[tech] AM100 progress

Harry harrymc at ucc.gu.uwa.edu.au
Mon Apr 30 21:05:57 WST 2007


Hello

This evening I moved the ex-WMC, Bernd-donated AM100 up onto the hardware
bench after returning tools to the cupboard and a general tidy up.

The main 50000uF caps had been running for several days wired independently to
a 5 volt supply:

      150K
5V---/\/\/\------|
                 |
                 = 50000uF
                 |
GND--------------|

Terminal capacitor voltages were 4.95V and 4.40V respectively with a drop
across the resistors of 71.2mV and 627mV representing leakage currents of
0.5 microamps and 4.2 microamps. Despite the difference in leakage, I think
the caps are ok. The lower leakage capacitor showed no voltage loss after
several minutes when loaded with a (10Mohm) multimeter whereas the leakier
capacitor lost about 4 millivolts per minute; which is self discharge from the
internal leakage.

These capacitors still hold a significant charge so please don't tinker with
the wiring in the box. I haven't removed the S100 boards yet so wire twiddling
may make fat sparks or partially power the boards both of which would be bad.

I've set up two 1 Mohm resistors tonight to independently charge the smaller
capacitors with a +/- 12 volts source. These supplies provide the unregulated
+/- 15 volt supplies (regulated on the S100 boards to +/-12 volts mainly for
RS232 drivers). I'll be back tomorrow in the early afternoon to check on those.

These gradual charges are at very small currents so the likelyhood of
catastrophic failure is low.

After this charging, I'll restore the wiring to the capacitors, remove the
S100 boards and use some wirewound resistors as a dummy load and see how the
power supplies stand up.

So power to the system to test for life is a few steps away yet.

Harry



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