Douglas Bohnert Posted June 10, 2012 Report Share Posted June 10, 2012 Hey All!!! Just thought I would share some recent experiences with the CT gurues... Anyway, the Flight School where I Part time teach and do MX has had a problem with one of the CT's (A CTSW) where the volage sometimes drops below 12 volts -A topic for another day. And we have installed in our CT's the external standard Hobbs because the internal Dynon Hobbs can be tampered with and these acft are rented out regularly. But what I just learned is these external Hobbs were 12-60V and if the Voltage dropped below 12 Volts the Hobbs would quit recording the time! So the easy fix was to install the 6.5 Volt to 16 Volt Hobbs in its place. Comments are always welcome! Link to comment Share on other sites More sharing options...
Roger Lee Posted June 10, 2012 Report Share Posted June 10, 2012 Hi Doug, Is it actually a Hobbs meter or count tach time? If it is a Hobbs time then every time the oil is at 15 psi or more it records and if it is a tach time then any time the master switch or avionics is on it records even if you are sitting on the ground just learning the instruments with the power on. The tach time also records at different rates. The slower the engine rpm, like at idle, the slower the time recorded and at cruise rpm then it records faster than real time. The tachs are usually off 15-20%. The Hobbs should be accurate because it records the same rate regardless of engine rpm. The 6-16V shouldn't be an issue. I understand your particular concerns for the flight school and rentals, but I hope all personal use Dynon users are setup to use Hobbs time. Link to comment Share on other sites More sharing options...
BMcCand - N248CT Posted June 11, 2012 Report Share Posted June 11, 2012 The hobbs wiring in my CTSW is clever. It uses the ALT light and regulator to enable the hobbs only when theengine is rotating. it does count on the light bulb working... so as preflight make sure it lights up with bothbreakers in prior to start. Originally I thought it was recording battery master breaker on but it reallydoes run only when charging, with the light out. Someone got in trouble adding an oil pressure sensor for hobbs up near the normal oil pressuresensor ; excessive vibration broke a tee fitting and didn;t have a capillary tube. Dumpedengine oil. I think I heard that in one of the Rotax courses. I think an LOA might be gottento put a pressure switch back on the firewall, but behind the narrow tubing as isrequiiredfor the remote pressure gauge anyway. Link to comment Share on other sites More sharing options...
Roger Lee Posted June 11, 2012 Report Share Posted June 11, 2012 The CTSW with a Dynon is already set up for the Hobbs with oil pressure over 15 psi. You don't need to add or do any thing. It is automatic. If you use a straight tach reading then your meter will show 15-20% higher engine times since you spend more time at cruise rpms over all others. Link to comment Share on other sites More sharing options...
Douglas Bohnert Posted June 15, 2012 Author Report Share Posted June 15, 2012 The hobbs wiring in my CTSW is clever. It uses the ALT light and regulator to enable the hobbs only when theengine is rotating. it does count on the light bulb working... so as preflight make sure it lights up with bothbreakers in prior to start. Originally I thought it was recording battery master breaker on but it reallydoes run only when charging, with the light out. Someone got in trouble adding an oil pressure sensor for hobbs up near the normal oil pressuresensor ; excessive vibration broke a tee fitting and didn;t have a capillary tube. Dumpedengine oil. I think I heard that in one of the Rotax courses. I think an LOA might be gottento put a pressure switch back on the firewall, but behind the narrow tubing as isrequiiredfor the remote pressure gauge anyway. CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2!!! This is the way ours are setup too. I thought they were not working correctly because of the Voltage sometimes dropping below 12 volts. But this is not true. If the Alternator Light is on, the Hobbs (External) is NOT recording time. Anyway, time to order a new regulator/rectifier because all my attempts at stopping the "Alternator" Light from coming on at idle engine speed have failed. So just to be clear: Flight Design wires the external hobbs to the outlet side of the regulator/rectifier. So if anyone using external hobbs to record time experience the "Alternator" light on anytime while the engine is running, the external hobbs does notrecord time. Personally, I like the internal Dynon Hobbs better. Link to comment Share on other sites More sharing options...
Roger Lee Posted June 15, 2012 Report Share Posted June 15, 2012 Leave the Dynon Hobbs turned off in the background and the people that use the plane may not even know it's there or how to access it. Or just record the Hobbs time on paper and compare when it comes back. The voltage can drop below 12V if you have the idle set low and or you're running the lights, especially the landing light. I usually never set and idle below 2000 even though I could pull it back to 1720. Link to comment Share on other sites More sharing options...
tennesseect Posted January 22, 2014 Report Share Posted January 22, 2014 My CTsw Hobbs meter (not in the Dynon) just quit working with about 700 hours on it. Is there something I should check before replacing the meter? Link to comment Share on other sites More sharing options...
