Well that sounds slick, Ian. The tubes delivered your text all the way across the pond(s).
Michael On Sat, Aug 28, 2021, 5:42 PM Ian Williams <i...@agcon.co.nz> wrote: > > > > > *From:* Ian Williams > *Sent:* Friday, 27 August 2021 4:30 p.m. > *To:* 'redinbau...@gmail.com' <redinbau...@gmail.com> > *Cc:* 'sto...@gmail.com' <sto...@gmail.com> > *Subject:* RE: Dimona stuff > > > > A slight addition …. Of course the other end of the pressure switch is > connected to ground. > > So no hour meters work until you are in the air. When engine is stopped > in the air, the Airframe one keeps going and the engine hourmeter stops. > > > > *From:* Ian Williams > *Sent:* Friday, 27 August 2021 4:25 p.m. > *To:* 'redinbau...@gmail.com' <redinbau...@gmail.com> > *Cc:* 'sto...@gmail.com' <sto...@gmail.com> > *Subject:* Dimona stuff > > > > Hi Kurt and Michael, > > I must have bad breath or something because some of my posts to the DOG > group seem to vanish into free space. However I hope I can help > > Because our Dimona was ex Thai, it had a lot of wiring which was not > needed, so I completely re wired it. Rather than use the original cable > driven taco, I installed a VDO electric taco Part No 333-953 driven by a > little Hall effect sensor from Aircraft spruce which screws into the bottom > vent hole of the Slick magneto. A real plus is being able to calibrate it > using a 50Hz mains sample … ie 50Hz equals 3000 RPM. > > > > Refer to the attached picture … the 2 hour meters are also from VDO. > > The way I connected them is the common (-VE) of both hour counters > connected to a small pressure switch (HERGA Manuf part No 6743-0003) .. > operated by pitot pressure at around 30Kts. The positive end of one switch > (airframe) connected to the plus bus, the other (engine) connected to the > relay next to the voltage regulator on the right hand side of the firewall > looking forward. > > If you refer to the wiring diagram on page 25 of the service and > maintenance manual, notice the oil switch (the oil pressure sender) has 2 > connections (actually 3 if you consider the earth being the case) It is > 12 and 17 …. One output drives the VDO oil pressure gauge (15) and the > other is a switched output driving the relay (9) > > That relay when active enables the voltage regulator to work only when the > engine is running. Presumably a cunning trick to keep the current draw as > low as possible when the engine is off soaring. > > So the plus supply for the engine hourmeter can be taken from the output > of that relay. > > It is a real simple system and has worked faultlessly for 500 plus hours. > > > > Of interest, I have since replaced the Cyl Hd temp gauge with a MGL 4 cyl > colour barograph unit > > > > I would be interested to know if you actually have received this email. > > > > Best regards > > > > Ian Williams > > ZK-GCB >
