery connected, they consumed 5oo W/hours, and with them off and the SLI battery handling the load, the car consumed 44 W/hours from the battery.

In light of those two discoveries, I made the rather easy decision to hook the DC to DC converters up to a contactor that's triggered with the ignition key. I want them off when the car is not running. It took a few hours to route the wires and such, but in the end it worked out ok. The new contactor is sitting atop the SLI battery in the right corner of the trunk. It's out of the way and should be safe from anything rattling around in the trunk.

The one thing that I'm going to have to watch carefully now is the voltage on the SLI battery. I'm asking more of it now since it will be providing all power to the car when it's off. Sure, it's not much, but in 3.5 days, it will draw that small 33 amp/hour battery down to 10.5 Volts. I have a battery tender that I'll be hooking up to it. When ever I plug in the car to charge it, I'll plug in the battery tender for the SLI battery to keep it healthy for any extended stays in the garage. One extra plug and the energy it will draw is so minute as to be nearly negligible.

This evening, I'll be taking the car out to a nearby park to take some glamor shots. The car is going to be featured in a book about conversions, with a section dedicated to particularly interesting ones. The EV Z3 is going to be in that section. Is that cool or what!?

1 comment:

Gam0ra said...

I hope you remember all the little people when you're a famous celebrity!