MK ll Battery wiring

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Jack Hutteball

I am finally changing my 2 - 4D batteries for 4 - 6 volt batteries and adding a separate starting battery as many have done.  I think I have had great use of the original batteries for the last 10 years, thanks to the info I read on this board about installing a smart charger early on.  Thanks guys :clap  I am keeping it simple by putting the start battery on battery 1 and the house bank on 2.  I have one question.

The batterys on my 2001 MKll, from the positive terminal each have a wire to the battery switch poles 1 and 2, and each have a wire to the battery charger.  There is a third red #14 wire from each positive post to somewhere I have not been able to determine.  They do not show up on the wiring diagrams in the owners manual.  I am the original owner so it was nothing added by a PO. 

Anyone with a MKll know what these wires serve?  Not a big deal really as I will reconnect one to the start battery and one to the new 4 battery house bank, but I would like to know what they do. :donno:

Jack
Jack and Ruth Hutteball
Mariah lll, #1555, 2001
Anacortes, Washington

Michael Shaner

Jack...wild guesses from a MK1 owner until you chase it down...alternator? Battery monitor? ACR?
Michael & Alison Shaner

Roc

#2
Jack,
That third wire may be going to the volt meter on the panel.  There should be a red wire from each battery positive, one going to 1 on the volt meter rocker switch, the other going to #2.  I put 4 golf cart batteries recently and followed the set up that my friend (C350) installed on his boat since he bought it new (about 6 years now).  I banked the golf cart batteries to battery switch #1.  I put the "reserve" battery (I'm calling it reserve because I have things wired to do everything with the house bank, and only use the reserve battery in an emergency) on switch #2.  I kept all OEM wiring intact.  The battery charger (Xantrex True Charge 40amp) has one pos to one set of golf carts, the other pos to the other set.  The golf cart house bank gets charged from the alternator (high output).  The reserve battery gets charged via a Xantrex True Charge 10 amp when plugged into shore power.  If cruising for a week or so, that battery will have enough power to start the engine (think of leaving your car in the driveway for a week, it will still start after being idle for a week).  I did buy a different battery switch.  Mine (and probably yours too) goes from 1-all-2-off (Perko).  In other words, to go from 1 to 2, you need to pass through "all" thus tying the batteries together.  I bought a Blue Seas Systems switch that rotates both ways in that you can to from 1 to off then 2, totally keeping the batteries separate in case the house bank is bad and you don't want to tie in a bad house bank with a good reserve battery for that split second.  I like this because it's a simple set up and keeps both banks totally separate.
Roc - "Sea Life" 2000 MKII #1477.  Annapolis, MD

Jack Hutteball

Roc,
I guess if I disconnect that third wire and it does go to the volt meter on the panel, I would not see any voltage there.  Will try that.  I am doing what you did, but do  not have a separate charger, so will just keep my Xantrex 20 tru charger with one lead on the new house bank and one lead on the reserve/start.
Jack and Ruth Hutteball
Mariah lll, #1555, 2001
Anacortes, Washington

Stu Jackson

#4
Jack, if they are indeed small wires going from the battery banks to the voltmeter, consider replacing or abandoning those small wires, and just wiring the voltmeter to the back of the 1 and 2 posts on the 1-2-B switch (or whatever switches you may have for selecting your battery banks).  The #4 wiring from the batteries to the switch will have a lot less voltage drop than the smaller wires.  Happy detective work!   :D
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."

Peter Taylor

Jack
They may go to the bilge pump to provide constant power independent of the switches. Thats what the extra wire does on my C36.

Peter Taylor
Altair C36 Mk11
Melbourne Australia
Peter Taylor
Altair
2005 C36 Mk 11
Melbourne Australia

Roc

My boat came wired from Catalina with the bilge pump wired to the common post on the battery selector switch, and not to the battery itself. 

