Friday, July 23, 2010

Testing: Stranger Still

I've been trying to determine which component is responsible for leeching power from the high voltage system when the car is idle. So far I've found that the Link-10 meter will unfailingly show a 700 Watt/hour per day loss, which I've determined to be largely inaccurate. I've run the same test with the ceramic heater hooked to the system (mind you it was off, just like the rest of the car) and it added nothing to the reported draw off the pack.

I finished a three day test yesterday in which I'd added the Manzanita Micro charger into the mix. At the end of the three day test I looked at meter, and what I found didn't surprise me at all. The meter read that there had been 2.15 kWhs drawn from the pack. That lines up exactly with what I would have expected, and so I can infer that the charger didn't draw any additional energy from the batteries. Again, not to surprising, but I have to test everything if I'm going to be thorough.

What was surprising is what happened when I charged the pack. In the first two tests, I saw that 2.15 kWhs had been drawn off the pack (according to the Link-10). But when I charged it, the charger read the pack as fully charged within minutes and when it finally shut off, it had only added 200 Watt/hours to the pack. So really, there was only 65 Watt/hours per day that were actually consumed. The first two tests had nearly identical numbers. Well, when I charged the batteries this time, the charger said the battery pack reached it's target voltage while I was turning the dial up to increase the current. When it finally kicked off, it had replaced a mere 60 Watt/hours. So, in this test, with only the Link-10, ceramic heater, and charger hooked to the high voltage system, their combined draw was 20 Watt/hours per day.

How could there be such a discrepancy? And how could the three components combined draw less energy than two of them? I think the answer is they didn't really. In spite of the fact that I'm trying to run these tests in the most controlled manner possible, I'm limited by the quality of the equipment. After all, it's not high dollar lab equipment, they're EV components. There is some inaccuracies inherent in each, i.e. the consistent 700 Watt/hour per day error in the Link-10. In this situation, I think we've exposed another inaccuracy in a different component, the charger.

The Manzanita Micro charger is fantastic as a bulk battery charger, and I think it does a terrific job. It is not a high dollar piece of bench lab testing equipment. It uses a potentiometer adjustment, made by the user, to determine the cutoff voltage for charging. I've set it such that the charger starts it's ramp down when the battery pack gets to ~165 VDC. It then ramps up to ~168 VDC before the timer runs out and it turns off completely. Now, the reason I use a "~ " is because it is it's all relatively approximate. Sometimes the timer comes on at 165 VDC, sometimes it comes on at 165.5 VDC. In addition, you may remember I'd said the algorithm it uses for how to ramp the current down is a complete and total mystery. So sometimes it will dump an additional 150 Watt/hours into the pack after the timer starts and sometimes (apparently) as little as 20 Watt/hours.

I guess the short of it is that using the charger as an instrument for doing the fine measurements I'd like to employ on this test is silly. At best I think I can only hope to get an idea of what's drawing current off the pack when the car is off. I've already discovered that the meter is responsible for most of what I've seen simply due to the error inherent within the meter. Am I going to find where that remaining 300 Watt/hours per day are going? I'm not sure, but I'm going to keep trying, and my feeling is that I'll find the DC to DC converters are drawing some of that current.

In any case, the next component to check is the Zilla controller. How much does it draw? Well it's supposed to be just a few milliamps. Over a 24 hour period, I'd be surprised if that registers on the meter. But I intend to test it anyway. That test began 30 minutes ago.

Stay tuned for the increasingly irrelevant conclusion!

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