Battery Switch Wiring Diagram

[AaronJ]

Hello, electrical wizards. This is probably an easy question for the experts out there. I've attached a diagram of my battery banks hooked up to a switch, alternator and house/starter loads. I want to be able to switch between the house and starter banks in case of emergency. I also want to avoid an "open circuit" with the alternator, which is why I want to wire it directly to the battery.

If you have any improvements or see any flagrant fouls in my diagram, I'd love to hear it. Thanks!

Aaron

[sailvayu]

I would recommend hooking the alternator up to the start bank and then using a electronic voltage sensing relay to connect the 2 banks when running the engine. This will connect both banks when charge voltage reaches 13.25 volts (or something like that) and disconnects them when voltage drops to 12.75. Not sure those are the exact voltages but close. Some units are voltage adjustable as well. I have been using the BEP unit for a year now and like it. I would stay away from the West marine one as it gave me problems with cutting out for over amps even when well below its rated load. I don't like to have to manually switch as I always forget to switch back. With the auto setup you never run your engine bank down leaving it connected to the house bank. I have never had a dead start battery using this setup.

Good luck

Wayne Canning, AMS
projectboatzen.com

[Maine Sail]

Originally Posted by AaronJ

Hello, electrical wizards. This is probably an easy question for the experts out there. I've attached a diagram of my battery banks hooked up to a switch, alternator and house/starter loads. I want to be able to switch between the house and starter banks in case of emergency. I also want to avoid an "open circuit" with the alternator, which is why I want to wire it directly to the battery.

If you have any improvements or see any flagrant fouls in my diagram, I'd love to hear it. Thanks!

Aaron

Aron the only thing I would add would be either an Echo Charger or an Automatic Charging Relay. By doing this you'll only ever need to use position #1/House yet your emergency (start) bank will always be sufficiently charged if and when it is needed. This charging of the start bank will all be done behind the scenes and is automatic. Doing this avoids the large "human error" factor..

If you kill a bank don't fall into the trap of combining the dead bank with a perfectly good one. Simply switch to the second bank when you need to. Combining a good bank with a dead bank only bleeds off precious cranking amps from the good battery..

If you are never discharging the house bank below 50% state of charge you should be able to start your engine just fine using the house bank and will only ever use the battery switch when you get to the boat to flip it to position #1/House. When you leave turn it to OFF...

You made the right choice in feeding the alt to the house bank and not the start as the start bank is for back up or emergency, in your situation, and would usually be at or near 100% SOC. An Echo Charger is designed to bleed off up to 15 amps from the house bank, to top off the start bank, but you'll rarely see it using more than an amp or so if the emergency batts are mostly full..

[AaronJ]

Thanks for the replies, Wayne and Maine Sail. I've updated my diagram with the charging relay you recommended. I'll use the switch in the following ways:

At dock, AC charging: Off
At dock, AC charging with me in boat: House Bank
Cranking Engine: Starter Bank
Cruising, Alt. charging: House Bank

So, I'll just remember to switch from Starter to House after I get the engine started.

Thanks,
Aaron

[sailvayu]

Personally I would do away with the switch and hook the engine starter to the start bank and house load to the house bank. Both banks will automatically charge together anytime a charge source is connected to the start bank. This could be the alt or a 120 VDC charger. If you need a parallel circuit I would install a momentary push button on a solenoid this way you never accidentally leave them connected. Some of the auto relays have a tap for such a button that makes it simpler. You could use the switch for that but if you are like me you will forget and leave it connected lol.

Wayne Canning, AMS
projectboatzen.com

[sailvayu]

Sorry i forgot you still need a switch to disconnect the batteries in the even of a short or other fault. Sorry my mistake

[AaronJ]

I agree. I want the control of being able to disconnect the batts from loads. If I leave out the charging relay that you recommended, could I move the switch to "BOTH" and accomplish the same thing? The current from the alternator would flow to the house bank, through the switch to the starter bank and charge both (I assume).

[Maine Sail]

Originally Posted by AaronJ

Thanks for the replies, Wayne and Maine Sail. I've updated my diagram with the charging relay you recommended. I'll use the switch in the following ways:

Cranking Engine: Starter Bank
Cruising, Alt. charging: House Bank

So, I'll just remember to switch from Starter to House after I get the engine started.

Thanks,
Aaron

Aaron,

Way to confusing and far to much potential for human error. You do not need to use your start bank to start your engine with a small sailboat aux engine.

Starting the engine consumes far less than you would think. For over 20 years I have started on my house banks and this included starting a very large Cummins on my Down East single screw cruiser with a set of 6V golf cart batteries.

Watch this video it may help you understand why you do not need to use a starting battery to actually start an engine.

What Happens When I Start My Engine

[Maine Sail]

Originally Posted by AaronJ

I agree. I want the control of being able to disconnect the batts from loads. If I leave out the charging relay that you recommended, could I move the switch to "BOTH" and accomplish the same thing? The current from the alternator would flow to the house bank, through the switch to the starter bank and charge both (I assume).

Yes of course but you are back at the human error thing again. Far to often I have come across boaters with dead two bank systems and had to row one of my batts over to get them up and running. This was almost always caused by leaving the switch set to the BOTH/ALL position.

