Gentle Friends,
It occurred to me that since I have a variable voltage PA supply here I could do a couple of interesting tests. After again verifying my unit is OK from 6.9 to 9.1 Volts in PA mode I decided to do two series of tests, one with the PA set at 7.5 Volts and again at 8.5 Volts. In each series I ran 3 tests at step 2, 3 at step 4 (where I normally run) and 3 more at step 7. Each test consisted of timing (to .1 seconds as best I could with my stopwatch) the on and off times of the heater after it was stable. This actually takes a minimum of six cycles of course if you're not doing 'splits' (as I did in this test). The times came out within .5 seconds of each other worst case, I averaged each set of 3. The average on/off times were:
At 7.5 Volts in, step 2, 4 and 7:
5.2s/13.5s *** 28%
6.2s/11.2s *** 36%
8.0s/09.6s *** 45%
Going to 8.5 Volts gives:
4.6s/16.1s *** 22%
5.3s/13.8s *** 28%
6.8s/11.7s *** 37%
The raw data makes sense for the most part. There seems to be some 'funny business' with the off times mostly in the second run? I suspect the temperature sensor isn't exactly right in the unit, that is there's a location issue that doesn't really matter. I spot checked the data, it seems solid.
This fits with the power usage. The measured current is about 2 Amps, the battery about 2Ah so we'd expect an hour of on time, give or take. Since it's only on about 1/3 of the time we're looking at closer to 3 hours under these conditions, at 12 minutes per that's 15 theoretical sessions of which perhaps a third are blocked to save the battery from an early grave. We get less than that since we're pulling air through (rather than leaving it laying on it's side like I did with no load) making the typical values reported (say 6 to 8 sessions?) reasonable.
Notice, however, the numbers say that total sessions number will vary a lot with step level even after we back out the changes in timing with discharging battery.;
Anyway, time for some reflection later, but I thought some folks might like a look at the raw data?
OF