Keeping stereo batteries separated
 

A few years ago I put a large stereo in the boat and thought that it would be a good idea to use the starboard alternator and batteries to work all of the electrical needs of the boat except for the stereo. I wanted both engines to start using the stbd batteries however I wanted the port alternator to only charge the port (stereo) batteries. I had to run a ground wire to connect the engines together so they could both would start off the same batteries. I noticed that both voltmeters would pulse with the stereo so obviously I didn't get something right. Maybe I need to remove the common ground and set the port side engine to start using the stereo batteries? My master battery switch is DPDT however it can combine the batteries too. Thanks for your comments.

You hook up the stereo to one battery only , that`s your "house battery"
You get an isolator that will charge the battery but will isolate it from the starting batteries so if you run it low it doesn`t matter.

https://cimg1.ibsrv.net/gimg/www.off...c1eeb9d5bf.jpg

PQ290,

This might be impertinent because I'm a single engine, but....

Personally, I run both batteries through the standard Perko switch. I also run the charging circuit though it, so I'm always charging the active battery. The only thing I have bypassing the switch is the lead that supports the memory in the stereo head unit. I never run on both batteries. I'm always on one or the other. The only time I have every had the switch set on "both" is when I had neglected to charge them and needed both to start the engine. I try to switch from one battery to the other each time we drop it in the water, as I do my pre-launch prep routine (checking oil, etc...) I also put both batteries on a trickle when we put it away for the weekend. I have seen many a twin-engine boat with four batteries and two switches, with isolated systems for each engine. I can't find fault in that setup.

Thanks. Brad.
(937)545-8991

This, and since most people’s engine run time is too short to fully charge the stereo battery back to 100%, put it on a charger when you get back.

SB,

OK. So, I like the idea of charging both batteries simultaneously, but I've always refrained because they will communicate, and a dead battery will drain the other one dead. I've considered installing diodes in the leads between where they would split and the two individual batteries, but never gotten to the point of figuring out the specifics.

SI-ACR Automatic Charging Relay - 12/24V DC 120A - Blue Sea Systems

Explain the diagram at the bottom to me. I see the two batteries, the isolator and the engine. What is the symbol at the top left? Charging? Stereo?

Thanks. Brad.
(937)545-8991

That's the switch I have. I bought it because it kept the batteries separated which is all I thought I would need. I tried to wire each system independently however as previously stated, I have something wrong. I normally run all batteries all the time. I do have the boat plugged in while on the lift. I had 2 batteries for the stereo and 2 for the "house batteries". Funny enough going back to my chine walk question where I was talking about shedding weight, I actually had a pair of I think group 27 for the house and group 31 for the stereo. Stereo batteries were a lot heavier and I'm sure not helping the chine walk issue. I'll get matching batteries this time. This charger won't work with AGM batteries will it?
https://cimg3.ibsrv.net/gimg/www.off...30ab33afc7.jpg
https://cimg6.ibsrv.net/gimg/www.off...a1af0251cd.jpg
https://cimg8.ibsrv.net/gimg/www.off...f6d850f814.jpg

Several different ACR set ups including the add a battery kit.
See here:
https://www.bluesea.com/products/cat...harging_Relays

SB,

I'm still not getting it.

990170140.pdf (d2pyqm2yd3fw2i.cloudfront.net)

The diagram seems to show one battery for starting and one for accessories. I wouldn't want that. It would seem the only purpose for this device is to ensure that both batteries are charging from the alternator. But what happens if the engine battery eats itself for whatever reason? If this is the only function of this device, I'll pass. I've got a very functionable system, aside from a lack of capacity for charging both batteries from alternator input.

Or is it that the switch is not accurately represented in the diagram? The Perko switch has two inputs, one for each battery, and one output that handles starting, accessory load and charging, with the switch serving to select which battery is in use or receiving charge current. If this device could be included in this setup, I might consider it.

Or would two inline diodes serve the desired purpose?

Thanks. Brad.
(937)545-8991

I have mine wired pretty much as shown in the diagram except....I have 2 single on/off switches for the batteries as they are smaller and I like the looks better plus it keeps the batteries actually isolated from each other. I wanted it this way to be able to run my stereo when off and not worry about draining the start battery. A normal 3 way switch would achieve this however through your charging circuit you still technically have them hooked together. I installed this device to allow totally independent charging on whichever battery needs the juice. As for starting if your start battery takes a dump I installed a third single on/off switch that's sole purpose is to tie the positives on both batteries together I.E. combining them. Fire it and you can turn the connection for the 2 off in normal operation and the device above allows for charging of the dead battery WITHOUT drawing the other down in the process which was my end goal.

Clear as mud right? hahaha

Just some more info...you could run the device above only in your charging system and leave all other switches/cables alone and basically achieve what I have. It will keep your batteries truly isolated from each other and it will only send charge current to a battery in need and you still have your 3 way switch to combine the batteries if needed....just a thought