Dual Battery Setup ???

[majed1965]

Hi,
I want to setup my boat with dual batteries. I currently only have one. Does anyone know how this is done, or do i need an electrician?
Is it recommended? I'd rather have the electricial gadgets running off a separate battery. Thanks.

[Roughasguts]

You know the best way out of it is to buy a Kmart battery and a case to put it in.
Then a battery charger and a set of jumper leads, hundred bucks all up.

Keep the battery in the boat if it all goes flat, I bet it won't, provided the battery is less than 5 years old and charged up before your trip out.

For best results you need a deep cycle battery for your electrics, but your boat motor won't charge that, cause it takes a long time. So best to charge both at home on your battery charger before you go out.

[blaze]

IMO a dual battery set up is one of the best safety features that can be fitted to a boat. dont believe a battery that is not fix and jumper leads is the answer (ever tried hooking the suckers up in big seas, murthyies law says that when you will need it)
The simple way to do it is to buy a dual battery switch that gives these postions. off- bat1- bat2 and both.
Neg itives of both battries are connected together and the engine earth connectted to one terminal, also connected to this negitive terminal is the negitive wire going to the bus bar.
Postive of one battery goes to bat1
positive of second battery goes to bat2
Positive of the engine goes to the positive output terminal of the switch, also connected to this terminal is the positive wire for the bus bar.
What I do is run on one battery, this covers all power useage and still use this same battery for night anchorage and nav/work lights. In the morning I will still normally use this as a start battery but have bat 2 just in case at the flick of a switch. Next trip out I use the same procedure with bat2. This way both battereris get around the same use and once or twice a year I put each battery on a trickle charge for 24 hrs.
Never had a flat battery
cheers
blaze

[FNQCairns]

I have had a few dual battery setups over the years this fittout I will be going to a more simple dual battery design that incorporates a HD solenoid, a switch and meter (x2) on the dash.

cheers fnq

[newchum]

I have the same setup that blaze has discribed, the only thing i do a bit differently is i start and run on both batteries until i get to where i am going then switch to No1 or No2 battery, the battery that is due to be cycled. it has worked for quite sometime this way with me and the previous owner following the same pattern

[blaze]

Hi Rodney
The only problem I see with running on both is the average outboard is struggle to charge one battery let alone 2 (in saying that later model motors have a better charge system than my 89 merc)
cheers
blaze

[Roughasguts]

Newchum, the thing that worries me is charging both batteries, I don't know if the rectifier can take that sort of load in Amps, for to long with out going bang.

Don't get me wrong two batteries are ideal in a rig that's always running.
But for a short 5-10 min hop between stops for the regular puddle crosser,
I have doughts the outboards electrics are really up to it.

It's a hell of a load charging two high demand batteries for a few minutes.

[Marlin_Mike]

I have dusal batteiies. When starting i run it on both. This seems to charge both OK.

When at rest i turn it to one only, then if that battery goes flat, i still have a good one to start her. never had a problem, never had them not charge running along with switch on both.

Mike

[newchum]

Newchum, the thing that worries me is charging both batteries, I don't know if the rectifier can take that sort of load in Amps, for to long with out going bang.

Don't get me wrong two batteries are ideal in a rig that's always running.
But for a short 5-10 min hop between stops for the regular puddle crosser,
I have doughts the outboards electrics are really up to it.

It's a hell of a load charging two high demand batteries for a few minutes.

hi guys, my trips are normaly 90-120 mins each way, and i charge my batteries before use, do you think that this will still load up the regulator on my 99 model 200 yamy?

[Roughasguts]

newchum, that being the case, with a good fresh battery to start with, it wouldn't be charging to many Amps for very long, maybe 3 mins.
Geezus 120 mins out you carry your passport.

You got an Amp gauge just to see how there going??

[FNQCairns]

Gut's is that the way it works? my understanding is electrically limited although I didn't think the O/B cared if the batterys were flat or partly charged.

cheers fnq

[Roughasguts]

FNQ, If you got an Amp gauge then you will know for sure. Thats why I asked newchum.

Usually the Amp gauge will show huge Amps just after start up and reduce to a trickle after a few minutes. Provided you have fairly new fully charged batteries to start with, if not then your going to boil your batteries dry, and in the process maybe cook the rectifier.

