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Author Topic:   Dual Batteries - 1 Stern and 1 console + ACR and Charger
ChiTown Cetacean posted 10-21-2008 10:52 PM ET (US)   Profile for ChiTown Cetacean   Send Email to ChiTown Cetacean  
I am considering going to dual batteries in my '73 Outrage 19. Currently, I have a single battery mounted in the starboard stern splashwell. The port stern splashwell has the VRO tank.

I don't think there is enough room in either splashwell to fit two batteries. My thought is therefore to put the house battery in the console and keep the starting battery in the splashwell.

If I go to dual batteries, I would want to use the Blue Seas ACR system and switch. I also have an on board battery charger which is capable of charging two batteries.

My question is, how would I set this up? I think I would need to connect both the negative terminals on the house and cranking batteries. The ACR and switch would handle the positive side of the connections to both batteries.

I would mount the ACR and switch near the cranking battery in the stern, and then mount the charger nearby in the stern as well.

I was thinking that I could connect the charger leads to the batteries via the switch terminals on the positive sides for both batteries. On the negative side, I would connect the charger to the negative post on the cranking battery and thus also to the house battery since they would be interconnected on the negative side. This way, the positive and negative runs to the house battery would be essentially equal in length.

Also, I have heard that it would probably be best to use matching brand new batteries when setting up a dual battery system. My thought is to use two new dual purpose batteries.

Would this work? Any better ideas?

And finally, I am now using 4 AWG Ancor wire for the run from the single battery to the console to feed a Blue Seas fuse panel which then supplies the Fishfinder/GPS, VHF, lights, horn and 12V accessory outlet. Would this same run of wire be sufficient using the dual battery set up to connect the ACR and switch to the positive side of the fuse panel and to interconnect the two batteries on the negative side? Obviously, a short run of 4 AWG would need to run from the house battery to the console fuse panel as well.

ChiTown Cetacean posted 10-21-2008 11:02 PM ET (US)     Profile for ChiTown Cetacean  Send Email to ChiTown Cetacean     
As I think about this more, I would probably need to run two positive wires to the console. One from the house battery back to the "power in" side of the switch, and another from the "power out" side of the switch to feed the fuse panel.
dino54904 posted 10-22-2008 09:57 AM ET (US)     Profile for dino54904  Send Email to dino54904     
Hi Chi'Town,

I recently restored a 1972 19' Outrage and installed my dual battery system in what seems like the exact way you are planning. One battery in the stbd side of the spashwell and the other under the console VRO tank in the port spashwell within a battery box. I used a dual battery Perko selector switch mounted on the side wall of the stbd side of the cockpit just ahead of the bench seat. The fuse panel is under the console as is a 30 amp breaker for the system. I did not mount an on-board charger but opted for a dual bank Battery Tender brand charger that I mounted to my garage wall and plug in wheneven the boat is in the garage (which is all too often). I have a 150 Johnson and a 8hp Yamaha kicker with electric start. I have used the boat set up this way for the last year and everything has performed flawlessly.


pglein posted 10-22-2008 05:26 PM ET (US)     Profile for pglein  Send Email to pglein     
I'm having a little trouble following your plan, but I thought about what I would do if it was me.

I would locate your charger and the ACR in the console if there's room. That way they're protected from the elements and it simplifies the wiring.

I drew up a wiring diagram for how I would do it if it was my boat, keeping in mind that you want one battery located aft.

You only need heavy gauge wiring between the start battery and the engine. The rest can be relatively low gauge, say, maybe 10 or 12 AWG. The only exception would be if you expect to have to rely on the combined power of the two batteries to start, in which case the wiring from the house battery to the ACR, and then from the ACR to the start battery would need to be upgraded. My understanding is that the ACR can be manually "closed" so that you can combine the two batteries for starting. If not, you could easily install a short bypass with a ON/OFF switch.

I showed you using two bus blocks for the negative wiring. I did this because you will undoubtedly have multiple smaller circuits to connect, both forward and aft. These bus blocks allow you to have only one negative whire (I suggest 4 or 6 AWG) running through the rigging tunnel. Your engine, bilge pump, stern light, and any other items you may have located aft, can be connected to the one in the stern. Your electronics, 12v receptacle and any other items in the console can be grounded to the one forward. The positive leads for the items located aft would still need to be run through the rigging tunnel to the switch panel.

Note, you may need to consult the installation instructions for the ACR to determine exactly which side you connect the charging lead to. I couldn't remember exactly how it was set up, so I drew it the way I thought it was supposed to be, as best as I could remember.

