RPM Pulse from Jab 3300 Ignition Coil & Hall Effect

[JimJab]

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.

Thanks wdmac50 for your post about the Jab ignition signal conditioner, I would be right into making this but for one thing. I don't have 2 RPM input on my RDAC, so I am also wanting to over come this issue of losing the RPM when checking one of the mags.

So I am thinking I will look at reto-fitting a Hall Effect unit, to the pickup the flywheel coil magnets, see my next post.

Cheer
JimJab

[JimJab]

Hi Rainier, a quick question,

Is there a preference for any Brand and Model Hall Effect sensor to pick-up the revolutions from the magnets in the Jabiru flywheel?

After much consideration, reading and googling, I am heading towards fitting a Hall Effect sensor. This will solve the problem of losing the RPM from the coil wire when checking mags and hopefully will give a much more stable pulse for the RPM.

I have found in the Jabiru Aircraft Technical Manual JTM001-9, page 264, Figure 198 &199 this refers to the fitting of a plate and an Hall effect sensor.

The Hall Effect sensor used by Jabiru here, is a Hamlin P/No. 55075-00-5-A, that has a M12 Barrel and adjustable thread length of 36mm, there seems to be other Brands that are similar style and electronically spec's.

Sorry about the poor quality of the print and picture, but for the interest of other Jabiru owners, I have attached the Jabiru Aircraft Technical page.

In my situation, I will have to machine a hole for the Sensor plate in the Alternator Spider bracket.

Cheers
JimJab

JTM p. 264 may no longer be Correct. Please check first.

Jab Flywheel Hall Effect .jpg (235.48 KiB) Viewed 8708 times

[rainier]

You can use anything that produces a clean pulse with a minimum of 1V peak to peak - if you use a hall effect sensor - most of them are open drain drivers so they can switch to ground or are "floating" - this means you need a pullup resistor - perhaps to 5V or 12V (check data sheet of the sensor how high you can go).
The RDAC will accept a minimum pulse of about 1V at maximum sensitivity.

BTW, it would appear that the standard Jabiru pickups (just a coil) work well - they create a large enough pulse for the RDAC. Like all such pickups you should load them lightly to avoid too large a voltage (lots of volts but little energy). A 1K resistor across the coil should be good.

[JimJab]

You can use anything that produces a clean pulse with a minimum of 1V peak to peak - if you use a hall effect sensor - most of them are open drain drivers so they can switch to ground or are "floating" - this means you need a pullup resistor - perhaps to 5V or 12V (check data sheet of the sensor how high you can go).

The RDAC will accept a minimum pulse of about 1V at maximum sensitivity.

BTW, it would appear that the standard Jabiru pickups (just a coil) work well - they create a large enough pulse for the RDAC. Like all such pickups you should load them lightly to avoid too large a voltage (lots of volts but little energy). A 1K resistor across the coil should be good.

Thanks Rainier for your knowledge, post and confirmation on what can be use with the MGL RDAC.

I will purchase a Hall Effect sensor as I think this will be the best way to get the pulse signal I am looking for.

For any Jabiru owners like me who may purchased their Jabiru secondhand with a MGL panel and then you feel, hey my Tacho is not as stable as I would like, here is a link to the Jabiru Owner's Forum, it talks about retrofitting a Hall Effect sensor your a Jabiru engine.

http://www.jabiruownersgroup.org/viewto ... f=30&t=576,

Here is a pic from the Jabiru Owners Group forum, the owner here has mounted his sensor slightly differently to the way Jabiru has done it and shown in the Jabiru Technical Manual above.

Retro Hall Effect SensorR1.png (144.6 KiB) Viewed 8704 times

Cheers
JImJab

[JimJab]

Hi, it's been number of weeks since my last post on this topic.

It has taken some time to understand which type of sensors could give me the best RPM results with the Jabiru engine. Also what is the best way to mount the sensors to reduce engine vibration.

Hall Effect Sensor are those sensors that have at least 3 wires coming out and need a power supply (5 to 36 DCV). There are a number of different ways these sensors are activated, e.g. using Magnets (South Pole Only), using Ferrous Metals ( Gear Teeth and also Magnets), there are other types, eg inductive etc.

I see people are using different Hall Effect Sensors with success, "NJK-5002c", "RS 765-9328", "Hamlin 55075-00-5-A", so I googled them to see what, if anything was the difference. This just opened a bigger can of worms as there is many different types of Magnetic Hall Effect Sensors, I end up getting a "NJK-5002c, and it is a NPN-NO".

I stayed with the Magnetic Hall Effect Sensor as these have a greater working distance of 10mm between the flywheel magnets and the sensor, the other types had working gap of 3-4mm.

The different Magnetic Hall Effect types are NPN-NO (Normal Open), NPN-NC (Normally Closed), PNP-NO (Normally Open), PNP-NC (Normally Closed), so if anyone has any ideas why one type may suit the MGL RDAC better than another please let us know. I am wondering if a PNP-NO (Normally Open) might be a better option?

After much reading, I found the RDAC-XB can handle 100 DCVpp on the RDAC RPM input, so the RDAC input is good to go for 12VDC.

I have some Questions

Is the RDAC-XB, RPM input electrically isolated?

The wiring of the "NJK-5002c" sensors to the RDAC, I am guessing it can wired with the Pos+ and Neg - to the aircraft 12 volt bus and the Black wire to the RDAC RPM input without any RDAC ground differential issues?

