Monday, March 19, 2012

Project ST5000: The end of haywire and lash-ups

Since the lash-up tests were successful, I have moved ahead.

Relays permanently mounted
First, I have mounted the relays in their final position, inside the cast aluminum case cover.  Before mounting, each relay got a dab of silicone on its aluminum back plate to ensure good thermal contact with the drive case.  You can see 4 holes on the end where I originally had two relays mounted - this location did not work out because one of the relays interfered with the main terminal strip in the drive.  For ease in wiring, and because I am visual sort of guy, the relays are physically arranged as they are in the schematic - makes for fewer wiring errors on my part.  In this picture, I have completed the inter-relay wiring.

All hooked up
Now that the relays are permanently mounted to the cover, it is time to do the real hookup.  Here you can clearly see the additional 8-terminal terminal strip that is used to insert the diodes in the control lines coming from the H-bridge.  (I think some of those leads are going to be too long, and the wire routing could be better.  Some zip ties are called for as well.)  When I do this in our installed unit, I'll drill a couple of holes in the case for screws to mount the terminal strip.  I plan to just trade the case covers.

Finally, here's the detailed schematic (as always, click on the picture for a full-sized version):
I am a little nervous with the inductive kick protection/dynamic braking diodes installed across the output terminals of the relays.  The ones I have used are rated at 1 amp, which seems light.  But they haven't blown yet...

A little later, I will publish a step-by-step guide to the minor modifications to the drive wiring that are needed to make this work.

Next steps... take a deep breath and modify the installed drive unit, and then do sea trials.  For this to be effective, I need to at least install the compass temporarily somewhere, and I really need to install the rudder reference transducer.  And pull a lot of wire in difficult places.  It's a big commitment.

The next step is a big one.


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