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Alternator shutoff switch?

Sep 11, 2019
121
Hunter 49 2 San Diego,Ca
Hey fellow sailors unfortunately after an awesome trip to Catalina my first time, motoring back towards San Diego my alternator took a shit and completely froze up disabling my engine anyway now I have to pull it out and replace it but I can’t figure out how to turn the power off going to the alternator, i’ve tried tracing the wires but I just thought I would ask to see if anyone could steer me in the right direction I could always take it apart with power going to it but I’d rather not and then I could always put a shutoff switch in in the future?
Scotty
 
Sep 11, 2019
121
Hunter 49 2 San Diego,Ca
Disconnect the battery
Gotcha I just did that but was hoping there would be a switch.
Or at least an inline fuse but I think it’s important not to have something between the alternator and the batteries in case it gets turned off and the alternator keeps putting out power
thanks
 
Jan 18, 2021
43
Hunter 40.5 Burnt Store Marina
Gotcha I just did that but was hoping there would be a switch.
Or at least an inline fuse but I think it’s important not to have something between the alternator and the batteries in case it gets turned off and the alternator keeps putting out power
thanks
Yup. You do not want anything between the alternator and blackhole to absorb the angry pixies.
 
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Sep 11, 2019
121
Hunter 49 2 San Diego,Ca
Disconnected positive wire from both house and start batteries still power at the alternator turned everything off, must just be some power in the system only after I turned off the parallel charge circuit did power go off at the alternator weird… LOL
 

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May 24, 2004
6,765
CC 30 South Florida
Turn the DC breaker to Off at the panel. The engine should not have been disabled as it does not need power to combust the fuel. If frozen remove the alternator belt
 
Sep 11, 2019
121
Hunter 49 2 San Diego,Ca
Turn the key switch to Off. The engine should not have been disabled as it does not need power to combust the fuel. If frozen remove the alternator belt
Thanks Benny much appreciated already did that on the way back from Catalina currently disassembling everything now…
Underway the problem was you can’t just take off the belt because then the water pump won’t turn so the engine won’t cool…
 
Sep 11, 2019
121
Hunter 49 2 San Diego,Ca
Basically after tracing all the wires there’s no shut off switch to the alternator.
Best thing as suggested was to disconnect the batteries.
 
Jun 1, 2009
1,337
Hunter 49 toronto
Don’t see why you wouldn’t just disconnect the field winding.,youd have no output current on the alternator, and there would be no current consumption to energize fuels.
Alternators don’t work if you don’t have a spinning electromagnet. (Rotor) inside a stator
By disconnecting field current, you have no magnetic coupling between rotor & stator
 
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Sep 11, 2019
121
Hunter 49 2 San Diego,Ca
Don’t see why you wouldn’t just disconnect the field winding.,youd have no output current on the alternator, and there would be no current consumption to energize fuels.
Alternators don’t work if you don’t have a spinning electromagnet. (Rotor) inside a stator
By disconnecting field current, you have no magnetic coupling between rotor & stator
Well I had power at the output lug and didn’t want to attach a wrench to it and accidentally ground it to the engine.
 
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Jun 15, 2012
617
Hunter 50 AC St. Petersburg
I have actually placed warnings in the engine compartment that the red 4 gauge lead to the alternator is always "hot". There is no switch from the factory to de energize this connection directly to the house battery bank. I have seen a good idea from Maine Sail where he installed an on/off battery switch in his engine compartment to be able to de energize this connection. When I upgraded my alternator I wanted to follow Maine Sail's idea, but the engine compartment on the Hunter 50 is so tight that I wasn't able.
 
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Oct 22, 2014
15,801
CAL 35 Cruiser moored EVERETT WA
power at the output lug and didn’t want to attach a wrench to it and accidentally ground it to the engine.
Smart man. You discover that using a DVM or use the old school screwdriver shock method.

Here is some good source info on the project you are starting.
Manufacturers generally have not installed a "safety cutoff" switch. Partially out of electrical ignorance, because of cost, due to how they wire their systems, and hope that owners will just disconnect the battery before doing any electrical work.

We boaters, wanting to get the most out of our charging systems learned that wiring the battery to the alternator means better charging current going to the battery. Risk is the Alternator is live. So you can install a simple cut off switch between the alternator and battery. Put it in the engine room near the alternator to remind you to turn it off if you are feeling lazy and do not want to disconnect the battery. Put up a sign or label warning future owners of your system.