Roger Lee Posted January 22, 2014 Report Share Posted January 22, 2014 Check the wiring and use a voltmeter on the back and see if you have a connection. Link to comment Share on other sites More sharing options...
cdarza Posted January 23, 2014 Report Share Posted January 23, 2014 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2 CHANGE 2!!! This is the way ours are setup too. I thought they were not working correctly because of the Voltage sometimes dropping below 12 volts. But this is not true. If the Alternator Light is on, the Hobbs (External) is NOT recording time. Anyway, time to order a new regulator/rectifier because all my attempts at stopping the "Alternator" Light from coming on at idle engine speed have failed. So just to be clear: Flight Design wires the external hobbs to the outlet side of the regulator/rectifier. So if anyone using external hobbs to record time experience the "Alternator" light on anytime while the engine is running, the external hobbs does notrecord time. Personally, I like the internal Dynon Hobbs better. Correct! Had experience with same issue. I was having Alt Light coming on and off at different times. (Usually at slightly lower RPM of even 2000 but would turn OFF at higher Rpms) After many hours of flying, the ALT light would stay ON at any RPM - aside from no charging i also noticed an estimated loss of over an hours flight on the Hobbs. Regulator/Rectifier was the problem in my case. Link to comment Share on other sites More sharing options...
tennesseect Posted February 3, 2014 Report Share Posted February 3, 2014 Well today I did some checking on why my Hobbs isn't working. When I jumpered 12V from the battery directly to the terminals on the back of the Hobbs it starting clicking off time - so the meter itself works fine. Then I looked at the pressure switch down near the oil pump. I saw that it only has one wire lead. Since it is a normally-open switch I assume that wire would have to provide the ground that makes the Hobbs turn. So I disconnected the wire connector from the switch and jumpered it to the engine case. I turned on the battery master switch expecting the Hobbs to start turning. It did not! I deduced that the switch isn't the problem either. So... I conclude there either is another switch (perhaps in the 12V supply?) that isn't closing or a wire is broken. I neglected to verify that 12V is getting to the Hobbs when the BATT master switch is on. That's my next troubleshooting step. If I find no 12V at the Hobbs is that because there shouldn't be until the engine starts or should I suspect my Regulator/Rectifier - as discussed above? I'm afraid to open up the panel to check connections while the engine's running. Is that necessary? Link to comment Share on other sites More sharing options...
Anticept Posted February 4, 2014 Report Share Posted February 4, 2014 You just need battery voltage. There is no need to have an engine turning to drive a hobbs, it just needs electricity. Check continuity in the wiring to the hobbs, and make sure you didn't reverse the polarity (may or may not matter). Link to comment Share on other sites More sharing options...
Tom Baker Posted February 4, 2014 Report Share Posted February 4, 2014 I'll have to try and get my wiring diagram out and see. While it is true that the Hobbs only needs battery power it is not wired to the master switch. The Hobbs is tied to the generator system some where. I have had times when I forgot the generator switch and the hobbs didn't run. There might also be a fuse in the line some where. Link to comment Share on other sites More sharing options...
Tom Baker Posted February 5, 2014 Report Share Posted February 5, 2014 Just looked at the wiring diagram and pins 5 and 6 coming off the plug at the rectifier go to ALT/GEN light. The pin 5 wire goes splices off from the light and goes to the Hobbs meter, and the other side of the Hobbs goes to ground. Link to comment Share on other sites More sharing options...
Anticept Posted February 5, 2014 Report Share Posted February 5, 2014 That doesn't make sense. Are you referring to the ALT/GEN warning light? If so, the only time the hobbs would run is if the light was ON, aka when the generator is off! On the other hand, now that I think about it, why would they use both pin 5 and pin 6? Perhaps pin 5 is an excitation connection, and pin 6 is a switched ground that the light's ground wires to... That would make a lot more sense, although still highly goofy. EDIT: I can't find the wiring diagram that you are referring to Tom. Is it a CTLS diagram, or a Rotax diagram? Link to comment Share on other sites More sharing options...
tennesseect Posted February 6, 2014 Report Share Posted February 6, 2014 Tom, you're saying that the 12V supply for the Hobbs comes from pin 5 of the rectifier and is in parallel with the ALT/GEN light - right? Therefore the Hobbs should run whenever the rectifier is putting out sufficient charging voltage AND the oil pressure switch closes and provides the ground - right? Link to comment Share on other sites More sharing options...
Jacques Posted February 6, 2014 Report Share Posted February 6, 2014 ..although my Hobbs is connected as Tom described it, I don't find it in the diagram that came with the planeand...there is NO oïl pressure switch 'usually' on the CTSW Link to comment Share on other sites More sharing options...
