options for two battery setup

[Brylk1830]

I'm wondering what my options are for wiring in two batteries- one for starting and one for everything else. I'm aware of the battery selector switches but i'm unsure of how to wire them in..
I want to wire the batteries in parallel to maintain 12 volts but after looking at the wiring diagram posted in http://www.boatdesign.net/wiki/Elect...#Basic_Example
it looks like I would have to wire the switch in with the engine?
If anyone has any tips for wiring in a selector switch or if there is another way I can wire it to serve the same purpose it would be appreciated!
The main reason I need two batteries is so I can use a trolling motor.

[Landlubber]

Brylk1830,

If you wire two 12 VDC batteries is series you will have 24 VDC.
I think that you may need this for the trolling motor? We have to be careful here as you may not understand the basics.....lets start here first. Do you need 24/

[Brylk1830]

You're right, I changed it. I understand the difference there and am at least that far past the basics. I've actually done quite a bit of research on how to go about re-wiring my 16 ft fishing boat but the more I learn the more questions I have. I'm at the point now where I understand the basics but i'm unsure of how to incorporate the wiring from my engine into the equation.

My plan is to use two batteries like i stated above, and to run a wire from the pos of my deep cycle battery to a fuse panel and a wire from my neg to a neg bus bar. Using the bus bar and panel I plan to wire in my depth finder, lights, and radio.

The confusion sets in when it comes to wiring in gauges like the voltometer that need to be connected to the engine. Similarily, I'm unsure of how to wire equipment in that needs to be wired in with the ignition. Also, as stated above, the wiring of the selector switch. I thought I had it pretty well figured out until I glanced at the wiring diagram posted above and noticed the switch is tied into the engine electrical?

[murdomack]

I may be in a minority, but I have never used a selector switch for my batteries on any boats that I have owned. I have seperate isolation switches for each battery and on my present set up I also have a crossover positive through another isolating switch in case I need a jump start from my deep cycle services battery.
My crossover goes from the battery side of the services battery switch to the starter side of the engine switch, letting me isolate the flat battery and the services. This switch is always in the Off position without the key, unless needed, which has never happened for real so far, touch wood.
I run my mains charger leads to the battery terminal of each switch. I take my alternator charging lead to a low loss diode and run two wires direct to the battery positive terminals. I've never noticed that I lose any voltage with this diode.

If I don't switch on at the engine battery it will not start and if I don't switch on at the services battery my sounder etc are not working, so it keeps me right.
With a selector switch you probably have the two battery feeds and the outlets to both the engine and the services panel, but as I said, I've never used one. If you are not sure you could set up a test lamp or whatever before you start.

Wiring in gauges etc normally follows the engine wiring diagram and depends on what panel is used and sometimes there will be safety systems on the engine that are part of the wiring.
If you run through these diagrams from Westerbeke you will see some panels with gauges wired up and some simpler systems with only warning buzzers, but you should get the drift.
Can you get a diagram for your own particular engine? It may be easier for you.

http://www.westerbeke.com/technical/wiring_diagrams.cfm

[Brylk1830]

Thanks Murdomack, that was helpful and sounds like a reasonable way to seperate the two batteries. If it would be possible to see a simple wiring diagram of how your system works that would be extremely helpful. I understand that gist but i'm just trying to picture it all in my head.

[murdomack]

I've been reading your post #3 again. Is your engine an outboard? I was talking diesel inboards there. I've found another forum that might help. There is a wiring diagram on post #5 but read on down.
You could probably use a splitter diode system here instead of the voltage sensitive relay if you so wished, but the advantage of the relay is that your engine battery gets charged up first. Using a splitter diode would let you have isolating switches nearer the batteries, but I'm not sure that will be so important in a sixteen footer.
When you reach the end of the attached thread you will see that you might want to fit an isolating switch on your feed from battery #2, between the relay and the fusebox.

http://www.westernangler.com.au/foru..._1/key_/tm.htm

[murdomack]

Here's one showing a diode isolator set up. If you go this route search for a low loss diode. Some are expensive, but do a lot of searching and check how high your output voltage is as a cheaper one may do even if it drops the volts a little.

