RPM Pulse from Jab 3300 Ignition Coil & Hall Effect

[JimJab]

Hi All,

I had the opportunity to put an oscilloscope over my Tacho/RPM pulse coming from one of my ignition Coils.

Whilst I feel my Voyager EFIS RPM is working OK, it does seemed to be a bit flaky at lower RPM's and this scope picture might be showing why.

I do have a resistor in the cable from the Coil to the RDAC.

Anyone who would like to comments on the shape of the pulse, I would be interested to hear any thoughts, especially with the near mirror image at the beginning and end of the pulse.

Since listing this post some time back, I have been reading about the electrical pulse from automotive ignition systems and this scope pulse trace below is somewhat typical of an automotive type ignition coil pulse.

Any wonder we don't see a rock solid RPM pulse signal through the whole rev range when using the ignition coil for the EFIS's rpm signal.

Cheers
JimJab

Pulse for EFIS Tacho from Jabiru 3300 Ignition Coil

Scope RPM Pulse From CoilR3.jpg (138.31 KiB) Viewed 8357 times

[Paul Sistern]

I can't offer anything regarding the shape of the pulse, but I know from owning a Jabiru aircraft that getting a good RPM signal from the alternator is not always possible. Like you, at one stage, I had a Voyager installed, and I did manage to get a good stable RPM display across the rev-range but only if the alternator was under a bit of load. Once the starter battery had been topped up, and demand from the alternator dropped, the RPM would become less stable. One solution was to fly with the landing light permanently on - not a bad thing to do anyway from a safety perspective. However, the best solution was to ditch the alternator feed and fit a Hall effect sensor over the flywheel and use the two tabs normally used by the (Jabiru supplied) VDO RPM gauge pickup as the trigger.

Paul

[JimJab]

I can't offer anything regarding the shape of the pulse, but I know from owning a Jabiru aircraft that getting a good RPM signal from the alternator is not always possible. Like you, at one stage, I had a Voyager installed, and I did manage to get a good stable RPM display across the rev-range but only if the alternator was under a bit of load. Once the starter battery had been topped up, and demand from the alternator dropped, the RPM would become less stable. One solution was to fly with the landing light permanently on - not a bad thing to do anyway from a safety perspective. However, the best solution was to ditch the alternator feed and fit a Hall effect sensor over the flywheel and use the two tabs normally used by the (Jabiru supplied) VDO RPM gauge pickup as the trigger.

Paul

Thanks Paul for your help and advise, I was thinking about changing my rpm pick over to the alternator wire. But after read your experience, I think it would be much better to go straight to a hall effect sensor as you have said.

If I got the same sensor that Jabiru uses for their VDO Tacho, that would be easy to mount on the motor and it works off those very small tags on the inside of the flywheel, would that sensor work Ok with the Voyager EFIS or would you suggest another type of Hall Effect sensor?

Thanks
JimJab

[Paul Sistern]

No. The VDO sensor does not work with the MGL system, which is unfortunate as it would be a simple solution. You need something like RS part number 765-9328.

Paul.

[JimJab]

No. The VDO sensor does not work with the MGL system, which is unfortunate as it would be a simple solution. You need something like RS part number 765-9328.

Paul.

That's a shame about the Jab VDO sensor, I will check out this other sensor, thanks for your help Paul.


Cheers
JimJab

[Tasmag]

I use an rdac xf feeding explorer lite, I use two feeds, one from each coil.

I had to turn the rpm sensitivity to the minimum on the rdac before I could get a stable reading, but now they are spot on, having two gives the benifit of seeing any issues with the coils.

[wdmac50]

I developed a conditioning circuit for the Jabiru to RDAC XF RPM input that has worked well for me for over 5 years. See that attached JPG. A 10k 1/2 watt resistor is attached at the ignition control lead and connected to the junction of D1 pin1 and C6. I do not recall exactly why I did it this way, but I think it was to pick off the negative pulses, which are very consistent and stable. I combined two of them, along with some other filtering circuits onto a PCB that pairs up with the RDAC XF.

[JimJab]

I use an rdac xf feeding explorer lite, I use two feeds, one from each coil.

I had to turn the rpm sensitivity to the minimum on the rdac before I could get a stable reading, but now they are spot on, having two gives the benefit of seeing any issues with the coils.

Thanks Tasmag for your help,

I don't think I have two Rev input on my RDAC-XB, so when I check the mags one is done by ear for rev changes, I can only see one Rev input on my RDAC, unless you can use another input.

This rpm sensitivity you are talking about, is this adjustment made on the RDAC, I can see in the manual there is a variable trim pot on the RDAC, but I don't have that trim pot on my RDAC XB. So just checking, that are you changing the rpm sensitivity on the RDAC or is that in the EFIS menu for RPM.

cheers
JimJab

RDACXB R3.jpg (239.56 KiB) Viewed 8319 times

RDAC-XB ResistorV3.jpg (172.98 KiB) Viewed 8319 times

[Tasmag]

Jimjab,

The sensitivity adjustment is on the rdac, might not be an option for yours then.

Apologies for the bum steer.

Mike

[JimJab]

Jimjab,

The sensitivity adjustment is on the rdac, might not be an option for yours then.

Apologies for the bum steer.

Mike

Hey Mike, this is not a bum steer to me, you have just confirmed there is different types of RDAC's with in the RDAC-X series and I had those pic on file, so posting them was no a big deal either.

So looking down the track of installing a Hall Effect sensor, dare I mention it.

I wonder what type of rpm sensor Jabiru uses with that glass brand they currently option. That sensor should just bolt straight onto the 3300 engine without any modification. I will check to see what sensor they use and if it would work with Voyager/RDAC. I like the idea of just being able to bolt the sensor on.

No. The VDO sensor does not work with the MGL system, which is unfortunate as it would be a simple solution. You need something like RS part number 765-9328.

Paul.

Paul or Anyone else that using this RS part number 765-9328 sensor, I see it has a M12 x 1 thread size which seems quite large. Does anyone have pics they can post of their sensors mounting bracket for a Jabiru 3300 engine.

Boy, I miss the past forum, I could have search through and maybe have found that very information and pic I am asking for, thanks for any help.

Cheers
JimJab