i have had this discussion with quite a few people,and,just yesterday,i had it again with a potential customer.dual batteries,or multi batteries,it's like this,if you have a single engin,and you have a selector switch,a standard selector switch the 1,2 all and off sitch,when the switch is turned off,nothing,including your electronics work,you do not have a seperated system,your electronics are not wired to only one battery.this is a matter of opinion and preference,and i hate this system,it's terrible,most people use the "all" position,meaning the batteries are "paralleled",again,meaning you're drawing from both batteries,not just one,they're connected electrically.by running a system like this,you're running the risk of not having enough power to crank the engine when the time comes.you're also running the risk of having the electronics "crash" upon cranking the engine,due to a low voltage situation.also,if you don't run the switch in the all position,you really can't charge both batteries at the same time,menaing,you're gonna have to move the switch position to charge both batteries.
there's a better way of doing this-a much better way...
it's called a seperated and dedicated system.works like this,2 batteries,one for the engine,one for the 12v system,2 simple on/off switches-one switch controls the 12v system,the other controls the engine."bep" and blue seas both make these set ups,i prefer to use a different approach,there's nothing wrong with using either of these 2,i prefer not to.i use a "sense relay",this senses voltage at the batteries,it senses the voltage at the one battery is 13.2v or higher,the relay then engages and allows both batteries to charge at the same time,same thing happens when the engine is shut down,the relay disengages,due to a low voltage situation.trick huh ? there's a little wiring that's involved in this,but it's not that bad.this is an excellent addition to your boat,and i highly reccomend it...

I did something along these lines two years ago I went away from the single switch to a system like described above (I think). One of the best moves I made. I still religiously check the water levels in the batteries but since switching I have not had to add water at all, before it seemed like a monthly event. I assumed this was due to them being combined all the time. I can now just turn on the house battery and listen to the radio without energizing everything.

I would be curious to your opinion on the system I went with Jim. I went with the BEP system, (716-SQ-100AVSR) which was very easy to install, it is actually made to replace a single switch and in most cases you can use your existing wiring. They have many different configurations, sing engine, twin engine, triple engine, two three or four battery banks.

Main reason I went with BEP was that was the brand of components that were already installed and they would mate together with what was already there and seem to be some of the smaller components on the market and space was at a premium for my installation.

http://bepmarine.com/Dual-Battery-Charging-Cluster-180-1464.html BEP Battery Clusters

I've been using a different system for a number of years on my single engined boats.
A single "off-1-2-both" switch and two batteries. Battery A is a cranking duty battery, Battery B is a crank/deep cycle duty. Electronics are permanently wired to Battery B. This works for me since all electronics are unplugged and stowed in the locked cuddy. If one does not like this, then a seperate on/off switch could be wired from Battery B to the electronics. ( Although if you can't remember to shut off the individual electronics how could you expect yourself to remember to shut off the main switch?)

With this setup
1) I normally start and run the engine on Battery A with switch at "1".
2) Every second or third trip, I use switch position 2 so that Battery B gets recharged once in a while.

3) Battery B is available as an emergency "start the engine" battery should Battery A not be able to crank the engine.

Long days at drift or on anchor with electonics running will not discharge the main (engine start) battery...ever.

There have been times on some of my boats, that I used a simple charge splitter conected to the "off-1-2-both" switch to keep Battery B charged (well mostly charged).

ONE SHOULD ONLY USE THE "BOTH" POSITION IN AN EMERGENCY, where an emergency is defined as NEITHER battery alone will crank the engine. Keeping the switch in BOTH position under certain battery conditions can ruin the batteries.



, I NEVER use Both unless neither battery on it

Aside from battery damage, I thought that having it set to both, cranking the motor and attempting to let the alternator charge both at the same time to damage the diode in the alternator? I was under the impression that if you needed to parallel the batteries to start the motor you should parallel them, wait 10-20 minutes, disable or switch off the combine or parallel and then attempt to start as normal.