The rectifier is only diodes and electronic bits I don't fully understand, but cost big bucks when replaced.

[newchum]

FNQ,
The rectifier is only diodes and electronic bits I don't fully understand, but cost big bucks when replaced.
not to be smart but a rectifier is the diode bridge and add some electronic bits and you have a regulator. 90 - 120 mins is the best of the close reef we have here . i have a tong tester and have tested the chargeing amps before on not fully charged batteries.results 25amps out of the alternator 12 port battery and 13 to starboard battery. i didnt think this would cause any problems. do you think there is reason for concern?

[Roughasguts]

newchum I guess that is only initial charge rate, in Amps. So do you know if it decreases over say 10 - 15 mins.

[newchum]

newchum I guess that is only initial charge rate, in Amps. So do you know if it decreases over say 10 - 15 mins.

R.O.G., that was the reading after starting, i was only running on muffs so i didnt run i for long, but the batteries are two years old and since i have had the boat i have never had to top them up. i guess to be on the safe i will have have to test them on the water when the wind drops. are they like a car and drop off to minimal charge after a while?

[Roughasguts]

Well that's what I thought they would do (or most would ) but FNQ, has me thinking maybe some don't like a petrol generator on 12 volt, it don't care how much charge is in the battery just keeps pumping out it's max Amps until you shut it down.

Electronics elude me I make no bones about that, but I know if you charge a flat battery with only a 4 Amp charger, it will thermal over load and cut Out.
But i'm worried about charging 2 batteries with a Outboards fairly light system and burning it out, be only diodes and such but the price of these things is around 800 bucks. Ooouch.

[newchum]

R.A.G.just checked the spec for my motor . it has a current regulator with max. continuious output of 25amp 13.8 volts, 2000rpm, looking at that i would believe that charge will drop off as the batteries come up . i feel a bit better after looking that up. thank for the interest and input, helps me find out more about outboards

[FNQCairns]

Yeah my understanding is simplistic, the outboard will make the charge regardless (total amps dependent on revs) the problem for the reg and rect is if there is nowhere for that charge to go, while it meets low resistance in the battery (flat) it should be working at it's easiest and I guess harder at batterys full. Got no idea where the extra amps go at WOT with fully charged batterys as the charge coil should still be puming the amps out- to earth??

cheers fnq

[Roughasguts]

No worries newchum, glad it's regulated.

So if you got fresh good batteries I can't see you burning the guts out of your charging system.

But this is where Amp gauge come in handy, they will tell you how good your battery is in charge rate, and recovery time for the years to come.
With those sort of miles out, there a pretty cheap investment.

[newchum]

FNQ, they way i understand it, the regulator controls the amount of current required to maintain full charge in the battery. so this mean at low battery charge the reg allows full current flow, as the battery charges up the reg reduces it's current output. the alternator only response to the regulators needs I.E. there is no excess current to get rid of. someone might be able to more technical than this but i like the k.i.s.s. principle

[Scalem]

I have only ever tried to Zip start my 70HP donk once because I had to, my single battery was flat. Never again! I was running out of puff myself after about the 12th attempt, and she fired up, thank God!! That's when I put the dual battery setup in.

You guys have given great technical input as to how it works ( good thread) but I have not ever had trouble with flat batteries since so maybe my ignorance is bliss.::)

I bought 2 x M70 seconds ( with 30 day warranty) which are not even Marine batteries, but truck batteries 4 years ago. I keep the switch in the 1+2 position all the time, get the boat out every 3rd or 4th week, probably 60 mins running tops. Considering I have now about 4 years life out of them, I am going to start testing them individually to make sure they are still OK. I probably have not followed all the best practices when it comes to batteries. Yes I know the difference between a Marine battery and a truck battery before anyone feels the need to point that out, but what are the chances of both failing at the same time? I was on a tight budget when I set it all up and only paid $75.00 each, so I consider I have done well, and won't change a thing except the batteries which are about due for replacement IMO.

Scalem

[Graybags]

Having two batteries charging at the same time will not stress your outboard motors charging system. The electrical load is on the batteries. The charging system is designed to output a certain amount of electrical current regardless off the electrical system. One word of advise, any one running a dual battery system remember to never switch batteries over while your outboard motor is running. I know of a couple of friends who have damage there ignition systems on Mercurymotors (i think the stator coil) doing this resulting in expensive repairs.::)