18.4V coming in but only 12.8V going into battery bank

Discussion about the MX60 Charge Controller

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pioneerMan
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18.4V coming in but only 12.8V going into battery bank

Post by pioneerMan »

We are attempting our first Equalize after having our system many years. How will we ever reach the 14.4V needed to do a successful Equalize if only 12.8V are going out into the battery bank?

Thank you.
volts.jpeg
raysun
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by raysun »

The battery must be fully charged before starting an Equalize cycle.

The OUT voltage reflects the battery voltage, and isn't set by the controller. Rather it is used by the controller to manage the charging stages.

Stop the EQ charge, initiate a Bulk charge, and when the system reaches Float, THEN start the EQ stage.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by provo »

pioneerMan wrote: Mon Dec 21, 2020 8:58 am
We are attempting our first Equalize after having our system many years. How will we ever reach the 14.4V needed to do a successful Equalize if only 12.8V are going out into the battery bank?

It would help if you could tell us more about your system. Please fill out your system profile, including the following:

1. Number of batteries, make and model, and wiring scheme.
2. Number and wattage of solar panels, make and model, wiring scheme.
3. Make and model of all charge controller(s) and inverter(s).
4. Battery monitor showing state of charge, if any, make and model.
5. Do you have either an old Mate (small oval) or a Mate3/Mate3s (larger box with control wheel)?

What are your settings for absorb voltage, absorb time, and float voltage? How often do you achieve a full absorb at those settings, and how is it done (ie, from the charge controller and panels, from the inverter/charger and a generator, or some combination of both)?
pioneerMan
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Location: Northern Utah

Re: 18.4V coming in but only 12.8V going into battery bank

Post by pioneerMan »

From the tables I've seen on various websites, 12.7 is considered 100% charged, right? My screenshot above shows that voltage at 12.8. And the charge controllers said Float in the bottom right corner of the LCD screen. So it was appropriate to start the Equalize charge, right? After running the generator all day, and it being mostly sunny, the voltage still is only 13.1. Might this require running the generator all day long, for multiple days, to get up to 14.4?

Thank you.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by provo »

It's important what the make and model of the battery is -- are they flooded or fully sealed? Raysun knows all about AGM's, mine are flooded and for 12V nominal, would want ~16V in an EQ.

Also, if you really have 13 parallel strings of 2 series batteries in each string, you may have some serious imbalances in the states of charge of the various monoblocks.

And if you really have 13 x 210Ah = 2730Ah which you're trying to charge with 12 x 125W = 1500W of panels, you'd probably have to use the generator any time you wanted even just an absorb cycle.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by raysun »

pioneerMan wrote: Mon Dec 21, 2020 3:27 pm From the tables I've seen on various websites, 12.7 is considered 100% charged, right? My screenshot above shows that voltage at 12.8. And the charge controllers said Float in the bottom right corner of the LCD screen. So it was appropriate to start the Equalize charge, right? After running the generator all day, and it being mostly sunny, the voltage still is only 13.1. Might this require running the generator all day long, for multiple days, to get up to 14.4?

Thank you.
If the battery has properly reached Float, then an EQ charge can be started.

2713AH is a very large battery. If its flooded lead acid, then the charging current should be in the 10-13% range for the Bulk phase. That would be around 270A. The 12 PV panels and charge controllers aren't going to approach that rate of charge.

I suspect the battery is lightly discharged (relative to its capacity) and lightly charged. That leaves the potential that the electrolyte will stratify. To get sufficient "mixing" of the electrolyte, an Absorb phase of a good number of hours would be necessary. Not knowing the battery model, its hard to be precise, but 4 or more hours wouldn't be out of the question for a flooded lead acid battery.

As @provo mentioned, parallel strings of monoblocks increases the likelihood of cell imbalance. The general guidance is no more than 3 parallel strings in a battery.

To perform a proper EQ is going to require generator assist to engage the inverter charger along with the charge controllers. Its also going to require a whole lot of specific gravity testing to assure each cell in the battery is being fully charged and in balance with the other cells.

Does the trimetric battery monitor track charge and discharge current?
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by provo »

raysun wrote: Mon Dec 21, 2020 4:20 pm
Does the trimetric battery monitor track charge and discharge current?
.

Yes, both into (pos amps) and out of (neg amps) the pack, as well as Ah pos and neg. No logging, though, as far as I know (I have the 2020).
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by sbrownian »

Years ago, I knew a guy who got surplus telco batts that were around 2000ah. Had one cell that kept dropping and he didn't even have gen capacity to even begin to get that bank working right. Pretty sure it was only about 75 amps or so.

I suggested he get a 2.3v charger that was designed to be used across low cells like that. It could put out well over 500 hundred amps if I remember correctly, depending on configuration... I told him he'd have to watch it like a hawk, though, keeping track of the SG, temperature and voltage..
I think I heard he finally added another array, and got new batteries that were sized a bit more appropriately...
Information, you get not; if incorrect question, you ask..
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by raysun »

pioneerMan wrote: Mon Dec 21, 2020 3:27 pm From the tables I've seen on various websites, 12.7 is considered 100% charged, right? My screenshot above shows that voltage at 12.8. And the charge controllers said Float in the bottom right corner of the LCD screen. So it was appropriate to start the Equalize charge, right? After running the generator all day, and it being mostly sunny, the voltage still is only 13.1. Might this require running the generator all day long, for multiple days, to get up to 14.4?

Thank you.
12.6V can be considered fully charged, under some conditions, however during charging, the "fully charged" voltage is usually higher. 13.6V is more in the ballpark.

