Cruisers Forum

Join CruisersForum Today

Thread Tools Rate Thread Display Modes
Old 26-11-2015, 02:28   #1
Registered User

Join Date: Nov 2015
Posts: 84
Help - Battery System Advice Needed


We have recently purchased a 31 ft Mariner (Australian boat) flybridge cruiser. The boat is currently on the hardstand and needs a few bits and bobs doing to it.

The first one one is the electrical system is a mess. There are five batteries (why five?) Can anyone tell me me why it might have five?

The four batteries are connected in parallel with four batteries having their negative terminals connected to each other. Is that parallel?

Then the first battery is connected to other things but mainly the inverter.

The boat is located in Hastings in Victoria.

Would love some advice on what this all means. The boat is a 1985 model so I assume that things have changed a lot since it was built and would like to take this opportunity to improve the system while I have the credit card out and my wife is okay with burn marks on it.

Thanks in advance.

PS. Happy to employ someone in the area for some advice but keen to do most of the work myself so I can learn.

tronic72 is offline   Reply With Quote
Old 26-11-2015, 06:08   #2
Registered User
AnsleyS's Avatar

Join Date: May 2007
Location: Maine
Boat: Nicholson 39' ketch
Posts: 142
Re: Help - Battery System Advice Needed


It sounds like the boat has four house batteries wired together in parallel and a single starting battery. I am on the other side of the world so I can't help with local infomation but there are a lot of folks with experience on this forum when you have specific questions.

Sent from my SM-T810 using Cruisers Sailing Forum mobile app

AnsleyS is offline   Reply With Quote
Old 26-11-2015, 06:29   #3
Registered User
S/V Illusion's Avatar

Join Date: Oct 2007
Location: Lakewood Ranch, FLORIDA
Boat: Alden 50, Sarasota, Florida
Posts: 1,731
Re: Help - Battery System Advice Needed

A 'starting ' battery would not be connected to the inverter.

What you are looking at sounds like a mess. Answering specific questions might help you in the short term but you would be better served by reading one of many marine electrical system books, some of which are available free via Internet such as the Ample Power Primer.
S/V Illusion is offline   Reply With Quote
Old 26-11-2015, 07:51   #4
Registered User

Join Date: Aug 2013
Location: Miami Beach
Boat: Catalina C34
Posts: 136
Re: Help - Battery System Advice Needed

If the positive terminals of the four batteries are connected to one another and the negative terminals are connected to one another, then the four batteries are connected in parallel. This is probably the "house" bank which is used to power the various loads on the boat; e.g. lights, instruments, radio and the inverter for 120 volt devices. Wiring four batteries in parallel creates a bank with the voltage of one battery and four times the capacity of of a single battery. Therefore the bank will serve loads four times longer than a single battery will, provided you have the charging capacity (alternator, charger, solar, wind) to fully charge the bank.

The fifth, single battery is probably a "starting" battery. The only load connected to the starting battery should be the engine starter. The starting battery is a backup that allows the engine to be started in the event that the house bank becomes fully discharged.
jkishel is offline   Reply With Quote
Old 27-11-2015, 04:30   #5
Registered User

Join Date: Nov 2015
Posts: 84
Thumbs up Re: Help - Battery System Advice Needed


Thanks for all of your feedback so far.

My next issue is that the "connector" cables are of different lengths and grades. Some really thick and others thinner. I want to standardise them. The stats of the batteries in the house bank are as follows: 4 x 4 x 12 Volt Batteries (730 CCA, 875 MCA, RC 180, AH 100 ) = 12 Volt 400 AH.

What size cables should I use to connect them? (from a negative to next batteries negative terminal) I was thinking 50mm but they seem hard to come by. I can source 30cm 35mm cables with 8mm holes. Are these adequate or should I try for 50mm or even bigger?

Thanks again.
tronic72 is offline   Reply With Quote
Old 27-11-2015, 05:11   #6
Registered User

Join Date: Mar 2012
Location: Aus
Boat: Owner Builder
Posts: 115
Re: Help - Battery System Advice Needed

35mm cables should be ample unless you have exceptionally long runs with high amp draw (eg. Anchor winch) in which case 50mm would be the answer.
BriaF is offline   Reply With Quote
Old 27-11-2015, 05:24   #7
Registered User

Join Date: Aug 2013
Location: Miami Beach
Boat: Catalina C34
Posts: 136
Re: Help - Battery System Advice Needed

First, make sure you really need all four house batteries. Prepare an energy budget and make sure that your system has the capacity to recharge the bank.

