Another Battery Question???

[Luna Sea 5]

since most know i had to replace both batteries on my last trip.  The tow guy said he found it strange that both batteries are dead and we couldn't jump it.  He claims it may be my alternator, but with 2 engines, he also finds it difficult to believe that both of them would have blown.

MY QUESTION.. 

If the alternators are blow, how long would I have to be on the water to kill both batteries, (without an alternator, which then will make be believe that I have a alternator problem.

If I survive one trip without killing the batteries, would that be enough time to say that (there isn't a problem)?

[Uncle Luna]

I would say so nick. I once replaced my battery in my car and put a new alternator in at the same time. I made 1 35 minute trip to work and battery was dead, turned out the rebuilt alernator was no good Once I changed it again it was OK.

[Kenny]

Nick,

how long the batteries last depends on how strong the batteries and how much of a draw you have on them, ie: ff, gps, radio etc. Strong batteries with none of the above running would give you a longer run time. Weak batteries with everthing running would not last long.

Either you had a voltage draw taking down both batteries, or a shorted cell in one which would kill them in a hurry.

The odds of both alternators being bad at the same time are very high.

do you have volt and or amp meters on the boat?

[Luna Sea 5]

no, i don't have a meter on the boat.  I replace my old batteries with 2 brand new, fully charged ones directly after my last trip.  Now, this weekend, the test...  I do run the radio, live well, gps, ff, all day, so if the batteries die after this weekend, then I can assume its the alternators.

[wb]

Nick, get yourself a cheapo digital voltmeter and stop guessing and or assuming. with motor off and battery fully charged, no current draws, across battery should read 12.5-12.9 volts

with motor running and rpms above 1500 or so if the alternator's good across battery should read 14.0 volts or above- no guessing needed.

do one set (motor & battery) at a time, make sure the other is isolated (out) of the circuit.

many ff's have a voltage readout built in, I know my Garmin does. be careful there could be 1.0 volt or more drop from the battery to the ff depending on how far away it is mounted.

[mckee17]

WB good advice.  Definitely need volt meter to determine if it's an alternator problem which I doubt, unless reverse polarity destroyed the diodes.

[wb]

learned it all the hard way

throwing money away and busting my knuckles

[CapBob]

Gotta have the volt meter

[Livewire]

Did you check out your battery switch? Sounds like poor connections,which would also affect your charging system. If you didn't exchange those batteries,try charging them.  -Livewire-

[IrishAyes]

I have to ask. Did you turn your battery switch (going from battery 1 to battery 2 or both) while the motors were running? If so, I believe you could damage both alternators at the same time. Just a thought...

[Luna Sea 5]

nope.. i put each side on all, then ride..

[IrishAyes]

 

[Capt. Mike]

nope.. i put each side on all, then ride..

I was always told not to run them on all when you have two motors that will cause damage. They need to be isolated. Running them both on all for an extended period of time can ruin the alternators and batteries. All is for emergency only, then isolate them. Have that said I did install an electronic switching and combining system on mine so that you can safely have both alternators charge one battery at a time. Not two alternators charging 2 batteries that are now combined.

[Luna Sea 5]

i have to have both batteries on all, since one battery runs one engine and the other runs the other.

[Hunter 2]

i have to have both batteries on all, since one battery runs one engine and the other runs the other.

This sounds strange to me    But I have a single engine.

[wb]

I agree with Eddie- one or the other or both batteries should be able to run any or all engines, accessories, etc depends on how you set the switch. Otherwise I'd say your wiring is afu from the start but with a newer boat I doubt that. Check the wiring before assuming. Give me a call if I can help.

[Luna Sea 5]

i will have to check it out.  I have 2 batteries, and also 2 rotory switches on each side.  1 battery cranks 1 engine, and the other cranks the other engine and runs all electronics.  I am not sure how my marina set it up.  He just told be to put both batteries on ALL.   

[wb]

2 batts 2 engines 2 switches is the right way to go

if wired correctly any or all batteries can run any or all engines and or accessories.

easy to isolate with that setup too.

[Luna Sea 5]

If I turn on my starboard side battery, my starbord side engine will start, but not my port engine, unless the port switch is also turned to all.

Maybe I need to keep both batteries on battery 1.  Maybe that will work.  I will check tonight.

[wb]

yes Nick that should work the way you describe

both set to 1 - batt1 runs both

same for both 2- batt2 runs both

same for both all- both run both

1 to 1 and 2 to 2: yep you guessed it

I have attached a schematic of the best way to do it perhaps that will help. Dont worry too much about the alternator details-- the connections to the battery switches are what is important.