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Old 23-02-2010, 14:43   #1
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What EXACTLY Is this?

I kind of know what this is but I'm not sure why it's important...



The start battery leads into it
It then feeds the engine starter
It loops over to the house bank
There is a remote switch. You can clearly hear a solenoid click when activating the switch.
My continuity meter says that in one switch position, it connects the start battery. In the other switch position it connects the house bank.

I thought it would connect both start & house batteries but apparently it does not.

So what is the importance of this vs. a 1/2/both selector switch?

Is there some other feature not apparent to me?

Thanks
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Old 23-02-2010, 14:52   #2
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My guess is that if your starting battery is dead, this lets you start the engine with the house bank. You don't want the "both" setting-- if you used it in this case, the house bank would drain into the starting battery.

Make sure it's a "make before break" kind of switch, or if you switch back over to the starting battery (to charge it) once the engine's running, the momentary disconnect will fry your alternator diodes.
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Old 23-02-2010, 15:09   #3
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It looks like a starter relay. You select which battery bank to use for starting the engine by turning your switch. That's why both the banks are connected to your relay.

/Hampus
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Old 23-02-2010, 15:17   #4
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It may also be a battery isolator. If so, it will connect both batteries together when the engine is running, to charge them both. Then the engine's off, it disconnects them to protect the starting battery from discharge. The remote switch lets you use either for starting.
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Old 23-02-2010, 15:30   #5
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Thanks, but I'm looking for definitive answers.
I know I can choose one bank or the other as I learned with the continuity tester. It seems more sophisticated than simply a switch for either battery. If all it did was choose between 2 batteries then a simple 1/2 selector switch could do that without electrical stuff to complicate things
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Old 23-02-2010, 15:43   #6
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maybe the previous owner didnt have the luxury of a 1/2 selector switch. Everything I've read above is right on pending any further infor from you to negate it.
It appears that you have the infamous cheap version that's reliable and simple and easily changed just about anywhere in the world.
The solenoid activation wire (The light weight yellow one) is no doubt coming from your selector switch.
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Old 23-02-2010, 15:59   #7
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Quote:
Originally Posted by gettinthere View Post
Thanks, but I'm looking for definitive answers.
It's a starter relay. It's there because it's unsafe to pump full current for the starter through the switch you put your finger on, plus the switch can't handle that. There's an awful lot of corrosion on all the terminals too, I'd be mildly surprised if it worked in that condition.

Quote:
It looks like a starter relay. You select which battery bank to use for starting the engine by turning your switch. That's why both the banks are connected to your relay.

/Hampus
Yup.
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Old 23-02-2010, 16:40   #8
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Thanks, but I'm looking for definitive answers.
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Old 23-02-2010, 16:41   #9
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It sounds like this is a parallel solenoid that allows you temporarily connect your house bank to the starting circuit. It was intended as a quick alternative to a large 1/2/Both battery selector switch, so that in an emergency, you could just throw the switch you mentioned (that makes the solenoid click), rather than have to climb down to your battery switch.
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Old 23-02-2010, 16:45   #10
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It is a relay - typical of what you would see for windlass operations with top deck control.
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Old 23-02-2010, 16:55   #11
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It just looks like the starter solonoid to me just like on an older car but with extra cables from the house bank.
Steve.
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Old 23-02-2010, 17:55   #12
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So why is this solenoid preferred over a 1/2/both rotary switch?

Seems like it doesn't do anything extra.

It does not combine the two banks, it's an either/or setup.

I'm considering replacing it with a rotary switch. I also have a yandina battery combiner I'll be adding. Eliminating the solenoid will simplify the whole setup. Looking for some reason it needs to stay.

Thanks
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Old 23-02-2010, 18:04   #13
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Whatever you do, either remove those old heatshrinkless crimp terminals or replace them with new ones that have been heatshrinked.
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Old 23-02-2010, 19:07   #14
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Doug86 is absolutely correct...it's solenoid for a parallel circuit. If the starter battery is almost dead you can flip the switch and cross the juice over to help start the engine. Let me know if you need a schematic...I sort of have one. Most boats just use a 1/2/both battery switch, but even brand new fancy boats often use this setup...
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Old 23-02-2010, 19:35   #15
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Thanks all. This is what I thought but it has a lot of wires and I wanted to make sure it doesn't do more than I expected.

I have a Cole Hersee rotary switch I'm going to use instead. The yandina combiner will keep both banks charged while also keeping them from discharging each other.

Thanks again
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