Back to the main site

Battery Wiring Question

kaydano

kaydano

Well-Known Member
Messages
4,310
Reaction score
2,213
Which wire on the positive terminal of the battery is the charging current from the alternator coming from? Does it share the same wire that goes from the battery to the starter (the large #4 gauge wire) or does the charging current return from the alternator to the battery via the smaller wire (#10 or so, not sure)?

I'm pretty sure the charging current returns to the battery via the large conductor, but I'm thinking about installing a second battery and an isolator and many online wiring diagrams show a separate cable coming back to the battery from the alternator (separate from the starting cable). My battery only has two cables attached to the positive terminal (also two to the negative too, with one being much smaller than the other).

I also assume the smaller wire runs everything else on the boat (lights, CD, depth, etc). Is this correct? Anyone know?
 
I looked at my Honda wiring diagram and the alternator "hot" wire goes to the starter and charges through the battery cable. it should be a piece of cake to do the 2 battery setup.
 
Kaydano,

I just did this project a few months back. You'll have a hot/positive 4awg which goes directly to the motor. The smaller 6-8awg runs to your starter/helm (house) for other electronics.
 
Thanks for the comments and checking. My boat is at the marina, so I couldn't go check under the cowl to see if the alternator and starter are wired together until the next time I'm down there.

Spin - What isolator or combiner did you buy? Seeing a lot of mixed reviews on different models online... Not sure what to get.
 
I installed the Blue Sea system. Its the switch and isolator. So far, so good. I've been running my stereo and amp non stop while anchored and flip the switch to crank up and get home. It was super easy to install. Trust me, I'd much rather pay someone than do difficult projects myself!
 
As in the boat would not start.
 
I thinking the starter soleniod/relay circuit operates off the starter battery, but I'm not sure.

In other words, if the smaller house wire off the battery was disconnected (for example) would the motor still start?
 
That's the one I installed. I read great reviews on it.

The best part about this system is that you connect the engine positive to the starting lead and your accessories to the house lead. Everything is running off the battery you want it to use. The switch will allow you to cut power to everything when you are done, so no need to worry about leaving anything on and if your starting battery gets too low for some reason, you can combine them for a short boost to get it turned over.

Otherwise, just get a selector switch. 1,2, &1/2. Connect engine positive and house to the common post, run a short positive to each battery from the 1 & 2 posts, then connect engine ground to one battery and jump connect both batteries' grounds. Done. Select 1 for cranking and 2 for when you are just listening to tunes. That way you can leave the boat on 2 for the valet service (as long as you get a deep cycle that has enough cranking amps to turn over your motor). If they fail to turn the switch off, only the house battery will die. Your cranking battery will still be fresh and will start the engine so you can recharge the house battery from the alternator next time you are out.
 
Last edited by a moderator:
Excellent info! Just what I needed. Leads me to a new question, but first this...

My only concern with the switch is you can damage the alternator (not covered under warranty) if someone accidentally switch both batteries OFF while the motor was running. That is the only RISK I see having a switch, but it's a pretty expensive risk.

So, I was thinking about just installing an isolator since if someone left an accessory on, it would only drain the house battery. That isn't nearly as bad as it sounds, since all you have to do is start the motor (the isolator prevents the starting battery from draining), and the motor charges the dead battery and runs the house stuff (stereo, etc). The only inconvenience is I won't be able to run the stereo with the engine OFF until the alternator has a chance to put some juice back in the battery. My guess is by the time we get to a cove, there'd be enough to run the accessories. If not, no biggy. Especially compared to a wrecked alternator if someone turned the switch to OFF while the motor was running.

If someone reading this thinks I'm all wet on my logic here, PLEASE let me know, as I've not done this kind of wiring before.

The other reason for my NOT putting in a switch is then I won't have to drill a hole in my brand new boat, and then have my wife complain about this big red knob being someplace where she doesn't like seeing it! You all know what I'm trying to avoid here.