One advantage of going this way is that your batteries need never be in parallel and you can use an ordinary starting and a huge services battery. That's what I do.

For your fuse box take a seperate lead from the battery #2 positive, or from teminal 2 on the selector switch shown, with an isolating switch as near the battery as possible

http://forums.iboats.com/showthread.php?t=168270

[Brylk1830]

Thanks again Murdomack.. and btw my motor is a 97 4O hp 3 cylin Mercury outboard.
Ok, just to get this all straight, and correct me if I'm wrong, if I want to connect both batteries using a battery selector switch I would need to also use an isolater to make sure each battery gets charged independantly?
If this is right, in order to hook up the switch and the isolater I would ground the negative of each of my batteries to the engine block and the positives of each battery to the #1 and #2 slots on the selector switch. The selector switch would also be wired in with the starter and the isolater would be wired into the alternator to supply the charge.
If this is correct, how exactly do I ground the batteries to the engine block and where?
I think i'm almost there! Thanks again for the help.

[murdomack]

They say there's more than one way to skin a cat and that is also the case here. You have mentioned a selector switch before so I assume you have one already.
If not you do not necessarily need one, you could have a switch between the battery #1 and the starter with the wire from the alternator going to the battery terminal or to the battery side of the switch. If you do this you will need a jump lead to use battery #2 to start the engine.

Battery #2 and it's supply to the fuses needs to have its neg terminal connected to the engine earth point. To charge it from your alternator, you have two choices.
1. Split the feed before it gets to battery #1 with an isolator (diode) or an Integrator (I've never used one)
2. install a voltage sensitive relay (VSR), also called an automatic charging relay (ACR) between battery #1 pos and battery #2 pos.

You could use a selector switch on its own but you run the risk of flattening both batteries or of switching both off when the engine is running.

The best solution for you is either of the two systems shown previously, the selector switch with the isolator or the relay, it's your choice. If the output of the alternator is low the relay may be best as you do not want your starter battery not being topped up quickly, but if it is enough for the two batteries I like the diode isolator.
Regarding the earthing point, if the engine has been wired to a battery before it must have been used, so it should not be hard to find.

[murdomack]

I notice the earlier site I posted is down, here is some info on relays

http://bluesea.com/category/2

[Brylk1830]

I think i'm going to go down to the local West Marine retailer tommorow afternoon and ask a few more questions before I start buying the supplies.
Is there anyway to look up exactly what kind of charging capabilities my alternator has?

[murdomack]

Hi, I don't know anything much about outboards but I'm sure someone will step in. There has to be a charging source in there somewhere.
The wire that charges your battery will link into the red wire from your battery to the starter, probably at the starter solenoid post, if you follow this back it should lead to your alternator.
You could get information about your engine and alternator on the internet or from the engine maker.

[murdomack]

What I have found out is that some outboards have a charging coil and a rectifier instead of an alternator.
Before you go buying anything you should establish what you have and how many amps you have to play with.
You should still be able to add a second battery with a relay, although you may need to charge it up from the mains a lot.
I have also seen 50 amp alternators on the internet for a 97 Mercury 40hp. If you have one of these, or even 60% of that, then you will be able have the isolator system.

[FAST FRED]

I hate batt selector switches on an outboard as the brain box and alternator frequently will need to be replaced if the switch is turned off with the engine on.

My suggestion is to leave the engine system as it is and simply add an RV solenoid to charge the trolling batt .

The ignition switch in the run position sends current to trhe $17.00 solenoid which combines the batts together.

NO THINKING , you can loan the boat to your great grandmother , and no problems will occur.

FF

[Brylk1830]

Thanks for the tip Fred. How would I install RV solenoid to the engine? I could probably figure it out if I could find one for sale online lol but i'm guessing I would just wire off of my engines starter? Thanks again!