You will also notice that I did not show any "ON/OFF" switches. Since you'll be using an ACR, there is no need for a three position "1/2/ALL/OFF" switch. You may, however, want to install two "ON/OFF" switches; one between the start battery and the engine, and one between the house battery and your switch panel. Depending on your load, and how you set up your switch panel, you could potentially have your main house "ON/OFF" switch just be another toggle switch like all the others located on the outside of the console. The load associated with these draws is generally not all that much unless you're installing downriggers, anchor windlasses, or other high-draw items. It's quite possible that a single toggle with a 30 or 50 amp fuse (or breaker) would be more than sufficient. All the other switches would then feed from that switch, preferably via some sort of bus bar.

Here is the diagram I drew up:

Chuck Tribolet posted 10-22-2008 09:32 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
If you are going to install a switch to allow the house
battery to be paralleled with the starting battery, it
and its wiring better be REAL beefy. 100 Amps or more, check
your engine manual.


ChiTown Cetacean posted 10-22-2008 09:56 PM ET (US)     Profile for ChiTown Cetacean  Send Email to ChiTown Cetacean     
Thank you all for your suggestions and for the effort to draw out a schematic. I will let you know how it all turns out.


andygere posted 10-22-2008 10:21 PM ET (US)     Profile for andygere  Send Email to andygere     
An alternate consideration is this, Chuck's excellent points about protecting electric gear notwithstanding: Put the VRO tank in the console, and have a battery on either side of the splashwell. Oil hose is a lot cheaper than 2 AWG battery cable. I have my VSR and switch cluster mounted under the aft gunwale, and after 2 years it's showing no signs of corrosion, even on a wet slipped boat. I did seal the cable openings with a generous amount of silicone goop.
andygere posted 10-22-2008 10:21 PM ET (US)     Profile for andygere  Send Email to andygere     
An alternate consideration is this, Chuck's excellent points about protecting electric gear notwithstanding: Put the VRO tank in the console, and have a battery on either side of the splashwell. Oil hose is a lot cheaper than 2 AWG battery cable. I have my VSR and switch cluster mounted under the aft gunwhale, and after 2 years it's showing no signs of corrosion, even on a wet slipped boat. I did seal the cable openings with a generous amount of silicone goop.
kwik_wurk posted 10-22-2008 11:47 PM ET (US)     Profile for kwik_wurk  Send Email to kwik_wurk     
I have never understood the batteries in the aft splashwell. I know it is quite common, almost standard.

But it seems to invite a swamping of the battery (or batteries). Has anyone heard of this actually happening.

I have had this problem on a sailboat: We got T-boned during a regatta on the port side. We started taking water fast, and thus tacked to raise the hole (on the port side) above the waterline. The batteries (installed on the starboard side low in the boat but no bildge) were submersed and shorted. Poof! No engine or navigation equipement; except a handheld VHF. We made it back after unloading all but two of the crew (one to sail, the other to operate the handheld pump).

On my Montauk, I have flooded the aft deck with at least 4-5 inch of water while fishing. And as I accelerated (to move the water aft) I had stuff floating over the splash well and around the steering arm. I can't imagine what would have happened a battery strapped in the stbd aft corner. It would have been under water.

I would suggest at least one battery up forward. And if it is going to be wired as a backup starter, then the proper AWG is going to be needed.

andygere posted 10-23-2008 11:41 AM ET (US)     Profile for andygere  Send Email to andygere     
I agree that boats with a bilge or storage area below the cockpit sole used to store batteries is a bad idea, because they can easily become submerged. On my Outrage, there is a large flat, shelf designed by Whaler for holding the batteries. This is separated from the cockpit by a low splashwell dam that goes the width of the boat. The top of the battery boxes is well below the height of the transom, so that if the boat were fully swamped, the batteries would still be above the water line. With the "lawyers vents" on my battery boxes sealed, the overlapping lid does a remarkably good job of keeping water out of the boxes, even when taking following seas over the transom. Also, The archives of this forum report that the battery will continue to function for some period of time, even when swamped. In general, I think it's generally better to have shorter cable runs when looking at high amperage applications like cranking a primary starter. This can be offset by large gauge primary cable, but it's expensive. I also worry about the impact of having lead acid batteries constantly off gassing inside a closed console, and the possible corrosive effects on switches, fuse blocks and wiring behind the instrument panel. Since both battery locations seem to be in practice with good results, it probably comes down to a matter of preference. For me, easy access to the batteries, and retaining dry storage space (and easy access to wiring, steering, etc.) inside the console won out over any fear of swamping my batteries. Note that I mounted my VSR and battery selector switches as high as reasonably possible, and under the gunwale to provide some protection from spray and splashing. I also sealed the cable routing area to prevent water from dripping inside the switches and shorting them or corroding the terminals.

