Low Voltage alarm whilst Victron BMV showing 90%+

[jamesconnell]

Hi All,

I'm new to the forum so please forgive any faux pas. Can I please get some thoughts and advice on a battery issue I’m experiencing on my boat?

I have a 36' Cruising yacht which has 2 x 110Ah sealed house batteries. I fitted a Victron 712 BMV last year and replaced the batteries about 4 months ago. The boat lives on a swinging mooring and I have a 32W solar panel which keeps the batteries topped up when the boat is not in use.

Usually the BMV is showing 100% when we open the boat up plus we have, on average, a 45min motor against the wind to get out of the river before we sail so the batteries are usually pretty fully charged.

When the boat is sailing there is between 20W-40W load on the batteries for the instruments, autohelm and radio etc. If we turn the fridge on the load goes up to around 90W when the compressor kicks in.

The issue I'm experiencing is that when the fridge compressor runs the battery voltage drops to a level which triggers the low voltage alarm (<12.2V). When the compressor shuts off the voltage recovers to around 12.4/12.5 again whilst the BMV is still showing a battery level around 95%

Given that I have a capacity of 220Ah I would expect to be able to pull 110Ah out before the battery voltage dropped to this level, which even running at 90W would be after 14.5hrs, not less than one which is what I'm experiencing.

Have I missed something critical about the battery behaviour under load, or do I have a problem lurking.

Many thanks
James

[john61ct]

Voltage sags under load, then recovers at rest over time.

Inverse with charging.

Resting V is one (only approximate) measure of SoC.

All that is normal, but if the V sag is great relative to Ah capacity, that may be a sign the battery has worn, lost capacity from the original rating.

Good quality batteries designed for deep cycling stand up to it better, and different chemistry types resist sag better than others.

There may also be connection issues, high resistance from loose or corroded points for example.

[a64pilot]

Well just from an outside observation how do you know the panel keeps them topped up?
Very often charge sources drop to float prematurely and chronically undercharge and over time charge can slowly walk down.
I am not saying this is what is wrong, but maybe is, if possible I’d take them home and equalize them, if you can, if they improve then I’d be even more suspicious of chronic undercharging.
Four months isn’t long, something is going on.
Is there any load on the batteries when it sits on the mooring?

[john61ct]

Yes how are you confirming they get to Full? Best not to take the charge source's word.

Note with sealed batteries confirm the maker recommends equalizing, and if so, follow their specified protocol.

Among good AGM makers only Lifeline still does.

But some have different "conditioning" routines at lower voltages.

[conachair]

Originally Posted by jamesconnell

The issue I'm experiencing is that when the fridge compressor runs the battery voltage drops to a level which triggers the low voltage alarm (<12.2V). When the compressor shuts off the voltage recovers to around 12.4/12.5 again whilst the BMV is still showing a battery level around 95%

Given that I have a capacity of 220Ah I would expect to be able to pull 110Ah out before the battery voltage dropped to this level, which even running at 90W would be after 14.5hrs, not less than one which is what I'm experiencing.

Have I missed something critical about the battery behaviour under load, or do I have a problem lurking.

Many thanks
James

Something sounds wrong for sure - this is accurate data from 2 x T105's so 225Ah @ 12v. Looking at the voltage probably not too far from fully charged , temperature can pull voltage down quite a bit as well , think this was Feb so they must be pretty full. Easy to see the voltage dip a bit when the fridge cycles. Actually, can't be hot as the duty cycle of the fridge is so low.
Voltage shown is straight off the battery posts - where does your alarm connect to? 12.4/12.5v sounds maybe a little low for 95% and 2/3A - though I'm used with trojans which handle the loads well.

[sailorboy1]

No way is 45 minutes of motoring getting those batteries fully charged!!!!! And I serious doubt a 32W panel makes much difference.

When you are motoring what is the BM amps going into the battery? If it isn't 14.6+V and less than 1.1amps the battery isn't fully charged. Even if the charging gets to the 14.6+V and less than 1.1 amps it would need to stay there hours to be truly fully charged.

The OP needs a 100W plus panel and/or a Honda of something to acturally get fully charged once in a while.

[zboss]

Could be something as simple as a loose/old wire or corroded fitting to the fridge compressor which can cause voltage problems.

[donradcliffe]

Is the wire that is reading less than 12.2v a non-current carrying wire which is connected directly to the battery terminal?? If it is, its a battery problem. If it isn't, its a wiring problem.

