How to wire up 2 batteries?

[harbormaster]

Got a 95 18 with battery under the rear seat. there is room for 2. I would like for both batteries to be charged but be able to discharge one battery at a time via a switch.

For example: sitting watching fireworks and listening to radio. If the battery get to low to start the boat, swith to the other. Voilla! we can start the boat.

How easy is it?
Can someone draw me a schematic?

[tmdog]

Any boating store has them even Wal-mart. Comes with simple instructions.

[RickR]

I use a "1" "2" or "both" battery selector switch available at marine outlets.

It is wired so #1 bidlge pump is on both and #2bidlge pump is on #2battery. When mooring overnight I switch to #1 for redundancy(thanks Madpoodle)

I do not use an isolator, replace both batteries at the same time and run on "Both"

BTW DO NOT switch batteries while the engine is running unless the switch is designed for it. That would cause diodes in alternator to fail.

[Moody Blu']

harbormasster, how can you fit two batteries in there?
can you take pics?
they must be two small batteries?I only have one in there and it is a 950 ca battery(fairly large)

[Ranman]

Scot, Here are a few pics of my dual battery switch setup. I used the Gil composite battery boxes and they work well. Be sure to use a quality heavy duty wire. My boat was done by an audio shop prior to my purchasing the boat. They relocated the batteries to the engine compartment from under the seat. I just swapped the cheesy black boxes for the Gil units. I believe you want to wire them in parallel so you maintain a 12V system while increasing capacity. Wiring in series will net a 24V system which is no good. Hope this helps. Good luck. Randy

Dual batts in engine compartment
http://www.donzi.net/photos/Dual_Battery.jpg

Perko Switch
http://www.donzi.net/photos/Perko_Switch.jpg

Port Battery
http://www.donzi.net/photos/Port_Battery.jpg

Starboard Battery
http://www.donzi.net/photos/Starboard_Battery.jpg

[Moody Blu']

sweet!

how come only one side has the inline fuse?

[harbormaster]

I was wanting to put the batteries under the rear seat as to avoid engine heat. here is a photo.

http://www.donzi.net/photos/battery.jpg

[mattyboy]

harbor,
ranman right
parrallel same volts more amps
series same amps more volts
we use car batteries for power failure in all our comm systems, when I hook em up my guys call me SPARKY,
not sure about discharge one at a time thingy

good luck like your new ride

matt

[Moody Blu']

ok now i see, I guess thats one more thing that separates the new donzi's from the old ones...

I have enough room for one battery, if you guys know what the old battery setups are like then you understand.

looks like you coudl definately throw two batteries in there.

[MOP]

Hi the idea of two batteries is to have one in reserve IE: redundancy, a way to get home after you fix a problem. I have had alot of formal schooling like alot of guys up here, running even two new batteries on both is not good. One will always be a little stronger than the other it will seek charge causing a slight overcharge on the strong one shortening its life. Old rule of thumb run odd battery on odd dates and even on even dates. Always run independant grounds to the block. Wiring bilge pumps is very easy, go to Radio Shack ask for two heavy diodes solder inline and heat shrink make sure you install with current flow in proper direction toward the pump and after the fuse( Granted you will run both batteries down if the pump runs along time, But much better than sinking!). The diodes will keep the batteries isolated from each other. For you guys that need alot of cranking power use a simple solinoid paralell set up with a dash switch, flip the swith both batteries crank. Also Isolators are a very good idea to keep both batteries hot all the time. Between the two diodes, the two ground cables, two solinoids, spring loaded two way switch and the isolator you will only add about 1-1/2 to 2 pounds to you rig and will have a proven setup that is used on most properly wired boats.

[tailwind]

Easy mount here Scott:

Ditch the battery box, get an optima, or two, with the appropriate Perko switch. Sealed batts
are also availible under many other names such as Champion, evem with the NAPA name. Willl
be doing the same with my 91 18 Classic for stereo amp considerations. Total cost including the Perko switch and optima batt should be less than $ 150.00

Best regards
Randy

[rong]

I agree with M.O.P. except I wonder what your preventing with the diodes? Charging two batteries from one alternator really requires an isolator for reasons stated above. If you want to run both batteries you better buy two of the same kind at the same time and replace them as a pair. Really not a good option. If not the batteries are only as strong as the weakest battery and creates the same problem with charging without an isolator. The battery combiner switch is a good option (like having jumper cables wired as an option to your secong battery.No having to switch to both when a problem is incountered. Once started both batteries charge with an isolator. I would rotate which battery is used occasionally. Also run your accessories from the battery switch. To answer the wiring question, the grounds are run seperately and the positives are run through the switch. The isolator is wired seperatly (comes with instructions). Switches also have a field connection that most people don't use.
This is for hookup to the alternator to prevent accidental shut-off and blowing the diodes in the alternator. Most people know not to shut off the battery while running so I didn't use it. Don't forget that a battery is 40 or so pounds of ballast.