The reason why I didn't connect both batteries (house bank made up of 6 volt golf carts and new "reserve" battery) to the Xantrex 40 amp charger is because the charger doesn't charge both batteries separately, as the instruction manual kind of says.  My friend investigated this (he has same charger) and talked to Xantrex and found that the charger is not really a true independent charger (after prodding them about it and got them to admit it). I forget all the specifics about this but it has something to do with how the charger treats having one battery vs two batteries connected to it and how it distributes the charging to them all.  The newer chargers are true independent chargers, in that each battery is read independently and charged with the exact profile that's needed.  So that's why I bought a Xantrex 10 amp and have that wired solely to the reserve battery and the 40 amp wired to the golf carts (a positive lead going to each positive lead of the golf carts).
Roc - "Sea Life" 2000 MKII #1477.  Annapolis, MD

Jack Hutteball

Interesting.  So if my reserve battery is fully charged and the house bank is down a quarter, the house bank might not see much charging or the reserve might tend to get an overcharge?  With my 2 - 4Ds one bank was always down more than the other when I would return from a weekend and they both got charged.  Not sure how efficient it was as they were always ready for the next weekend.  Maybe the best solution is adding an echo charger between the house and start banks as Stu and others have done rather than adding a separate charger.  Cost about the same?
Jack and Ruth Hutteball
Mariah lll, #1555, 2001
Anacortes, Washington

Roc

Jack,
The True Charge 40 amp doesn't sense each battery independently, although the hook up can have more than one battery.  It sets the voltage based on the lowest battery and goes through the charge cycle with the same format for both batteries.  The instruction manual leads you to believe that's not the case, that it's an independent charger for EACH battery.  Not what my friend found out after talking to Xantrex Tech Service.  The new Xantrex chargers have been redesigned to really give you independent charging, and each battery gets what it needs. 

About cost, that wasn't the factor that made me go this route.  It was the simplicity of the set up, and the fact that BOTH batteries will always be separate and the only way they can be connected is if YOU put the selector switch to BOTH.  An echo charger will combine them.  My thinking is I always want a battery to start my engine and I don't want that battery to be compromised by combining it with a dead, shorted, very run down, etc. house bank.  At first I thought I needed to charge my reserve battery with the engine, whenever it was running (hence with some kind of echo charger), but if it's fully charged via shore power, and it sits idle for a week or so during a cruise, I feel confident it will be ready to fire up the engine if necessary (my car parked in the driveway senario).  Actually, I originally bought an echo charger to make the hook up like what is seen on this site, but then after talking to my friend (an EE) and thinking about what my goal is....which is a way to start my engine in an emergency, and not really a battery to be used just for starting, I returned the echo charger and bought the 10 amp charger.  The 4 golf carts give you about 440 amp hours which is pretty big, considering I used to use one of the 4Ds to start the engine and use it as a house bank (I used to change which battery I was using after a full charge at shore power, in order to try to use both 4Ds consistently and equally).  One 4D is less than half the amp hours of the 4 golf cart batteries.
Roc - "Sea Life" 2000 MKII #1477.  Annapolis, MD

Jack Hutteball

Roc,
Seems like I will "cook" the reserve battery if I just connect both banks up to the same charger while needing to put a lot back into the house bank, so will probably go your route.

Stu,
Regarding the 3rd wire from each battery bank, I determined they do in fact connect to the volt meter on the main panel.  I wonder why they were run clear to the other side of the boat when the 12B switch is just below the panel.  The wiring diagram does show the wires from the volt meter going to the 12B switch, which is why I was confused about the wiring.

Jack
Jack and Ruth Hutteball
Mariah lll, #1555, 2001
Anacortes, Washington

Roc

#10
Jack,
I don't think you'll 'cook' the reserve battery.  It's just that you think the charger is looking at both battery banks independently and charging them at a profile that fits the state they are each in.  But actually the charge is shared among both banks and the profile is suited for the one needing the most charge.  You think with this charger is like having two chargers in one, but it really isn't.  The newer Xantrex chargers do that, but our model doesn't truly to that.

You could dump the True Charge 40 amp charger and get the newer Xantrex model, or just get a 10 amp for the reserve.  I think it's cheaper just to get the 10 amp.
Roc - "Sea Life" 2000 MKII #1477.  Annapolis, MD

tonywright

At least one of those wires probably also connects to the stereo system, so that it will keep its station memory as well as the cd changer memory if you have one installed.

Tony
Tony Wright
#1657 2003 34 MKII  "Vagabond"
Nepean Sailing Club, Ottawa, Canada