Maybe a confusing Battery question, anyone??

wilf

.
Jan 25, 2017
124
oday 25 oday 25 long beach
Most confusing is why the bottom battery 24dc shows 28v between its terminals, i am a contractor and build my own houses , i can frame , plumb, roof, drywall, tile and everything on them but electrics drives me crazy!!
 
Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
The battery switch may be wired wrong, but I don't think that is the case. Again, I would recommend removing the ground wire from the batteries so they are no longer connected to anything. Then just read the three batteries from + to - but only on each battery, not between batteries. That will tell us exactly what the voltage is on each battery.

Start reading this thread if you haven't already done so.
https://forums.sailboatowners.com/index.php?threads/1-both-2-off-switches-thoughts-musings.137615/
 
May 17, 2004
5,032
Beneteau Oceanis 37 Havre de Grace
I'm confused too as to what's causing the 28V readings. I agree with Brian that you really need to separate all of the batteries by disconnecting the grounds and measure them each individually.
 
May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
28volts (14+14 where your 12v batteries are fully charged) is easy to get if you have 2 sets of batteries where the negative is tied together and positives are isolated, which is the case of about 99% of marine installs with two sets of batteries (house and start). Getting 24v within a set is more unusual.
 
Jun 23, 2013
271
Beneteau 373 Newport
My guess - I'm not an electrician.
From the drawing , looking at the voltage readings, my guess is all bats are 12v and the readings were taken with the switch in the BOTH position. If true, the 2 bat bank is wired in series and should be in parallel.
WILF, the normal way to wire is so that either bank (or both together) will supply power to everything - engine, lights, etc. Using one to start eng and the other for house requires you to switch between position 1 and 2 as appropriate.
Mainsail has the best recmendation for this arrangement - use the larger "house" bank for everything, keep the "start battery" as an emergency backup - make sure you check it and keep it charged. I believe if the combiner is properly wired it will ensure the start is kept charged.
 

wilf

.
Jan 25, 2017
124
oday 25 oday 25 long beach
I
My guess - I'm not an electrician.
From the drawing , looking at the voltage readings, my guess is all bats are 12v and the readings were taken with the switch in the BOTH position. If true, the 2 bat bank is wired in series and should be in parallel.
WILF, the normal way to wire is so that either bank (or both together) will supply power to everything - engine, lights, etc. Using one to start eng and the other for house requires you to switch between position 1 and 2 as appropriate.
Mainsail has the best recmendation for this arrangement - use the larger "house" bank for everything, keep the "start battery" as an emergency backup - make sure you check it and keep it charged. I believe if the combiner is properly wired it will ensure the start is kept charged.
I was trying to figure out which was the house and which was the starter battery, my concern is that im somewhere at sea and i run down the starter battery and need to start the motor, so its normal for everything to work on either 1 or 2? My motor cranks on either but i did notice it cranked a bit faster on one than the other, another question if im anchored which battery should i be using for power, either of them as long as not switched on both?
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
The 2 6v GC batteries are wired in Series, that gives you the 13 v (remember batteries voltages are nominal, i.e., a 12 V battery is really about 12.5 when charged and at rest) and then the 12v battery is wired in series with the 2 6v batteries. That's how you get to 28v.

The question then, is how did the 2 banks end up in series? I think part of the problem is that the negative cables are connected together at a battery post. Break that connection and check the voltages. The other problem is going to be at the positive end. Somehow, the positive wire is connecting to the negative to make a series connection between the 2 banks.

Time to trace the other end of the circuit. It could be at the switch or the refrigerator or starter. How are the negative cables connected to the engine block? Where do the positive cables go?
 
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wilf

.
Jan 25, 2017
124
oday 25 oday 25 long beach
The 2 6v GC batteries are wired in Series, that gives you the 13 v (remember batteries voltages are nominal, i.e., a 12 V battery is really about 12.5 when charged and at rest) and then the 12v battery is wired in series with the 2 6v batteries. That's how you get to 28v.

The question then, is how did the 2 banks end up in series? I think part of the problem is that the negative cables are connected together at a battery post. Break that connection and check the voltages. The other problem is going to be at the positive end. Somehow, the positive wire is connecting to the negative to make a series connection between the 2 banks.

Time to trace the other end of the circuit. It could be at the switch or the refrigerator or starter. How are the negative cables connected to the engine block? Where do the positive cables go?
I am going to try to trace them today and see where they go, i only got the boat a month ago and everything is as it was when i got it so maybe its been wired wrong by the PO. ?
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
Heres a diagram showing where each cable is positioned and also showing the volts between the different terminals, does this configuration of the batteries look correct ?

Some of these readings are as close to an impossibility as there is. For instance you can not read 28.5V across the positive post & negative post of a 12V battery, the DC24N, without the battery having already exploded. If you are reading 28.5V across the pos & neg terminals on the 12V battery that means the battery is at 28.5V and that is simply not going to happen without some rather explosive results and LOTS of current......

I would check your DVM then check all your wiring...
 

wilf

.
Jan 25, 2017
124
oday 25 oday 25 long beach
Some of these readings are as close to an impossibility as there is. For instance you can not read 28.5V across the positive post & negative post of a 12V battery, the DC24N, without the battery having already exploded. If you are reading 28.5V across the pos & neg terminals on the 12V battery that means the battery is at 28.5V and that is simply not going to happen without some rather explosive results and LOTS of current......

