A - B - Both Switch Wiring Diagram

[mech1521]

My Imperial that I'm completely renovating came with an a-b- or both switch, and it was'nt wired right. I would like to use this switch w/ 2 batteries, if I can locate the proper way to wire this type of switch. It's an 84 Imperial with a 115 merc, elect start, depth finder, fish finder, cb radio, am-fm-cd radio, elect. tilt, and nav lights. If anyone can point me in the right directions or has any imput on the a-b switch, your help is greatly appreciated. Also, if the switch is dialed to both, does that mean both batteries should be charging?

 

[drewpster]

Re: A - B - Both Switch Wiring Diagram

Yes, Wired correctly BOTH position on the switch will charge both batteries. To properly wire it, connect one battery positive to the bolt Marked "1" on the switch, connect the second battery positive to the bolt marked "2" on the switch. Connect ALL the loads, hot wires and 12 volt positives to the bolt marked "Com" on the switch.

In position 1- everything runs off battery one- only 1 gets charged
In position 2- everything runs off battery two- only 2 gets charged

In BOTH position everything runs off both batteries-both batts get charged.

Just don?t forget to switch to 1 or 2 when the engine is off or you drain both batteries defeating the purpose for the switch.

enjoy
drewp

 

[mech1521]

Re: A - B - Both Switch Wiring Diagram

Thanks Drewster

 

[captain zac]

Re: A - B - Both Switch Wiring Diagram

http://www.cmsquick.com/tech_03_batsys.html

 

[QC]

Re: A - B - Both Switch Wiring Diagram

 

[mech1521]

Re: A - B - Both Switch Wiring Diagram

Thanks for all the replies. I have one more question about this: if the switch is selected on both, will the starter be charged with 12 or 24 volt upon starting, or will there be 12 v at the starter and high CCA?

 

[QC]

Re: A - B - Both Switch Wiring Diagram

What you describe is the basic difference between Series and Parallel circuits, you do NOT want Series (24 volt to starter), you want Parallel (12 Volt to starter) which is what you get if you follow the diagram above. I assume you effectively get double the CCA, but don't ask me because I am basically pulling the Holiday Inn last night routine . . .

 

[LippCJ7]

Re: A - B - Both Switch Wiring Diagram

QC is correct, if you wire batteries as QC's diagram describes you have two batteries in a parallel circuit and 12Volts to the starter, I don't believe you increase the CCA's (Cold Cranking Amps) of the batteries but you increase the amp hours of the system meaning you can draw more amps for longer, either way the amps don't make a difference in this, you have plenty.

 

[mech1521]

Re: A - B - Both Switch Wiring Diagram

Thanks again for the help!!

 

[captain zac]

Re: A - B - Both Switch Wiring Diagram

Be caeful with the wiring above (i am not saying that it is incorrect)
although it is correct you should research on how to operate when wired this way
It is my understanding that without an isolator the alt. will only charge the selected battery
If bat switch is in the both position then both bats will charge (not a good situation)
This puts you in the position of overcharging one of the bats (over charging might be one of the worst things that you can do the the Bat.)
In most cases operators will have a starting bat in the #1 position and a deep cyc. in the #2 position
They start on the number #1 and run to there destination on #1 then switch to #2 when they are on the hook or where ever isolating the #1 from the system so that you know that you have a bat. with full charge when you decide to leave
Knowing how the system is wired so that you can properly manage the system is very important

Harry

 

[drewpster]

Re: A - B - Both Switch Wiring Diagram

cap zach makes a good point in that you need to manage the system properly. However I have to disagree with the possibility that you could overcharge any battery from a boats charging system. Keep in mind that the output of the engine's alternator or stator is designed to replace the amount of current used to when starting the battery, not as a charger for a deeply discharged battery. It is more likely that you will need to charge your batteries on a charger at home if you use them for long lengths of time on the lake. The engine simply wont keep up unless you are taking trips with the engine at running speed for 20 hours or so. So I doubt overcharging will be an issue. Even if when combined the batteries cause the alt or stator to go to full output the discharged battery will accept what it needs and the fresh battery will accept what it needs. Keep in mind that BOTH on the switch will turn the batteries it to one big battery.
This is why I always recommend that you start with topped off batteries at home. (get a charger) Use battery one while on the lake for everything until it gets low, then switch to two. Then charge them both up when you get home. It makes more sense in the long run as well because you end up buying one well used battery every two years and you keep the other one topped off.

