Monday, July 19, 2010

Testing Continued

Before I talk about the results of the most recent tests, I thought everyone might enjoy seeing one of the shots I took of the car, which I sent off for the book the EV Z3 is going to be in. Behold:

Considering the day was a bit cloudy and I don't own any lighting equipment other than a camera mounted flash, which I didn't use, I thought this turned out pretty good. Say what you want about the conversion, but it is a pretty car.

Anyway, back to the test results. So, over the weekend, I left the car idle, in the garage with only the following items attached to the high voltage side: the Link-10 meter, and the ceramic heater. As I mentioned in the last post, there is really no way for the heater to draw any current, but I swore I'd do more thorough tests, and that's what I intend to do. In fact, I decided against the idea of cutting that test short because I didn't expect the addition of the ceramic heater to amount to any difference. After all, if you allow your expectations to influence the method of your testing, your expectations influence and then determine the results of your test.

What did I find, you ask? Pretty much what I expected. The addition of the heater didn't change results at all. Over the time frame, the meter showed that 2.15 kWhs had been consumed. That is bang on what it said when I had only the meter attached. But if you remember back to that test, when I charged the batteries, they only accepted 200 Watt/hours. And after all, that's really what I need to know; how much energy was actually drawn out of the pack. This time was no different. About 3 minutes after I turned on the charger, the battery pack reached it's peak charging voltage and the charger began to ramp down.

By the time it had finished, 220 Watt/hours had been pushed back into the pack. I'm not concerned with that extra 20 Watt/hours that showed up in this test versus the first test. If I did the same test 10 times I'd expect 10 slightly different results because the charger introduces some randomness to the equation. The algorithm it uses to determine how many amps to push out while it ramps back down to zero during the cool down phase is anything but predictable. A 10% difference at this level is not a big deal. Considering the 2.15 kWhs the meter originally stated had been drawn off the pack, that 20 Watt/hours is only about 1%.

On the surface it would appear that I didn't learn anything. But really I did learn that the ceramic heater is definitely not drawing any current when it's off. It's true I expected that, but I also learned that the Link-10 showed the same error in metering 2 tests in a row.

In order to charge the battery pack I had to hook up the charger. That means that right now the Link-10, the ceramic heater and the charger are the only things hooked to the high voltage side. That sounds like a perfect recipe for the next test, which commenced 30 minutes ago.


Michael said...

Hi Tim,
what about a precharge resistor? My Curtis 1221C needs a Resistor (750Ω 20W) along the main contactor to protect the circuit while charging the capacitors of the Controller.
I don't know, if you use one, but at 120V this would be 20W in my case.

btw: my beetle starts spinnuing wheels at the weekend and the first testdrive was great! :-)

Tim Catellier said...

Hi Michael, Congratulations on the Beetle's first run! Very good news.

The Zilla does have a precharge sequence that it goes through and I believe it includes a precharge resister in it's circuitry. The wiring diagram didn't specify I install one, so I didn't.

I know the Zilla uses some current when idle, I read it somewhere once, but I can't remember where or how much it used. I do remember that it wasn't much. However, I'll be testing the Zilla next, so we'll know soon enough.

Gam0ra said...

Hurray for the scientific method! Always to see it put to use.