lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> >When I first start my engine, the starter appears to draw so much power that the VisionMicro shuts down. This is very annoying, as it takes about 5 or 10 seconds to reboot, during which time their is no RPM, oil pressure... monitoring available.< My comment to this problem is that it may not be a Vision Micro Problem but a wiring problem specific to the aircraft. When the starter engages, the things that cause the voltage to drop is battery internal resistance and resistance in the wiring, master relay contactors, and wiring connections. Resistance in the wiring is usually due to too many connections, poor connections or too small a wire size. To give an example of how critical resistance free connections are let's suppose that a connection at the battery has only 1/100 ohm resistance. The starter pulls 150 amps. The voltage drop across that single connection is 150amps x 0.01ohm which is 1.5V. That means 1.5 Volts that are not available to the starter. Now introduce a few more poorly done connections in the circuit and voila, low voltage for the starter and many other problems with components like the VM which apparently trips off at 10 Volts. BTW, DC starters try to put out the same power regardless of voltage available. The lower the voltage the more current the starter draws. This causes even more voltage drops at the poor connections, which causes even lower voltages to the starter and the starter to draw even more current. The end result is large system voltage drops during start and also a shorter life for the starter motor. Some ideas to prevent the start up problems above include the following: RG batteries have very low internal resistance due to the plates being closer together. A good starting circuit has a connection at the battery and one at the starter and none inbetween except possibly the master relay. The starter is grounded at the engine and the engine must be grounded to the battery with a single big grounding wire again with no connections inbetween. Nonetheless, all sensative digital electrical equipment should be on a radio bus. The proper power up sequence is to start the engine, activate the alternator field, then power the radio bus. The digital engine monitoring equipment will come up in a few seconds just as the oil pressure is stablizing. Remember the old days when there was an oil pressure line to the analog pressure guage? In colder climates like here in Minnesota, it was not unusual for the oil pressure not to indicate anything for nearly a minute until the sense line sludge started moving. Jim Frantz >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>