Note that I had the identical experience to Kwik Wurk in my old Montauk, which had batteries in the aft corners, and the selector switch mounted in an arguably poor location, low on the front of the splashwell. I had no problems with shorted batteries, and just a tiny bit of water in the bottom of the battery boxes.

jimh posted 10-23-2008 10:48 PM ET (US)     Profile for jimh  Send Email to jimh     
I have not had the time to make a thorough study of this problem, but my first impression is to proceed along these lines:

Since the two batteries are separated physically, the primary battery distribution switches should be separated, too. Instead of the usual OFF-1-BOTH-2 single switch, three individual switches should be used. An ON-OFF switch for each battery should be located close to the battery case. A third switch will be the EMERGENCY PARALLEL switch. For this application the separate single-pole BEP MARINE switches seem best.

The negative terminals of all the batteries should be bonded together. If the battery in the console is to be used for emergency engine starting, you will need a large capacity conductor to make the connection.

jimh posted 10-24-2008 09:37 AM ET (US)     Profile for jimh  Send Email to jimh     
I sketched out a trial layout, and it certainly looks like using three separate switches for control of the batteries is more appealing than using on common dual-pole switch like the new Blue Seas switch. I'd go with the BEP switches.

The size of the conductors that link the house battery in the console to the engine cranking battery in the stern do not have to be huge if you only intend to use the house battery as a helper battery to get the engine started when the cranking battery is low. A cable of 8-AWG can handle 80-amperes without a problem, and for a momentary load like engine cranking, it can probably handle even more. An extra 80-amperes ought to help get most engines to crank over.

Of course, the voltage drop becomes the limiting factor. Using the ANCOR wire calculator at

you predict the voltage drop for a particular length, gauge, and current. For a run of 20-feet (which is 10-feet up and 10-feet back) and a gauge of 8-AWG you will only have a 10-percent voltage drop with an 80-ampere load current. If you want to reduce this to three percent, you have to increase to 2-AWG cables, which are significantly larger and more expensive.

If you got into a real bind and the cranking battery was completely exhausted, it would be easier to move the house battery to the stern and connect it there to get the engine started. And with good battery management you will probably never need to do that.

pglein posted 10-24-2008 12:20 PM ET (US)     Profile for pglein  Send Email to pglein     
I agree, there is no need to link the two batteries together with 2 AWG wire. At most, 4 AWG would be more than sufficient. But truthfully, 6 or 8 AWG would be fine for keeping the house battery charged. Given the cost of copper these days, it seems prudent to not overdo it.

If you really found yourself in a pinch, you could physically swap batteries, as jimh suggested. It all depends on how much you want to spend, and how much wire you want to cram into that rigging tunnel.

One thing is sure; there is no limit to what a person can spend rewiring a boat.

pglein posted 10-24-2008 12:33 PM ET (US)     Profile for pglein  Send Email to pglein     
Oh, and as for battery and oil tank placement, I think both can be sufficiently protected in either location. I think the idea of one battery and the oil tank aft is smart. It saves money on wire, and keeps the oil hose short and visible. One problem with running your oil hose through the rigging tunnel is that it can develop a leak, become pinched, or in some way stop working, and the first you would know about it would be when the VRO pump stopped working and the engine died. Also, I've found filling the oil tank in my console to be difficult to impossible. At the very least, it's messy, as I have to remove it from the console, fill it, and then put it back in. I'm relocating mine aft, under the stern seat.

A properly maintained battery with appropriately insulated wiring, should not "go poof" when it is submerged. In fact, it should continue to work as nomral, except with accellerated corrosion of exposed wire terminals. The terminals of a battery kept strapped down in a battery box, assuming it has no vents in the lid (some do, some do not), and that it stays relatively level, should stay dry, in a pocket of air under the lid.

Likewise, a VRO tank shouldn't suck in water in any great amount unless it, or the cap, is cracked (many older ones are). Regardless, it's prudent to cover or enclose it. However, unlike the battery, it's useful to have the tank iself visible, so that you can gauge how full or empty it is. My plan for this is to place only a battery box lid over the top, and strap it down with the tank (no box, just the lid). That way, I'll be able to see the level in the tank, yet the top of the tank will be protected by the lid from rainwater and submergence. Also, I will be placing it under my stern seat.

ChiTown Cetacean posted 10-26-2008 11:42 PM ET (US)     Profile for ChiTown Cetacean  Send Email to ChiTown Cetacean     
Many thanks again for your help. Was out of town for a few days bow hunting for whitetail deer. Needed to do something to assert my place in the food chain, now that the Lake Michigan salmon are safe with my Whaler having been put up for the winter...

Your assistance is much appreciated.


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