SonexBuilders.net

Howdy guys,

Are there any other ways to get a tachometer output from an Aerovee other than one of the alternator wires? I'm thinking of swapping to the B&C AVC1 voltage regulator, but after asking some questions about wiring I got this info from their tech support:

The AVC1 works a little differently than many regulators for permanent magnet type alternators and as a result, the alternator wire no longer provides a reliable tach signal. If you use the AVC1, you will need to come up with another source for a tach signal.

What other options are there? I guess I don't really understand why the AVC1 would make the alternator wire not work for the tachometer anyway...

Well that was nice of them to come up with that after I already bought one. I've installed mine but haven't run my engine yet, so I don't know if there is an issue or not. I thought if you didn't get a good tach reading off of one side of the alternator wires you just switch to the other Wire. The Rotax on my ultralight has a specific tach wire but tach can also be taken off a lighting coil wire as well. Since we don't have lighting coil wires I suppose you have to pick it off the ignition somewhere? That is some high voltage stuff. Maybe a series resistor off a coil wire or something. I'll be looking for Jeff Schultz to be chiming in here. I'll be following this as well Chris.

Here's some more info from the guy at B&C:

For a tach pickup, I’m familiar with what is being used with Corvair conversions because I’m using a Corvair in my project. Here is a link to the sensor sold at flycorvair.net. https://flycorvair.net/product/3411-tach-pick-up/



If Garmin can handle lots of pulses per revolution, then you can point the pick-up at the ring gear teeth. If you have to keep it to a smaller number of pulses per revolution, then the Corvair method is to put two bolts in the ring gear and have the tach-pick-up count the bolt heads resulting in 2 pulses per revolution.

For the folks using Grand Rapids, they require a minimum of 5V signal for the tach pulse. There is essentially no upper limit. So using a pick up that generates its own signal, verify what voltage it sends and what is required for the EFIS.

I ordered a Honeywell SNDH-T series sender from Newark. It requires a voltage input (+12V) and the signal is about 1V less than input voltage (+11V). I have not installed it yet.

The HONEYWELL sensor someone suggested here that others are using on the Jab has been discontinued.

Rick Caldwell
Xenos 0057

Rick, are you going to use that sensor on an aerovee? Where will you mount it?

Chris

In reviewing my GRT remote engine monitor manual, it shows that tach signals can be obtained from the P leads on the mags or the low side of the coils as long as series resistors are used to isolate and stabilize the signals to the EFIS. If B&C is suggesting that a tach signal from the alternator is unstable and therefore unreliable, then maybe a series resistor there may be a solution. Just a guess on my part at this point. At any rate, I may try the P-lead solution first if the alternator wire doesn't work. My GRT data shows a 1K series resistor if a coil is used or 27K to 39K resistor if the P-lead is used from a mag. Higher resistance needed there probably to prevent an approach to a ground connection.

This is an interesting and timely thread....

I just installed an AVC1 and am in the process of reinstalling my Jabiru 3300. I didn’t see anything in their manual about this, and previously was using the alternator for my GRT remote EMS to pick up RPM. I guess I’ll know soon if it still works. (I have a TinyTach as a backup anyhow, so I’m good either way)

Chris, No, I bought the Honeywell sensor for the CAMit/Jab tach mount. It can use the existing Jab tach sender mount hole with a 6 mm all-thread rod x 2" as a stand-off. I have no idea what you have for mounting on an Aerovee.

I'll try the CAMit 40A alternator signal first to see if that works. If not, then I'll mount & wire the Honeywell sensor.

Rick Caldwell
Xenos 0057/CAMit 3300 #0088

Please keep us posted Rick, as I may need to do the same.

Thanks

I had been thinking about trying to use that Corvair sensor or something similar mounted near the flywheel somehow, but I couldn't really come up with a good mounting location. I just had a different idea, what about mounting a sensor like that at the front of the engine to count the prop bolts? There's a tapped hole already right next to the prop flange that a little bracket could be bolted to, then just sense the back of the prop mounting bolts at 6 per revolution. Is there any reason not to do it this way? Seems like it would be pretty easy.