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Old 09-03-2019, 08:29   #1
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Battery drop

Hi everyone.
I am having an issue with battery voltage drop over night. I can have the batteries fully charged according to a Victron BMV-700 battery monitor and a voltage of 12.7V also displayed on a solar control monitor. With only a fridge, VHF and MFD on during the night at anchor the battery voltage drops to 11.8V between 9pm and 5am.
The Victron battery monitor says the ah discharge is around 50 to 60 ah.
I have 5 x 142Ah lead acid batteries as service and 1 as a start battery.
The batteries were new in 2 stages, August and October last year.
I had the batteries equalise charged and tested in a shop last month and was told they are in good condition.
Any ideas as to why and more importantly how to test for the cause?


I am new to the forum so apologise if I have posted in the wrong area or missed a previous post on the same subject.
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Old 09-03-2019, 08:35   #2
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Re: Battery drop

Maybe first compare voltage measured at the battery to what your monitor is saying, just to be sure it's on the right page.

Your fridge, VHF, and MFD will each have a specification for current draw. From that, you can maybe begin to estimate what our energy budget might be. Probably have to make some assumptions about how often/how long the fridge compressor might run overnight. The MFD might be a fairly substantial load (guessing).

You'll also have an anchor light on overnight? If not LED, that could be a significant load, too.

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Old 09-03-2019, 10:21   #3
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Re: Battery drop

How do know the batteries were fully charged? I bet they aren’t and you bm is resetting to 100% too early.

You most likely aren’t getting truly fully charged.
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Old 09-03-2019, 10:28   #4
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Re: Battery drop

Was that full 12.7 in daylight or after sun went down?

Could be many things.


Shunt not in right place. Says 60ah drawn but more power has be taken away unmetered.

One or more battery is toast

Batteries not all connected together. Ie you are drawing 60ah out of one battery and others are still at 12.7. (Seen this...).

Meter wrong.
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Old 09-03-2019, 10:49   #5
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Re: Battery drop

Quote:
Originally Posted by sailorboy1 View Post
How do know the batteries were fully charged? I bet they arenít and you bm is resetting to 100% too early.

You most likely arenít getting truly fully charged.


My money is on this, if your relying on Solar alone day after day to be fully charged, itís likely that your not.
Of course check your connections to be sure that are all good.
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Old 09-03-2019, 11:14   #6
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Re: Battery drop

Greetings and welcome aboard the CF, Khiimori.
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Old 09-03-2019, 15:22   #7
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Re: Battery drop

I had the batteries out of the boat and an equalizing charge complete. The solar charge controller also indicates a full charge and goes into conditioning charge mode according to the LED's.
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Old 09-03-2019, 15:30   #8
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Re: Battery drop

I have been running the engine to charge the batteries every morning until the battery voltage is up over 12.5v. Also of an evening if required around 7pm if the voltage I a bit low after the sun goes down.
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Old 09-03-2019, 15:53   #9
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Re: Battery drop

How old are the batteries? Are all connections clean and tight? What is voltage AT the terminals? Have you load tested batteries?

Absent this info, this is a guessing game.
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Old 09-03-2019, 17:06   #10
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Re: Battery drop

Quote:
Originally Posted by Khiimori View Post
I have been running the engine to charge the batteries every morning until the battery voltage is up over 12.5v. Also of an evening if required around 7pm if the voltage I a bit low after the sun goes down.
Your batteries arenít getting charged. You need to look up how to determine as Iím not typing it all.. it doesnt matter if you equalized or what your solar controller says.

But it you really feel they are getting fully charged then your batteries are dying.

But I donít feel they are getting charged because you have not responded to that question with the right answer of voltage and battery acceptance.
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Old 09-03-2019, 18:31   #11
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Re: Battery drop

Khiimori,

You really need to do some basic research about batteries and how they work.

If your solar panels are bringing them up to 12.7 Volts they are NOWHERE near fully charged.

Fully charged is holding at 14.4 Volts until the current drops to less than 5 amps--for your batteries.

If you have been cycling the batteries between 12.7 and 11.8 volts for a year, they are likely already dead beyond recovery.
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Old 09-03-2019, 19:47   #12
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Re: Battery drop

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Originally Posted by Khiimori View Post
I have been running the engine to charge the batteries every morning until the battery voltage is up over 12.5v. Also of an evening if required around 7pm if the voltage I a bit low after the sun goes down.
that doesn't make sense. as soon as you start the engine you should be at ~14v. if you battery is 12.5v with the engine running they are not even charging. or are supper dead. how many amps does your victron gauge say with the motor running? there is no way to tell how charged a battery is by voltage. because it will just stay at 14v during the whole charge cycle.

if your battery is at 11.8 volt, and yous start the engine and it climbs to 12.5v. you need to wait until it continues to climb to ~14.4v and then wait another few hours of running after that. if the alt is really small then even more hours.
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Old 09-03-2019, 22:42   #13
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Re: Battery drop

A couple of things may be going on here:



1. As SailorBoy said: you are not actually getting to 100%. Don't trust the Victron battery monitor. Check the state of charge with a hydrometer or open circuit voltage. A good proxy for open circuit voltage is simply system voltage under light load after surface charge is off -- see the other threads on this.


2. If the problem is not that you are undercharging them, then the batteries need replacing. Classical sign of bad lead acid batteries is that they apparently charge quickly and show a high state of charge, then the charge inexplicitly disappears, like overnight.


The two things are often related -- chronic undercharging, which results from believing an amp-counting battery monitor, particularly one which is not calibrated often, will kill the batteries, producing the second effect.
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Old 09-03-2019, 22:54   #14
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Re: Battery drop

And as Billknny said -- it is important to understand that the voltage achieved during charging is meaningless, without considering the current. Just because the voltage reaches 14.4v or whatever during charging does not indeed mean anything if the batteries are still accepting a lot of current.



Especially with bad batteries or batts starting to go bad, you might just put on a bit of surface charge. It takes a long time to get lead-acid batteries the last 10% or 20% to 100% because the acceptance rate falls off, but if you fail to do that regularly, at least once or twice a week, you will kill your batteries quickly. With solar, depending on the size of the installation, a good way to do this might be to put on what looks to you like a full charge in the morning with the alternator, then let solar work all day putting on the finishing charge.


Is your alternator externally regulated? Without external regulation, you might not be getting much of a charge from that, either.
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Old 10-03-2019, 13:37   #15
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Re: Battery drop

Voltage **at the bank** during charging should get up to the high end of what the batt mfg specifies for Absorb, usually 14.4V or higher, and hold there for many hours.

After charging is finished, Float should be somewhat lower, but that should only happen **after** 100% Full has been reached.

That is defined as Amps accepted by the bank, **measured there** while holding Absorb V, has fallen to under .5A - 1A per 100Ah of bank capacity, unless a different endAmps is spec'd by the batt maker.

If this Full point is not reached at least a few cycles per week, bank life is much shorter.

Your BM must be manually reset to 100% each time in order to remain at least somewhat accurate.

If you are also regularly drawing the bank much below 50%, its life can be **very** short.

Especially if not a great quality for deep cycling to start with.

It is also common for BMs to be installed incorrectly even by professionals.

An Ah-counter measuring each big load's per-24-hr consumption can also be very useful.
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