Below are information and
recommendations made by Martin, Mark, and Giles, after
they studied Paolo's report of May 20:
Mark Thoma has explained that the current from the mirror heater
system power supply to the mirror heater system chassis flows
down a single AWG 4 cable. (with another such cable for
the return.) This multi-strand cable is separated into two bundles
of conductors before being connected to the mirror heater system
chassis. Mark Thoma also explains that this cable is rated to
carry 100 Amps and should *not* be too hot too touch with
70-80 Amps. At this current, it should be only slightly warm to
the touch. Mark believes that there is probably a bad connection
somewhere. Mark suggests that the connections should be inspected,
and possibly repaired. Specifically, in the photo below, the part
of the system that is within the red oval is the part that Mark thinks
be damaged. He thinks that the heat or some other factor
may have damaged one or more of the four
crimp-on lugs that are on the ends of the awg 4 cable. These
should be inspected for discoloration (oxide layer) or loose-ness.
The heat could cause an expansion that can make the crimp-on
lug become loose. Mark has seen this happen before. If they are
discolored or loose then they should be replaced or re-connected.
There should be more crimp-on lugs in the Viper control room or
pump room. There
should be a crimp tool in the tool box. Alternatively, these
connectors can be soldered to the cable. This will work fine.
Giles suggests that the screws on the back of the *main
heater system chassis* should also be inspected in case
they too are loose.
Note that in the photo below
you can see that the mirror heater system power supply has
an adjustable current limit (two knobs - "fine" and "coarse").
Mark Thoma says that Giles' suggestion of reducing the current
limit to 40-50 Amps is not unreasonable. There are 8 channels
drawing 10-12 Amps or less per channel, so that explains why the
"full heat on" level is at 70-80 Amps.
Paolo writes: "The cable
is an AWG 4, with two conductors for each polarity."
However, as Mark explains, there is only *one* conductor
for each polarity.
Paolo writes: "I esteemed [estimate] about
(40-45 C) in this
conditions. However, as you can see the cable is safe till 194 F (90
C)." According to Mark, the cable should be safe to 200 C.
He thinks that perhaps the "90C" that is printed on the cable
does not refer to temperature, but is some other sort of
Paolo writes: "It is puzzling why the cyan
and white cables,
probably awg 14-16 or close (I can't really tell), visible in next
pictures are not overheat much worst." Mark explains that these
are awg 12 wires, rated for about 25 Amps, and that each wire carries
the current for only 1-2 channels. Because the maximum current per
channel is 10-12 Amps, these wires never carry more current than they
are rated for. That is why they do not overheat. Mark thinks that
the reason that the AWG 4 cable *does* get hot is because of a bad
connection, as explained above.
1) "Martin" heater PC
The leds situation is as follows:
Paolo writes: "As soon as the heater PC is switched off (and not
before) the system get
apparently completely out of control. not corresponding to the normal
condition as all the green lights
slowly switch off, while in standard conditions only a few of them switch off
and on time by time." Martin points out that the control of the main
heater system is completely analog. I.e., the control is by the main
heater system electronics chassis. Thus
it seems very unlikely that
turning the computer off should have any effect on the operation of the
main heater system electronics chassis. So none of us here in US can
understand how it is possible that the green lights should slowly
turn off following a computer power-down. We suggest that Paolo should
this experiment and pay close attention to the result. Probably the green
will start to come on again if you leave the computer off for long
enough. Paolo further writes:
"This means in my humble opinion that the electronics is
still measuring the correct temperatures and that seea the various subsystem
overheating." This statement is confusing because it is the mirror
heating system that is overheating and the main heating system
chassis should be operating normally and under analog control
computer on, and should
continue to operate normally and under analog control when the
computer is turned off. The overheating of the mirrors should
not cause the main heater system to react, as the main heating
system is completely separate from the mirror heating system.
One last point - Martin thinks that
he understands why the mirror system goes into full-on mode
when the computer is powered down.
Basically, there is a pull-up circuit that pulls the output
up to 5 V (=OFF) when there is "no activity". But when the
computer is turned off this pull-up does not work as there
is no more 5 V reference. This seems to be a "feature"
of Martin's system that we have to live with.
Paolo: I hope this is helpful
in some way. Please send e-mail or call me to clear up
any confusing points in this document.