IF both batteries are more or less at the same, non dead, state of charge, then there won't be any damage to the diodes.

If both batteries are very low, then starting and running in "both" will give the alternator a bit of a workout for the time that the switch is set to both. In reality, the alternator is rated for xxx AMPs charge rate and that's pretty much what comes out of it. The current is determined by the difference between the voltage coming out of the alternator and the voltage of the battery (if it were disconnected) at any given time.
Batteries come up out of a low state of charge fairly quickly and as the battery's voltage rises, the rate of charge decreases, so that as the battery becomes more and more charged, it takes longer and longer for charge to get "put" into the battery.

As to how long to run in both.... If depends on the state of the battery, i.e., is it new or on its last legs. If new, then being on "both" for 5 mins or so should be enough to change to then just start on one. IF both batteries are on their last legs , they may never recharge enough for a restart on just one. If I was "at sea" and had to swith to "both" to start and the batteries were more than a couple of years old, I'd probably run home on "both".

a few things wrong with this...

first,paralleling batteries will not damage alternator diodes,what damages alternator diodes is "open fielding",which is turning the battery switch to the off position while the engine is running,do this,and you just wasted the alternator.running the battery switch in the "both" position,it puts a strain on the alternator,it will not damage it,it parallels the batteries.ruining the batteries ? new one on me,never heard that one before ?i think perhaps you mean,a bad battery will take a good one out ? that is true,a bad battery will discharge a good one,meaning,let's say you have this set up,#1 battery is dead,as in dead,you throw that switch in "both" and you light up the engine,you take a ride over to the spot you wanna fish,shut down and start drifting,you left the battery switch in "both",guess what,no power ?? how can that be ? a bad battery will take a good battery out...

battery switches,for the most part are "make before break",meaning,the switch will make contact with the other posrtion of the switch before it breaks current with another portion-again,"make before break".the system "retriever" mentioned is not really the best choice.it's best to be able to control all the power from batteries and it's best to be able to shut off that power.one thing that should allways be "hot" on a boat is the auto bilge switch,for dual battery systmes,i like to see 2 bilge pumps,one on each battery,this assures you of having at least one "hot" pump.if you're running your boat offshore,i reccomend you look into setting your boat up with a seperated and dedicated battery system.it assures you of avoiding the "no crank" situation.
connections,you never want connections for equipment,including battery chargers,connected to batteries,make all connections behind the battery switch,for feeds,and use "ground busses" for the grounds,the only connections you want at a battery is battery cables,use a seperate battery cable to feed a ground buss.never use "wing nuts" on battery terminals,use lock nuts only,be sure to use waterproof inline fuse holders for the auto bilge leads...

this isn't brain surgurey,but,there's a little more to this than meets the eye...

The danger in running with the switch on "both" is that if there is a substantial difference in the charge level of the batteries, that the higher battery will "charge" the lower battery without any limit to the current and it is possible to buckle the plates on the battery.

Someone will of course say..."Hey why doesn't that happen when I jump start my car?"
Two reasons... 1) You don't run for hours with the batteries jumped.
2) The battery cables used when jumping a car are typically longer than the cables in the boat and the clip on connections are not as low a resistance. Put simply, the short cables and the very good contacts in the switch in a boat's system provide a low resistance path, that allows a higher current to flow than in the jump the car scenario. Contrary to popular belief, when you jump your car (or truck) the good battery is not providing the cranking amps to start the dead one. It can't... the cables are too long and the connection too ratty to allow the several hundred amps that the starter needs. What happens, is that the good battery ( you all notice that things go a bit faster if you rev up the charging vehicles engine a bit for afew secs!) fast charges the bad battery so that IT can mostly supply the current to crank.

RE:"the system "retriever" mentioned is not really the best choice.it's best to be able to control all the power from batteries and it's best to be able to shut off that power."
mmmm... guess you didn't read..."a seperate on/off switch could be wired from Battery B to the electronics." When this switch AND the "main" (1-2-both) switch are both in OFF... no power to anything...except to the bilge pumps which as you pointed out should be hard wired to the batteries.

