SonexBuilders.net

For those who have connected a Jabiru 3300 to an MGL RDAC, Im curious of anyone has installed an inline resistor to the RPM #1 hookup.

I don’t have a resistor installed and continue having an intermittent RPM fluctuations between approximately 1700-2200 RPMs. Above or below that range and it works great but when I’m in that range, the RPM bounces up to maximum RPM ranges.

I saw a diagram recently from MGL that claims a 10.00 Ohm resistor is used for that pickup; I just wanted to see who else has done this.

Thank you!!
Mike

I have an rdac xf map and a hall effect sensor pickup, on my 3300, no problems. Just had to adjust the gain pot for
a solid reading.

Rick
C-GRIX

Hi Rick, thank you for responding. Do you remember which sensor you used? I assume you mounted it to the point next to the flywheel?

I used an alternator output that plugs into the voltage regulator and it’s reliable most of the time; there’s just an RPM range where there’s an error.

Thank you!

Hi Mike. These are the ones used by Jabiru https://au.rs-online.com/web/p/motion-c ... s/0304166/ They pulse a small voltage, triggered by tabs on the flywheel. As Rick said they work well with the MGL rdac XF.
Steve
Sonex 892

I drive the tacho off the low tension terminal of one of the ignition coils. It's the terminal that you normally connect to the kill switch. The method is described on the last page of the RDAC manual. The RDAC manual is a little confusing on this. It says "We strongly recommend that a resistor is inserted into your wire as shown. A good value would be 10.000 ohms (10K). A normal 1/4 W resistor is just fine."
The correct value is 10K ohms. I have used this method for 9 years and found it to be completely reliable.

Peter

I use a homebuilt hall effect sensor, described by Brian Anderson on the old list. I have installed pictures and schematic but don't know
how to post them here. I'd be happy to email them to you. A good commercial sensor like the Honeywell 1GT101DC works well, but
it looks like they are getting difficult to find.

Peter's setup sounds good too. I'm guessing you only get an rpm reading on one mag when doing a mag check?

Rick
C-GRIX

Peter's setup sounds good too. I'm guessing you only get an rpm reading on one mag when doing a mag check?

You will definitely notice if the engine stops. However, you are correct Rick. If you are trying to pick a speed drop that is more than it should be all you have is sound to go by for one ignition. I'm not sure why, but the indication is no speed drop at all when that ignition is switched out. Maybe there's some software in there that says "Nah, that can't be right. I'll just show him the last number for a while to see if it comes back".

Peter

Peter Anson, or anyone else that might help,
I know this is a 6 mo old thread but need some help. My jab 3300 has been giving me issues with my tach not being reliable. I know its not a new problem so i put a tiny tach as a backup that has been flawless. I just realized that my hobbs will not read at all when rpm reads zero. It reads zero more often than it reads even a wrong or fluctuating rpm. I see you use the lead coming off one coil. Did you just hook a wire directly to the kill side of the coil, put a 10 k resister inline and run it to the rpm input of the rdac? Or was there some kind of sensor in there somewhere that i am missing?
Thanks Mark

Mark. Not sure about other RDACs but if you have the XF it has a potentiometer sensitivity screw and 3 dip switches, filter, ballast and high gain for each RPM input. These are adjusted to either reduce the signal for the RDAC or amplify it. A strong signal would be picked up from the alternator or ignition or a weak input would be an inductive pickup.
Steve
Sonex 892

Hi Steve,
Not sure which i have I believe it is the xf. I have what i think is a cammit fly wheel tooth counting tach sender. It has basically quit on me and i am looking at other options. I was interested in the coil wire tach setup . I could be completely wrong but my understanding is that a wire comes off the kill switch side of the coil with a 10k resistor inline and then goes to the rpm plugin on the rdac. That seems very simple, almost too simple. Am i missing something. Will i need to go into the mgl enigma and change settings?