The 1/2/ALL/OFF switch is a great device, if wired appropriately. When wired in the fashion most builders do, it sucks.

The 1/2/ALL/OFF switch retains all the original features yet looses the frying of diodes and the switching back and forth if you wire the alt direct to house and use an ACR or Echo type charger to top off the start bank.

For instance if your ACR or Echo Charger failed, which could happen, you can always use the ALL/BOTH feature to charge both banks just as you always did. No repairs or jumper wires just flip the switch to ALL, for charging, and you're back in business.. You will not however fry the alt because it always has a load on it by wiring directly to the house bank.

[CharlieJ]

My recommendation is to install a Blue Sea Systems ACR p/n 7610 (Product Documents for 7610-SI-Series Automatic Charging Relay - PN 7610 - Blue Sea Systems) with a properly sized and fused conductor from the start bank to one stud on the ACR and a properly sized and fused conductor from the hose bank to the other stud on the ACR. Install a B- wire with a 15amp inline fuse from the ground tab on the ACR to vessel ground and you are in business. Two optional connections will isolate the starting battery from the house bank while cranking the engine and you can have a remote indicating LED to show when the batteries are combined.

For a belt and suspenders approach, connect a Blue Sea Systems p/n 6006 ON-OFF switch in parallel with ACR. If the ACR fails and you need to combine your batteries, turn this switch ON and you are connected.

While you are upgrading, and to stay in compliance with ABYC Standards and good industry practice, install a p/n 6006 between the start battery and the starter and upstream of the over current protection device that is feeding your main panel from the house bank.

Hope this helps.

[Cheechako]

If you are going to have only one fuse... wouldnt it be better to have it on the load side instead of the charging side?
ref: start battery... yes, only one of my boats had a starting battery. (came that way) I usually just have two house banks....

[sailvayu]

I personally like to have my engine wiring completely separate from the house wiring. This way if there is a fault or other problem with one system it does not effect the other. The only time they are ever connected is during charging. But that does not mean any other system is wrong everyone has there way of doing things. But since using this setup I have never had any trouble with being able to start my engine. I like knowing that when I push that button I have enough power to start the engine no matter how long I have been at anchor or what has been running. No switches to mess with in an emergency or anything else just good starting power. Also my engine batteries last longer with this set up.

Cheechako I agree there should be a fuse on the charging side as well. ABYC wants a fuse withing 7" of any power source, that could be the battery or/and the alternator. Of course that does not include the starter cable.

Wayne Canning, AMS
projectboatzen.com

[Maine Sail]

Originally Posted by sailvayu

Also my engine batteries last longer with this set up.


Wayne Canning, AMS
projectboatzen.com

What is the scientific explanation that makes them last any longer than a 1/2/ALL/OFF switch and an ACR? You're still combining the batteries to charge them in exactly the same manner, an ACR..

I've never had trouble starting my engine either and in in 20 years have only ever "needed" to use the emergency/start bank once, and that was because a wrench fell across a terminal and fried my ANL fuse for the house bank.

I only suggested the wiring I did because the OP already has a 1/2/ALL/OFF switch. Re-wiring, removing and replacing switches to create a dedicated start bank, utilizing divided wiring house and start banks, and completely changing his set up, is not really necessary and could get expensive.

[sailvayu]

Maine
The reason the batteries last longer is because they never get discharged. Sort of like your car battery. Of course you could use deep cycle batts but these are not designed for rapid discharge a starter uses. Ok I am not saying change everything out I am just saying this is what I like to use so others have something to think about. Yes using the ACR combiner with the switch is fine. Just make sure the combiner is rated for your load. This is the type of thing where there really is no "right" answer as there are many "right" ways to do it, I was just offering a suggestion.

Also I am not sure I would have a fuse on my starter circuit as you say. The common method is to run the starter cable directly to the battery, (with a off switch in circuit) But if that works for you then I see no harm. Fuses do get old and fail at the wrong times so I personally would not do that and ABYC does not require it in that location. Surge amps can get high and if the engine has a problem starting you could blow the fuse. Also if you have to crank a long time it could over heat the fuse and blow it. But on the other hand it is nice to have that protection.

I just feel it is best to keep the house wiring and engine wiring separate. Just my opinion. Your setup is fine too not saying you are wrong. And you are right if you are not doing a major rewire I would not say rip it all out and start over.

Thanks
Wayne Canning, AMS
projectboatzen.com

[Maddog]

Sailvayu - I have the same setup as you discribe, (seperate banks with an ACR), and I agree that both stratigies have their pros and cons. Keeping the the banks seperate works well for my style of cruising, usally extended weekends. Often 3 to 4 days without any charging except for the engine, (Which I hate to do). I'll add a small Honda generator next season. If I was doing extended costal or blue water cruising, I think I would switch back to the old 1-2-B switch with more passive charging on the boat, (solar, wind.).

In my view the key to either setup is charging the House directly with an ACR to the start batts.

Mr. MaineSail, you are a demigod amongst boaters and all your articles have helped educate me. In particulare, How to Rebuild a water pump">Raw Water Pump. Could you please start concentrating on Perkins specific parts?(joking). On this issue, I think it is coming down to different horses for different courses.