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Battery Switch Wiring

Feb 26, 2019
16
Pearson 31-2 Chester MD
I'm working on a detailed schematic of the wiring system for our newly purchased '88 Pearson 31-2. Everything on the boat works well and it is in mint condition - previous owner took excellent care of the boat. Here's the problem - battery switch appears to be wired wrong. Just want to make sure I'm not missing something obvious before I change it as things do seem to work just fine. Battery #1 positive is connected to switch position #1, Battery #2 is connected to switch's "both" position and switch position #2 seems to be the output from the switch. Also - when I totally disconnect battery #1 from the switch NOTHING works. Battery voltage levels are fine. Everything else seems normal; connections from batteries to engine and battery charger, etc. Can anyone think of a reason why one would wire a battery switch this way? Thanks!
 
Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
Can anyone think of a reason why one would wire a battery switch this way? Thanks!
The PO made a mistake? Or didn't understand how to wire the switch.

It was an attempt to wire the batteries permanently in parallel?
 
Feb 6, 1998
11,436
Canadian Sailcraft 36T Casco Bay, ME
A 1/2/BOTH switch does not have a “both” terminal.

It has BATTERY/INPUT 1, BATTERY/INPUT 2 and COMMON/OUTPUT.

COMMON/OUTPUT or what is commonly referred to as the “C” post, connects to your system loads such ad DC panel, starter/engine, windlass etc. BATTERY 1 & 2 connect directly to their respective banks... A 1/2/BOTH was not designed to have a bank connected to the “C” post for typical use scenarios..

This may help..
https://forums.sailboatowners.com/index.php?threads/1-both-2-off-switches-thoughts-musings.137615/
 
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Ward H

.
Nov 7, 2011
3,092
Catalina 30 Mk II Barnegat, NJ
Mama Boy,

Is it possible you are assuming the stud connection for battery #2 is the stud behind the #2 position on the switch and the same for the other stud connections? Or maybe the PO did?
You need to examine the markings on the back of the switch to identify the correct stud connections for position 1, position 2 and the common connection.
Once you identify the stud connections, you can double check the battery cables are from the correct battery.
Leave the battery switch in the off position. Remove the cable from battery #2. At the switch use a volt meter to identify the switch end of cable for battery #1. Then put the cable back on battery #2 and take the cable off of battery #1. Back at the switch use the volt meter to identify the switch end of the cable for battery #2.
Let us know how you make out and remember, photos help.

Here are photos showing a Blue Sea switch front and back.

 
Feb 26, 2019
16
Pearson 31-2 Chester MD
I believe you have nailed this - I was assuming the stud connections are/were directly behind the markings on the front side of the switch. Weather here on the bay has turned ugly (rain/cold) so I won't be able to check this out for a couple of days but it sure seems like this is the issue and things may be just fine. Would disconnecting the #1 battery cause everything to not work - would that be a normal scenario; ie., even if battery #1 were to completely "die" would it still need to be wired in?
 
Aug 22, 2017
1,608
Hunter 26.5 West Palm Beach
Assuming that the OP means the common terminal on the switch when he says “both position”, The switch function would be as follows:

Both = both batteries connected to systems – OK
1 = battery 1 connected to battery 2, systems disconnected - not normal
2 = Battery 2 connected to systems - OK

Maybe he had a solar charger & he wanted to have both batteries connected to the solar when he was off the boat, but wanted everything else disconnected????? I'm not recommending this as a good idea, I'm just looking for a possible motivation to wire it that way. If one battery went bad & you left a good battery wired to it, the good battery would get killed prematurely.
 

Ward H

.
Nov 7, 2011
3,092
Catalina 30 Mk II Barnegat, NJ
Would disconnecting the #1 battery cause everything to not work - would that be a normal scenario; ie., even if battery #1 were to completely "die" would it still need to be wired in?
If battery #1 dies or is disconnected, you should be able to move the switch to position #2 and run off battery #2. The switch allows you to select which battery you want to use. When talking about positions 1 and 2, they are isolated from each other. Only when you set the switch to "Both" are positions 1 and 2 both electrically connected together and to the output.
A lot of boaters always use the "Both" position but there are two problems when doing so. 1. You can drain both batteries at once and be left with no battery to start your motor. 2. If one battery goes bad, it can drain the other battery leaving you with no good battery to start your motor.

