Discovery lite and tacho

[Brett]

Hi all, asking those in the know. I am having trouble reading a correct value for the tacho on my aerovee and discovery lite. At a steady rpm of around 1000 I am seeing erratic readings like 7,142,230,4,37,115. I have set the pulses per revs as per the manual and hooked the wiring up to the alternator as per the diagram. In fact the wiring is exactly the same as my other aircraft with aerovee and mgl rdac and that reads fine on the ultra horizon xl.
I have tried selecting the filter dip switch in the rdac however that only results in a 0 reading. The wiring is zip tied together with other wiring like the oil sensor, cht's and so on but thought surely they couldn't be interfering?

Has anyone else had an issue like this or if not did you wire up the tacho input any differently or change a setting in the menu?

Thanks:)

-Brett

[Rynoth]

I'm also having this issue. I haven't flown the plane yet so can't give input on consistent higher tach readings, but at lower/idle settings on the ground it's highly irregular. Also wired per the plans to an mgl rdac connected to an mgl iefis discovery lite.

[Brett]

Ok, that doesn't sound good. I will try and email the company and see if they have a solution. I'll let you know what they come back with .

-Brett

[13brv3]

I'll be interested to hear how this goes, since that's the same combination I was planning to use.

Rusty

[jjbardell]

I have mine wired off the voltage regulator. Followed Matt's setup in the menu and it seems to be fine at idle. Where is you tach wire coming from? Also, is your RDAC ground at the same spot as the starter/engine ground. You may want to check to ensure no poor ground for the rdac.

I grounded mine all at the same spot. Starter, engine and rdac all ground on the bolt hole right behind the oil cooler.

Hope this helps.

Here is a photo.

http://i1204.photobucket.com/albums/bb4 ... 2E8B87.jpg

[fastj22]

My experience with MGL RDACs and using the alternator pulse for RPM pickup is problematic.
It seems to be very susceptible to noise. My first RDAC, a XD, worked fine from an RPM range of 0 - 1300, was jumpy 1300-2000 and stable from 2000 up.
The XD failed this fall and I replaced it with an XF. Now RPM is stable from 0 - 2500, but goes nuts above 2600. I've tried lots of setting adjustments, per MGL. Also have been fighting other sender issues that generally get solved by grounding everything to the engine, not the firewall.
If you guys figure out the perfect settings, please publish them.

[gammaxy]

I haven't had any problems with my MGL RDAC XF and the Aerovee alternator. Mine is connected to the voltage regulator as shown in the Aerovee plans and seems to measure reliably and steady as low as ~200 rpm (the slowest I see when the starter is engaged). I haven't noticed any problematic ranges all the way to 3400 rpm.

At a steady rpm of around 1000 I am seeing erratic readings like 7,142,230,4,37,115.

I'm curious if your sensitivity gain is too low. This might explain why you have really low rpm measurements. Does it get better at higher RPMs? I think if noise were your problem, your readings would be higher than the engine's rpm.

Someone should hook an oscilloscope up to the tach input. I'm curious if the nature of the signal changes when the voltage regulator kicks in--this might explain the problem fastj22 noticed.

[jjbardell]

Speaking of when the voltage regulator kick in, I have only started my engine 2-3 times and haven't tuned my carb yet so no high rpms. But I have noticed my efis always shows the low voltage and the voltage reading on my efis is 0. All of this is below 1500 rpm.

Does the regulator not provide voltage that low of rpm or do I have another issue?

[Rynoth]

But I have noticed my efis always shows the low voltage and the voltage reading on my efis is 0.

Even with the engine off, the efis should display battery(system) voltage (12.x) Not sure why it wouldn't be displaying the source voltage to the efis.

[Brett]

Well the short version is its now working fine :)

I took the wiring out of the loom to eliminate interference and made no difference. I replaced the wiring in case there may have been a bad connection but still no good. Earths were good.
Played with the settings and also tried the RPM 2 input.
Essentially I cleared all my settings in the RPM 1 screen and set it up again.
Stared the engine and wham,,,, had a reading of like 10530 RPM,,,,nice.
Went back into the screen and readjusted the scale rpm back to 1 and then it read a rock solid correct figure.
So I guess all the issue was seemingly an incorrectly set up figure. Funny thing is I can't see what actually is changed. I just reset all the rpm figures and now it works fine. Anyway I'm happy as and it's working fine so all good.
I have photos but unsure how to upload without burdening the website in terms of data traffic as mentioned in earlier post somewhere.