Alternate tachometer output for AVC1 voltage regulator

[Spaceman]

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...

[T41pilot]

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.

[Spaceman]

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.

[racaldwell]

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

[Spaceman]

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

[T41pilot]

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.

[Sonex1517]

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)

[racaldwell]

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

[Sonex1517]

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

Thanks

[Spaceman]

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.