Second Battery

[Souellette]

Any advice on the easiest way to add a second battery to a Catalina 275? I've installed a chartplotter and VHF radio and have plans for more stuff. I'd like a dedicated house battery for these items so I don't run the starter battery down. I'm not the most versed in marine electronics so go easy on me

I've been thinking about the add-a-battery kit. There's plenty of room in the starboard settee to put a second battery but the feed to the circuit panel for the house electronics seems to be off the switch near the engine.

 

[Davidasailor26]

What size battery do you currently have (e.g. group 24, 27, 31)? If what you have is large enough for your house loads on its own you could consider adding something small as a second battery and just using that for the engine. You could use an ACR to combine the batteries when charging and disconnect them otherwise.

 

[Souellette]

Here's the link to the battery. It's a group 24. Thanks.

 

[Souellette]

I like the idea of the ACR. Was referring to this diagram from Blue Sea Systems. Not sure where the current feed to the distribution panel is located right now, though. Obviously this is showing an outboard motor and the existing switch is not shown but you get the idea.

 

[Davidasailor26]

That diagram is pretty much the right idea. The group 24 you have is better suited for the engine than house loads, so you’d probably want a larger true deep cycle battery for the house. Make up an energy budget and see how many amp hours you’ll routinely need, then roughly double that to find the minimum battery size you’ll want.

 

[Joe]

This book is a must for sailboat owners.

It's very easy to read and understand. No matter which way you go with adding a battery, you should have a guide to 12 volt systems.
A sailboat's 12 volt electrical systems are relatively simple to understand, diagnose and repair. Things like energy budgets for your boat are explained in detail.
As far as a second battery, for sure. I have 2 group 27's with a hard wired smart charger. I highly recommend the batteries be identical in size and output.... much much easier to manage. My system has a selector switch (off-1-both-2) for house and one for the engine. There's a couple ways to wire this up, with one or two switches, and this book will show you how. Mine is set up to use either battery, or both, for either function. If you start adding refridgeration or AC or a windlass that'll jack up the load big time. That's why you want a reference like this to explain how to manage all that.

 

[SycloneDriver]

I much prefer to use separate batteries for start and house. Use two battery switches and some form of battery isolator on the alternator or an ACR.

 

[dlochner]

Separating the house and start/reserve batteries is a good idea. The Blue Sea Add a Battery Kit is a good place to start.

 

[Souellette]

I bought the Add-a-Battery kit and I have a solid plan to wire everything up. The ACR has a connection for a start/isolation wire that will temporarily disconnect the starter and house batteries when starting, thereby eliminating voltage sags on the house battery that would cause my electronics to reboot.

I believe this start/isolation wire gets connected to the start relay on the wiring harness behind the control panel. Of course, I have no idea which relay and where to connect the wire. Does anyone know the answer to this question?

 

[MikeHoncho]

It was my understanding that the intent for the circuit was to combine the two in the event that your starter battery gets drained and was to be wired with a temp on switch. I guess it would work for that also but I would have all of my electronics in the house bank and the starter only on the start battery which would eliminate the need as you described it.

 

[dlochner]

I believe this start/isolation wire gets connected to the start relay on the wiring harness behind the control panel. Of course, I have no idea which relay and where to connect the wire. Does anyone know the answer to this question?

it attaches to the wire that activates the solenoid on the starter. When current is applied to this wire it activates the disconnect on the ACR, once the engine starts and the starter is disengaged, the ACR resumes normal functioning. Without knowing what kind of engine is in the boat and how the starting circuit is wired, it is difficult for anyone to be more specific and the place to connect the starter interrupt wiring.

It was my understanding that the intent for the circuit was to combine the two in the event that your starter battery gets drained and was to be wired with a temp on switch. I guess it would work for that also but I would have all of my electronics in the house bank and the starter only on the start battery which would eliminate the need as you described it.

Pretty much this is correct. The ACR allows the start battery to be charged from the house battery and prevents one battery for over discharging into the other. The Add A Battery kit adds a CP2 switch which has three positions, Off, On for each of 2 circuits (house and start) independently, and combined or paralleled.

The feature of the ACR that @Souellette is inquiring about disables the ACR while starting. What can happen while starting is the start battery voltage drops quite a bit, the ACR sees this as the battery needing charging and allows a high discharge rate from the house bank. In a smallish house bank this can cause a significant drop in the house bank voltage which causes problems with electronics. Once the starter stops, there can be a voltage spike which can also cause havoc with the electronics.

 

[MikeHoncho]

The directions on my said it won’t close until it sees a certain volt value and then it will take seconds to do so. I m thinking this means that it wind close (complete circuit) until it is running and the alt is excited.. Maybe I have a different one.

 

[Davidasailor26]

The directions on my said it won’t close until it sees a certain volt value and then it will take seconds to do so. I m thinking this means that it wind close (complete circuit) until it is running and the alt is excited.. Maybe I have a different one.

The ACR could be closed before starting the engine if another charge source like shore power or solar are charging or floating the batteries. A common ACR profile is to open when the voltage drops below 12.75V for 30 seconds or 12.35V for 10 seconds. So if you’re, for example, charging with solar and floating at 13.3V, then start the engine, the short duration voltage sag could bring the house down enough to reboot electronics before the ACR would open. The Start Interrupt prevents the house bank from sagging in that situation.

 

[drewlamparello]

I have two Group 27s installed. As you know the 275 came with just one forward of the sink below the seat. It also came with a single battery switch. I added my second in the starboard lazarette right behind the switch. I changed the switch to a two battery switch so that I could select Off, Battery 1, All or Battery 2. This meant my wires simply needed to go from the new battery to the second position on the new switch, and new battery to the Engine ground. Simplest and most cost effective option IMO. Given the size and price of the needed wire its best to minimize the length of wire you need to have made up