The battery cables should be sized to handle the current drawn by the starter motor. This is a function of the engine displacement and the round trip distance between the battery bank and the starter motor (google "boat conductor sizing"). Because the starter current only lasts a few seconds, you can get by with cables a size or two smaller than the calculated size. If your boat still has the original cables from the 1980's, they are probably small by today's standards. If you upsize the cables, be sure there is room for the larger cables in any conduits, penetrations, etc. Use the same cable size to interconnect the house batteries. Make sure the lugs match the battery bolts. Replace any wing nuts with hex nuts. Connect the positive output cable to the positive terminal of one of the end batteries and connect the negative output cable to the negative terminal of the battery at the opposite end of the bank.

Also, if there is none now, add overcurrent protection. A fuse and holder are a lot cheaper than a boat fire.
jkishel is offline   Reply With Quote
Old 27-11-2015, 08:41   #8
Registered User

Join Date: Sep 2014
Posts: 112
Re: Help - Battery System Advice Needed

Read, read, read then draw a schematic of your supply and the loads. Check the age and condition of your existing batteries. My guess is that at least a couple of the batteries are ready for replacement.
AlwaysFORSAIL is offline   Reply With Quote
Old 27-11-2015, 09:51   #9
Senior Cruiser

Cruisers Forum Supporter

Join Date: Mar 2014
Location: Anacortes
Boat: previous - Whitby 42 new - Goldenwave 44
Posts: 1,769
Re: Help - Battery System Advice Needed

Your situation with your wiring is pretty common actually. Strongly recommend that you diagram/sketch out your current wiring, paying particular attention to all the larger cables that go to/from the batteries, but also include any battery switches (noting which terminal each and every wire goes to on the back of the switches), and also include any smaller wires off of the batteries. Note any fuses or circuit breakers you find in your inspection. I would note the color and size of each cable/wire and any place where the wires are terminated, even if one wire goes to a terminal post and only one other wire goes from that to somewhere else.

Look also for any places where wire size changes from where it started to where it ends (and color too). Do the same for both the positive and the negative wires, in the same detail. You may want to pull out your hair in frustration in doing this so you may want to wear a hat.

It will be easy to make a mistake when a wire or multiple wires go through a bulkhead or go underneath something, anywhere where you cannot actually see the wires the whole distance. I do this professionally and it is VERY easy to make an incorrect assumption, sometimes even assuming that because you trace one wire under something and find a wire coming out where you think it goes, and it is actually a completely different wire that came from somewhere else.

You do all this to learn how you current system is wired. You will learn what happens when you turn a battery switch to any position (a common confusion with all owners - even professionals - who get a new boat). This is critical to understand what happens, or should happen, when a switch or switches is turned to a specific setting.

You should draw this out, and keep the drawing/diagram/sketch as a prized possession, worth its weight in gold. You don't want to have to do it again and it will save you literally hundreds of hours later in troubleshooting issues or rewiring. I do this for my boats and I do it for all my customers. I get very angry when I come back to a customer's (or friend's) boat and they have lost this critical document. I then have to charge them to redo the parts I need to work on their problems. Trust me, you will appreciate doing this later. Why do I go on about this - because it is something that people either don't understand how important it is, or, they think they can remember it while they do it. I haven't met anyone that can keep all this straight without a drawing.

This will be your starting point to understand your wiring. You can do selected other systems (electronics, DC panel, AC panel, fuses, bilge pumps, etc.) later as needed.

Concerning your current setup: you do have four 100 amp-hour batteries in parallel per your description. This adds the power of each battery to all the others so you in effect have 400 amp-hours of batteries. Amp-hours are a measure of the capacity of "deep cycle" batteries and this setup is typically the "house" battery bank that is the primary system to power everything on your boat. Some people do not have a "start" battery but use the "house" bank to start the engine and run the rest of the boats electrical systems.

Your one separate battery could either be a start battery, or, it could be a dedicated battery for your inverter. I wouldn't recommend doing it that way but I have seen it several times. Doing your complete inspection and drawing of all the wiring will show you what this separate battery or the house bank are used for. If the one battery goes to a battery switch post and the other house bank also goes to the same switch (1-2-both/all) switch it is so you can use the one battery to start your battery or to use the house bank, or both, to start the motor or other systems. If you have two switches, one of them would usually have it's output (the common "C" terminal) go to the starter and the other would go to your DC panel and/or other uses.