A switch like this allows you to leave the connection always on with the key removed. But you can shut it down with the key.
1630338184091.png
 
Oct 29, 2016
1,765
Hunter 41 DS Port Huron
When wiring a switch into the alternator output line you need to wire your B+ terminal between the ignition and the alternator through the switch so power is also interrupted to the internal voltage regulator of the alternator when the switch is open.
 
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leo310

.
Dec 15, 2006
434
Catalina Catlina 310 Campbell River BC
Alternator are wired to the starter then to the starter battery ... so unless you disconnect the battery you will always have power to the alt. What I will be doing this fall is wiring the alt to a FET (victron) then the starting battery will only see the starter. The FET is an isolator so it will be connected to both house and starter battery and I will not have to worry about someone turning the power selector to off after starting the engine and blow the alt.
 
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Oct 29, 2016
1,765
Hunter 41 DS Port Huron
Alternator are wired to the starter then to the starter battery ... so unless you disconnect the battery you will always have power to the alt. What I will be doing this fall is wiring the alt to a FET (victron) then the starting battery will only see the starter. The FET is an isolator so it will be connected to both house and starter battery and I will not have to worry about someone turning the power selector to off after starting the engine and blow the alt.
You are correct that is the way they are wired from the manufacturer, but, a far better way is to run dedicated cables direct to the house bank. As for the FET I would suggest a Blue Seas ACR, from what I have read there is a sizable voltage drop through an isolator.
 
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leo310

.
Dec 15, 2006
434
Catalina Catlina 310 Campbell River BC
Yes diode battery isolators do have a high voltage drop but the Victron FET isolators have virtually no voltage loss.
 
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leo310

.
Dec 15, 2006
434
Catalina Catlina 310 Campbell River BC
Argo FET Battery Isolators

Similarly to diode battery isolators, FET isolators allow simultaneous charging of two or more batteries from one alternator (or a single output battery charger), without connecting the batteries together. In contrast with diode battery isolators, FET isolators have virtually no voltage loss. Voltage drop is less than 0,02 Volt at low current and averages 0,1 Volt at higher currents.
Argo FET Battery Isolators - Victron Energy
 
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Oct 29, 2016
1,765
Hunter 41 DS Port Huron
@leo310 That's what I love about this place, you can learn something new every day, just wondering what would be the advantage of using an isolator over an ACR? The ACR which I installed has the ability to isolate (start from house) or automatically join when a charging system is active or on the particular model I installed has a remote mounted switch allowing automatic and or manual functionality. The ACR is also able to allow full current flow, upto I believe 500 amps.
 
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Feb 6, 1998
11,436
Canadian Sailcraft 36T Casco Bay, ME
Argo FET Battery Isolators

Similarly to diode battery isolators, FET isolators allow simultaneous charging of two or more batteries from one alternator (or a single output battery charger), without connecting the batteries together. In contrast with diode battery isolators, FET isolators have virtually no voltage loss. Voltage drop is less than 0,02 Volt at low current and averages 0,1 Volt at higher currents.
Argo FET Battery Isolators - Victron Energy
While we sell these, as a Victron dealer, for certain applications, we've also seen a few failures. We advise our customers to over-size these by a pretty hefty margin. Eg: 200A model for a 100A - 125A alternator.. Not yet seen a single Blue Sea Systems ACR fail, even when incorrectly wired. Also, keep in mind that an ACR works with all charge sources and the ARGO FET, or any diode or FET isolator only works with the alternator. If simply replacing an antiquated diode isolator they are a good fit, but if you can start from scratch an ACR is often a more optimal choice. If chemistries/charging voltages are different then a DC-DC charger is the best fit.
 
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Jun 15, 2012
617
Hunter 50 AC St. Petersburg
Alternator are wired to the starter then to the starter battery ... so unless you disconnect the battery you will always have power to the alt. What I will be doing this fall is wiring the alt to a FET (victron) then the starting battery will only see the starter. The FET is an isolator so it will be connected to both house and starter battery and I will not have to worry about someone turning the power selector to off after starting the engine and blow the alt.
The alternator in the Hunter 49/50 is directly wired to the house bank, It is not wired to the starter or the start battery.
 
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