I've decided to go with a Tiny Tach. ThanksYou must wrap the inductive pickup wire tightly around the spark plug wire. 5 or 6 wraps is in the ball park. The more wraps the stronger the signal --too many wraps and you pickup electromagnetic interference. ::)
| March 21, 2012: On our DE, we have a tiny-tach TT2A-O, which we rec'd last Dec. It is a bit erratic on the plane, but I think that is a problem of finding the right spot on the plug or coil wires and the right number of wraps to get a steady signal. At least I hope so. This is the third one we've tried. The first was part #TT2A, description "Tiny-tach adjustable firing mode". The package card was marked "2A Adjustable". This unit locked up on the plane. Steve at Tiny-tach told me how to reset it by peeling off the front cover, and digging out the rubber to the right of the switch button, then shorting out two traces on the circuit board. I think what this does is short the internal battery momentarily, allowing the unit to re-start. We tried to make this unit work, but it kept locking up. Steve then sent us an older, non-adjustable model, shown as part #TT4RX, description of "Tiny-Tach 4C reset w/ filter". On the back was written "4RX". The package was marked "TT226R-4cx". This unit also locked up on the airplane. Then we got the current unit, part #TT2AO", description "Tiny-Tach RPM/HOUR Meter - Adjustable/Filtered". The package card was marked "2AO". On the back of the unit was printed "411TT2A", followed by hand-written "10". We have a Tiny-tach on the LEU, older non-adjustable model, and it worked great. So, we are optimistic that we can get this latest unit working well. May 1, 2012, Here is an update on our quest for a working tachometer for our DE, and some other related "good" ideas: Update on the Tiny Tach TT4RX, "Tiny-Tach 4C reset w/ filter" - This is an older version, calibrated for one spark per 2 revolutions, and not adjustable. After it locked up, I was able to reset it to operation by peeling off the front cover, digging out some rubber, and shorting the terminals. I think these units lock up if there is too much signal. Our DE has dual ignition, primary is distributor ignition, secondary is magneto. We had run our Tiny Tach wire alongside the magneto on/off switch wiring, and I think it may have been overcome with the signal noise from magneto. As part of the effort, I found someone on the web that ran his TT wire through the grounding braid of a piece of coax that he had removed the inner conductor and its insulator from. A lot of coax is too tightly constructed to allow this, but I had a piece that I was able to do it. I worked the TT wire through it. The TT wire is itself a coax; its inner wire is wrapped around the spark plug wire, and the shield is connected to a ground at the engine. On the added, outer coax I insulated the engine end, but grounded the panel end of the coax. Also, I routed the coax away from the magneto wiring. This all seemed to work, and work well, too. Problem is, this TT model accumulates total time in whole hours. Not hours/minutes, or hours/tenths of hour. We wanted to see better accumulated time resolution than whole hours. A couple of extra tidbits of this older model. There is a reset button, and it will reset the accumulated time back to zero. I had made a plastic cover to protect the button to prevent accidental time reset. I also found that a run signal can be faked into these OLDER models. Connect the ground wire and the signal wire of the TT to the secondary of a 12 volt, AC transformer (not a DC power supply, has to be AC). I used this technique to build the run time back up to match our engine run time. Kiblinger and Spencer came up with a TTO tachometer. I ordered one and tried it out. It worked great. No wandering, steady updates, no lock-up. It shows accumulated time in hours/tenths of hour, non-resettable. Immediately after shutting engine down, it shows the max rpm for maybe 10 seconds, then shows the accumulated hours. It is smaller than the Tiny Tachs, but the display is about the same size. It has a setting button on the back surface, and can be set for # pulses/crank rotation, fast/slow updates and for high/low sensitivity. The wire is not a coax, and it does not require a ground connection at the engine, just some wraps around the spark plug wire. I did take care to route the wire away from the mag wiring, because it could possibly be confused with all that electrical noise. I like it. It is a "Trail Tech TTO Tach/Hour Meter 72-A00", ordered from PowerSportSuperStore.com, and it cost $29.65 total. There are sources a few cents cheaper, but I had purchased from this place previously, so went with them. Only problem, it had zero time on it, and I wanted it to match the engine time. During my testing of Tiny Tachs, I found that the newer, settable versions could not be fooled to operate with the 12 VAC transformer trick. I figured that these newer tachs sense a signal that has a faster transition time than 60 hz. I had a switching power supply from an old TV digital converter, and thought that there may be some fast transition signal available in there, so I opened it up and tested it with one of the newer model TTs (TinyTachs). Just to be sure not to get any higher DC voltage in the TT, I put a 100 pf capacitor in series with the signal lead, and began touching points of the power supply circuit board. I found a spot that tricked the TT to operate at about 15,000 rpm and it started accumulating time (Didn't have to connect the ground wire to anything to make the tach work, so I simply connected the ground wire of the TT to the metal work bench (yeah, I know, electricity on a metal bench). I connected a house light timer to it and set in a dozen hours and let it run. Next day the TT had the right amount of hours on it. Problem solved. I tried the same trick on the TTO and it worked, although there is no ground wire to connect to the bench. So, I was able to set the TTO with the correct engine hours. We put it in the airplane and have a couple add'l hours on it. The switching power supply is a wall wart, 120vac input, 5 vdc output, 1.72 amps. I can't guarantee that any other PS will work; may have gotten lucky with this one. I think what is happening here is that the switching power supply converts 60 hz to maybe a couple thousand hz in the process of making the DC in the output. I suppose the tachs sense this higher frequency as a spark signal. A previous method I used was to connect a neon transformer (120vac input, approx 5,000 vac output) to a spark plug with spark plug wire, and wrap the TT signal wire around the spark plug wire. This worked great, but I did not like running the sparking plug unattended for a dozen hours, and it was somewhat cumbersome. The newer TTs, even with the wire run away from the mag wiring, did not operate as smoothly as the TTO. I still think that the newer TTs can work well in some applications, but may be more sensitive to extraneous electrical noise, causing the display to constantly fluctuate. Maybe the added outer coax would work. But, I probably won't be messing any more with them soon. Gonna try to do some flying. Update, August 2020: Not mentioned in the above accounts are my attempts to get TinyTachs working well. I tried replacing the single sense wire with a coax cable, grounding the shield at one end. I tried putting the TT in a metal enclosure, using the coax, to help shield it from electrical noise. I tried various resistors and capacitors in the sense wire to modify the signal that was being sent into the TinyTach. Nothing I tried worked well. On the DE, we use a TTO tach on one ignition, and the TinyTach on the other. The TinyTach occasionally goes berserk, but the TTO works well. When we put the Verner 3VW on the LEU, we tried a TinyTach, but it was erratic. We finally ended up with an imported tach, same concept as the TinyTach, but it works well. I don't know exactly which one it is - one of the guys purchased it. But, as Dan suggests in a previous note, look around in Amazon (or Ebay) for something similar to tinytach. I know TinyTachs work well in some situations, but I have seen plenty of folks struggle with them. Unfortunate, because they are made in the USA, as far as I know. Seems all the alternatives that I tried are imported. But, we had to go with what works. Hope all this helps. |
Using a Morse Fairbanks magneto, doesn’t have shielded plug wires.I have tried different places on the wire and different amounts of wraps. Always the same thing, good to about 1800 or so, above that it goes nuts. Maybe I should try the other wire? The engine also is breaking up at wot, still gotta figure that out.