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On only after engine has started

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Member - Posts: 1
Member spacespace
Joined: April 18, 2015
Posted: April 18, 2015 at 5:03 AM / IP Logged Link to Post Post Reply Quote elmwood1
I am needing a little help with this problem. This is for use in a boat. I am adding a windlass to my boat but I want to be able to use it only after the engine is running. The reason for this is I don't have a generator and the windlass does draw a fair amount of power. Where would be a good source to get the power from? This is just a security measure so nobody can use it by forgetting to start the engine first.
Thank you for any and all help
howie ll 
Pot Metal - Posts: 16,466
Pot Metal spacespace
Joined: January 09, 2007
Location: United Kingdom
Posted: April 18, 2015 at 5:21 AM / IP Logged Link to Post Post Reply Quote howie ll
Latching relay from Omron etc. Fed from the starter wire.
Or see latching relay, Relays section here.
Gold - Posts: 630
Gold spacespace
Joined: May 27, 2011
Location: California, United States
Posted: April 19, 2015 at 4:08 PM / IP Logged Link to Post Post Reply Quote davep.
You didn't specify how big your boat is, and thus I can't guess to how big the windlass is, but I'm assuming your winch (like most) has a separate solenoid pack that switches the heavy current to the motor. If it is a reversing windlass, it absolutely has a divorced solenoid pack. This method will work:
Install a Normally Open, 2 terminal, 2-4psi oil pressure switch on the engine. (0psi= switch open, >2-4psi = switch is closed)
Wire the switch in series with the control circuitry from the foot-switch or handheld controller so that the winch can not be commanded to run unless the switch is closed, which requires the engine to be running.
Because the switch is in the control circuitry, the wiring can be 14ga, as the current is very low. This would be a sure-fire, simple, and reliable way to do what you wish.
Howie's idea has a mode where it can be by-passed, which my method does not. It is possible to operate the winch without the engine running, by blipping the starter, but don't let the engine start. The relay will latch on and the winch will operate until the key is again shut off.
If your winch is fairly small, the battery cable is probably interrupted directly by the foot switch (ie, the entire motor current is carried through the foot switch). You will have to add a solenoid to switch the motor current, and use the foot switch to trigger the solenoid. You can insert the oil press switch, or Howie's latch in the "control" circuitry.
Suggestion: I've been captaining and maintaining boats and yachts for 4 decades. The #1 rule of designing and installing systems for marine use is "keep it simple". In your case, my recommendation is just start the engine first. If you're weighing anchor, you're going to power away when the anchor comes up, so it needs to be running prior to windlass operation. IMO, you don't need a failsafe device like you propose. The engine is going to be running when the windlass is in use anyway.
Silver - Posts: 1,350
Silver spacespace
Joined: December 11, 2003
Location: California, United States
Posted: April 28, 2015 at 8:40 PM / IP Logged Link to Post Post Reply Quote hotwaterwizard
We do this on Hot water Pressure Washers all the time so the burner does not come on unless the engine is running. On only after engine has started - Last Post -- posted image.
John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

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