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Tach / regulator problem

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Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Mon Jun 28, 2010 9:04 am Post subject: Tach / regulator problem

I'm having a bit of an electrical problem on my UltraStar. 



 The plane has a Westach tach/EGT combo; the tach runs directly off the lighting coil on the Cuyuna and always worked fine. I just added a Key West regulator so I can have 12VDC power for my strobe and radio. The tach and regulator are wired in parallel to the lighting coil (unlike the Rotax, the Cuyuna has a single lighting coil). No battery. However, with the regulator connected, the tach reads low.



 Here's the weird part. When I first installed the regulator, the read low, no more than about 2500 rpm indicated at full throttle (6500 rpm). However, when I switched on the strobe, it read correctly, except for a momentary blip as the strobe fired. Figuring I needed a load on the regulator, I added a 50 ohm resistor to the output to draw a constant 1/4 amp. Now it indicates about 5000 rpm when the engine is actually doing 6500, regardless of whether the strobe is on or off. I then disconnected the resistor, which made no difference (still reads 5000). Finally, I disconnected the regulator, and the tach again reads correctly.



 I went up to the airfield yesterday with some other components and test leads, etc… figured on trying a capacitor across the output instead of the resistor, or a smaller resistor on the input between the tach and regulator, but it was too hot to fiddle with t… much nicer to go up a couple thousand feet and cool off.



 Has anybody else seen this problem? 



 -Dana 

 

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Richard Pike

Joined: 09 Jan 2006
Posts: 1670
Location: Blountville, Tennessee

Posted: Mon Jun 28, 2010 10:45 am Post subject: Re: Tach / regulator problem

I had a similar situation several years ago when I went through months of weirdness with my tach and my Key West regulator. Ended up buying a Tiny Tach and have had no more problems. You wrap a sensing wire around the spark plug lead and it counts the actual pulses. Simple, reliable and a digital readout.



Richard Pike

MKIII N420P (420ldPoops)

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Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Mon Jun 28, 2010 1:40 pm Post subject: Tach / regulator problem

At 02:45 PM 6/28/2010, Richard Pike wrote:

 [quote]--> Kolb-List message posted by: "Richard Pike" <richard(at)bcchapel.org>



 I had a similar situation several years ago when I went through months of weirdness with my tach and my Key West regulator. Ended up buying a Tiny Tach and have had no more problems. You wrap a sensing wire around the spark plug lead and it counts the actual pulses. Simple, reliable and a digital readout.



 Richard Pike

 MKIII N420P (420ldPoops)



 



 

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