 

[captain zac]

Re: A - B - Both Switch Wiring Diagram

I would rethink it
A starting bat should be used to start
a deep cycle bat should be used to run 12v items on the ship when the engine is not running.
This is due to being able to discharge a deep cycle and bring it back to a full charge without damaging the bat.
A starting bat is designed to put out high amps for short periods of time.
on charging both bats while running without an isolator
no two bats will need the same charge for the same amount of time
if you are charging one bat. and it gets full and the other still needs charging the alt. still sends current to both bats. unless you have an isolator.

 

[captain zac]

Re: A - B - Both Switch Wiring Diagram

Take a look at this
I am most likely doing a poor job of explaining and I am sorry
This guy explains it very well

Harry

http://www.thefishingline.com/marine.htm

 

[dingbat]

Re: A - B - Both Switch Wiring Diagram

on charging both bats while running without an isolator
no two bats will need the same charge for the same amount of time
if you are charging one bat. and it gets full and the other still needs charging the alt. still sends current to both bats. unless you have an isolator.

Your confusing issues.
Two batteries tied together become one large battery and will normalize each other.

Look at it this way.

You have two 5 gallon buckets with a pipe connecting them at the bottom. Even though you pour unequal amounts of water in each bucket, the water level in both buckets will normalzie and the water level in both buckets will always be equal. It's the same if you have a single point of discharge. Both buckets will drain seeking the normalized state.

An isolator is nothing more than a one way valve in the pipe connecting the two buckets together. The isolator will stop the normailization process by stopping the discharge of water from one bucket to the other but it has absolutely no affect on the flow of water going into the buckets.

 

[jhebert]

Re: A - B - Both Switch Wiring Diagram

I recommend you go to the local public library and find a book about fundamental electrical principles that is written for about a 7th-grade or Junior High School level. This will give you background on electrical principles such as voltage and current, parallel and series wiring, and an understanding of these principle will enable you to understand how to wire a simple OFF-1-BOTH-2 switch to distribute electrical power from two batteries to a single load.

I often see attempts to turn electrical values into analogous parameters involving water and water flow. Most of the time the water analogy that is describted is wrong, that is, the qualities of the water are not properly correlated to the qualities of electricity. (Alas, that is the case in this discussion.) Also, these water analogies seldom contribute to a clearer understanding of the electrical principles involved.

An OFF-1-BOTH-2 switch is a very simple mechanism. There are three terminals. One terminal, usually marked "C" for common, is connected to the electrical load. One terminal, usually marked "1", is connected to the first battery. One terminal, usually marked "2", is connected to the second battery. There are four positions for the switch. In the OFF position there are no connections. In the "1" position there is a connection between 1 and C. In the "2" position there is a connection between 2 and C. In the BOTH position all three terminals are connected together.

 

[Fed]

Re: A - B - Both Switch Wiring Diagram

Take a look at this
I am most likely doing a poor job of explaining and I am sorry
This guy explains it very well

Harry

http://www.thefishingline.com/marine.htm

I read your link Captain and the "pumping life giving electricity and current through the vessel" brought a wry smile to my face which turned to tears by the time I got to the last sentence, "always connect the positive last".
A little 'knowledge' can be a dangerous thing.

 

[drewpster]

Re: A - B - Both Switch Wiring Diagram

"always connect the positive last"

BRAVO! Fed saves the day. LOL

 

[smallboatlover]

Re: A - B - Both Switch Wiring Diagram

just a question because iv'e installed one of these last week on my boat. can i put it in battery one to start it then switch it to both so they both get charged?

 

[Silvertip]

Re: A - B - Both Switch Wiring Diagram

Yes -- and that's why the switch is so versatile. Whatever you have the switch set to is what is starting the engine, powering everything and being charged.

 

[PuddleJumper]

Re: A - B - Both Switch Wiring Diagram

Be carefull If it's an older A-B switch it may not be a 'make before break' style Switching batterries while the engine is running can result in frying diodes in alternator or rectifier.