Battery Voltage

[further]

Hi All,
last season i noticed my voltage gauge on the dash reading a bit low; did some research and checking with my multi meter and determined it was the alternator. Replaced the alternator beginning of this season and just took her out for the first trip. Boat ran great, but gauge still reads under 13v while running. I have a dual battery setup with a 1,2,both, off switch and isolator. Checked both batteries w multi meter and they read around 13 when no load, with a load (switch on 1 or 2) they read 12.7. No difference while running. Is it the batteries going bad? 3rd season on interstate cranking batteries.

 

[dingbat]

Nothing wrong with your batteries.

Track down the wiring in the voltmeter on the dash and clean the connections on the back. Clean the connections at the batteries as well

 

[further]

All connections on the battery side are spotless. I’ll check the voltmeter but why would the batteries read 12.7 while the motor is running. Shouldn’t it be in 13.5 range?

 

[dingbat]

At what rpm?

They don’t charge much if at all at idle.

Should be @ 14 VDC with the motor running at elevated rpm.

Bad stater or voltage regulator

 

[further]

Stays pretty constant through all rpm ranges according to the voltmeter. Used to be between 13-14 then at the end of last year it dropped to below 13 at all rpm ranges and was hesitating a bit at higher rpm range so I thought it was the alternator. Is there a way to test the voltage regulator? Stator- not sure I have that...
thanks for the help

 

[further]

Voltage regulator apparently built into the alternator so I’m at a loss. Guess I could’ve picked up a faulty new alternator? I’ll check the voltage at the alternator or maybe pull it off and have it tested.

 

[dingbat]

It would help if you would note what you are working on.

Have you traced the wiring from the alternator to the battery for loose, broken and or corroded wiring and terminals?

 

[Chris1956]

Battery isolators cause a voltage drop. You might so some research to see if that is the cause.

 

[further]

It would help if you would note what you are working on.

Have you traced the wiring from the alternator to the battery for loose, broken and or corroded wiring and terminals?

In my sig.... 2004 Volvo penta 5.0gxi-D. Will be doing some testing/tracing today.

 

[further]

So... alternator checks out at 14.45 at 1500 rpm and battery is at 13.45 at 1500 rpm. Is that normal? Shouldn’t it be closer?

 

[further]

Ok after running a bunch of tests... looks like the culprit is the isolator. It’s a 70amp 2 bank and is original from 2003. Any suggestions on a replacement brand? Assuming I can go with any 70 amp, 2 bank marine rated isolator?

 

[sam am I]

So... alternator checks out at 14.45 at 1500 rpm and battery is at 13.45 at 1500 rpm. Is that normal?

Yes, through that diode isolator it is...

Shouldn’t it be closer?

No, not much if any, assuming silicon isolator, then Vf(Forward voltage drop) running at say 10 amps or higher will typically be around 1V. Sounds like it's working as expected


If you want to stay with diode type, use shottky type, best pratice in that Vf(Forward voltage drop) is lower/better then silicon. With less voltage drop at a given current= less heat, less heat = longer life.

Also, with less Vf, battery will top off at a higher voltage...

e.g.,

Silicon 14.45V - 1V = 13.45V
Shottky 14.45V - 0.4V = 14.05V

https://www.victronenergy.com/upload...olators-EN.pdf

 

[sam am I]

Stupid web page is such a POS sometimes!!!

 

[further]

Thanks! Would it make better sense to replace the isolator with an ACR? Would the connections be the same?

 

[sam am I]

Would it make better sense to replace the isolator with an ACR?

Personally, I prefer(and run) this and would run it and the Shottky Iso long before I'd ever run an ACR.

ACR's require paralleling your 100%'ish charged batt (start batt typically ) with the dis-charged batt (house batt typically) in order to charge it. When you parallel a charged battery with dis-charged battery, they are forced to "equalize".

Meaning? The full battey (e.g.,@ 14.4V) is instantaneously forced(can be huge current inrush) by the paralleling relay(a switched wire) to dis-charge ("back-charge") some % down at the instant the ACR parallels it with the lower battery (e.g., @ 11V).

Mixing (paralleling and/or series) dis-charged batt's with fully charged batt's in order to just charge them all back up again isn't efficient (hence 2 and 3 bank chargers were invented...duh!!) and is NOT best practice. ProIso's switches out the 100% charged batt keeping it full 100% of the time, saving it's energy and directs 100% of alt's charge current to the batt that requires it, the dis-charged battery!!

Diode isolaors are similar in nature to the Proiso and work very well as they never allow back-charge however, the downfall of diode iso's is the "Vf" of their diode junctions as you've recently discovered. As advised, best practiced with diode iso's is to reduce Vf as much as possible, hence the Shottky recommendation.

Would the connections be the same?

No, if you choose to use an ACR....You'd need to take out the diode iso (and its two "output" wires), then run the alt charge wire (iso "input" stud wire) direct to batt #1's (start batt) pos post.

Then add ACR between batt #1(start batt) pos post and batt #2 (house batt) pos post.

 

[further]

Thanks for the detailed info. Much appreciated! Ordered a shottky today! Hopefully that’ll do the trick

 

[sam am I]

Yes so those units come with a integral comp diode to use with your alt "sense line"(see manu's install instructions) so this config then can automatically "boost" up the alt's output by the value of Vf.

AND!!

As the Iso unit heat and cools due to charge currents and ambient temps, Vf of the diodes to each batt can change slightly (Vf goes up with temp/current, spec says 0.3V to 0.45V), the beauty of this internal comp diode is it has to track similarly due to being integral to the unit because it gets heated to the same temp as the iso diodes.(old school push pull audio amplified driver trick)

And because this comp diode is in the alt's sense line feed, it is not only making up for static Vf drops, it now automatically adjusts the Vout levels to comp differing Vf's for differing temp levels......Win win!!