Please Help Me Understand

[Capt.Bill11]

...and that maybe hard to achieve in some setups. At least it is on my boat. The fuse protection is after about 5' of 2/0 cable.


Jim
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I wouldn't sweat it. It's not like all those boats with out them are having issues because they don't have the inline fuses.

 

[what_barnacles]

BTW Alaskan Sea-Duction, if you are going to be making any changes to your setup, now would be a good time to ensure that you have a fuse in any Wire/cable that is connected to the house bank. Current ABYC standards call for a fuse to protect the wire within 7 inches of the battery and many older boats never had this.

I know its been said a million times but here's 1,000,001. The fuse is to protect the wire, not the load it's powering. Thats why it needs to be close to the source.

 

[Marin]

Why do you need two start batteries for a twin engine vessel?

Our 1973 cabin cruiser still has it's original battery system and selector switch system. The only change we have made it to change the two 8Ds for six 6vdc golf cart batteries, three of which fit in an 8D box. Four of the golf cart batteries are assigned house power duty, while the other pair is the start "battery."

We always run the boat with the Off-1-2-All battery switch in the 2 position, which is the house or 4 golf-cart battery position. This prevents the start battery (2 golf cart batteries) from being drawn down by house loads. The battery switch only serves to select the battery combination for house power.

However..... our vintage of GB is fitted with a battery combiner relay in the engine room which is activated whenever an engine start button is pushed. So regardless of the position of the battery selector switch, pushing a start button automatically connects both battery banks together to feed the starter motor. When the start button is released, the combiner relay opens.

This is a pretty nice setup and it saved us on at least one occasion when we had a cell in the earlier 8D start battery go bad.

 

[dhays]

...and that maybe hard to achieve in some setups. At least it is on my boat. The fuse protection is after about 5' of 2/0 cable.

Yup, it can be very hard/impossible to do on some refits. So, get the fuse as close as you can to the battery.

I ended up using terminal fuses from Blue Sea. I couldn't find a good spot to put the ANL fuses I was going to use initially so went with those instead. The fuses now sit right on top of the terminal. It was a bit of a tight fit vertically, but that wouldn't be a problem for most power boat setups I've seen.

 

[dhays]

This is a pretty nice setup and it saved us on at least one occasion when we had a cell in the earlier 8D start battery go bad.

Unless a cell goes really bad, then you don't want to parallel the good bank with the bad.

Out of curiosity, where did your alternator +out go?

 

[Marin]

Out of curiosity, where did your alternator +out go?

If by that you mean where did the ammeters for the engines go I assume they didn't indicate anything until after the engines started. But to be honest I don't recall watching them at the time so I don't know what they did.

I remember that when we tested the battery the bad cell was totally dead. However, I do not recall any abnormal instrument readings once the engines were running.

Back then we put the battery selector on both before starting engines. Not because this had any effect on which batteries sent power to the starters, but to have both alternators charging both batteries (this was when we still had the stock dual 8D setup).

With the battery selector on 1 or 2, the port alternator charges the port battery and the starboard alternator charges the starboard battery. Because we use the port battery as our house battery most of the time, this means that the port alternator recharges it and picks up the ongoing house load (including our plotters, radar, radios, etc.) while the starboard alternator is just along for the ride once it"s brought the starboard battery back up to charge.

So we would always switch the battery selector to Both before starting engines, which meant both alternators were sharing the load of charging both batteries and carrying the house/instrumentation load. So we'd see the same load on both ammeters. After engine shutdown we would move the battery selector back to 2, our house battery.

When we changed from the two 8Ds to the six 6vdc golf cart batteries, we doubled our house battery capacity so now we just leave the battery selector on 2 all the time and let the starboard alternator "coast" once it's brought the starboard battery's charge back up after engine starting. So we see our house/instrumentation load on the port ammeter and very little load on the starboard ammeter once the start "bank" has been brought back up to charge.

Don't know if that's what you were looking for with your question but that's the past and present situation with the setup.

 

[markpierce]

I'm pleased with the battery set-up as described in post #6. Don't see the value in having two equal battery banks in boats of our type.

 

[Tony B]

I have 3 battery banks. One Start Batt. the port eng, one Start Batt. for the Stbd engine and then the House Batts. I set my 2 battery switches for each engine appropriately. That is, Batt Sw 1 is set for Batt. 1 which will only start my port eng from Batt 1. The second battery switch, Batt Sw 2 is set for Batt 2 which will only start my Stbd eng. In case one of my batteries dies and fails to start its allocated engine, I have the option of setting that switch for that eng to the other battery position or set it for "Both". These switch's have nothing to do with the house batteries. These switches are strictly for starting batteries. I know this for 2 reasons, one it makes sense and the other is because when you buy a battery Isolator, there are several to choose from and your choice is based on your personal configuration.
I chose a Battery Isolator designed for 2 Engines, 2 Switches and 3 battery Banks. When you look at the schematic, it is complete including the re-wiring required for the 2 switches. My battery Isolator itself is easy to wire up. There are 2 inputs, one for each alternator and 3 outputs - one for each battery bank. With this configuration, I can run on one engine if I choose to and it will charge all 3 banks from that particular engines alternator.


This is not to say that you cant do it any way you want. If you have a single engine, you should only need one switch. Batt Sw. pos 1 can be for the start battery and switch position 2 can be the house batteries and obviously, the "Both" position (sometimes Labeled as "All) would combine all of your batteries.


I am not including my Gen Start Battery in the above. It has it's own battery and is not connected to any of the other circuitry. It doesn't need to be. If I run the generator, it will automatically power my 120V AC input Battery Charger which in turn will charge all of my battery banks except for the Gen Start Battery because the Gen Set charges it's own battery.