Battery / switch system upgrade log

[ferret30]

I wanted to stop cluttering other people's threads and start my own to work out issues and track progress with an electrical system upgrade.

My setup currently consists of:

* Suzuki DF90
* Interstate Group 24 cranking battery (6 years old)
* Interstate Group 27 deep cycle battery (6 years old)
* Guest battery switch (A, A+B, B, off)

This type of switch has both house and motor output coming off a single terminal -- the house circuit is always connected directly to the motor. My goal is to upgrade this system to use isolated circuits, and to use identical batteries.

The new items I will be installing are:

* Interstate SRM-24 deep cycle/cranking battery (house)
* Interstate SRM-24 deep cycle/cranking battery (motor)
* Blue Sea Add-A-Battery (parallel switch + ACR)

By using group 24 batteries on both sides, I can fit them in the lazarette hatches without tilting them completely sideways like the group 27s. If I find that one group 24 is not sufficient for overnighting, I can always add a second (parallel) in the port lazarette, which is where the house battery is going anyway.

The switch is different from my existing one in that it only has off and on positions (for normal use at least). When off, both batteries are disconnected. When on, one battery is connected to the house circuit and the other is connected to the motor circuit. So there are 2 input studs and 2 output studs (the Guest switch had a common output). There is a third position (emergency!) that combines the batteries for starting -- same as the old switch.

If I just installed this switch, I'd have a problem... With isolated circuits, I'd never be charging the house battery unless I ran the motor with the combined switch setting. That's what the ACR is for. It is basically a link between the batteries that monitors voltage on either side. When one side has an elevated voltage (due to motor alternator output or battery charger), it connects the batteries and lets the other battery feed off the charge current. It is bi-directional, so a charger placed on either battery will ultimately charge both. The charger will isolate the batteries if a) the motor is being started, or b) the battery that would be receiving current has a voltage below some minimum amount.

[ferret30]

Now, before I can start I need to work out some details and do some shopping. My switch/ACR are coming in the mail today, and I'll be getting the batteries tomorrow once I get a chance to remove the old ones (for core trade in).

The negative cables will stay exactly the same as far as I can tell.

The positive outputs from both batteries will go to the 2 input terminals on the new switch.

The positive motor lead will connect to the motor output terminal on the switch.

All other wires that were previously connected to the old switch's common output will move to the house output terminal on the new switch.

Up to this point, there is no new cabling required. But when I install the ACR, I will need to choose appropriate cables and fuses for the wires from the ACR to the batteries. Also, I will need a few short runs of 16AWG with inline fuses for the ACR ground connection and the ACR start isolation connection to the ignition output (tells the ACR when the motor is cranking).

So, any ballpark ideas on what cables and fuses should be used to connect the batteries to the ACR? It seems to me that if 2 batteries with different voltages were just connected together (+ to +, - to -), the current would only be limited by the internal resistances of the batteries. Hmmm.

[ferret30]

By the way, here's a link to the installation manual / diagram for the setup:

http://bluesea.com/files/resources/instructions/990310020.pdf

[Wandering Sagebrush]

A group 27 fits nicely in the port lazarette. If you currently have condensation issues there, you might consider drilling some 1 inch holes in the bottom for ventilation.

Here's a link to a few photos. I stayed with the manual switch.

http://www.c-brats.com/modules.php?set_albumName=album713&op=modload&name=gallery&file=index&include=view_album.php

[ferret30]

[thataway]

As I understand the circuit--and I have not used this specific Blue Seas ACR--the only current you will have flowing to the ACR will be battery charging. The max of that will be the out put of the Suzuki 90. I doubt that you will be using an inverter/charger which will put out 130 amps.
I believe that the Suzuki puts out 27 amps (and you will probably not be using all of that--but figure 30 amps). So you want to figure the round trip from the ACR to the battery--and I would say that it is probably no more than 20 feet. You could get by with #12, but I would use #20.

Any place that you have the full load of the starter, then you would want want to use the same gauge as the engine or more--at least # 1 or 0.

[ferret30]

[thataway]

Mea culpa --that should have read #10 wire! Sorry. Yes I am using the # to relate to gauge. Yes, if the max charging current is going to be 30 amps, than a 30 amp fuse would be appropriate. The fuse is to protect the wire, and prevent overheating and causing a fire. But if you are to put a 40 amp charger on the circuit--then you definitely want to use #10 wire, and go with 40 amp fuse.

[ferret30]

My current charger is a Schumacher Ship N Shore Speed charger that does 15A/10A/2A with charge rate monitoring for deep cycle batteries. But I will install 10A anyway. Who knows what I'll be using for charging after our first active season on the boat.

I'm still waiting for the Add-A-Battery thing to come today, and I'll see what comes with it -- ideally it would come with the 16# wire for the ground and starter wires, but probably not!

[Jazzmanic]

[thataway]

Fuse for the larger source at the origin of the source--for example if you run a long wire to the battery charger, there should be a breaker at the battery charger and a fuse near the ACR. So in the Jazzmanic you fuse the charger at 10 amps (not sure if your charger will put out 10 amps to one battery and 5 to each of two batteries, or is limited to 5 amps per battery--but 10 amps for that circuit works well.

The only issue with an alternator is that you want to have adequate fusing for any spikes. You don't want to have an alternator feeding an open circuit--it will blow the diodes. Thus I would fuse the alternator to 50 or 60 amps. (actually put in a breaker, since that is more practical).

[Two Bears]

A tip on working in the lazarettes. The cover/ hinge comes off easily with the removal of the 8 screws holding it on. It gives you several more inches of opening to work in and around the batteries and to deal with the wires that seem to hide in hidden cracks.

Chuck

[ferret30]

I spoke to a Suzuki dealer that was fairly sure that the 2006 Suzuki DF90 had fuses on the alternator output, so I might not worry about that right now for my setup. It would be more convenient to have the fuses near all the switchgear, but I can add that stuff in later.

It seems like it wouldn't be an issue unless the switch was turned off while the motor was running, which would almost have to be intentional.

[thataway]

Yes, all of the outboards are fused by the alternator. However, you also want to fuse a wire which has current flowing near its terminus,

[ferret30]