Voltage Dropping

tniggeltniggel Member Posts: 66 ✭✭
I'm in need of some help locating a voltage demon. 2007 270, volvo 5.7gxi-g.   I am getting a consistent drop in voltage when running.  Here is what I have replaced and checked
 - All new batteries, 2 - 27 group AGM deep cycle on battery2, 1 - flooded group 24 started 1000MCA battery 1
 - Swapped isolator
 - Replaced alternator with brand new OEM volvo direct replacement.  Also replaced the serpentine belt when I did this.
 - Checked all ground connections at ground bar, no apparent corrosion, all connections tight
 - Checked ground on engine, mild chalky coloring, disconnected coated all with dielectric grease and reconnected
 - All connections on DC distribution panel are tight
 - Checked voltage on both sides of 70A charger breakers at DC panel.

Here is what happens after all of the above, I come to the boat after a week away (charger on), battery meter on dash reads 13.3 volts.  This is consistent with the voltage on the GPS.

I disconnect shore power, drops to 12.8. 
 -With battery switch on 1 (24 group starting)Turn ignition to On and voltage will drop to 12.5.  Start engine, drops to 12.2.  Voltage then continues to drop slowly while running, even on plane 4K RPM's. 
 - With battery switch on 2 (2-27 group deep cycle AGM), voltage is reading 12.6, ignition on drop to 12.5, start and it stays there)
 - With battery switch on emergency start, voltage reads 12.5, starts and stays there.

I return to dock, with voltage going between 11.9 and 12, turn off ignition and it returns to 12.2.  2 weeks ago voltage dropped to 10.8, triggering a low voltage alarm.  Seems to me that it is something triggered by the ignition being on.  I don't understand why the alternator would not be charging.   I suspect that the AC battery charger is going, as the battery voltage on the dash drop as soon as I disconnect the shore power without turning anything else on.   I have had this boat since new (2 hours on the boat) and have started to have these issues last year and assumed the 2 year old batteries were going bad.

 Is it the battery switch?  How do i check that?  
 Should I have done a continuity test on the battery charger breakers instead of voltage in and out of the breaker when motor was running?
 

Any and all things to check (and how to check them) is appreciated.  I am literally losing sleep over this (as you can tell by the time of the post.  

Comments

  • Handymans342Handymans342 Member Posts: 8,503 ✭✭✭✭✭
    I don’t think you should have used dielectric grease. You could have a short on the DC side causing a fast drop. Do you have a DC amp meter so you can amp the battery cables? 
  • LaReaLaRea Alexandria VirginiaMember Posts: 4,371 ✭✭✭✭✭
    If you disconnect power and leave the engines off, it stays at 12.8V and doesn't start dropping after a few minutes?  Meaning, it drops ONLY when the engine runs?  Or does it drop when you turn on the blower?

    It sound like alternator current is not reaching the batteries.  You replaced the isolator ... did you check both ends of the cables to/from the isolator?  Trace along the cables for damage?  
  • reneechris14reneechris14 Pawcatuck river CTMember Posts: 2,698 ✭✭✭✭
    I'm with @LaRea start at the back of the alternator volt meter should be at 14.1 then isolator in should be the same, isolator out will drop to 13.7 then trace wire to start battery that should be 13.7 also. To make a 12 volt amp meter uou need to break a connection and put the volt meter between thise 2 points. The isolator may go to the battery switch?
    2005 Rinker FV342  Pawcatuck river,Ct
  • tniggeltniggel Member Posts: 66 ✭✭
    LaRea said:
    If you disconnect power and leave the engines off, it stays at 12.8V and doesn't start dropping after a few minutes?  Meaning, it drops ONLY when the engine runs?  Or does it drop when you turn on the blower?

    It sound like alternator current is not reaching the batteries.  You replaced the isolator ... did you check both ends of the cables to/from the isolator?  Trace along the cables for damage?  
    The battery voltage will drop by about 0.2v  when I turn the blower on.  The voltage will drop during the day when Anchored, but I haven’t been switching battery switch.

    the voltage into isolator is 13.9-14.5 depending on engine speed.  Voltage out (on leads on isolator and batteries)when I checked the old isolator and the new one is 12.8 and 12.4.  That didn’t make
    sense to me, but it was the same with both isolators.





  • LaReaLaRea Alexandria VirginiaMember Posts: 4,371 ✭✭✭✭✭
    So you're seeing a voltage drop of 1.5 volts across the isolator?  That seems high.  You should expect some drop in voltage.  A conventional diode isolator has a voltage drop of around 0.7 volts.  But I don't think it should be 1.5 volts.  

    There are isolators with essentially zero voltage drop.  They are a little more expensive.  For example, this one is $160.  The benefit is that your batteries receive higher charging voltage when you run the engine.  

    https://www.amazon.com/ProMariner-ProIsoCharge-Battery-Isolator-180Amp/dp/B004VBGUBC
  • YYZRCYYZRC Georgian BayMember Posts: 939 ✭✭✭
    Is the AC charger original?  I would start by completely disconnecting the AC charger from the isolator and then see if you're still experiencing the big draw.
    2008 330 EC on Georgian Bay
  • tniggeltniggel Member Posts: 66 ✭✭
    YYZRC said:
    Is the AC charger original?  I would start by completely disconnecting the AC charger from the isolator and then see if you're still experiencing the big draw.
    Good thought.  @Cableguy Greg thinks it’s the charger as well.  Never thought to just disconnect it.  Is it possible that there could be a short in the charger causing the drop
  • tniggeltniggel Member Posts: 66 ✭✭
    Changed the battery charger.  Now getting 14.5 volts at the gps.  Hasn’t been over 13.3 on the charger for a couple years. Still dropping when starting, but I just did the swap, going to come back In A couple days after it has time to charge.  So far promising.  Also, my gos was on the fritz for a couple years now, I’m thinking this has been a problem for a while because my gps is working great now
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