Why did voltage drop?

Friends, I'm hoping for some thoughts on the behavior of my charging system.

I left the boat Sunday afternoon, plugged in to shore power and charger on, fully charged, showing 13.6 volts. When I boarded tonight at 9PM both monitors showed around 12.6 volts. Hmmm,

I flipped on the 12V breakers that I normally turn off when I leave (fresh water pump, head, lights) and the 120V circuit for the hot water heater. Immediately the battery monitors (Victron SmartBMV) popped back up to 13.4 volts.

The Victron allows me to look at the battery voltage and amperage history, so I did. What I found is that for whatever reason, yesterday (Wednesday) at 2PM voltage started to drop steadily from 13.6 until 4PM when it hit about12.8v. It then spiked temporarily to 14.5v for an hour, and then it dropped back to 12.8v. It then just tailed off over the next 26 hours until it hit 12.6v and I arrived. A screen shot is attached. Both battery banks show identical behavior. I have no idea if shore power was lost when the spike occurred, but I didn't do anything to turn it back on when I arrived, and it was working.

Interestingly, current never varies. It sits right at 0 amps, presumably because the charger us supplying power for the few 12v things that are still running (auto bilge pumps, LED on phone charger left plugged into USB port, etc.). Yet voltage tails off, not significantly, but slowly and surely.

For completeness, the charger is a ProMariner ProNautic 12-40. The batteries are FLA and are 1 year old.

Any thoughts on why voltage would drop off with no current draw?

Thanks,
BD

My thought and I could be wrong. The charger went into a sleep mode since the batteries where fully charged. When the voltage went down, it turned back on. Try giving ProMariner a call to if this is the case.

Thanks. I'll look at the manual first. Good suggestion.

First I'll say I think the ProMariner ProNautic are the same as the Sterling Pro Charger are the same hardware designed by Sterling marketed under different names. If you disagree with that then disregard what I'm saying.

I have the Sterling that exhibits similar behavior. It has two modes. One is powerr supply. The other, I forget the term, is California energy compliant. I was advised by Sterling to put the charger in power supply mode to remedy this problem. Instructions are in the manual,

Sounds like charger is entering a float cycle or similar and voltage is set to maintain 12.6. Could even be a state that in the Victron world is called "storage". Dig into the manual and settings.

Yes, the charger appears to be switching from "standby" to charging. On Show Hand with the Siren Marine monitoring system you could see the charger go to standby and the voltage slowly decline over hours until it switches back to float for a few hours, and then the process repeated.

In your situation, the charger may be initially going to Bulk, then absorption, and finally settling on float. That will be a function of the charger's programming on whether it reverts through the whole charging phase or goes directly to float based on voltage.

Ted

We had ProMariner chargers before, similar bahavior. Seems to be a "sleep" stage -- separate from the normal bulk/absorbtion/float modes...

In your case, 13.6V is probably your float setting, and lower voltages (12.6, 12.7, etc.) are when the charger is doing nothing. On purpose, near as I could tell.

I don't remember much about it in the manual -- although you might check both the ProMariner and Sterling manuals, since they do sometimes say things differently in each. Our current Victron mentions a "sleep" (or maybe "storage") mode like this...

-Chris

Thanks for all the leads! Yes indeed, upon review of the manual there is a "conservation mode" that it goes into and supposedly monitors the battery and only engages if it drops below the established range for that battery type (12.8 to 13.6v).

I do see history of voltage dropping well below that established range unfortunately (as low as 12.0). But it's possible (likely) that the charger or shorepower itself was turned off, as I had workmen on the boat doing a project (indoor winter storage). I will have another period where the boat will be unoccupied for a couple weeks at the end of this month, so I'll be interested to see what happens over that period.

Thanks again. I do recall reading about that conservation mode, but it never really sank in until I saw it in action in the monitors. I do love the ability to see all of that data.

BD

I just looked at the graph of the start battery last 24 hours. No charger between engine starts yet a roller coaster between 12.74 to 12.78. Have learned to ignore. House bank similar sitting on float charge.