Cruisers Forum
 

Go Back   Cruisers & Sailing Forums > Engineering & Systems > Electrical: Batteries, Generators & Solar
Cruiser Wiki

Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 27-09-2011, 05:45   #1
Registered User

Join Date: Apr 2010
Location: Newport News VA
Boat: Egg Harbor sedan cruiser 1970
Posts: 829
Three-Prong Oil Pressure Switch and Electric Fuel Pump - Is a Fuel Pump Relay Needed?

I am converting the boat to a holley red marine electric pump.

The safety switch I am going to use is a gm 3986857 3 prong oil pressure switch. Has a common, NO, NC prongs.

Can the electric pump use the switch without a relay OR is the electric load running threw the switch too much for it and it needs a relay?


The reason I ask is simply I want to replace the current low pressure idiot light switch with this 3 prong switch without a 'T' hookup.
the 3 prong switch will just be turning grounds on and off. I will put a relay running off the start wire to the starter and that relay will just ground the pump negative wire to make it run. If I do this, then all I need is the one pressure switch to run the idiot light and the pump. The relay will turn on and ground the negative pump wire when the starter is cranked.
When the oil pressure builds up, the safety switch will close and ground the negative on the pump and it will run.

If I dont do this, I will have to put in a T and have 2 pressure switches. I currently have an oil gauge pressure switch, so really then I would have to have 3 oil switches on the block. See what I mean?

Currently there are 2 oil pressure switches on the block. One for the idiot light-buzzer, the other for the pressure gauge. I dont want to loose the buzzer idiot light.
__________________

__________________
sdowney717 is offline   Reply With Quote
Old 28-09-2011, 17:28   #2
Registered User

Join Date: Sep 2007
Location: FL
Boat: Pacific Seacraft 31 - Cielo Azul
Posts: 351
Images: 3
Re: Three-Prong Oil Pressure Switch and Electric Fuel Pump - Is a Fuel Pump Relay Nee

Quote:
Originally Posted by sdowney717 View Post
I am converting the boat to a holley red marine electric pump.

The safety switch I am going to use is a gm 3986857 3 prong oil pressure switch. Has a common, NO, NC prongs.

Can the electric pump use the switch without a relay OR is the electric load running threw the switch too much for it and it needs a relay?


The reason I ask is simply I want to replace the current low pressure idiot light switch with this 3 prong switch without a 'T' hookup.
the 3 prong switch will just be turning grounds on and off. I will put a relay running off the start wire to the starter and that relay will just ground the pump negative wire to make it run. If I do this, then all I need is the one pressure switch to run the idiot light and the pump. The relay will turn on and ground the negative pump wire when the starter is cranked.
When the oil pressure builds up, the safety switch will close and ground the negative on the pump and it will run.

If I dont do this, I will have to put in a T and have 2 pressure switches. I currently have an oil gauge pressure switch, so really then I would have to have 3 oil switches on the block. See what I mean?

Currently there are 2 oil pressure switches on the block. One for the idiot light-buzzer, the other for the pressure gauge. I dont want to loose the buzzer idiot light.
What's the draw of the pump?
I had a 2A pump directly connected, but now have it drive a relay because the run to the engine panel was long and wires small. Also I can drive the electric pump to prime the lines after changing the fuel filter without needing to turn the engine over. The NC and NO are connected to the ignition switch 12v ACC/START lines.
Tom
__________________

__________________
teejayevans is offline   Reply With Quote
Old 29-09-2011, 06:54   #3
Registered User

Join Date: Apr 2010
Location: Newport News VA
Boat: Egg Harbor sedan cruiser 1970
Posts: 829
Re: Three-Prong Oil Pressure Switch and Electric Fuel Pump - Is a Fuel Pump Relay Nee

it draws 2 amps
I came up with 2 ways to do this, one switches positive side, the other switches negative ground side.
I am going with the positive switching.

positive switching with momentary prime switch and relay


negative switching allowed the use of only one sender but someone said it is bad if boat burns and pump ground energized pump will run.

__________________
sdowney717 is offline   Reply With Quote
Old 29-09-2011, 06:59   #4
Registered User

Join Date: Apr 2010
Location: Newport News VA
Boat: Egg Harbor sedan cruiser 1970
Posts: 829
Re: Three-Prong Oil Pressure Switch and Electric Fuel Pump - Is a Fuel Pump Relay Nee

I found even 18 gauge runs the pump fine with a distance of 12 feet.
I have 2 pumps, both marine, one is carter the other Holley red.
The wire is cable from a vacuum cleaner, has heavy fiber strands in the cord to resist breakage and is tough. One wire is 18 gauge, the other 17 gauge. I too wondered about the gauge but It pumps fine.

The flow is like this,
tank
anti siphon valve at tank fitting
separating filter
pump mounted behind engine on a wood support
regulator
carb

Putting filter before pump works. the filter top is at same height as tank top, the pump about 5 inches lower than filter top. The filter acts like a small tank right next to the pump so it flows. I do fill the filter housing with fuel first after a change but dont know if need to do that.

USCG has a rule that pump should be mounted within a foot of engine, mine is about a foot behind the engine. I have seen pumps on other boats mounted all over bulkheads even far from motor. So dont understand that rule except perhaps have it close to engine for monitoring function?
__________________
sdowney717 is offline   Reply With Quote
Old 29-09-2011, 07:06   #5
Moderator Emeritus
 
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 24,605
Images: 240
Re: Three-Prong Oil Pressure Switch and Electric Fuel Pump - Is a Fuel Pump Relay Nee

Quote:
Originally Posted by sdowney717 View Post
I found even 18 gauge runs the pump fine with a distance of 12 feet...
FWIW, ABYC specifies:
11.14.1.2 Conductors shall be at least 16 AWG.
And:
11.14.1.3 In engine spaces the conductor insulation shall be oil resistant and have a temperature rating of at least 167oF (75C) dry.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Reply

Tags
electric, electric pump, fuel, fuel pump

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Electric Fuel Pump for Generator Refill US1Fountain Electrical: Batteries, Generators & Solar 7 20-07-2011 12:32


Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

RV & Travel Trailer Communities

Our RV & Travel Trailer sites encompasses virtually all types of Recreational Vehicles, from brand-specific to general RV communities.

» More about our RV Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities


Copyright 2002-2012 Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 07:39.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2014, vBulletin Solutions, Inc.

Sailing News Delivered to your Email!

Stay up-to-date with the latest cruising news.

unsusbcribe at anytime with one click

Close [X]


ShowCase vBulletin Plugins by Drive Thru Online, Inc.