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RPM indicators for Rotax engines.

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torgemor(at)online.no
Guest

Posted: Sat Feb 03, 2007 4:37 pm Post subject: RPM indicators for Rotax engines.

Hi there,



For a long time, I've been looking into this RPM problem related to our  

Rotax engines.



You know, I've had it, on my "very" old (sorry lady), engine setup.



Well, this RPM indication problem is NOT related to the "simple" Rotax RPM  

indicator!



Hey, this very same principle is used in the most reliable RPM setups we  

know about out there!



There is only two wires going into the RPM indicator, just a signal and no  

power(?).



OK., since the signal is just an alternating voltage, we simply "steal" a  

little of this energy for the indicator, using a full wave (or half wave)  

rectifier for power, then we measure the RPM(frequency) of this  

alternating voltage, you see, -simple.

The thing is that our "well known" charging system is the problem!



Before any protest here, (  ); Try this:



Make sure that you can see the problem, yes -your RPM indicator is reading  

to low (as always -and normal)!  This might be confirmed with the hand  

hold optical device.



Now, discharge your battery a little (well -make sure there's enough juice  

for a restart of the engine), start your engine, switch on a little of the  

load that you have, LDG lights etc. -if necessary.



What kind of RPM reading do you see now?  Right, normal - but how can this  

be?



This is something we'll discuss, but first some confirmation, from those  

with the problem..

Torgeir.





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Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Feb 04, 2007 4:44 pm Post subject: RPM indicators for Rotax engines.

Hi Torgeir:



Following the wiring diagram of my R582-UL the lighting coils are completely

separate from the ignition coils.  So loading the lighting system shouldn't

and in fact, doesn't make any difference to my Kitfox tach.  My analogue

reading tach is quite linear in it's error.  Approximately 200RPM/1000RPM or

20% always consistent and always low.



My tiny tach is powered by a built in battery and triggered by pulses

passing through the plug wires.  The pulses are no doubt digitized, de

bounced, frequency counted, divided by 2 (2 firings per revolution) and then

the end result displayed.  I believe the highest resolution is 10rpm.  As

with most things digital trends are quite difficult to follow ( how fast an

RPM is increasing/decreasing)  and steady RPM are easy to attain.



For that reason I still have my old erroneous Kitfox analogue tach in the

dash as well as the digital tach.



BTW. My understanding of the original tach is that it also reads pulses not

signal amplitude.  Apparently there was a problem with them burning out with

too much current passing through them so a nice healthy resistor was placed

in series to protect the input of the meter.



Noel



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_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Mdkitfox(at)aol.com
Guest

Posted: Sun Feb 04, 2007 9:17 pm Post subject: RPM indicators for Rotax engines.

In a message dated 2/3/2007 7:38:33 P.M. Eastern Standard Time,  torgemor(at)online.no writes:

  	  Quote: 	
		  There is    only two wires going into the RPM indicator, just a signal and no     

power(?).



	


 I have the Rotax RPM indicator for my 912S and while the engine has only 2  wires going to the tach, the Tach has 3 terminals.  They're numbered  1,2,3.  Does anyone have any idea which terminals get wired to the engine  and what's the extra terminal for anyway?

  

 Thanks,



  

 Rick

Series V Speedster - N39RW

  [quote][b]

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torgemor(at)online.no
Guest

Posted: Thu Feb 08, 2007 4:00 pm Post subject: RPM indicators for Rotax engines.

Hi Noel,



Right on there, yes the newer has it's own coil (the gray wire) winded  

parallel on one of the ignition coils. There's also a 1Kohm (1000 ohm)  

resistor in serial with this line to prevent too high voltage entering the  

RPM indicator.  The early model engines had them installed inside the  

flywheel house, but later one removed to outside of the engine due to  

experienced failure modes.  The SI 5UL90E contain information about  

"disturbance of tachometer 9667 072" and this resistor. Remember, one "582  

engine" rev give 6 pulses (shaped sinus).



So 6800 RPM will produce a frequency of:  f=RPM*(number of poles)/60  

second(one minute)=6800*6/60=680  I.E. Hz



When the engine is running at 6800RPM the frequency of pulses arriving  

 from the engine is 680 Hertz.  Then it should be easy to check with a  

"tone generator" (use less than 10 VAC) and an accurate frequency counter  

your RPM indicator.



I've been thinking that this error only was limited to the old engines  

without the special thacho wire (Grey), but this Service Instruction "SI  

15UL94" also warn about the influence from the lightning coils even the  

fact that they are separated from each other. Just thought this might be  

interesting for someone out there.



On my Fox, the lightning coil is used for the RPM indicator giving two  

periodes pr. rev.



Check here for all the different kind Wesberg (Westach) instruments and  

their setup.



http://www.westach.com/



Here's lot's of instruments and connection setup (that's not very  

readable).



And this site, some other brand of tachometer for our engines.



http://www.umainstruments.com/Tachometer.htm



Their home site, here's lot's of instruments:



http://www.umainstruments.com/

Torgeir.

On Mon, 05 Feb 2007 01:44:10 +0100, Noel Loveys <noelloveys(at)yahoo.ca>  

wrote:



[quote] 



 Hi Torgeir:



 Following the wiring diagram of my R582-UL the lighting coils are  

 completely

 separate from the ignition coils.  So loading the lighting system  

 shouldn't

 and in fact, doesn't make any difference to my Kitfox tach.  My analogue

 reading tach is quite linear in it's error.  Approximately  

 200RPM/1000RPM or

 20% always consistent and always low.



 My tiny tach is powered by a built in battery and triggered by pulses

 passing through the plug wires.  The pulses are no doubt digitized, de

 bounced, frequency counted, divided by 2 (2 firings per revolution) and  

 then

 the end result displayed.  I believe the highest resolution is 10rpm.  As

 with most things digital trends are quite difficult to follow ( how fast  

 an

 RPM is increasing/decreasing)  and steady RPM are easy to attain.



 For that reason I still have my old erroneous Kitfox analogue tach in the

 dash as well as the digital tach.



 BTW. My understanding of the original tach is that it also reads pulses  

 not

 signal amplitude.  Apparently there was a problem with them burning out  

 with

 too much current passing through them so a nice healthy resistor was  

 placed

 in series to protect the input of the meter.



 Noel



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torgemor(at)online.no
Guest

Posted: Thu Feb 08, 2007 4:18 pm Post subject: RPM indicators for Rotax engines.

Hi Rick,



Find the type of instrument that you have, P/N or model then find the  

current setup at Wesberg site here:

I'll think that your tachometer is of the kind that need separate power  

supply, or is a combined type that can use only pulse signal, or pulse  

with own (steady) power.



Here's the link to Wesberg:



http://www.westach.com/



Good luck.



Torgeir.



On Mon, 05 Feb 2007 06:16:25 +0100, <Mdkitfox(at)aol.com> wrote:



 	  Quote: 	
		   In a message dated 2/3/2007 7:38:33 P.M. Eastern Standard Time,

 torgemor(at)online.no writes:



 There is  only two wires going into the RPM indicator, just a signal and  

 no

 power(?).



 I have the Rotax RPM indicator for my 912S and while the engine has only  

 2

 wires going to the tach, the Tach has 3 terminals.  They're numbered   

 1,2,3.

 Does anyone have any idea which terminals get wired to the engine  and  

 what's

 the extra terminal for anyway?

 Thanks,



 Rick

 Series V Speedster - N39RW


	


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