Hobbs Meter Question

Friendly

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I have a Hobbs 12 + hour-meter. I would like to hook it directly to the engine so it will record engine hours and not the time the switch is turned on.
Can I wire a diode between the AC wire on the Rotax engine and get the need 12+ volts or does a rectifier bridge have to be used. If a diode will do, does someone know what I need to ask for at Radio Shack?
Thanks for any help.
 
Hobbs Meter

Hobbs Meter

Hello Friendly

Here are links to two articles about adding Hobbs Meters Plus adding Strobe Lights for the rotax engine.

An alternative to the hobbs meter is the "Tiny-Tach" which is an internally powered tach and hour meter. It is a little more expensive than a hobbs meter and it only operates when the engine is running. It is marginal as an accurate tach in my opinion but the hour meter function is hard to beat. I also purchased a copy of the "TinyTach" a few months ago on eBay and it is called "SenDEC". The SenDEC functions are identical to the Tiny-Tach. I believe that I paid under $15.00. If you were to go with the Tiny-Tach / SenDEC route, you need to specify for 2 stroke because the pickup works off of the spark plug and they are made either for 2 or 4 stroke engines. I have 2 tiny tachs which I bought in 2001 originally for a powered parachute and they are still running fine.

This is probably old news to you about the tiny tach but it may be of use for someone just starting a build.


AND NOW, HOPEFULLY, THE ANSWER YOU WERE LOOKING FOR:

http://www.800-airwolf.com/pdffiles/ARTICLES/part33.pdf

Quotes from the above Airwolf PDF File:
"Hourmeters: To the best of my knowledge there is currently no hourmeter that will work off A/C voltage only. All hourmeters require from 4 to 40 volts
D/C to operate. It says so clearly on the hourmeter instructions. Yet the number of people that will hook them directly to the lighting coil staggers the
imagination! This indicates to me they simple do not understand what the engine's lighting coil is producing and hopefully we are taking care of this with
part #33. What you do have going for you is the fact that the voltage range that most units will work in is fairly large (4 to 40 volts). Using the #9251
regulator allows you to run an hourmeter with the only drawback being the possibility of not having enough voltage available at idle to get a reading.
Any RPM higher than idle and enough D/C voltage will be available. There is some discussion on where or not the 1 amp minimum load required by the
#9103 is satisfied by an hourmeter. My suggestion is to use a capacitor or charge a battery as outlined earlier of best results."

"Full Wave Bridge Rectifier: An interesting piece showed up in the February '92 issue of
Ultralight Flying! Magazine suggesting an inexpensive Hobbs connection with a full wave
bridge rectifier. Using a Radio Shack part #276-1171, costing around $2, A/C lighting coil
voltage is transformed into D/C. Figure #6 shows a simple schematic on this part. Being a
little skeptical, I contacted Westberg Mfg. for their comment on what looks like a great short
cut to an A/C driven hourmeter. They stated that this type of system would not work with
their hourmeters. This leads me to believe that Hobbs hourmeters and Westberg
hourmeters are configured differently and should be treated as such. Westberg tells me
that an A/C hourmeter is in the works and should be available sometime in the future."


http://www.800-airwolf.com/pdffiles/ARTICLES/Part 49 - 4 page.pdf Info about regulators you may be using.
And another alternative is the "Kuntzleman Hot Box". The auction has ended but you can read about it for your info.
http://cgi.ebay.com/ebaymotors/NEW-...003QQitemZ130138598154QQrdZ1QQsspagenameZWDVW Notice which regulator is attached to the Hot Box - DC power for hobbs meter.
P.S. the ebay link is not me, was just cruising eBay for anything aircraft several days ago.
Hope this helps
 

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Radio Shack part ?

Radio Shack part ?

Mac,
I tried Radio Shack for the part you listed above. They said they no longer carry it. Maybe some of the electronic experts can chime in. I have a SenDec tack on my retired Bensen and it was very accurate according to my watch. I do have the two articles you listed, but I thank you for a well informed post. It will help others who are wanting to learn more.
 
Hey Mark,
If you use just one diode. You would only get current every other cycle. You could try using 4 diodes. You would get current every cycle. It would not be a true dc like a true rectifier. If you have a old 12v power supply that plugs in the wall. It could be posable to connect to the output side of the transformer(not using the transformer) with your 12v ac to change it to 12v dc.
Just a thought.

Scott
 
I was hope Al Hammer or one of the electric experts would read this thread and respond.
Mac, Thanks for the links,
Tim, I want hour meter to operate only when the engine is running. not when the switch is on.
Scott , thanks email me with you new engine temps.
 
Mark,
Isn't the rectifier connected to the AC output leads of the Rotax engine? How would it be putting out voltage when the engine isn't running?
 
Hey Mark,
Tim's question made me think. You could use a relay that would pickup with the ac input and allow you to use the dc connection to your battery with the contacts. that should work. The relay would only work when the engine is running and you could use your battery for your dc input.

Scott
 
The DC side of the R is attached to positive side of Battery for charging. The Battery would power the hobbs meter all the time unless I am missing something. Which I may be.
 
Hey Mark,
That would work. They must be using a scr which would work like a relay. when control voltage is applied it will allow the dc current to flow. Good idea.

Scott
 
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Mark, My bad. I didn't know you were using a battery also. I thought you were just trying to power your hour meter and nothing else.
 
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