I would check your DVM then check all your wiring...
I Will do that,
anyhow i just got to the boat and the fridge (which started all these questions in the first place) is actually working so im just going to leave it all alone and see if its still on tomorow
 
Jan 18, 2016
782
Catalina 387 Dana Point
Wilf, If you're still having problems by the weekend, I'll happily volunteer to help you out (If your boat is in Orange County).
PM me if so.
 

wilf

.
Jan 25, 2017
124
oday 25 oday 25 long beach
Well As i said earlier i know nothing about electrics but i have figured out one thing, i must have had the voltmeter on the wrong setting! (dumb arse ha ha) because i tested it now and the new 12v battery shows around 14v and the 2 others show 6.2v each or 12.4v combined,
whats the reason for having 2x 6v batteries instead of 1 or even 2 x 12v batteries? The 6v ones are 9 years old but still show 6.2v so should they be changed?
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Well As i said earlier i know nothing about electrics but i have figured out one thing, i must have had the voltmeter on the wrong setting! (dumb arse ha ha) because i tested it now and the new 12v battery shows around 14v and the 2 others show 6.2v each or 12.4v combined,
whats the reason for having 2x 6v batteries instead of 1 or even 2 x 12v batteries? The 6v ones are 9 years old but still show 6.2v so should they be changed?
Sometimes it is the simplest thing that does us in. :banghead:

There are a lot of posts and threads that address the 2 GC vs 1 12v battery configuration. Read this thread:
https://forums.sailboatowners.com/index.php?threads/multiple-house-banks-vs-one-house-bank.184137/

It will answer most of your questions.
 
May 24, 2004
7,129
CC 30 South Florida
The 6V batteries are mainly designed for use in golf carts. They have a high Ah capacity and if properly maintained provide a long useful life. A reading of 6.2V by itself means little unless it was taken with the battery at rest (no loads or no charge)for at least a couple of hours. A battery that has been under load will show a lower voltage than actual and a battery that has been under charge will show a higher one. A fully charged 6V battery should show a voltage at rest of 6.33V so if we take your readings to be correct you then you are showing two batteries that have lost some capacity in Ampere hours (Ah) which is understandable after 9 years but could still be useful depending on the needs. A 6V battery with a voltage reading of 6.2V shows only 80% charge. At this point and without knowing if the readings are correct I would go with "the proof is in the pudding" method and suggest that if these batteries are meeting your electric needs between recharges there is no reason to replace them.
 
Last edited:
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
Well As i said earlier i know nothing about electrics but i have figured out one thing, i must have had the voltmeter on the wrong setting! (dumb arse ha ha) because i tested it now and the new 12v battery shows around 14v and the 2 others show 6.2v each or 12.4v combined,
This is why I said your readings were near impossible..:wink:

whats the reason for having 2x 6v batteries instead of 1 or even 2 x 12v batteries?
Because they are actually a "deep cycle" battery not just a dual purpose battery with a deep cycle sticker..

The 6v ones are 9 years old
You just answered your question from above. This is why you want to use actual deep cycle batteries not just dual purpose batteries with a "deep cycle" sticker.. Read the below article for a bit more information on deep cycle vs. light cycling batteries....

What is a Deep Cycle Battery?

but still show 6.2v so should they be changed?
6.2 + 6.2 = 12.4V and without knowing how that reading was taken, loaded, unloaded, unloaded and rested for 12+ hours etc. it is impossible to comment on state of health. Based on that voltage I would charge them to full, and if you have the equipment, equalize them.
 
Nov 17, 2009
20
Catalina C-310 Falmouth
OK, there's lots of confusion in this thread. The first thing you have to do is disconnect ALL the batteries. The safest way to do this is remove the negative (common) leads first. Then remove the positive leads. Then and only then can you get a definitive voltage reading from each battery. As an aside...first use your voltmeter to test a couple of other batteries...say on some cars, just to be sure the meter hasn't gone wonky. Car batteries should read around 12.5 Vdc.
Do you have an owners manual for the boat? If so it should have a section on the DC circuits that could be very helpful.
As noted in other responses, the voltage readings you have really don't make any sense so I would suggest that, while you have everything disconnected, you need to check for stray voltages and poor connections.
First, check each cable connection to be sure that it is clean and tight.
To check for stray voltage, find a place to connect your meter to ground that is clean, dry and away from the common connection used by the batteries. Disconnect from shore power when doing this test! Then put the meter's positive lead on each of the positive cables and then each of the negative cables. There should be ZERO volts at every one of these connections. If you see any voltage you have further problems and it's probably time to call in a pro.
Once you have determined that there is no voltage on these connections it would be a good idea to check the resistance reading on them, It should be zero or nearly zero ohms. Also check for voltage and resistance between were the negative cables connect to ground and the point you have chosen for the negative cable on your meter.
I hope this helps. Let us know what you find.
 
Nov 17, 2009
20
Catalina C-310 Falmouth
Well, a lot of information came in while I was writing my earlier post. It looks like a lot of the confusion has been cleared up and hopefully everything is working properly.
 
Dec 13, 2010
123
Hake 32RK Red Bank
It sounds like you have two 24 V battery banks. one has a 24 V battery and the other two 12 V batteries in series to create a 24 V DC battery. Not sure why someone would do this since you sre bound to have circulating currents due to differing voltages When in parallel with the battery combiner.