I haven't bothered doing this ( adding the additional on-off switch) on my current boat since as stated, all the electronics get unplugged... ALSO and a good idea for all... I have a heavy wire run from Battery B (the start/deep cycle one) forward to power all my electronics. At the point where this cable attaches to that battery, I have a 30 A fuse. Per stardards, this fuse is NOT to protect from the equipment over load ( that's what the individual fuses are for AT each piece of equipmemt), but rather that fuse is there to protect the boat from a short in the wire "bus". If I need to shut off that heavy feed (bus) from that battery to the helm, I just pull the fuse.

incorrect...lower charged battery paralleled with a higher charged battery,end result...2 discharged batteries...batteries will attempt to equalize,true...again,a battery with a bad cell,conected to a good battery,end result,2 discharged batteries...plates will not warp ?
again,a discharged battery,will take another good battery out...not sure what you're trying to state here...???

let's go a little further on this,shall we...

charging systems,we have "amperage" and "voltage",amperage,that's the force-think of it like pressure.voltage will vary,it will allways be hgher than battery voltage,which is 12.6v.you should see a charging system voltage of 13.5-14.5,somewhere in there...voltage is controlled by a regulator,if voltge was allowed to climb,fuses would pop.amperage is a little different,works like this,amperage will flow as needed,batteries "run down",amperage is gonna be higher when it starts,then gradually taper off-think of it like this,the battery is like your checking account,you write the mortgage check,a big one,account's low,you keep putting the money back in,then you taper off and put the money into the savings account instead-get it
there's "laws" to electricity,"ohm's law" is one of these laws.I=V/R what this means is,I is the amperage,V is volts and R is resistance,what this all means is,divide resistance by voltage and you will get the answer to how many amps are flowing in a circuit.
with all this,the amperage is gonna be the same in a circuit,again,menaing,this charging system and the batteries,the amperage flowing in this circuit is the same through out.this is a circuit,you've got 2 batteries,a charging device,and a ground,a complete circuit.a completel circuit,by definition,has a power source,with postive and ground,wiring,the resistance,or "load" and ground-the return path for the circuit.the amperage is the same through out the circuit.again,with all that,the batteries,both are getting the same amount of amperage.batteries will equalize,and a low charged or dead battery will discharge a good battery.

running power leads from a battery,batteries should have battery cables only going to them,nothing else,nothing should be hooked directly to a battery's positive terminal,except for cables.all connections should be made behind the battery switch,and a seperate ground buss system should be in place for the grounds.all poer leads need to be fused per abyc codes,and coast guard cfr's,as well as common sense.it's not required,but,i like a positive shut off system for ship's power.a boat is a moist environment,right ? water is an excellent conductor of electricity,i could tell you a few stories concerning wet 12v wiring causing all kinds of problems,not limited to "stray current electrolysis".you want a positive shut off system for you batteries.
if you're running a boat offshore,you need to limit the potential for problems as much as possible,common sense right ??you keep up on the engine(s),make sure you've got a full load of fuel,all these good things right this is another thing to look at on your rig.mabey,this is the year you're gonna try and make an overnite run to the canyons,or the inshore tuna grounds,your plan is to use the 12v spreader lites to lite up the deck and atract the squid ? you've got a wiring system like the one i described,1,2 all and off,you're gonna have a problem,that would be dead batteries...i've lost count at how many times i've been in the canyons for the nite and in the morning,guys are on the radio calling for a "jump start" or a "jump pack"...these are guys who need to look at their electrical systems,there's no excuse for this,there's a better way and a safer way...
and for the record,trying to run 12v lites for the nite,it's not the best approach,you're gonna need a few sets of batteries,just to power the lites,those 500wspreader lites use alot of power and they will kill a battery quick-try it for yourself,hook 2 up to one of your boat batteries,do it in the garage if you pulled the batteries,see how long they stay lit...we'll talk about a better way to lite up the boat for the nite...

