Hi Alec, First, great job on the test! With regard to fan amperage, the photos
look as if your radial fan was set up to draw air through the media as opposed
to blowing into- is that correct? Generally speaking, if a fan draws a
partial vacuum, amperage will drop (because the load is going down). Also, efficiency of the media should go up
with an increase in pressure. It would be very interesting to conduct the same
test with the fan “blowing” into the media instead. Greg From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Smyth, Alec Hi everyone, OK, let's try to answer some of all these
questions. First, my daughter is twelve but she's extremely tall for a
twelve year old, being already the same height as her mother. She
would still be on the light side for an adult, but she's definitely
more than half an adult. If I were diving with a crewmember of about my
size, my guess (and that is all it is) initial O2 setting would be 1.25
lpm instead of the 1 lpm used in the test with my daughter. I agree the initial concentrations of
CO2 are high, and I think they are due to the time taken up by
getting into position and dogging down the hatch. I was working in the sub up
to about ten minutes before the first test, so there was probably some
lingering CO2 from my earlier presence too. The getting-ready process was
probably about 4 minutes, the last minute or so being with the
hatch closed. Just to make sure the instrument is not reading high, I
tested it outside and it reads 0.02% CO2 and 20.2% O2. In terms of the permissible concentrations
of CO2, the air at the end of the unassisted dive did not yet feel at all
stale. We were at 1.6% CO2. But according to Phil's life support
white paper, the Navy's standard for manned submersibles is to keep
CO2 under 2.5%, while NASA's standard is 1% for indefinite exposure
and 3% for up to one hour. I could not tell any difference in air quality
between the three dives, other than by looking at the instruments. Yes, my O2 meter did track the Sub Aspida
readings, which is reassuring for when I ship the latter back to Jon! Problem
is, mine has one percent discrimination while the Sub Aspida goes to
a hundredth of a percent. On the unassisted dive mine went down to 19% and
then 18%, at which point its lower alarm went off, but on the two life support dives
mine didn't have the precision to show anything meaningful at all, and was at
20% the whole time. Its functional enough to tell you if you're in
trouble, with a backlit display and low-high alarms, but useless for a test of
any accuracy. By the way, with something as accurate as the Sub Aspida you have
to be a bit careful in the measurements. If you aim a breath in its direction,
the reading shoots way up. If you raise it into the dome, it shoots way up.
Just walking from outside into my home, the CO2 increases by 300%. Regarding the radial fan current versus
battery capacity, I've a new bit of information. Yesterday I noticed that the
fan's spec sheet lists the current draw as 0.22 amps, while the fan has
0.36 amps printed on it. Given the conflicting figures, I put down the
higher one. But Cliff's email prompted me to go out and measure the
current draw to settle the matter. It turns out the fan pulls only 0.2
amps with the scrubber full, so I guess the spec was right and the motor
sticker wrong. Another detail here is that Snoopy, being a little K250, is
a 12 volt boat with a single battery bank. The original K250 design
has three batteries wired in parallel. In the recent redesign I was
able to expand that with a fourth battery for a total of 316 amp hours,
but I still have the original single-bank configuration. Of course,
without a separate hotel battery, my reserve for the fan will depend on
the battery charge condition. If anyone wants the specifics, the radial
fan is a Delta Electronics model BFB0712H. Here are some photos attached
of scrubber and fan. Final point... I was not surprised by the
fan results. What really did surprise me was the stability of the cabin
pressure, in particular in view of the precision to which the Sub Aspida was measuring
it (1 millibar), and how easy it was to use a system with no feedback loop
regulating the flow. I wonder if that is typical or lucky? Thanks,
The
contents of this e-mail are intended for the named addressee only. It contains
information that may be confidential. Unless you are the named addressee or an
authorized designee, you may not copy or use it, or disclose it to anyone else.
If you received it in error please notify us immediately and then destroy it. From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace The CO2 readings are definitely high, especially in the test
without life support. I know that when I used the monitor out in the open
the CO2 percentage was between .01 and .03 so I don't expect a calibration
error is the cause of the high readings unless something happened to the device
during shipment. That should be easy enough for Alec to test however by
simply going to an open area and checking the CO2 reading. Alec, thanks for posting the life support test for
Snoopy. I quite enjoyed seeing actual test data. Your results of
axial vs. radial fans mirrored my results and my conclusions were the same;
i.e., radial fans are the way to go. Have you done any test or calcs to
see how long a 0.36 amp current load will take to burn your backup
batteries? My guess is that at this current, you would not make 72
hours. IF they don you may have to find a radial fan that draws less
current. |