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

PQ290,

PERKO Inc. - Catalog - Battery Switches

This is the switch I have. It is essentially just a single unit that accomplishes the same purpose as two single-pole switches.

Thanks. Brad.
(937)545-8991

BBYSTWY,

So, where would one insert the charge lead(s)? It would appear that all this device does is bridge the two batteries when it's seeing a charge from the alternator. I don't think I'd want that. I've heard horror stories about people setting their switch to "both", to charge them both as they tooled around the lake, shutting down for a moment, then hitting the key, only to find out that one of the batteries had a dead short and had drawn the other one down with it, as the boat was running and supposedly charging both batteries. Like I said, I never run on "both". The last thing I'd think you'd want is a device that does just that automatically. Maybe I'm missing something....?

Thanks. Brad.
(937)545-8991

It never connects the two...just sees voltage from both and sends the current to whichever one needs it....it does not connect both batteries together...when there is no input voltage present it simply shuts off and there's no current going anywhere and the batteries are still isolated from each other.

Let`s start with this .

Maybe Im not understanding you question but with dual battery charger you don`t go thru any switches, the charger will have 2 leads one for each battery . It charges them individually , one could be 20% , the other 80%, it doesn`t matter .
The Seablue relay is only for "house stuff" batteries . It Isolates the house battery from starting batteries but once the engines are running (or trickle charger ) it will recharge the battery.
So if you plug in your huge mechanical dildo into the house battery and but by the time you`re done the dildo battery is dead because of the huge dildo amprage drain, you can still start the engines and on the way home the dildo battery will be recharged and ready for action again.
Hope this helps!:lolhit:

Dan you always have such a way with words :ernaehrung004: hahahaha

So one engine 2 batteries and turning them on to both is your concern?
I think I get it now. I have one starting battery per engine, one dildo battery.

Mine are seperated till I hit a switch on the dash that pulls in a relay and connects them both for starting, it`s a momentary switch so I don`t leave it on like a dummy

This thread took a weird turn. :cartman: Thanks everyone for the help.

Dan,

My interest is in charging while running. I have a dual battery charger that I plug in and hook up while the boat is closed up.

I don't have a "house" battery and an "engine" battery. I have two batteries that serve all functions, and a switch that allows me to manually decide which one is active, or both. I'd like to keep that setup, but wouldn't mind being able to charge both batteries while the engine is running without fear of a faulty battery draining the other one.

And, for the record.... We don't have a huge mechanical dildo. She just sits on the edge of the headrest ridge of the sundeck while the engine is running. Just sayin'..... :kiss:

Thanks. Brad.
(937)545-8991

https://cimg9.ibsrv.net/gimg/www.off...fec64c6003.gif

Dan,

Nope. I would be interested in charging both batteries while I tool down the lake with the switch on either 1 or 2. I have never left the switch on "both". In fact, the times I've had to set the switch as such, the first thing I do after starting the engine is set the switch back to either 1 or 2, depending on which one seemed stronger. I charge that one first, because it is less likely to be toast.

Thanks. Brad.
(937)545-8991

OH got ya .. that relay won`t accomplish that .
A solenoid/relay would accomplish that, just don`t make the switch monetary .

Quick search:

PQ290,

Glad we could help. This is what happens when you ask boys for men's advice. :ernaehrung004:

Thanks. Brad.
(937)545-8991

Or a true battery isolator/combiner would also serve that situation well.

Could also just run this relay on the charge wire like I was saying....take your alt. wire to the in on this and two new wires from the outs to each battery. That's pretty much what the diagram shows and it won't over charge the battery that is not in use but if that battery were to drop it would sense that and kick some power to it while still keeping it isolated from the in use battery....kinda what it's designed for.

Or what happens when you try to explain something to someone who won't read instructions :ernaehrung004:

BBYSTWY,

I am looking at the wiring diagram, and it does NOT show a connection from the alternator to the isolator. It shows everything BUT.

That's OK. We've already established that this isolator will not do what I would want it to do. I'll stick with what I've got until I can find something that will. It's not like it ain't working.

Thanks. Brad.
(937)545-8991

Great read on ACR’s:
https://marinehowto.com/automatic-charging-relays/

If you only have a few minutes, wait until you have more free time.

SB,

So, I see a project ahead of me. What's the output of the stock alternator on a Merc 496. '02, if that makes a difference.

Thanks. Brad.
(937)545-8991

I don’t know for sure, but Merc seems to love 55 amp alt’s over the years.

Brad, Okay, found a few spec pages. They (8.1/496’s) appear to have 65 amp alternators.

Brad i think what yor looking for is a diode battery isolator:
https://www.sbmar.com/articles/how-t...an-alternator/

everything on the boat stays the same but the output of alternator goes to the isolator and it can charge both batts at once and not back feed each other.

The OP mentioned a big stereo , but not much other information .with 2 engines running v belt alternators , that alternator can experience belt slip , and or insufficient output ,trying to recharge 2 batteries and run a truly big stereo.serp belt alt systems typically can offer up to 100 amps output even at medium engine speeds which helps alot. I see alot of failures and voltage drop issues from isolators and prefer to run manual switches to combine left and right battery and left and right combo to house bank and of course never wire main amp.power wires through perk or isolator

I did upgrade my alternators. It's been a while but I think they are rated at 90amps. Bought them from a shop that works only with 12volt stuff rebuilding, selling new, etc. He mentioned that the stock Merc alternators are lucky if they put out 35amps. I do run the separate belts still. I agree that the serpentine system is superior however I am tapped out this season with other purchases so that will have to wait. I ran a 1/0 wire for pos and neg connected directly to the batteries to the location for the amps. Pos goes through a 150 amp breaker (at the batteries) which I have "popped" a couple times. No surprise that I didn't do the math to size it properly. I'm pretty sure that even tho I tried to keep the charging systems separate, I think they are tied together all the time just like if I had the switch set to "combine".

Has anyone tried going to lithium? My only experience with them is in a golf cart but I saved 300lbs and tripled my range. I know bass boat guys are using them a lot for trolling motors and weight savings...

You trying to say an alternator has more turning resistance if it`s pulling a larger load?
Thats not how that works in my experience

Yup, it draws more power (hp) the higher the load.

I have one in my Harley. Spins motor over instant, rarely needs to be on the charger and weighs next to nothing. It feels like an empty battery case.

Where you pick that up, I may need one soon for my street glide.

A lot of the motorcycle wholesalers also have their "brand" as does Harley itself.

I have one from here: https://antigravitybatteries.com/
They also have ones with a restart feature where if dead it has a "reserve".

You've never hooked up a set of jumper cables to a dead car and noticed a decrease in idle speed on the charging car from the load of the dead car?

Energy isn't free, same principles apply whether a car alt or a gen set powering a hospital.
If there was a inverse of power requirements going from mechanical to electrical energy they'd power hospitals with 80 pound Hondas instead of 80,000 pound diesels.