written by Giles 
July 25, 2003

Here is a summary of various E-mails and thoughts:

(I) Paolo's initial E-mail:

> Hi Giles,
> For reasons that I do not know :-), today I decided to swap the batteries,
> also if I did it 2 days ago. I usually do it every 3 days, but, in an
> attempt to debug the problem, I did it after 2 days only. First time in 6
> months.
> This is what I got:
> Thu 07/24/03 17:30 D2= 6.16, 6.26, -3.08, P1=12.53, -3.057 !!!
>                                    ^^^^^            ^^^^^^
> Last swap:
> Thu 07/22/03 14:00 D1= 5.87, 6.06, -8.77, P1=12.10, -12.20

(II) A Question for Paolo that I just thought of: 

you have P1 repeated in the above e-mail.  Does this mean that you used P1
twice in a row?  That would explain why we went to -3 Volts.

(III) Next, my original reply to Paolo, for reference:

> Hi -
> First, there is nothing urgent that can go wrong if power is not delivered
> to the preamp ("P") or data system ("D").  so we can proceed with care to
> debug and fix this without rush.
> Something is drawing too much current.  


> both the data system battery ("D")
> and the preamp battery ("P") are having trouble.  the data system is in
> the SPARO blue box and the preamps are mounted to SPARO.
> The negative voltage on the data sysytem battery provides the negative
> polarity of the analog power to the data system.  The negative polarity of
> the preamp battery provides the negative polarity to the preamp.
> You did not give me the complete set of measurements.  The preamp battery
> has an A and a B output channel, each with two polarities.  so there are
> four measurements to be made on one single preamp battery box, and you
> only gave me two.  I would like to know what the other two are.  assuming
> that they are normal, i would like to know which of the two preamps is the
> one that is depleting its negative supply.
> You will likely have some problems now, with the preamp power situation.
> There are two issues:
> (1) as a result of draining to 3 Volts, the JEFTs at 100 K inside SPARO
> will turn off and thus will stop self-heating.  they then will be cooled
> to 4 K and will stay at 4 K forever unless heat is temporarily applied in
> some other way.  There is a procedure to heat them that I can explain
> later.  it will be impossible to take data until you carry out this
> special procedure.
> (2) it is impossible to recharge a battery when it gets as low at 3 Volts
> without blowing the fuse that is in the battery box.  you have to short
> the fuse holder with a "satelite fuse" - an aluminum cylinder.  We had
> some made up and used them once before but i can't say where they are now.
> you could have more made.  some battery *might* be permanently damaged,
> but we have spares.
> we should talk by phone.  in the meantime, please get me the missing
> measurements for the (P) voltages.
> - Giles

(IV) My final thoughts of this AM:

Paolo, I noticed that even in your excel logs that you have been sending
me recently, you are reporting only five voltages, not seven.  This might
imply that when you swap batteries you are not checking all the relevant
numbers.  Thus, we cannot be sure that the charging is going well.  It
could be, for example, that the short white jumper has developed a
problem, or you forgot to use it once, or some other connector associated
with the charger is having a problem.  What I am getting at is that we
should not automatically assume that there are problems with both the data
system and one of the preamps drawing too much current.  Instead, the
problem could be with the charging process.

It will take us some time to debug this and get things going again.  We
will need to run some experiments.  We should start with the preamp
batteries.  The first thing will be to get all 4 +12 battery outputs and
all four -12 battery outputs fully charged, if possible.  It may be
impossible or difficult to do this for the battery that got discharged
from 12 to 3 volts.  But I can step you through it by phone.  We can work
on this in parallel with understanding the short cycles.