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Old 15-06-2019, 12:14   #1
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Battery Isolator question

Hi all,

My boat currently has a starter battery and a house battery which are kept isolated by a Sure Power 952 battery isolator. Unfortunately, I'm almost sure it is defective. When I charge the house battery with the DC charger, I see that the starter batter charging as well at way too high a voltage (they are not the same types of batteries). I tested the Isolator and current seems to flow in both directions on the Batt 1 post. A diode must be defective.

Anyhow, I bought a new isolator (NOCO IGD90HP) on line and the picture on the website, showed only 3 posts, like the Sure Power 952. Unfortunately, when I got it, it has a 4th post for Excitation power. From what I gather, this should go to the ignition. Do I need to wire this even if the alternator doesn't require it? I tried wiring it just leaving the EXT post not connected to anything, but the engine won't start. No power goes to the control panel when I turn the key.

Can anyone tell me if I must absolutely wire the EXT terminal, if so to what on a sailboat?

Thanks!
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Old 15-06-2019, 22:56   #2
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Re: Battery Isolator question

You should not need it if you had a diode block before. As the old alt was not being exiting by it.

The alterator and isolator have nothing to do with starting the engine. You have other issues.

If thst wire was needed. The alt would not chsrge. But the engine would start.
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Old 16-06-2019, 06:05   #3
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Re: Battery Isolator question

Thanks, that's what I thought as well. Very odd! I must have done something stupid like forgetting to reconnect the battery or something, I'll give it another try later. I'm eventually going to update all the wiring and install an ACR. I'll get into that at the end of the sailing season. For now, if I can't get the new isolator to work, I was just going to connect the alternator directly to the starter battery and manage the charging and discharging with the switch.
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Old 16-06-2019, 09:42   #4
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Re: Battery Isolator question

Quote:
Originally Posted by Laskadog View Post
Thanks, that's what I thought as well. Very odd! I must have done something stupid like forgetting to reconnect the battery or something, I'll give it another try later. I'm eventually going to update all the wiring and install an ACR. I'll get into that at the end of the sailing season. For now, if I can't get the new isolator to work, I was just going to connect the alternator directly to the starter battery and manage the charging and discharging with the switch.

If that's the case, save some $$, return the new isolator, and "manage the charging and discharging with the switch."


Connect the AO to the house bank.
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Old 16-06-2019, 11:04   #5
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Re: Battery Isolator question

I did just that. Is it normal that power only goes to the panel if the alternator is connected to the battery +?
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Old 16-06-2019, 11:12   #6
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Re: Battery Isolator question

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Originally Posted by Laskadog View Post
I did just that. Is it normal that power only goes to the panel if the alternator is connected to the battery +?

I don't understand the question. "Normal"?


AO directly to the bank instead of going through the switch simply means that the switch becomes a USE switch only, rather than both USE and a Charge selector, and that you avoid the potential problem of interrupting AO and blowing diodes.



AO power goes to the bank and is stored. Switch determines which bank to use and feeds the panel.


All discussed in detail in these threads:


OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowner...d.php?t=137615

This is a newer primer for boat system wiring design with a thorough digram: Building a Good Foundation (October 2016)
http://forums.sailboatowners.com/ind.../#post-1332240

The Short Version of the 1-2-B Switch Stuff: Electrical Systems 101 This is a link to the Electrical Systems 101 Topic, reply #2

What are ACRs, Combiners & Echo Chargers? (by Maine Sail) [scroll to the top]
http://forums.catalina.sailboatowner...d.php?p=742417 and Battery isolator / voltage regulator / batteries

Making Sense of Automatic Charging Relays (2019)
https://marinehowto.com/automatic-charging-relays/
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Old 17-06-2019, 03:29   #7
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Re: Battery Isolator question

Stu, thank you very much for all that info, it made for a good read and confirmed my understanding of the basic wiring.

Maybe instead of ďnormalĒ I should ask, is it intentional that when the AO is not connected to anything, no power goes to the engineís control panel? I assume that if you did start the engine youíd fry your alternator.

Getting back to the original reason for this post, although I probably wonít install the isolator, Iím still curious... Where to you connect the Excitation post on the isolator and what does this terminal actually do? How come my old issolator didnít need this and still worked?
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Old 20-06-2019, 12:40   #8
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Re: Battery Isolator question

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Originally Posted by Laskadog View Post
Stu, thank you very much for all that info, it made for a good read and confirmed my understanding of the basic wiring.

Maybe instead of ďnormalĒ I should ask, is it intentional that when the AO is not connected to anything, no power goes to the engineís control panel? I assume that if you did start the engine youíd fry your alternator.

Getting back to the original reason for this post, although I probably wonít install the isolator, Iím still curious... Where to you connect the Excitation post on the isolator and what does this terminal actually do? How come my old issolator didnít need this and still worked?

You're very welcome.


If the AO is not connected to anything and you start the engine, the diodes in the alternator could fry because the AO is "disconnected." Regardless of whether you employ the switch as a charge switch or just a use switch, if the switch is ON, with the engine on or off, there should be power to the boat's DC system from the energy stored in the batteries. The engine control panel is served from the DC distribution system.


I don't know the answer to your last paragraph because I removed the only isolator on our boat 21 years ago and never looked back!
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