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Old 08-14-2019, 12:25 PM
Draker's Avatar
Draker Draker is offline
 
Join Date: Jun 2016
Location: Livermore, CA
Posts: 278
Default Tip: Dual-circuit pressure switch for Hobbs

Hopefully this helps someone avoid buying the wrong part:

I'm planning on installing a Hobbs meter. The standard way to activate the Hobbs appears to be with an oil pressure-based switch. When oil pressure is present, the switch closes, and the Hobbs meter runs. I'm also planning on running a panel light that is on when the switch is open, indicating low/no oil pressure. For this application, you need a 2 circuit oil pressure switch.

The switch sold by Spruce is Honeywell part number 76575, which is only a single circuit (normally open, suitable for activating the Hobbs meter). The one you'd need to also support a panel light is Honeywell part number 76579, which has dual circuitry: both NO and NC terminals.

Information about these pressure switches can be found in their datasheet: https://sensing.honeywell.com/honeyw...oductsheet.pdf

I obtained mine from eBay, but there are a number of online vendors that sell this part.

Now I've got an extra brand new single-circuit oil pressure switch that I'll either return to Spruce or sell over in the VAF classifieds.
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Ryan Drake
Livermore, CA
https://stiletto.smugmug.com/RV7
Donated 1/2/2019
RV-7A: Empennage and wing kits complete minus fiberglass, fuselage in progress!
N12VD reserved!

Last edited by Draker : 08-14-2019 at 12:27 PM.
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Old 08-14-2019, 01:09 PM
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fl-mike fl-mike is offline
 
Join Date: Jul 2005
Posts: 1,131
Default

The one Van's sells does just what you say.
Oil pressure switch for activating Hour Meter and light IE SPDT PRES-15 SW $35.00
Pressure good = one terminal goes to ground (switch body)
Pressure bad/low = other terminal goes to ground

as long as you use low-side switching, it works.
i.e. +12V ---hobbs---switch---ground
+12V---warning light ---- switch---ground

The Vans part includes a sheet showing how to hook it up.
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Mike W
Venice, FL
RV-6A. Mattituck TMX O-360, FP, GRT Sport EFIS
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N184WM reserved (RV-8)....tail kit done, slow-build wing done, slow-build fuselage in progress.

Last edited by fl-mike : 08-14-2019 at 01:11 PM.
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