Back to my question, Spin, you mentioned a selector switch with 1, 2, and 1/2. You didn't mention the OFF position. Is this what you have? A switch with no "off"? I didn't know they sold those (or hadn't paid that close attention). Actually, my approach on all this has changed drastically several times just this last week!

Anyway, if your switch has no "OFF" position, then that totally eliminates the alternator damage risk completely. Plus, gives the benefit of shutting everything down completely.

All I'd have to do is clear the location with the wife...
 
My switch has an off position. :) it is true you can't switch it to "off while running but mine is installed in the battery compartment like the photos that Gerry posted in the gallery. It would have to be a conscience effort to switch it at that point!
 
Good point.

I was thinking if I installed a switch, I would put it out in the open for the valet/dock staff to see and use. Hadn't really thought about "hiding" it in the battery compartment.

I need to think more about how it will actually be used. There are a lot of ways to skin this cat.
 
kaydano, don't know if this helps or not but I have the standard type switch with an isolator. It's sole purpose for me is to isolate and be able to switch between batteries for starting. The start battery is tied to the motor only unless I need to go to combined. All my accessory wiring ties directly to the house battery. There is no way to kill power to the accessories with my switch. I am re-thinking this set-up for next year to give me the capability to kill everything but unless you run an extra wire your radio may not retain its settings. When I get this worked out next spring I will post. Steve
 
I had not thought about the radio settings being lost. That's another thing for me to think about.

What I hear you saying, I think, is if I just have the isolator, and my starting battery goes bad, I won't be able to start off the house battery (without wrenching and moving cables around). But, with the switch, the house battery CAN be combined with the starting battery (in parallel) to start the motor, if that's ever necessary.

My original goal was simply to not run the starting battery down by being in a cover too long with accessories on and then not being able to start the motor. An "isolator only" setup (I think) solves that problem.

But, the switch gives you the convenience of using the house battery to start the motor, if needed. That would be a rare event, but a worthy reason to add the switch. And, since the switch would rarely be used, I could put it in the battery compartment instead of mounting it in an easy to use (or accidentally use) spot. Am I right in my thinking?
 
kaydano, hope I have this right for you...if you have accessory loads tied to your starting battery an isolator will not prevent them from pulling the starting battery down,( as if something gets left on). Most tie accessory loads to the house battery and then the isolator prevents the starting battery from drawing down because it is isolated from the load. Like you said, without switching cables, you need a switch which will go from 1 or 2 or both and off. I hope I was not trying to answer a question you didn't ask! Steve
 
I like the Blue Sea Systems Add-A-Battery package. It has an isolator and switch, but it's not a traditional A - B - Both - Off switch, rather it's On - Off - Both. Basically you wire the House wires to one side of the switch, the Starter wires to the other. The switch is left to on, and anytime that a charging source is present, the batteries are combined and both charge. When no charging source is present, the batteries are isolated. So it's a set and forget solution. On the hook, you could run down your house battery completely, and still have a topped up battery for starting the engine - again no messing with a switch. The only times the switch is of use is storage (Off), or if the starting battery is somehow run down (not sure how this is possible if it's dedicated for starting), then you would switch to Both to combine with the house battery to start the engine. I've been using this system for years on my bow rider, and it will be among the first mods to my new to me 2275 RL.
 
After reading all your comments, and reading the technical briefs on the Blue Sea website, I'm convinced that the add a battery is what I need. Thanks all!
 
Last edited by a moderator:
I installed a Blue Sea 7610 charging relay this week. I decided not to put in a switch. Very easy to install. Works great! No more worries about the motor not starting after being in a cove for a couple hours with the stereo on.

I also bought one of these battery monitors on Amazon. By plugging it into the cig lighter socket, you can see when the charging relay kicks in (as the voltage bumps up from 12.5v to about 14.3v). For $15, this is nice to have. Can be used in cars too to help diagnose battery/charging issues.

http://www.amazon.co...f=pd_sim_auto_1

Here is the Blue Sea 7610 I used:

http://www.amazon.co.../ref=pd_cp_pc_0
 
Last edited by a moderator:
You must log in or register to reply here.
Back
Top