One last question, can Hall Effect Sensor be powered up with and share the power from the FF5v+ on the RDAC and have the neg lead grounded to the engine?

[rainier]

Is the RDAC-XB, RPM input electrically isolated?

The wiring of the "NJK-5002c" sensors to the RDAC, I am guessing it can wired with the Pos+ and Neg - to the aircraft 12 volt bus and the Black wire to the RDAC RPM input without any RDAC ground differential issues?

One last question, can Hall Effect Sensor be powered up with and share the power from the FF5v+ on the RDAC and have the neg lead grounded to the engine?

It is A/C coupled. Yes you can use the 5V supply but the signal may be a little on the low side - better to power from the 12V side. Most senders will need a pull-up resistor for the high side.
Some senders may need to be powered from a 5V source but are open collector design and you can pull up to a higher voltage.

[JimJab]

Just to follow up on this post with a few pic's and words.

I decided firstly to draw up a 3D drawing in Fusion 360 to suit the NJK-5002c Hall effect sensor, so I could test the sensor by having it mounted on the spare ignition coil mount on the Jab Gen 4 3300 engine. Well this Hall Effect sensor past with flying colors, the RPM was stable through out the RPM range. So the next step, I will mill up an alloy bracket.

Fusion 360 Jabiru Bracket

Jabiru Gen4 NJK-5002c Bracket B..jpg (50.73 KiB) Viewed 8511 times

Here is a pic of the 3D plastic bracket and sensors on the Jab Gen 4 engine. This Hall Effect sensor only switches when a magnetic south pole goes past. As the center part of the flywheel ignition magnet is magnetic north, the outside two poles are magnetic south, so you will get 6 magnetic south pulses per revolution for a 3300, your EFIS RPM setting will be set to 6 pulse per revolution. Warning, don't try to use this 3D plastic bracket in flight, you will find when testing the sensor on the ground the bracket will deform from heat and mounting bolts will lose their torque after a bit.

Bracket and Sensor Mounted

3D Print of the Hall bracket for Jab Gen 4.jpg (139.03 KiB) Viewed 8511 times

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Now if you remember the scope picture at the beginning of this post, I had a very strange pulse pattern from the ignition coil wire as the RPM sensor, yes it worked, but in my case very poorly. Here is a blurred scope picture, but it shows this Hall Effect pules with a nice regular pulse pattern.

Sorry its not a good picture

Scope of the NJK-5002c Sensor.jpg (36.41 KiB) Viewed 8511 times

Cheers JimJab

[JimJab]

Hi,

One last thing you may ask, how did I wire up the NJK-5002c Hall Effect Sensor.

Here is a bit of a drawing, I have not added a pull-up resistor, (between 1 and 2) this might be wrong, but I think this brand of Hall Effect sensor has one built into it?, as it does not seem to have any floating state on the signal lead.

But if anyone feels there is something wrong with the drawing or anything else, like not having an in line resistor on the signal wirer please don't hesitate to say so, I have put this drawing up here for future reference for all Jab owners and I want it to be right for me and everyone else.

The final result, its been time consuming going through the process and having to check stuff along the way, this has caused me a bit of uncertainty but the result was worth the effort. I am really happy as my engine now purrs along nicely with a stable rpm.

One last thing, you can make the bracket many other ways, but if you would like to have the CAD drawing, just ask.

Cheers JimJab

Wiring drawing of Hall Effect Sensor.

Hall Sensor bracket for Jab Gen 4.jpg (74.63 KiB) Viewed 8511 times

[JimJab]

Hi All,

Here are some Fusion 360 drawing with the dimensions of the Hall Effect Bracket for the Jabiru Gen 4 Engine.

Whilst I was able to mill this bracket, many may not have the gear or want the cost of getting someone else to mill it. I reckon you could use 10mm x 25mm aluminum straight bar to make this bracket, with some straight cutting of the mounting tab's using a hacksaw.

When drilling the mounting holes 6.5mm or for some wiggle room 7 mm holes, drill them as close to the fly wheel side of your bracket as possible. This will give you as much clearance as possible between the bracket and the flywheel/magnets when mounting the sensor.

The Hall Effect sensor was about $11.00, the aluminum bar stock was about $ 3.00 AU and the rest was in time. Well worth the effort for the small amount of money to get away from the ignition coil pickup and to have a stable EFIS RPM

Jab 3300 Hall Effect Bracket Top Dim

Hall Bracket Top 800 x 600 Dim.jpg (76.1 KiB) Viewed 8447 times

Jab 3300 Hall Effect Bracket Front Dim

Hall Bracket Front 800x 600 Dim.jpg (73.74 KiB) Viewed 8447 times

Final Milled Bracket

Hall Bracket on Plane.jpg (53.76 KiB) Viewed 8447 times

My final bracket does not have the same rounded edges as the drawings, but it works for me.
I hope this helps someone in the future.
Cheers
JimJab

[Rowdy]

Hi Gents just jumping in here with my Jabiru 3300 install to a MGL IEFIS challenger.
Am I right in guess my normal analogue magnetic pickup as fitted to most Jabirus will not work?
If I use the coil P lead can two leads, one from each magneto Both be connected to RPM 1 ?? or do you need to rpm guages?
Thanks