Tom Baker Posted February 6, 2014 Report Share Posted February 6, 2014 Tom, you're saying that the 12V supply for the Hobbs comes from pin 5 of the rectifier and is in parallel with the ALT/GEN light - right? Therefore the Hobbs should run whenever the rectifier is putting out sufficient charging voltage AND the oil pressure switch closes and provides the ground - right? The diagram shows it connecting to the pin 5 side of the light, and yes it would be in parallel. Link to comment Share on other sites More sharing options...
Tom Baker Posted February 6, 2014 Report Share Posted February 6, 2014 That doesn't make sense. Are you referring to the ALT/GEN warning light? If so, the only time the hobbs would run is if the light was ON, aka when the generator is off! On the other hand, now that I think about it, why would they use both pin 5 and pin 6? Perhaps pin 5 is an excitation connection, and pin 6 is a switched ground that the light's ground wires to... That would make a lot more sense, although still highly goofy. EDIT: I can't find the wiring diagram that you are referring to Tom. Is it a CTLS diagram, or a Rotax diagram? I got the diagram when I went to factory training on the CT. Yes it shows connection from the pin 5 side of the light, and then to ground. It would make sence, because it only runs when the ALT switch is turned on. Link to comment Share on other sites More sharing options...
Anticept Posted February 6, 2014 Report Share Posted February 6, 2014 I got the diagram when I went to factory training on the CT. Yes it shows connection from the pin 5 side of the light, and then to ground. It would make sence, because it only runs when the ALT switch is turned on.That depends on what pin 5 is. In my CT, the alternator light is a warning light. I assume this is the light you are referring to. That would mean the hobbs would only run while there is a generator malfunction if this is the pin that triggers the warning light. However, if pin 5 is an excitation pin, then it all makes sense The wiring diagram above doesn't give me enough information (i need to see more of the diagram). I will pop open the rotax manual to see what the pins do. Link to comment Share on other sites More sharing options...
Tom Baker Posted February 6, 2014 Report Share Posted February 6, 2014 Here is the part of the diagram that has the Hobbs meter. diagram.pdf Link to comment Share on other sites More sharing options...
BMcCand - N248CT Posted February 8, 2014 Report Share Posted February 8, 2014 A little more - I said it was a clever design. When the power is off, pin 5 is low, so no hobbs motion. When power is on, but not charging, pin 5 is low, and the ALT light is on. When power is on, and charging, the ALT light is off. However, the power to the hobbs, which is very little, is now flowing though the light bulb, and the hobbs turns. So, if your light is burned out (or is illumnated due to not charging) the hobbs doesn't run. Bill Link to comment Share on other sites More sharing options...
Anticept Posted February 9, 2014 Report Share Posted February 9, 2014 Hi Bill! There's a couple different ways that could work, and I was suspecting what you said is the design. I'm still looking for the pin functions, because I'm curious why they have so many. As I understand it, pin 4 and 6 must be in a closed loop, or the charging coils will not function. This page has a nice reverse engineering diagram of the ducati regulator, and I am going to sit down sometime to study it. http://contrails.free.fr/elec_ducati_en.php Link to comment Share on other sites More sharing options...
tennesseect Posted February 9, 2014 Report Share Posted February 9, 2014 Today I noticed that in addition to my Hobbs, my ALTERNATOR warning light doesn't illuminate when you switch on the master switches. Funny how I never noticed that before - I'd better add it to my start-up checklist. The bulb checked open with an ohmmeter. So I have a feeling when I replace the bulb the Hobbs will start working too! Thanks Tom Baker - for helping me determine the type. It's apparently not too common - a 12V, 0.1 amp with an E-10 screw-in base. I couldn't find one locally today. The Flight Design part # is C9997168. Link to comment Share on other sites More sharing options...
tennesseect Posted February 10, 2014 Report Share Posted February 10, 2014 OK, after talking with Aaron at Lockwood I finally have a good description of how the ALT / Hobbs circuit works on my 2007 CTsw. Here it is in case anyone else is wondering: Rectifier pin 6 supplies 12v to the ALT bulb whenever the master switch is on. Pin 5 provides a ground for the bulb, BUT ONLY WHEN THE RECTIFIER IS NOT CHARGING. And a wire is bridged onto the pin 5 side of the bulb to supply power to the Hobbs. With the master ON, but with the engine not running, current flows from pin 6 to pin 5 of the rectifier through the bulb. This low resistance path effectively shunts most of the current away from the Hobbs so it won't run. But when the engine starts and the rectifier starts charging, the ground at pin 5 goes away and the only path for current is through the bulb and the Hobbs back to ground - so the Hobbs starts running. And that is why the Hobbs won't run if the ALT bulb blows. Thankfully I have the EMS ammeter as a backup but I intend to begin verifying the ALT lamp works as part of my startup checklist. Link to comment Share on other sites More sharing options...
Tom Baker Posted February 10, 2014 Report Share Posted February 10, 2014 I understand the diagram and the explamation, except why doesn't the light glow when the ground goes through the Hobbs meter? Link to comment Share on other sites More sharing options...
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