[MOP]

Ok the diode is strickly to supply power from both boat batteries to the bilge pump with out feeding back from one bat to the other. I did not add the weight of the extra battery as I felt that was a given. The object is to have two completely seperate electric sources that only come together when switched together. I had mentioned a parallel start switch also, on boats with a fair amount of electronics needing clean power, I used to set them up with one dedicated battery using an isolator, in the event of starting battery problems I would tell my customers to shut all the electrics down to protect them then either the manualy switch or use the parallel start circut to get started. Many a guy has spiked or surged a nice piece of electronics during starting as most boats do not have electronic circut isolators. Most of todays marine electronics have a much higher tolorence, look at the voltage ratings usualy 10-18 volts shown in the specs.

[Ranman]

Broque, The inline fuse is the power feed to my amplifiers.

Scot, Engine compartment heat is reall not a concern since the exhaust manifolds are cooled so well. Under the hood of my F150 is much hotter that inside the boat. The nice thing about mounting the batteries in the back is that you have more and better storage space under the seat. I believe when Donzi does a dual battery setup on a classic, they mount them similar to my setup.

Tailwind, Where can you get Optima batteries for $150 or less? The marine versions of these batteries are like $175+ each!

[Mark Albers]

Donzi Aficionados :rolleyes:

I can contest to the topic of running 2 baterieas at the same time

The guy I bought my 22-Classic from recomended it
Well...
A couple of months a go battery #1 was nearly dead
So...
I bought a new battery charger
The battery would not take a charge
Luckly the battery (sears marine) was under warranty
Now battery #2 will not take a full charge
and the new battery charges right up

All this do to running both at the same time

Good Luck

Mark 311 :cool:
Sarasota - - - W F O (close to the factory and far from a dream)

[Forrest]

In my Magnum, I'm running three batteries. Two Optima blue top 1000s - one for cranking each engine. The third battery is a group 27 deep cycle and it is used for accessories, such as the stereo, GPS, etc, only. That way I'm not running down a cranking battery listening to tunes when the engine is not running. What I really like is the solenoid-type parallel-switch that was installed many years ago which allows both Optimas crank either engine together if necessary with just with the flip of a dash switch. Also installed, as all boats with twin engine should have, are two battery switches. One switch for each engine and its Optima cranking battery when on position #1 and position #2 on each switch both connects the third battery. That way, if necessary, I can parallel three 12v batteries to start either engine. This is the only time I would ever use the BOTH position on either battery switch, and that would be on just one swath only. The downfall is setup is that you may forget to charge the deep cycle accessory battery. I can do this while running with one battery switch in the #2 position. I could install an isolator to charge two batteries at once with one alternator, but its probably better to charge a deep-cycle battery with a smart charger anyway. Also, I've seen to many electronic battery isolators in RVs fail, and I therefore I don't think that they are reliable enough for salt water and offshore use in an open boat.

I second the use of GIL composite battery hold downs, though now I see that West Marine sells something very similar for around $10.

[HyperDonzi]

this seems much more complicaded than i thought.

[MOP]

If all this complicated stuff is to much, do a simple two battery setup with just a bat switch with the accessories wired and fused to the common pole. Then use the rule of thumb odd bat odd days even bat even days it clean simple and has worked for many years. I did not see an isolator till about 25 years ago, dual bats have been around alot longer!

[harbormaster]

Can someone just draw up a simple 2 battery schematic with diodes and post it?

[MOP]

Ok I sent Scot a crappy drawing of easy battery setup. The diodes can be hi jacked from an old alternators diode bridge, they will hold more capacity than you will ever need. Use OHM meter to get direction of current flow correct.

[nick]

i would run the 2 batteries to a all switch. pick 1 - 2 or all. you could install a parrell for starting for a weak bat not really needed but i always have one. when running chargeone at a time i always did with my single screw boat. Oddevendays or the way out bat 1 the back bat2. also install very 110volt small atoumatic trickle chargers on each battery for on trailer usewith allswitch off the trickle chargers is av. at any good marine store.groud bats separtly _perko all swicth come with all the instruction not as hard as i sounds

[MOP]

Honestly it is a rare not to find the batteries in the engine compartment of any production power boat. In sail boats and outboards it is the opposite. Hey does you car or truck have its battery in the cab or trunk?

