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Oil Pressure Switch for engine hourmeter

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Troy Maynor

Joined: 10 Jan 2006
Posts: 162

Posted: Sun Jan 17, 2010 10:31 am Post subject: Oil Pressure Switch for engine hourmeter

Roland, 

 I know it's not in the UK but here is the switch I  used on mine and it works well. Oil pressure idiot light that also says "Hey  dummy you forgot to turn off your master switch", and runs the Hobbs meter when  the engine starts. 

  

 http://www.bandc.biz/pressureswitchspdt.aspx

  

  

   [quote][b]

rparigoris

Joined: 24 Nov 2009
Posts: 797

Posted: Sun Jan 17, 2010 11:42 am Post subject: Oil Pressure Switch for engine hourmeter

May be worth investigating a power genie??http://www.aircraftspruce.com/catalog/elpages/powergenie.php On my 914  am using an oil pressure sender, remote mounted with an extra set of contacts (on and off). I think the switch is reversed so will use a relay to run hobbs.Ron Parigoris   [quote][b]

frans(at)paardnatuurlijk.
Guest

Posted: Mon Jan 18, 2010 8:23 am Post subject: Oil Pressure Switch for engine hourmeter

Maybe I'm stating the obvious, but you can of course also use the

alternator warning light for registering engine hours.

True, if the alternator fails the hobbs will stop, but without

alternator it won't take long before the hobbs stops anyway.  Also,

the same logic could be applied to using the oil pressure as source for

the hobbs.



Using an oil pressure switch is just introducing another part with the

potential of leaking, getting loose, etc. And it also comes with a

weight penalty. And costs some money.



The alternator warning light is free, without risk or weight penalty. I

can't really see the benfit of an oil pressure switch for a

non-mission-critical part like a hobbs...



And no, you don't need a relay for it to hook up the hobbs to the

alternator warning light. Just put the hobbs in series with the bulb,

and connect the alternator warning output to the joint between bulb and

hobbs. The other end of the hobbs should go to the opposite part of the

power supply (that is, if the bulb is connected to ground, the hobbs

should go to the 12V, if the bulb is connected to 12V, hobbs to ground.

Yep, I don't remember whether the warning light is switched to 12V or

ground, am too lazy to look it up.  ).



The bottom line is that the bulb is used to complete the circuit of the

hobbs. As the hobbs uses far less power than the bulb, the bulb won't

lit, and the hobbs will see the full voltage. When the alternator light

comes on, the hobbs will now not get any voltage difference accross its

terminals, and thus stops counting.



I certainly would have done it this way, but I already have an engine

hour hobbs in the Smart prop controller.



Frans

Rowland_Carson

Joined: 04 Jul 2008
Posts: 155
Location: Cheltenham, England

Posted: Mon Jan 18, 2010 12:27 pm Post subject: Oil Pressure Switch for engine hourmeter

At 2010-01-17 13:25 -0500 Troy Maynor wrote:



 	  Quote: 	
		  here is the switch I used on mine and it works well. Oil pressure 

idiot light that also says "Hey dummy you forgot to turn off your 

master switch", and runs the Hobbs meter when the engine starts


	


Troy - thanks for the link. I could probably get that from Airworld 

as he does other B&C stuff. However, it's 1/8" NPT so I'd have to 

come up with an adaptor for the M10 fine thread on the oil pump. I'm 

leaning towards the vacuum switch suggested by Ivor as it needs no 

further firewall penetration, and plumbing it in near the hourmeter 

should be easy.



regards



Rowland

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Rowland_Carson

Joined: 04 Jul 2008
Posts: 155
Location: Cheltenham, England

Posted: Mon Jan 18, 2010 12:27 pm Post subject: Oil Pressure Switch for engine hourmeter

At 2010-01-18 17:16 +0100 Frans Veldman wrote:



 	  Quote: 	
		  you can of course also use the

alternator warning light for registering engine hours


	


Frans - thanks for yet another way to skin a cat! I had been looking 

at the wiring diagram and wondering why the wires to the alternator 

warning light were not protected by a fuse, but the penny didn't drop 

that they could be put to other uses.



 	  Quote: 	
		  I don't remember whether the warning light is switched to 12V or

ground, am too lazy to look it up


	


One end of the warning lamp is connected to the C terminal of the 

regulator (also commoned with R & +B) so that better be at 12V when 

the donkey is running. The other side of the lamp goes to the L 

terminal which presumably is normally floating, open circuit (or even 

+12V?) but drops to 0V when things go pear-shaped.



The diagram calls out a 30A slo-blo fuse to protect the 12AWG wire 

leaving the C, R, +B terminals. However, there is NO protection for 

the 20AWG wire leaving the same spot and going through the firewall 

to the alternator warning lamp. I presume the wire itself is intended 

to provide the smoke if it gets chafed to ground at the firewall! I 

think I will be fitting a fuse.



regards



Rowland

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frans(at)privatepilots.nl
Guest

Posted: Mon Jan 18, 2010 6:07 pm Post subject: Oil Pressure Switch for engine hourmeter

On 01/18/2010 09:25 PM, Rowland Carson wrote:



 	  Quote: 	
		   One end of the warning lamp is connected to the C terminal of the

 regulator (also commoned with R & +B) so that better be at 12V when the

 donkey is running. The other side of the lamp goes to the L terminal

 which presumably is normally floating, open circuit (or even +12V?) but

 drops to 0V when things go pear-shaped.