One of the key things you will find out is how the batteries are charged on your boat. If you have an AC shore power charger, the DC output could go to the back of a battery switch, direct to one or both of the battery banks, or to somewhere else that then goes to the batteries. But the output has to go to the batteries somehow and you want to figure this out. Same for the alternator on your motor.

What you will want to do with all this is to trace how the electricity from the batteries gets to everything that needs power, and how the power if put back in to the batteries. One of the most important things to know on your boat.

A common mistake (that I make when I get in a hurry) is to assume I have traced a wire correctly. The only way to absolutely be sure is to run your finger the entire length of a cable if it is in a bundle of similar wires. Often they are intertwined and it is easy to make a mistake. I often will pull on the wires from one side of a bulkhead or in a bundle and put my fingers on the other side or end and see which wire moves. It is often not what you think by just looking, but sometimes you can't figure it out any other way.

My apologies if this is too basic and you already know all this but from your comments it may be helpful. You will come up with additional questions as to why something is wired how it is and how it should be wired.

A basic electrical multi-meter (volt, ohm, amp meters in one) will be very useful in all this and in the future. For instance, I often will measure the voltage on a terminal and then get the voltage on each battery bank. If the battery bank voltages are different then I can tell from that which battery is connected to that terminal (at that time since it may be switched). If both batteries are exactly the same voltage, then it indicates that all the batteries are connected somewhere (via a battery switch usually). If so you can turn the switch off or to another setting and put your voltmeter leads on the rear terminals and determine which post is connected to each battery. Different banks will almost always have different voltages (but you have to let them rest unconnected for an hour or more sometimes to let them settle to their individual specific voltages).

If you are new to batteries and DC electrical systems, this may seem like Greek to you. But with experience, starting with tracing the wiring, it will start to make more sense. Some people pick it up naturally and some people do not, ever. Just the way people are "wired" differently, like for math or poetry or singing or whatever. Just the way we are. So don't beat yourself up if it hard and be happy if it comes natural.

May seem overwhelming but just dive in. Good luck and have as much fun as you can. It can take several hours or even days to do this sometimes.
exMaggieDrum is offline   Reply With Quote
Old 27-11-2015, 10:13   #10
Registered User
Stu Jackson's Avatar

Join Date: Jan 2011
Location: Cowichan Bay, BC (Maple Bay Marina)
Posts: 6,618
Re: Help - Battery System Advice Needed

maggie's right. Discussing electrical stuff at this level without a wiring diagram is not something that is useful.

Here are some examples:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings | Forums

They come from this thread which has a ton more electrical discussion links:

Electrical Systems 101 Electrical Systems 101

Good luck.
Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
Stu Jackson is offline   Reply With Quote
Old 27-11-2015, 10:43   #11
Registered User

Join Date: Oct 2013
Boat: Alberg 35 1966
Posts: 23
Re: Help - Battery System Advice Needed

Hello Tronic72,
I'd suggest taking this opportunity to do some rationalization and redesign of your system. Several issues you mention will bite you eventually otherwise. Also take the time to read through some of the basic books others have mentioned.
Firstly: 1)Add up all the Ah of all loads. Then group them logically and spread them over 2 banks. Don't include the starter load, it is a separate one, separate circuit.
2) Get a smart ACR such as BlueSea 7601. It is basic but very helpful. This will automatically always charge your starter battery first before charging the house banks.
3) Then rewire the distribution panel to somewhat evenly share the loads between two banks (ie, between 2 pairs of your 4 batteries). You will have to install if not already there, a 1,2,Both selector switch to manually select which bank to charge.
This could be a non trivial exercise, maybe hire some help. If you do, show him this post and ask him to flesh it out for you, I have omitted a bunch of stuff for brevity.

Issues that will bite sooner or later.
a) Issue: Running multiple batteries in parallel rapidly becomes a bad idea as the batteries age. The most common failure mode being unevenly aging cells, one or more eventually becoming more or less shorted internally. This will cause its parallel mates to discharge into the bad one. Fix: Use an SG (specific gravity) bulb to test every cell and record the readings. Then fully charge each battery using a smart charger, remeasure SGs and toss any battery with a low SG cell. You want to end up with 2 pairs of like batteries.