Here's how I learned it in engineering school when I got my degree in electrical engineering...

RE:"voltage is controlled by a regulator,if voltge was allowed to climb,fuses would pop....amperage is a little different,".

Amperage is what "pops" a fuse. Regulators are rarely fused and many have internal current limiting circuitry. Voltage rise per se will not pop a fuse directly, only insomuch as the increase in voltage causes a high current to flow.


RE:"the amperage is gonna be the same in a circuit,again,menaing,this charging system and the batteries,the amperage flowing in this circuit is the SAME THROUGH OUT."

Not true ( according to my DC circuit analysis class )... You can have one current flowing from the regulator towards the batteries ( its limited by the regulator and/or the capacity of the alternator to deliver current) and another different current flowing between the batteries..

I REPEAT... the current flow BETWEEN paralled batteries is totally "uncontrolled" (i.e. by any external control device) and the current BETWEEN them is limited mostly, (if you ignore the source impedance of the batteries) by the difference in the voltages of the two batteries and the resistance of the cables and switch contacts. It is entirely possible to generate enough of a current flow to distort the battery's plates... and cause...a shorted cell!

Being a mech engineer I had to jump in on this, first off all you guys are way over the top, batteries cost about 70 dollars a pop, I run two with a standard perko switch, this is about 140 in batteries. I spend more than that in fuel on any given trip, what the heck are you worried about. Also I agree with jaws, your not going to mess up the alternator unless you turn the switch hot. End conclusion buy new ones when they crap out.

Last time I priced a decent start/deep cycle marine battery it was $129. Its not about replacing batteries (for me anyway), its about having them fail at inconvenient times.

wrong...
if the voltage regulator fails,as in,it allows the voltage to climb,this can and will pop fuses,amperage will also blow a fuse,the voltage will too...remember,can't have amps without volts...
true,if you have a shorted cell,current will flow uncontrolable,absolutley correct...
now,if 2 batteries are paralleled,no current flows untill a load is placed upon them,then,the 2 batteries act as one,they are one,they're paralleled,which means,the amperage of them is combined...

wrong about the current flow,current flow is the same in a circuit,it will not vary...

and again,and alternator diode will not be damaged by charging multiple batteries...sorry...

I have to agree with emals. I buy the cheapest marine batteries possible ($79). Usually last five or six years. I only use one battery at a time for the whole day then switched to the other one next time out. I start the boat with one battery. My thinking on this is if the battery is starting to weaken I'll know by the sound of the start. If one battery goes bad I replace both at the same time. The information that you guys are giving shows a lot of knowledge but for the average person like myself it gets to technical.

if what you're doing is working for you,then keep on doing it...you must be doing something right,most marine batteries are good for approx 3-4 seasons,you're getting 5-6 seasons...good job !!

usually,guys who are engineers,they like to show how smart they are...

RE: "usually,guys who are engineers,they like to show how smart they are..."

Actually no... Generally engineers are "fact oriented" and don't tolerate factual errors well.


"You are entitled to your own opinions, but not your own facts!"
. Daniel Patrick Moynihan

I have twin engines. Each engine has it's own battery. I have a "house" battery that I beleive is basically to provide voltage for my electronic shift. (yamaha dual station controls) I installed a radar last summer. When I turn the radar on and transmit, my voltages goes waaay down to almost 10.5. If I use another electronic device like lights or washdown pump, the radar shuts off due to lack of power. Any ideas on how to upgrade my system? I was thinking of adding another battery to parallel the house battery and hook the house battery into the main system. I have the perko switches and can parallel both engine batteries if needed. Any suggestions would be appreciated.

i would have to see the set up...
first a few questions...
how is the "house" battery recharged

electronic shift ? not sure what you're talking about ?

