batteries not charging?

[boatman37]

well last year when on switch position 1 the boat died a couple of times. we were anchored and playing the radio and forgot to switch back before we pulled anchor so i chalked it up to a drained battery and an old alternator. so over the winter i replaced the alternator and just last saturday bought a new engine battery. the house battery is 2 years old. i switched my configuration so my engine is switch position #1 and house is #2. so sunday we went out on switch #1 engine battery and about 1/2 mile up river it died out. switched to #2 and went back towards the marina. went back to #1 and about 100 yards later it stalled again. back to #2 and into the slip. monday morning started doing some testing and the alternator is putting out 13.0 volts at the isolator. here are my findings:

1986 Sundancer 250 single merc 260 with dual battery setup

switch position #1 is engine battery
switch position #2 is house battery

with the switch in #1 position i have neither battery charging
with switch on 'both' neither battery charges
with switch in #2 position my engine battery charges (but i'm running off the house battery at that point)

none of the switch positions charge the house battery

my band-aid would be to switch my batteries around so when i'm running on #2 it is actually the engine battery and is charging. i ran all day monday on #2 position (house battery) and it was fine. every time i have had this issue it was with the switch in the #1 position (last year with the house battery and this year with the engine battery).

i'm new to this so not real sure how it is even supposed to work. i'm not real concerned with charging the house battery because the longest we are ever anchored is a few hours. my onboard charger will charge both on shore power but it is hooked directly to the batteries.

i know i can band-aid it and be fine but i would like to figure this out and fix it right, just don't know what to do other than check connctions. i need to pull a trim panel off to get to the back of the switch so hope to do that friday.

also, i have a wire near my alternator that is taped off. i don't know where it goes to but will trace that friday too. my manual shows an orange wire going from the alternator to the starter and i believe this wire is orange. but if that is needed would the engine even start? what would this wire do?

 

[Bt Doctur]

Most likely its the wire from the alt to the starter post. normally cut away from the alt and a new wire from the alt output to the isolator "C" common post. From there a wire from post1 to battery1 and from post 2 to battery 2.
Check post 1 and 2 for battery voltage and record
Start the engine and read alt output, check output on post 1 and post 2

 

[boatman37]

Thanks. When you say post #1 and post #2 you are talking about the isolator?

 

[skibum]

I'm sure that he is.

 

[boatman37]

checked some stuff yesterday. voltage at the 'COM' on the isolator was 6.6v? Both post #1 and #2 read 13.3v. the terminal on the back of the alternator that goes to the isolator 'COM' reads 6.6. i didn't take it out yesterday so not sure what will happen. i switched the battery leads so #2 is the engine battery and #1 is house. Plan to go out today so will see what happens

 

[boatman37]

talked to shop today that is rebuilding my original alternator. they said it is done and was good but the voltage regulator needed replaced. i asked about the 2 wires coming out that had broken insulation and they said that was the VR. so not sure if the VR was bad or they replaced it because of the bad wires? supposed to pick it up tomorrow so will try to ask them then

 

[boatman37]

Just a follow up...
still only seeing about 11.5 volts on my gauge and 10.5 with the bilge blower on. was out late sunday night and with my nav lights, VHF, and dash lights i was only seeing 10 volts. made it back in as we weren't far away. checked today with a handheld multimeter and only getting 11.5 at the alternator. the house battery is 2 years old and the starter battery is brand new (same symptoms with old starting battery so doubt batteries are the issue). installed a brand new DB Electrical alternator this spring and the original alternator was sent to a shop and they tested it and said it was good. they did replace the VR because the wires were pretty crappy. so now 2 alternators and 3 batteries and the same symptoms.

researching tonight i found a corvette forum that said to check voltage between the big terminal on the alternator and the positive on the battery. they said it should be close to 0. a higher reading means you have resistance somewhere. the end result for that guy was a loose connection on his starter. he had very similar symptoms.

my next thing is to heck all connections. not knowing much about these electrical systems i was under the impression that my low reading taken directly off the alternator meant that it had to be the alternator. after researching i see that the alternator has to receive power to output power? so my problem sounds like it may be between the battery and (flowing back to) the alternator? i have to look at my manual but in the corvette case the battery+ went to the starter. not sure if my boat is the same?

ughhh. i hate electrical

thoughts?

 

[paulswagelock]

Keep us updated. These are the posts we we all get to learn something we might not have encountered before.

 

[boatman37]

well i pulled all wires off my perko switch and scuffed them with sandpaper and put it all back together with dielectric grease. also put the old alternator back on it. now getting 15 volts from the alternator and my gauge reads slightly over 13.0 and with all switches turned on it dropped to about 11.5 (both the gauge and handheld multimeter), which is higher than i got before with nothing turned on. i also checked my solenoid and everything was tight there.

also, i checked voltage from the back of the alternator to the positive battery terminal and got slightly over 2 volts. is that bad? my cable on the starter runs up to my perko then back down to my starting battery. i am going to continue checking and cleaning connections and maybe replacing cables and wires along the way

 

[Bt Doctur]

What is the alt showing at the output lead ?
What is the battery showing with the motor off, and then running?
USING A METER NOT THE GAUGE METER As isolator will show a lower voltage after the diode so for testing place a jumper across all 3 posts and then check voltage on the dash

also, i checked voltage from the back of the alternator to the positive battery terminal and got slightly over 2 volts. is that bad.
If you mean 1 lead on the alt and 1 lead on the battery post then yes, thats bad .You have a hi resistance someplace .That short of a run should show 0 . battery cable ends, where the ends are crimped on, the cable strands themselves (green/corroded/oxidized) or the physical connections .

 

[boatman37]

I checked that wire with an ohm meter. it runs from solenoid to battery switch and back to the battery and get 0 resistance. does that mean that one is fine or could it still be bad? i saw no corrosion on any ends