Battery isolator issue

[Bogart]

G'day all

Bogart is a 2007 Hunter 45CC equipped with generator. I have 1 AGM starter battery (which starts both the motor and the generator) and 3 x AGM house batteries. My issue is that, when running the motor, the house batteries are not charging.

I have located the Guest battery isolator behind the main 12V circuit panel. It is model 2430, apparently no longer made. The battery isolator has 3 pins on the top, ordered 1, A and 2. A photo is attached.

There is no direct cable from the alternator to the battery isolator. Rather, the cable from the alternator goes to the starter motor then it runs to the starter battery on/off switch. (There are also cables running to the generator, irrelevant for current purposes.) On the other side of that switch the + goes to the starter battery itself and it is from that side of the switch that a cable goes to the battery isolator.

On top of the battery isolator, the cable from the starter motor/starter battery goes to the pin numbered 1. The house cable goes to the pin labelled A. There is nothing attached to the third pin numbered 2. Photo attached.

When running the motor (and I have turned off the solar charger/MPPT Controller) at about 2000rpm, on the voltmeter I am getting a reading of 14.28VDC at pin 1 but only 12.38VDC at pin labelled A. My assumption is that, after 14 years, the battery isolator has failed. I intend to buy a replacement part with a similar capacity.

However, I have not been able to find any manual for this specific Guest model, nor have I been able to find any reference to someone wiring up the isolator in this fashion. Everyone seems to have a separate cable from the alternator, with the starter and house batteries connected to the pins numbered 1 and 2 respectively.

Any useful suggestions (please don't tell me to rewire the boat) about replacement and wiring would be greatly appreciated.

Cheers.

 

[Davidasailor26]

That type of isolator is an old design that’s fallen out of favor. It relies on diodes to isolate the batteries, and those diodes will always introduce some voltage drop that reduces your house battery charge. It sounds like the diodes may have completely failed in yours.

A well respected potential replacement would be a Blue Seas ACR - SI-ACR Automatic Charging Relay - 12/24V DC 120A - Blue Sea Systems. You could likely wire that in the same way as the existing isolator.

 

[Davidasailor26]

Also, here is the manual for your existing isolator - https://www.marinco.com/en/~/media/inriver/316335-11180.pdf

And for the Blue Seas ACR, including a wiring diagram for when the starter and alternator share a wire - https://d2pyqm2yd3fw2i.cloudfront.net/files/resources/instructions/990170140.pdf

 

[dlochner]

The labels on the pins suggest the Alternator output should go to A and the batteries cables should go to 1 and 2.

It is a pretty standard wiring arrangement for the alternator output go to the starter and from there to the batteries, however, this wiring is not done for the boat owner, it is done to reduce labor costs for the manufacturer and warranty costs for the engine manufacturer.

It is better to connect the alternator to the house bank and then use the ACR to connect the two battery banks as @Davidasailor26 suggests. There are many references to these issues on the Musings With MaineSail forum here on SBO and on MaineSails website. I'd encourage you to spend some time on his website and think about changing the charging circuit.

Marine How To - DIY for Boaters - Marine How To

For DIY boaters in an attempt to try and keep the sport as affordable & safe as possible. How To articles for sailboats and powerboats.

marinehowto.com

 

[NYSail]

I rewired my boat so that the alt feeds the house bank. Then I have a ACR leading to the starter bank....... Logic is that the house bank is the one that gets drawn down most with the starter battery seldom used. The ACR will charge it as needed and stop charging when it is fully charged. The house bank needs more work. so is the primary connection. As stated above, read the article Marine How To..... Wealth of great information.

Good Luck
Greg

 

[Stu Jackson]

It is a pretty standard wiring arrangement for the alternator output go to the starter and from there to the batteries, however, this wiring is not done for the boat owner, it is done to reduce labor costs for the manufacturer and warranty costs for the engine manufacturer.

Correct.

Here's why:

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

1-2-B Considerations (New 2020 - Rod finally got around to diagramming what I had done in the above link in 2009 )
1/2/BOTH Switch Considerations

And you might find these helpful. They are the diagrams mentioned by others, I figure it's easier for me to show them to you than for you having to go hunting for them.

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)
1/BOTH/2/OFF Switches Thoughts & Musings

This is a newer primer for boat system wiring design with a thorough diagram: Building a Good Foundation (October 2016)
Building a DC Electrical Foundation

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]
Battery Switch Question ? and Battery isolator / voltage regulator / batteries

Making Sense of Automatic Charging Relays (2019)
Making Sense of Automatic Charging Relays - Marine How To

**************************************************************
All these links come from my collection, which givew you a lot more to read, too:
Electrical Systems 101 Electrical Systems 101

 

[DArcy]

Here is my wiring diagram using an ACR, this is essentially what Main Sail shows for the "1/2/Both with dedicated starter battery" towards the bottom of this page 1/2/BOTH Switch Considerations . I don't have a generator but I believe it should connect the same way as the main engine does.

 

[Bogart]

Many thanks for all your help. I obviously have some research, and work, to do if I am to have a more modern and efficient set up.

However, a question: There are still diode battery isolators on the market which are fairly cheap, and a bit more efficient than the old ones. If, as I suspect, and @Davidasailor26 suggests, the diodes have failed, could I get away in the short term with just replacing the old battery isolator with a new one and wiring it the same way? My reason for asking is that we have only just commenced our cruising season here in Australia and I don't really want to have to sit somewhere while I sort out how I should update the wiring.

Look forward to hearing from you.

Cheers

 

[leo310]

https://www.pysystems.ca/site/assets/files/2532/pys_battery_isolator.pdf

Take a look at this site. I use the same isolator Victron Argo FET cost is more but no power loss or diodes.

 

[dlochner]

Many thanks for all your help. I obviously have some research, and work, to do if I am to have a more modern and efficient set up.

However, a question: There are still diode battery isolators on the market which are fairly cheap, and a bit more efficient than the old ones. If, as I suspect, and @Davidasailor26 suggests, the diodes have failed, could I get away in the short term with just replacing the old battery isolator with a new one and wiring it the same way? My reason for asking is that we have only just commenced our cruising season here in Australia and I don't really want to have to sit somewhere while I sort out how I should update the wiring.

Look forward to hearing from you.

Cheers

If you wire it the same way you will have the same problems. If you wire it correctly you will still have some problems.

The diode based isolators reduce the voltage reaching the batteries, this is a battery killer. I believe there are a few applications where diode based isolators are OK, but sailboats are not one of them. Emergency vehicles (ambulances, fire trucks, etc) that are always connected to the grid and a battery charger and when working always have their motors running and the alternators running can use them because the primary power source is not the battery it is the charger or the alternator.

Because the diode based systems reduce the voltage coming off the alternator, it would be necessary to raise the output voltage of the alternator sufficiently high to overcome the voltage drop caused by the isolator. With a charger this is not a big issue, with an alternator trying to recharge a battery, it is. Upping the output voltage on a stock alternator 1) may not be possible because of the internal regulator or 2) if the alternator is externally regulated the increased output may damage the alternator.

The simplest cheapest and most effective solution will be to add an ACR or a similar device that does not rely on diodes.

 

[Maine Sail]

If you insist on replacing it like for like, the only somewhat reasonable replacement is a Victron ARGO FET. They have considerably lower volt drop than diode based isolators. An ACR is an excellent option but the need to be wired correctly, alternator directly to house bank, which will mean some reconfiguration.

 

[Bogart]

Thanks again for all your input.

Heading the ACR way.

Cheers