	


Well, you don't have to connect the lamp to the C terminal, any 12V

connection would be fine. I have mine connected behind the master

switch, and behind the panel fuse. The only wire going to the alternator

controller is the L wire, which doesn't need a fuse at all.



About the hobbs: Connect the + of the hobbs to the L wire (either end

would be fine, but the end near the bulb would be practical). Connect

the - of the hobbs to ground.

This will cause the hobbs to run as soon as the master switch is on,

unless the bulb lights up. So, it will effectively count the engine hours.



That's really all there is to it. No need for oil pressure switches or

other gadgets.



 	  Quote: 	
		   The diagram calls out a 30A slo-blo fuse to protect the 12AWG wire

 leaving the C, R, +B terminals. However, there is NO protection for the

 20AWG wire leaving the same spot and going through the firewall to the

 alternator warning lamp.


	


No, because you are supposed to connect it behind the fuse. The 12AWG

wire is connected to the C terminal, so instead of connecting the lamp

to the C terminal directly, you could as well use the other end of the

12AWG wire. 12 Volts is 12 Volts after all.  In fact, any 12 V line

would serve the same purpose.

You should indeed not connect any unfused wire to the C,R or B terminals!



Hope this is clear now.



Frans

raimo.toivio(at)rwm.fi
Guest

Posted: Tue Jan 19, 2010 11:32 am Post subject: Oil Pressure Switch for engine hourmeter

How about connecting it to the radio power line? 



So that is then a radio hobbs in fact.

We normally always start the engine first and then a while after switch radios on.

Radios off and then engine quit vice versa.

That is a rule for radio safe.

During engine tests and trial runs we do not wanna maybe count engine hours at all.

When there is an intention to fly, radios are always on I assume.

Bad side: during radio tests only you count also engine hours.

But, how often you do make radio tests only (w/o engine running)?



In my case in the hobbsmeter there are 202,9 hours logged and in the logbook there are 154,1 pure flight hrs. 

The difference between those numbers are mostly because taxiing and those exciting early taxi tests (and radio on!).



Other possibilities: hobbs is on when gyros and/or FMS are on.



If I had liked to count only pure flight hours I would have connected it to the main gear´s retracted position micro switch. In the other hand; at least GPS and autopilot (Trio) are logging pure flight hours so that was not an option for me.



That is real flying when the gear(s) is(are) up, is not it? Unfortunately only possible for monos...



To service my engine I use flight hours (with high revs) - not engine hours. That is a fair play!



Raimo from Finland 



OH-XRT grounded for an annual service and some extra which will make it even heavier again.



---

frans(at)paardnatuurlijk.
Guest

Posted: Tue Jan 19, 2010 11:49 am Post subject: Oil Pressure Switch for engine hourmeter

On 01/19/2010 08:31 PM, Raimo Toivio wrote:



 	  Quote: 	
		   If I had liked to count only pure flight hours I would have connected

 it to the main gear´s retracted position micro switch. In the other

 hand; at least GPS and autopilot (Trio) are logging pure flight hours

 so that was not an option for me.


	


I have my "flight-hobbs" connected to a pressure switch, hooked up to

the secondary pitot tube (which also feeds the SmartASS talking airspeed

indicator). The pressure switch is set in such a way that it closes a

switch when the speed reaches 42 knots.

I guess this is close enough to really register flight hours (with in

mind the option to use the Europa as a motor-glider, so flight hours

might differ substantially from engine hours).



 	  Quote: 	
		   To service my engine I use flight hours (with high revs) - not engine

 hours. That is a fair play!


	


For the mandatory registration, you are allowed to use flight hours. For

all engine run-ups in your backyard, you don't need to register

anything. Although I unofficially keep an eye on the actal engine hours,

and just perform some maintenance accordingly, earlier than officially

required with regard to the flight hours.



Frans

Rowland_Carson

Joined: 04 Jul 2008
Posts: 155
Location: Cheltenham, England

Posted: Wed Jan 20, 2010 2:25 am Post subject: Oil Pressure Switch for engine hourmeter

At 2010-01-19 03:03 +0100 Frans Veldman wrote:

  	  Quote: 	
		  On 01/18/2010 09:25 PM, Rowland Carson wrote:

 > The diagram calls out a 30A slo-blo fuse to protect the 12AWG wire

 > leaving the C, R, +B terminals. However, there is NO protection for the

 > 20AWG wire leaving the same spot and going through the firewall to the

 > alternator warning lamp.

 No, because you are supposed to connect it behind the fuse. The 12AWG

 wire is connected to the C terminal, so instead of connecting the lamp

 to the C terminal directly, you could as well use the other end of the

 12AWG wire. 12 Volts is 12 Volts after all.  In fact, any 12 V line

 would serve the same purpose.

