‎Engine Start CB-Oct2010-descript01

Background:

• For a few weeks (approx. thru October 2010):
  • Occasionally the engine would not turn over (crank) to start when the START button on the cockpit engine panel was depressed.
  • Resetting the 40-amp circuit breaker (CB) on the engine would enable the engine to turn over with the cockpit START button. [see URL http://sailing.mit.edu/mediawiki/index.php/Engine_40_10_CBs_panel_access (top photo.)]
  • With this ability to crank the engine, we realized that -- if the CB was not set -- the pre-heat function won't have worked either. Therefore, especially for starting when the engine is cold, we have to re-perform the pre-heat sequence, and then we expect the motor to turn over and start normally. It did.
  • On some sail, the crew did a test with the STOP plunger UP (it wouldn't crank) and then with it DOWN (it cranked.) After positing a safety switch in the plunger, which the skipper shouted down, we had to conclude that -- if there was any cause-and-effect at play -- movement of the plunger wire and its sheath might be mechanically moving some of the nearby wiring bundle from the control panel to the engine, causing a connection of either open-circuit in the push-buttons or short-circuit to trip the CB.
  • We next observed that, while pre-heating, the voltage shown on the Nav Station digital voltmeter (DVM) is depressed enough to know that the CB is NOT tripped (perhaps 0.2 to 0.5 volts, approx 20-amp load.) The voltage reading doesn't change if the CB is tripped and we push the PRE-HEAT button.

• On the 30Oct sail (Kenn S's trip)
  • Having an easy way to see from the cockpit when the CB is not tripped by pressing the PRE-HEAT button, we can see when to expect the engine to crank when we press the START button. Note that we had fairly heavy wind and seas; in fact, we used the engine a couple times to e.g. double-reef the main. Unfortunately we didn't keep track of how many times the CB was found to be tripped.
  • NOTE: In the above item, the writer assumes the CB was tripping, i.e., breaking the current flow because of a short circuit somewhere. However, we haven't really thought about the possibility of the CB itself being susceptible to vibration, temperature, etc.
  • Toward the end of our sail, the DVM reading for the "PRE-HEAT" test showed us that the CB was tripped. However, this time, pushing its reset button DID NOT RECONNECT the power to the PRE-HEAT / START functions using the cockpit buttons.
  • We started the engine using the maintenance START button accessed from inside the cabin [see URL http://sailing.mit.edu/mediawiki/index.php/Engine_40_10_CBs_panel_access (bottom photo.)] The engine started because is was warm enough from previous uses during our sail, so didn't need pre-heating, which is NOT available using the in-cabin button.
  • We were able to start the engine at will while returning to Inner Harbor to furl sails, etc, Unfortunately, the writer doesn't remember whether we did the "pre-heat" check on CB closure, or what results we had if we did.

   TODO: Remember (for above item) how many times we started it in the harbor.

• The narrative continues with [Dave Weisman log of 03Nov tests at the dock.]
• TODO: list briefly the "failure modes" that Dave's test report covers.

original file 'nmore-starting_problem_background ... .txt

             ThomS  version 04Nov10-21:25