Oh, before you start, be sure not to mix automotive and deep cycle batteries in a pair. Closely monitor the SG of any house battery that is not a deep cycle, and be prepared top toss it, it will fail under repeated deep discharges, and bring down its mate.

c) Never connect any other load to the starter battery. Use the correct battery size specified. Never allow it to be fully discharged, each full discharge will subtract from its lifespan. Size the cables to be correct for your engine and the length of the round trip run. Do not assume the originals are correct. Be sure all terminals are clean, bright, tight. Do the same SG test as above.

d) There is no need to use starter size cables for the rest of the system other than an electric winch.

e) Take your added Ah total and compare it too the alternator capacity (if you have an ACR, exclude the starter battery charge load). Caution in overloading the alternator and its regulator with your 4 batteries. Check for correct wire size from the alternator output round trip, and for good terminal connections.

f) Investigate why the inverter was on the starter battery. Could be b/c the house batteries were chronically low. Now, the issue is most likely the starter battery has been repeatedly discharged and is now suspect. These are designed to "float" on the charging system and never be discharged. Buying a new one could be the best money you spent at this stage. Every time you leave the dock, it is your ticket home.

I hope some of this is helpful, enjoy!
phstol is offline   Reply With Quote
Old 27-11-2015, 13:01   #12
Registered User

Join Date: Nov 2015
Posts: 84
Re: Help - Battery System Advice Needed

This is awesome. Thanks very much for all your posts. I'm reading and re-reading as suggested. Visiting the boat today and will take my computer and build a map of the system.

I have a couple of questions based on some responses:

1. Should I ditch the parallel house bank? I now have 5 new marine batteries with specs as follows (730 CCA, 875 MCA, RC 180, AH 100 ).

2. I was recommended to read but I didn't see any specific texts. Can you recommend one that is simple?

If my new batteries are okay in a 4 X parallel bank I will design the system with them as a starting point.

Thanks again for all the great responses.
tronic72 is offline   Reply With Quote
Old 27-11-2015, 13:15   #13
Registered User

Join Date: Nov 2015
Posts: 84
Re: Help - Battery System Advice Needed

Oh, and one more question. The boat has two motors. Should I have two separate starting batteries or will the one single one work for both by use or the 1.2,both switches?

And on that topic. There are there are three of those switches two appear to be motors and one for the inventor. Is this normal and suitable ?

Thanks again..
tronic72 is offline   Reply With Quote
Old 27-11-2015, 13:20   #14
Registered User

Join Date: Nov 2015
Posts: 84
Re: Help - Battery System Advice Needed

And based on some of the above links I found this great blog on the 1,2,both,off switches.

1/BOTH/2/OFF Switches Thoughts & Musings | Forums

Great read for a newbie!!!! Kudos to the author. ����
tronic72 is offline   Reply With Quote
Old 27-11-2015, 13:23   #15
Registered User

Join Date: Jun 2013
Location: Australia
Boat: Swanson
Posts: 62
Re: Help - Battery System Advice Needed

Hi Tronic, my ex boat is still in Hastings, but I am in Qld now. My suggestion is first things first. Is it any problem with electrical functions. Somethings is not working?
Re - organising is last thing. If one of your bat. is weak ...whole system is discharging through weak bat. Can you find which one?. Regardless of different bat. capacity, system must hold the charge. Best cruising time in Westernport is now, you don't wont to spoil it. After Easter, time to dig in. Happy cruising , watch the huge breakers passing Phillip Island , I had 6 m high, they can be nasty.

Tikka is offline   Reply With Quote


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Need help on a new battery/charger/solar system... Brannon132 Electrical: Batteries, Generators & Solar 0 19-06-2015 14:38
Help needed to choose weather info system rfnk Weather | Gear, Reports and Resources 8 02-03-2013 08:38
Tax Advice Needed - Sailing Advice Given mparent General Sailing Forum 0 12-07-2010 07:16
Expert Advice Needed on Budget Cruising Boat - Help ! lutz33 Monohull Sailboats 20 01-06-2010 00:18
Help Needed on Refrigeration System - Where to Buy on Internet - or Repair ? Ram Plumbing Systems and Fixtures 27 05-05-2010 07:53

Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 14:53.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.