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Old 29-09-2012, 08:17   #1
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Install Volt Meter to Battery Switch

I've got a 24 volt system with two banks consisting of 2 each 12 volt batteries. Can I install a volt meter at the battery switch and if so do I just wire the positive to each positive pole and the negative to a common negative? In other words, I'm trying to use one volt meter and switch between banks to check voltage.
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Old 29-09-2012, 08:21   #2
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Re: Install Volt Meter to Battery Switch

Wire the positive lead to the common terminal on the batt switch, and the negative to the common ground.

You'll also want to add a momentary switch to the meter lead so it's not drawing current all the time (unless you want it connected full time).

The batt switch will do the switching between the batteries for you.
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Old 29-09-2012, 08:24   #3
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Re: Install Volt Meter to Battery Switch

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Originally Posted by Sailorman375 View Post
I've got a 24 volt system with two banks consisting of 2 each 12 volt batteries. Can I install a volt meter at the battery switch and if so do I just wire the positive to each positive pole and the negative to a common negative? In other words, I'm trying to use one volt meter and switch between banks to check voltage.
Not quite.
Assuming your battery switch is a 1-all-2-off style switch, then wire the positive of the meter to the common on the switch and the negative of the meter to the common negative.
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Old 29-09-2012, 08:25   #4
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Re: Install Volt Meter to Battery Switch

SM is faster than Wot
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Old 29-09-2012, 08:26   #5
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Re: Install Volt Meter to Battery Switch

So if I wire to the common, I can switch between one and two and read the voltage of the bank?
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Old 29-09-2012, 08:28   #6
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Re: Install Volt Meter to Battery Switch

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So if I wire to the common, I can switch between one and two and read the voltage of the bank?
Exactly
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Old 29-09-2012, 08:34   #7
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Re: Install Volt Meter to Battery Switch

I assume the common is the "both" connection? And thanks for the quick supply, I need a project for the rainy day today
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Old 29-09-2012, 08:47   #8
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Re: Install Volt Meter to Battery Switch

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I assume the common is the "both" connection? And thanks for the quick supply, I need a project for the rainy day today
No, the common is, well, the common connection.

The switch will have 3 connections. 1 for battery one, another for battery two and a 3rd for the "common".

When switched to battery one, the circuit is made from battery one to the common (with battery two disconnected).
When switched to battery two, the circuit is made from battery 2 to the common (with battery one disconnected).
When switched to "Both", both batteries are connected together and the circuit is made from both batteries to the common.

Hope this is clear
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Old 29-09-2012, 09:59   #9
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Re: Install Volt Meter to Battery Switch

While using the battery switch common terminal will get you the active battery voltage. It will not show you the resting battery voltage. Really its the resting battery voltage that gives you a better look at SOC. Reading the voltage on an active battery bank does not give a true indication of the SOC battery voltage. It always shows a voltage less then the true SOC

I use a DPDT on/off/on switch with a digital voltmeter, wired to the A and B sides of the battery switch. This allows me to read the active battery and the resting battery. Plus I can turn off the LED display at night or at the dock too.
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Old 29-09-2012, 10:07   #10
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Re: Install Volt Meter to Battery Switch

OK now I'm confused. My switch (Guest) has three poles. 1, 2, and both. No other connections. Sailorchic34, So you're saying run the positive from the meter to both the "on" connections on DPDT switch, then each of the positives from the switch to the 1 and the 2 on the battery switch?
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Old 29-09-2012, 10:25   #11
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Re: Install Volt Meter to Battery Switch

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OK now I'm confused. My switch (Guest) has three poles. 1, 2, and both. No other connections. Sailorchic34, So you're saying run the positive from the meter to both the "on" connections on DPDT switch, then each of the positives from the switch to the 1 and the 2 on the battery switch?
Nope, I'm saying adding a separate small DPDT switch. The meter connects to the center common lug on the DPDT switch (not the guest battery switch). Each outer lug on the DPDT goes to the separate battery lugs on the battery switch. So #1 goes to one side of the DPDT switch and #2 goes to the other side of the DPDT switch.

Its opposite of what everyone else said. I'm saying it works better with an extra small switch, that allows you to read each battery bank separate. Using the main guest switch does not really allow you to check the resting state of the battery. Only the in use state. The resting state is what gives a much better reading of SOC

BTW, I only have a voltmeter for checking SOC. It works fine enough on my simply boat

Darn blonde moments. I meant using a SPDT switch..
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Old 29-09-2012, 10:49   #12
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Re: Install Volt Meter to Battery Switch

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OK now I'm confused. My switch (Guest) has three poles. 1, 2, and both.
Your switch has four POSITIONS 1,2,BOTH and OFF

On the back you have three studs

Bank #1 = connected to battery #1
Bank #2 = connected to battery #2
"C" or Common = connected to DC loads, starter, alternator etc.

Common is your ON or connected stud when in #1,#2 or BOTH.

When the switch is in #1, Stud #1 connects to "C"
When the switch is in #2, Stud #2 connects to "C"
When the switch is in BOTH, #1 & #2 studs connect to "C"

The orange line depicts battery bank #1 turned ON.
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Old 29-09-2012, 10:51   #13
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Re: Install Volt Meter to Battery Switch

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Originally Posted by Sailorman375 View Post
OK now I'm confused. My switch (Guest) has three poles. 1, 2, and both. No other connections. Sailorchic34, So you're saying run the positive from the meter to both the "on" connections on DPDT switch, then each of the positives from the switch to the 1 and the 2 on the battery switch?
It's a nomenclature thing. Your switch has four positions (as labeled on the front); 1, 2, Both, and Off. It also has three poles (points where your connect the wires); 1, 2, and Common (Guest sometimes labels this Feed).

When the switch is in position 1 the poles 1 and Common are connected. When the switch is in position 2 the poles 2 and Common are connected. And when in Both all three poles are connected.

If you want to connect a voltmeter connect it to the Common/Feed (if it's not clear because of labeling, the one that's not 1 or 2) and to your negative someplace. Then you can read the voltage of the battery you are currently using. I agree with the other suggestions, however, install a small switch to allow you to read whichever battery you want regardless of which one you are using. This is really just another switch with the same functions as your battery switch, only much smaller.
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Old 29-09-2012, 10:54   #14
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Re: Install Volt Meter to Battery Switch

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Originally Posted by Sailorman375 View Post
I've got a 24 volt system with two banks consisting of 2 each 12 volt batteries. Can I install a volt meter at the battery switch and if so do I just wire the positive to each positive pole and the negative to a common negative? In other words, I'm trying to use one volt meter and switch between banks to check voltage.
HOLD THE PHONE EVERYONE. He said he has a 24 volt system. I'm hoping he meant a 12 volt system with 2 batteries as suggested by the switch question. A small single pole 2 position switch with center off would allow reading either battery without having to manipulate the battery switch, and allow disconnecting when not in use. Fairly good quality meters are available at reasonable prices, it may be much simpler to add a second meter.

Avoid typical marine dash board analog meters (with a non digital display). I've seen errors as much as 15% in some. And digital doesn't equate to accuracy, the price of some Harbor Freight digital meters is extremely attractive but they can be equally inaccurate.
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Old 29-09-2012, 11:13   #15
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Re: Install Volt Meter to Battery Switch

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A small single pole 2 position switch with center off would allow reading either battery without having to manipulate the battery switch, and allow disconnecting when not in use.
Bingo! I would add that you can also install a "self returning" switch so when you let go it returns to center, not 1 or 2, and turns off the volt meter. For owners who are forgetful these self returning switches work well to avoid parasitic draw especially if the boat is mooring sailed..
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