Here is a link to a great thread that talks about the 1 - 2- Both - Off switch. It provides a lot of detail about the switch and best uses. https://forums.sailboatowners.com/index.php?threads/1-both-2-off-switches-thoughts-musings.137615/
 
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Feb 26, 2019
16
Pearson 31-2 Chester MD
Wow - that's an amazing discussion of battery switches - thanks! I think I have enough knowledge now to verify that my switch is wired the way it should be. One last thing - my two batteries are connected to each other negative to negative - could that account for the fact that my entire DC system goes down with I disconnect battery #1?
 
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Oct 22, 2014
15,791
CAL 35 Cruiser moored EVERETT WA
Bama Boy... No. Ground (black or yellow wires depending on your system) Outside the battery box is the same. All connected together is fine. Just do not do that with the “RED” leads.

In the Battery Box you may find that the positive of one battery is connected to the negative of a second battery. This is done for a specific purpose. With 2 6 volt batteries connecting them in this way puts them in series. When you then check the positive of one battery with the negative of the second battery your volt meter will show 12 volts not 6 volts. In series two 6 volt batteries give you 12 volts.

Please explore the battery 101 info and the MaineSail articles here on the forum. You’ll find a wealth of knowledge about the batteries on your boat.

PS. Welcome to the forum and congrats on your new to you boat.
 
Feb 26, 2019
16
Pearson 31-2 Chester MD
Thanks for the welcome! I have connected 6V batteries in that manner on a previous boat. Thanks to everyone who has responded I have enough info and things to look at that I'm confident I can figure this out now. Like I said before, everything seems to be working as it should but I have the kind of personality that demands I know how everything is ACTUALLY working - almost a character flaw - hahaha!
 
Oct 22, 2014
15,791
CAL 35 Cruiser moored EVERETT WA
No Character flaw, just an owner who wants to be sure of what he is doing when going to sea. I call that a “Good Captain”.
In the Navy, a Captain signs for his boat/ship. The one’s I have known take a tour of all of the spaces, inspecting them, asking the sailors on watch what is this, what is that, how does it work. Looking for leaks or things out of place. To include the bilges. Only when satisfied that he/she is getting the boat/ship that is represented in the paperwork does he sign the documents. At least that is the way it is supposed to work. But at times there have been short cuts taken. Most times that comes back to haunt the “assuming” captain.

You are carrying on a proud tradition.
 

Ward H

.
Nov 7, 2011
3,092
Catalina 30 Mk II Barnegat, NJ
everything seems to be working as it should but I have the kind of personality that demands I know how everything is ACTUALLY working - almost a character flaw - hahaha!
To add on to what @jssailem said, the boat owner who knows how his boat systems work and why can: 1. Make his own repairs and save money 2. Quickly troubleshoot problems and perform repairs when trouble arises away from the dock.

Maine Sail also has a web site at www.marinehowto.com with many "how to" articles. Good reading on a lousy day like today as is the threads linked to by @Stu Jackson .
 
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Johann

.
Jun 3, 2004
250
Leopard 39 Pensacola
Wow - that's an amazing discussion of battery switches - thanks! I think I have enough knowledge now to verify that my switch is wired the way it should be. One last thing - my two batteries are connected to each other negative to negative - could that account for the fact that my entire DC system goes down with I disconnect battery #1?
Maybe. If the only battery connection to the DC negative bus is on battery #1 and you disconnect that it will depower the entire DC system. How many cables are (were) on the negative post of battery #1?
 
Aug 22, 2017
1,608
Hunter 26.5 West Palm Beach
Wow - that's an amazing discussion of battery switches - thanks! I think I have enough knowledge now to verify that my switch is wired the way it should be. One last thing - my two batteries are connected to each other negative to negative - could that account for the fact that my entire DC system goes down with I disconnect battery #1?
Having all 12v battery negatives tied together is normal. Having the whole DC system go down when you switch to battery 1 is not normal. If this is happening, either battery 1 is totally flat or your switch is not wired correctly. The description of the switch wiring at the beginning of this thread was not normal & would cause the systems to go down when the switch is set to battery 1. In other words, your switch is NOT wired correctly.