[sailcrazy]

Following. We have a similar issue. Our house bank is 6 T-105s. We have 320w of solar, and as we rely on an electric stove and a 230vAC motor for the refer, we run the genset (with the battery charger ON every day for 1-2 hours. Our Victron 712 shows the batts at 90%+, but when we use the windlass the "Low Voltage" alarm shows on the chartplotter and we occasionally get other indications of a lower voltage than we should see for that SOC. Our batt bank is 3 yrs old...looking for ideas.

[SV Sedna]

I had a similar problem with the Victron BMV602. My issues was a cracked inline fuse holder on the voltage sense wire.

[john61ct]

Check how many amps the load is pulling.

A windlass can be **lots** more than the 4A fridge discussed by the OP, and will pull down even the healthiest bank, if bank chemistry is low discharge-rate or sized too small Ah.

As banks wear out, their V sag comes sooner and grows greater, that is completely normal.

Or it can be wiring.

Point is, there is no one fits-all solution, varies for each case,

anyone remote will still need all the relevant details & numbers to make educated guesses as to the cause & remedy,

which means someone knowledgeable with an ammeter and DMM is needed on the boat regardless.

[a64pilot]

Originally Posted by sailcrazy

Following. We have a similar issue. Our house bank is 6 T-105s. We have 320w of solar, and as we rely on an electric stove and a 230vAC motor for the refer, we run the genset (with the battery charger ON every day for 1-2 hours. Our Victron 712 shows the batts at 90%+, but when we use the windlass the "Low Voltage" alarm shows on the chartplotter and we occasionally get other indications of a lower voltage than we should see for that SOC. Our batt bank is 3 yrs old...looking for ideas.

Well a couple of questions.
How big is the charger and when do you run it? How big is the bank in AH?
What kind of batteries and what is the absorption and float voltage, do they ever get to float? They shouldn’t if your only showing 90 ish percent charge.

How often do you reset the battery monitor?

Read this article, it may take some time to nug through it, and you May have to take a break or two and reread some of it, but try to get to where you understand everything.
Then there is also a wealth of information about batteries and the care and charging of batteries elsewhere on the site, he leans heavily towards Lifeline AGM, I suspicion it’s because they have an excellent manual and publish charts etc that the other manufacturers don’t, but the majority of the information is relatable to other manufacturers and even other types of lead acid batteries.
https://marinehowto.com/programming-a-battery-monitor/

Then I’d suggest that there are basically two ways to know for sure what your batteries SOC is first thing in the morning, become well educated about batteries and apply that knowledge and maintain the battery monitor you have, or buy and install a Balmar Smart Gauge.
Knowledge is however, power.

[sailcrazy]

a64...to answer your questions: T105s are Trogen LA, at 6v ea, with a total of 675amphrs. The batts are set up as 3-12v. The charger is a ProMariner 50amp electronic, with 3 seperate feeds (one for ea 12v set. I do have a Balmar SG installed, as well as the Victron 712 (2 diff technologies) The batts routinely go into float, especially when the sun is out (a Victron controller on the 320w of solar). The batt chgr often starts at a 40a-50a load, but is typically down to 6-9amps (that's 2-3 amps per 12v batt)when we shut down the genset. As both batt mon (Victron and Balmar) are only 2 yrs old, I have not reset them yet....on the list to do when we resplash this Nov. and yes, I equallize the batts 2/yr. The Victron solar, Promatic Chrgr, and SG have been set for the Trogen recommended settings for T-105s. Like I wrote initially, the bank usually shows 95%+, but occationally gets down to 90%-92%......yet the low voltage alarm on the chart plotter goes off when we're raising the anchor. And the digital voltage showing on the USB plugins and on the Blue Sea digital direct readout routinely show 12.2-12.4v when the BM shows 95%+ SOC. And I'm confused

[BruceS]

The Victron resets itself. From the manual.


[QUOTE]
2.2 Synchronizing the BMV
For a reliable readout, the state of charge as displayed by the battery
monitor has to be synchronized regularly with the true state of charge of
the battery.
This is accomplished by fully charging the battery.
In case of a 12 V battery, the BMV resets to “fully charged” when the
following “charged parameters” are met: the voltage exceeds 13.2 V and
simultaneously the (tail-) charge current is less than 4.0 % of the total
battery capacity (e.g. 8 A for a 200 Ah battery) during 4 minutes.
[END QUOTE]


It can also be done manually if desired.