you're more than welcomed to give me a call and discuss this...it's gonna be easier to talk rather than type...609-214-7556.you will get me on the phone untill 9p tonite,than,all day tomorrow...

let me add a little more to this...

a third battery powering electronics is definatley the way to go,it however,has to be wired to remain independent of the other batteries,but,you will need a way to recharge this.i like the "sense relay" method of recharging.most new outboard engines have multi battery recharge capabilities,personally,i don't do it this way,i still like the sense relays.

the reason i explain "call me,and we can discuss this",the idea is,i can explain it better this way versus,typing it,sometimes,what's being said gets confused,plus,when you're talking to me on the phone,other questions come up,we can cover those too..make sense ?

like i said,gimme a call,i can steer you in the right direction to get yourself squared away for the coming season...

Is that 10.5 at the radar or 10.5 at the battery terminals?
Should have voltage reading at both locations in order to figure out what the problem is, i.e., is it a battery problem or a voltage distribution system problem (or both?)

I get the low voltage reading at the radar. Jawz, I will give you a call. Thanks.

Dave

Sorry, I should have been more specific...
When you get 10.5 at the radar, what is the voltage at the battery terminals themselves?

let's go a little further on this again,shall we...

new digital electronics-these require a constant voltage to operate correctly.a common problem with the raymarine "c" series sets is the wiring to power the set,not the unit itself.what i'm saying is,you need a seperate feed and ground to a seperate ground buss and power buss for these style electronics,without these,you're kinda asking for trouble.i've seen way too many installers set these up wrong,or rely on the boat mfg's power and ground buss-a boat that's common to this is both the gradys and the parkers,terrible electical systems...these boat mfg's use a 10g wire from a main breaker to feed the entire electrical system-not good...think of it like this...you have a gardne hose running water to you,another guy,he taps into the hose,the flow of water to you is diminished,right ? another guy,he taps in to,the flow is even more diminished,right ? same thing applies with electricity...think about electricity as being water,both take the path of least resistance,right ?

it's very difficult to diagnose an electrical problem over the phone,things get lost in conversation-remember that...the system that most people have the most problems with is the electrical system,alot of guys get really confused really quickly too when it comes to electrical...all this is the reason,i have a one day seminar on the schedule,dedicated to 12v electrical systems...now,don't get thinking,"i'm never gonna be able to understand all this" and "i got no clue what this guy is talking about with "ohm's law" and paralleling batteries",don't sweat it...when you get done,you will be able to properly trouble shoot your electrical problems,you will also be able to make connections the correct waterproof way,and you'll understand the basics-even an electrical engineer will learn from this...it's on the schedule...
i read alot of these forums and i post things on them too...the whole reason i ever got involved in all this is due to the incredible amount of misinformation i see and read.the marine industry is an very interesting industry,nothing like the automobile industry.i first started running service seminars for maintaining outboards,i started this fall-never did it before,reason i started it was what i read concerning servicing outboards-some guy was giving completley wrong advice to an inexpereienced guy...ok,sounds harmelss engough right ? think about this for a second,someone else read the same advice,believed what he read,followed the instructions and destroyed his engine-not good huh ? can it happen ? sure can...same deal with electricity here...some of the stuff i have read and seen is down right scary...i had a boat in for service,it belonged to a gentleman who's an electrical contractor,a certified electrician...his bilge pump,the auto side was fed froma single piece of solid core copper wire,stripped and wrapped under the positive battery terminal,no fuse,and conectedto the auto switch feed using a "wire nut"...
here's the picture of it...

look at the thin black wire,this is the feed for the auto bilge switch...




these are the connections for the only bilge pump on the boat...




i forgot to mention the battery cable to feed the port engine,it was bolted together...nice huh ?




this is all done by a cerified electrician...nice huh ? this is the reason i'm not impressed with what people claim they know or what certifications and education the claim they have,trust me,i've seen just about everything...
i'll post up the dates i have for the electrical seminar...