 You should indeed not connect any unfused wire to the C,R or B terminals 	

 Frans - I agree with your last sentence completely, but here is what the diagram I've got shows:

 [img]cid:a06240800c77c835dfb6f(at)[10.0.1.2].1.0[/img]

 I don't usually paste graphics into my e-mails so am not sure if this will get through to the list unmangled.

 If the graphic is not visible in this e-mail, you can see a copy of it at:

 http://home.clara.net/rowil/grafix/alt_warn.gif

 You can see that the wire to the starter warning light does have a fuse, so why not the wire to the alterntor warning light?

 I think Mike Gregory was involved in the last modification of the diagram in the manual. Mike, if you're listening, have you any comments?

 I postulated 2 scenarios for what happens at the L terminal of the regulator when all is well (open-circuit or +12V) and am still not sure which is correct. Either will of course serve to supply the engine timer through the warning light, but if L is held at +12V, I feel the lead from it should also be fused.

 Maybe someone who's taken apart one these regulators might know what potentials should appear at the L terminal.

 regards

 Rowland

  	  Quote: 	
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jan_de_jong(at)casema.nl
Guest

Posted: Wed Jan 20, 2010 6:29 am Post subject: Oil Pressure Switch for engine hourmeter

Hi Rowland,

In 2008 I found a German language forum discussion concerning the Ducati 

regulator. Writer "Arrow" seemed to know what he was talking about.

I reported - 

http://www.sarangan.org/www/mhonarc/mharc/html//europa-list/2008-08/msg00133.html.

The 2008 entries have been removed (Rotax did not like them probably) 

but I saved the page from cache where you can still find it too probably:

google using "piloten arrow ducati regler".

If not I will attach (34 files, 425 kb).

In any case there is a circuit diagram and it shows L as shorted to 

ground via FET when C gets above some voltage, otherwise floating.

Jan de Jong

Rowland_Carson

Joined: 04 Jul 2008
Posts: 155
Location: Cheltenham, England

Posted: Wed Jan 20, 2010 10:32 am Post subject: Oil Pressure Switch for engine hourmeter

At 2010-01-20 15:14 +0100 Jan de Jong wrote:



 	  Quote: 	
		  there is a circuit diagram and it shows L as shorted to ground via 

FET when C gets above some voltage, otherwise floating


	


Jan - thanks for that, very useful. It's what I would have expected, 

but sometimes these things are done in a different way to my 

imaginings!



regards



Rowland

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jan_de_jong(at)casema.nl
Guest

Posted: Wed Jan 20, 2010 1:00 pm Post subject: Oil Pressure Switch for engine hourmeter

Rowland Carson wrote:

 	  Quote: 	

 At 2010-01-20 15:14 +0100 Jan de Jong wrote:

> there is a circuit diagram and it shows L as shorted to ground via 

> FET when C gets above some voltage, otherwise floating

 Jan - thanks for that, very useful. It's what I would have expected, 

 but sometimes these things are done in a different way to my imaginings!

 regards

 Rowland

I should have said, actually: when average input voltage (G's) gets 

above some level, which requires C powered (which by itself only 

provides a bias current).

Jan

raimo.toivio(at)rwm.fi
Guest

Posted: Thu Jan 21, 2010 9:00 am Post subject: Oil Pressure Switch for engine hourmeter

The pressure switch is set in such a way that it closes a

switch when the speed reaches 42 knots.

I guess this is close enough to really register flight hours (with in

mind the option to use the Europa as a motor-glider, so flight hours

might differ substantially from engine hours).



Frans



Oh yes you are more or less flying than taxiing when your speed is above 42 knots.

I assume Garmin & Trio think "hey we are flying" when the speed is above 20 knots or so.

So, their flight hour register ís not so exact than your method.

Counting flight hours only when the gear is upp means you loose let is say one or two minutes flight hour every leg...so what!



Raimo OH-XRT

Clive J

Joined: 03 Nov 2007
Posts: 340
Location: UK

Posted: Fri Jan 22, 2010 7:01 am Post subject: Oil Pressure Switch for engine hourmeter

I have an air pressure switch fitted to both my aircraft. Idea that came from the old Gliding spares company who I can't remember their name Maybe RD?

Measures Pitot/static pressure and is set to 40 knots. It switches a miniature Farnell hour meter (RS in the old Jab but I couldn't find one 3 years back). About £50 all in. 

Radio Spares part number 317-443 Calibrated by gently sucking 40 knots on the static line reading on the ASI with a meter across the switch.

I find this is very accurate as it measures hours with the engine under 'load', the only thing I care about.

The difference in actual engine running hours and flying hours is about 12%, that is an average over 1100 hrs (last time I looked).

That is flying from my base where engine running apart from flying is purely to warm the engine up and less than 50% of the time back tracking (prevailing SW) a 500 metre runway..

I do of course 'get about' and at some places taxiing can be a long time but maybe good average to use..



Oil pressure switches or anything else are just a compromise for engine load hours but the good thing is they will usually make you over maintain. 

There are gadgets on the TV screen things that maybe can do this for you but I'm still steam driven as I built before the TV thingy's were reliable.



Just myho, Regards, Clive

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