[RedDog]

From West Marine 2001 Master Catalog - 1 of many great tech tips included in their catalog

http://www.donzi.net/photos/floydts-bat1.jpg

[harbormaster]

Great! Wish it was legible.

[Rich]

Scot.....
West Marine sells battery combiners and has wiring diagrams for various set-ups (see previous post by Reddog). DIY magazine also did an electrical issue with a few wiring setups. diy-boat.com
Check out yandina.com. They manufacture for West Marine and sell the same stuff only cheaper.
I never did like the 1-2-both switches. I have 3 on-off switches. One for the engine battery, one to combine house battery to engine as an emergency backup (normally off), and third switch to turn on the house stuff. If I leave something on too long, only the house battery is affected.
As long as the emergency backup switch is left off, the batteries will stay isolated except when the battery combiner connects them for charging. I believe the bilge pump(s) should only be on the house battery. This way the engine battery is ONLY for the engine. Put in 2 bilge pumps with the backup pump mounted higher than the primary pump. Put a bilge pump alarm on the backup pump. This way you will know that the primary pump died or you have a serious leak that the primary pump can't handle. If your on the boat when this happens you can fix things and still have a fully charged starting battery. If the boat is moored or docked, someone should here the alarm and hopefully get hold of you before the battery dies.
Just me own 2 cents

[MOP]

Ok I am a lousy artist! I will try to draw a mind picture Scot. First Get the batteries located and well secured. I prefer boxes screwed through the bottom with 8 #10 counter sunk heads with a hunk of Star board cut to fit the bottom of the using silicone threads to keep the bottoms sealed in case a little acid gets out, Not an issue with gells. Use #2 wire well secured with screw down clamps about spaced about 8 inches for the whole job. rent, borrow the proper crimping tools Run seperate grounds for each battery to to the block, disconnect till done. Make up new starter cable to common on the Battery switch, make up the two positive leads from the batteries to the switch, again remove the wires till done. You can bend fairly sharp turns to keep it neat. A nice touch is to add a terminal block near the switch to pull power off for add ons #'s 8 or 10 wire works well this added leg should be fused 30-50 amp. If you want to supply the bilge pump with power from both batteries get two heavy capacity diodes. They can be scrounged from an alternators diode bridge or picked up at Radio Shack tell them what you are using it for to get good one. To avoid corroded pump connections with lead acid batteries run seperate leads from the #1 and #2 poles on the switch to the pump using the rated fuse and one diode in each leg. Make sure you attach the diode in the proper direction. The diodes prevent the battreies from passing current back and forth between themselves. It is very important to secure all wiring especially in our hot super boucey boats. Ok now hook up the battery leads and to apply Pro Clean or the like terminal connection spray. Strap the lids on and go boating.

[MOP]

Looked over that West Marine diagram, was disapointed to see they did not run the grounds seperate to the block but to a ground block then one wire to the block. The issue is to insure redundancy, run the two grounds then pull off a ground leg for add ons. Yeah if you carry tools with you you can repair you single grouded setup in the middle of the pond I would much rather flip a switch. Another thing I have done is to sister the grounds between the two batteries giving you added protection from loosing one of the grounds.

[Forrest]

Rich you are on to it and www.yandina.com (http://www.yandina.com) has the stuff. I just ordered a referbed 50 amp battery combiner (http://www.yandina.com/Refurb.htm). It looks much better that any stinkin' electronic battery isolater. They have some great information on that site, including wiring diagrams, as well as some unique items for sale. I like the Rain Activated Deck Hatch Closer (http://www.yandina.com/hatchInfo.htm) that shuts your hatch immeditally and automatically even in the slightest rain! Check it out.

[rong]

Now I'm wondering. If Scott needs two combined batteries, what on earth are you turning over. Maybe a little more than stock horsepower? What's in that sled of yours? Also I think Rich's idea for blidge pumps is good. I presently run everything except the alarm. Since my boat stays in the water what a savor if something should happen. At the moment I just have a light on the second pump. This is only good for the driver and if he's paying attension. It would be good if someone could post a diagram from a scanner. We could all see. My scanner is presently
not taking to me.