[amsat-bb] Re: AO-07 Healthy CW]

Tom Clark, K3IO K3IO at verizon.net
Tue Nov 28 20:30:19 PST 2006

W9GB noted

> I can identify the lab equipment on the bench (looks like my high
> school & college labs - 1970s) with the NiCad battery pak, EXCEPT for
> the rectangular box with metal handles to the right of the NiCads. 
> NiCad battery charger?   Homwbrew power supply?
Greg -- the high-priced hardware (HP+Tek) show NASA Goddard property
labels. The cheaper power supplies in the back are Heathkits with AMSAT

The box you are asking about has a yellow Goddard tag. I'm trying to
recognize it, and to the best of my recollection it is a Coulomb-meter
that measured (on the mechanical counter you see on its panel) the
integrated charge/discharge current. Also my fuzzy memory tells me that
the heatsink device on clip leads was a prototype BCR.

Sil asked:
> I guess there's a special "satellite design" reason that double wires
> are used (instead of one thicker one) for the current carrying battery
> leads?
The twin wires go to a pair of pins on the DA-9 connector, with two pins
providing greater current handling ability and redundancy. It also
appears that the V/2 telemetry tap has a pair of whit wires even though
it provided zero current. BTW -- the V/2 telemetry would be on 3B.
> Leaving aside Geoff's (vk2tfg) point that the telemetry may be
> irrelevant because of the doggy value in channel 6D, it would seem that
> the five top cells (between half volt point and +12V - numbers 2,3,4,5,6
> counting clockwise) are being charged with a current of 80mA and have
> reached a terminal voltage of 6.4 volts (8.8 - 2.4). This represents a
> voltage of 1.28 per cell (6.4/5) and is thoroughly reasonable. This idea
> is supported by the temperature of cell number 5 at 60.28 C. 

The top 5 cells are fed by the black wire and are the LOW voltage side.
The 5 "high side" batteries terminate in the orange wire on the bottom,
The thermistor on cell #5 is on the low voltage side.

The thermal design of the s/c ended up with internal temps ~20°-30°C
range (i.e. TLM values in the 40-50 range). I find it hard to believe
that a valid interior temperature would ever be in the 60°C range.

Regarding all the telemetry speculation -- AFAIK, there is no indication
that the A/D converter is showing ANY valid data at all -- see also
Jan's comments at http://www.amsat.org/amsat/sats/n7hpr/ao7_tlm.html.

FYI -- the TLM and its associate Morse encoder system was built with
discrete CMOS logic by John Goode, W5CAY in Texas. Memory fails me, but
I believe that the TLM/Morse board is on the "back wall" in the
photograph at http://www.amsat.org/amsat/sats/ao7/slideset/slide09.html
even thought the photo only identifies the module as the command
encoder. All the white IC's a early RCA ceramic 4000-series parts.
AFAIK, Oscar-6 & -7 were the first CMOS users in space. AO-7, with much
of this logic still functioning after 32 years and 2 weeks, certainly
holds the longevity record!

[In case you forgot, Nov.15th was AO=7's 32nd birthday -- my favorite
picture of the launch is the "7-UP" contrail left by the Delta booster

73, Tom

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