Electric tachs have been known to short, which would take down the ignition coil it's tied to. I've experienced that first hand. However, you are wiring to a Dynon unit, and Dynon already thought of that. That's why they recommend using a 30 kΩ "pull up" resistor. The Dynon unit isn't going to draw any current as it only reads signal voltage and requires virtually no amperage. A 30 kΩ resistor as shown in the installation manual should keep a shorted tach from taking down the ignition. That's why Dynon recommends using the resistor. It protects the Dynon from the ignition, and the ignition from the Dynon unit, but still allows the Dynon to read the voltage switching up and down at the ground side of the coil. If you are concerned about the wire getting shorted, put the resistor right at the - terminal of the coil. If you do the math on the 30 kΩ resistor at 12V, it only allows .0004 of an amp (4 ten thousandths of an amp) of current to pass through. That isn't going to affect the ignition if you had a dead short on the tach side of the resistor.
Hope this explains the installation well enough. -Jeff Scott > Sent: Sunday, March 24, 2019 at 7:57 PM > From: "Pete Klapp via KRnet" <krnet@list.krnet.org> > To: KRnet <krnet@list.krnet.org> > Cc: "Pete Klapp" <pke...@hotmail.com> > Subject: Re: KR> RPM source for use with Dynon Skyview > > Thanks Joe I’ll chew on this info before doing anything > > Sent from my iPhone > > > On Mar 24, 2019, at 11:07 AM, n357cj via KRnet <krnet@list.krnet.org> wrote: > > > > HI Pete/Jeff, > > I was not going to post to this thread but here I am. I have my EIS wired > > as noted from the negative of the coils (daul). i have a small toggle > > swithch right next to the tach on the panel when I switch ignitions I have > > to switch the signal to the EIS also to have a reading. I wired it this way > > as it was the most common way when I was growing up working on cars. I > > understood as Jeff has re-confirmed that it is basicly the way a mag works > > also. The disclaimer is that William Wynn strongly (my word) urges a > > alternate method, usually a tooth counter, to drive the tach. Granted this > > would elminate my need for the swich on the panel. The caution that I > > undersatand is the possibility/fear of a short in the wire from the tach or > > the instrument that takes the coil out and there by stopping the fan up > > front. Just because it hasn't happened does it mean it won't. So decide fro > > yourselves the best method. > > Joe Horton, > > N357CJ > > > > > > ----- Original Message ----- > > From: "KRnet" <krnet@list.krnet.org> > > To: "KRnet" <krnet@list.krnet.org> > > Cc: "Jeff Scott" <jscott.pla...@gmx.com> > > Sent: Sunday, March 24, 2019 10:11:25 AM > > Subject: Re: KR> RPM source for use with Dynon Skyview > > > > It occurred to me last night while I was working through some wiring > > diagrams for an ignition problem that I put an error in this advice to > > Pete. It is always the - (ground) side of the ignition coil that is > > switched, so it is the - side of the ignition coil that would be used as a > > tach signal and the equivalent of the "P-lead" from a magneto as a source > > for wiring the tach signal. I'm surprised about a half a dozen of the > > scholars here didn't correct me. > > > > -Jeff Scott > > > > ----------------------------- > > > >> Pete, > >> > >> I've not wired a Dynon, but in your case, I would assume the + side of an > >> ignition coil to be the equivalent of the P-lead on a magneto. The voltage > >> on the primary side of your coil may be a bit lower than the voltage on a > >> P-lead, but I would use a 30 kΩ "pull up" resistor the same as instructed > >> to connect a "P-lead" and go from there using the same instructions as > >> outlined for connecting to a "P-lead", then configure for a 6 cyl engine. > >> The pulse count should be the same as any 6 cyl Continental or Lycoming > >> firing from a magneto. > >> > >> -Jeff Scott > > ----------------------------- > > > >> > > > > _______________________________________________ > > Search the KRnet Archives at > > https://www.mail-archive.com/krnet@list.krnet.org/. > > Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. > > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > > options. > > To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org > _______________________________________________ > Search the KRnet Archives at > https://www.mail-archive.com/krnet@list.krnet.org/. > Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options. > To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org > _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org