The battery is a very big bucket to fill. Your notion that it may take several days of generator assisted charging to reach EQ voltage is likely true.
Last edited by raysun on Tue Dec 22, 2020 12:06 pm, edited 1 time in total.
pioneerMan
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by pioneerMan »

provo wrote: Mon Dec 21, 2020 3:39 pm Also, if you really have 13 parallel strings of 2 series batteries in each string, you may have some serious imbalances in the states of charge of the various monoblocks.
I'm not quite sure what you mean by 12 parallel strings of 2 serious batteries in each string. I just know that we have 3 old freezers that we converted into insulated boxes to hold the 26 batteries. Wired in series and parallel, I think, to make it one giant 12 volt battery bank. Should I upload some photos?
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by provo »

pioneerMan wrote: Mon Dec 21, 2020 7:33 pm
Should I upload some photos?
Sure, photos are always helpful :grin: . Are there any documents showing how the whole system (as well as the batteries) are wired up? If you don't know, and can't figure it out, it's hard for anyone on the forum to know either.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by raysun »

20201221_180400.jpg
The illustration shows 6 Volt battery monoblocks wired in series - parallel.

The two blocks marked "6V" are wired in series, - and + connected to make a 12 Volt string.

Three such strings are shown connected in parallel, + to +, - to -, to create a 12 Volt battery of higher capacity.

We assume your battery is 13 strings connected in parallel.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by SandyP »

pioneerMan wrote: Mon Dec 21, 2020 3:27 pm From the tables I've seen on various websites, 12.7 is considered 100% charged, right? My screenshot above shows that voltage at 12.8. And the charge controllers said Float in the bottom right corner of the LCD screen. So it was appropriate to start the Equalize charge, right? After running the generator all day, and it being mostly sunny, the voltage still is only 13.1. Might this require running the generator all day long, for multiple days, to get up to 14.4?

Thank you.
As stated you have a very large battery and your solar array is the minimum ~5% that could recharge your battery bank depending on your usage. But given you have had the system for some time it must be working OK for you unless you have to use a genset regularly to get the battery bank through the absorb charging stage?
It would be interesting to know what your absorb and float set points are in the FM60s (and the inverter/charger?)?
I ask as if the FM60 was showing Float then I would have expected the voltage to be ~13.6V assuming you did not have any loads.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by fcwlp »

SandyP wrote: Tue Dec 22, 2020 1:41 am ask as if the FM60 was showing Float then I would have expected the voltage to be ~13.6V assuming you did not have any loads.
@pioneerMan, please post what your float, absorb and EQ settings are on both the charge controller and inverter.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by pioneerMan »

I will check the float, absorb and EQ settings when I got out to the shed later today. I'm guessing they are the factory default settings. But for the moment, here are some photos that make up the 3 "monoblocks" as you guys call them. If this is a bad way to wire batteries together, then what should have been done differently? You say it's a large battery bank, but we have to rely on the use of a generator quite often. Many times charging several hours in the evening is not enough to keep the electrical system from shutting down during the night due to low voltage. This mainly happens during the winter months. We are quite conservative in our electrical usage. The largest appliances we use are a fridge, propane clothes dryer, iMac computer, and a 55" TV for a few hours at night.

Mr. Provo, do you live in Utah?
bank3.jpeg
bank2.jpeg
bank1.jpeg
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by raysun »

A picture is worth a thousand words.

To clarify a bit of battery trivia - a "monoblock" is a collection of cells in a container. Each of those 6V "containers" is a monoblock. In the pictured example, the Monoblocks are interconnected to create a battery.

Looking at these pictures, it's easy to see the series connections between each pair of 6V monoblocks. Its the short cables that connect the minus (-) terminal of one block to the plus (+) terminal of the other block in the series pair. Connecting the 6V blocks in series adds the voltage so creates a 12V "string".

The long metal straps are creating a "bus bar" that connect the 12V strings in parallel: positive (+) terminals are connected on one side of the strings, and negative (-) terminals on the other side. When connected in parallel, the voltage stays the same (12V) and the Amp Hour capacities add.

The three "battery boxes" are in turn connected in parallel.

All those connections must be kept scrupulously clean and free of corrosion in order for all the cells to charge and discharge evenly. Its a pretty good bet, that even with regular cleaning, a battery with that many parallel strings is very likely to become unbalanced at the cell level.

How long has this battery been in service?

Has it been tested by measuring the specific gravity of the individual cells?
Last edited by raysun on Tue Dec 22, 2020 1:53 pm, edited 3 times in total.
pioneerMan
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by pioneerMan »

This system was built in 2008, but the individual batteries are from 2016 and more recent.

We did recently test the batteries with a gravity tester. All of them came up in the "yellow" zone instead of green or red.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by provo »

pioneerMan wrote: Tue Dec 22, 2020 12:47 pm
Mr. Provo, do you live in Utah?
Nah, surname is Provost :-)

Wow, those are some pictures! They look like Interstate -- what's the model number (I assume they're all the same model # ?)
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by SandyP »

raysun wrote: Tue Dec 22, 2020 12:55 pm A picture is worth a thousand words.
../..
All those connections must be kept scrupulously clean and free of corrosion in order for all the cells to charge and discharge evenly. ../..
Yep, what stands out is the corrosion which may result in poor electrical connections.
The nuts of each connection also need to be tightened to the same torque.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by sodamo »

pioneerMan wrote: Tue Dec 22, 2020 1:06 pm This system was built in 2008, but the individual batteries are from 2016 and more recent.

We did recently test the batteries with a gravity tester. All of them came up in the "yellow" zone instead of green or red.
Assuming this means the monoblocks are of various ages?

I’m guessing that besides the potential of uneven charging there is great potential of under charging.
Screenshots of all charge setting would be helpful.
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by sbrownian »

SandyP wrote: Tue Dec 22, 2020 1:39 pm
raysun wrote: Tue Dec 22, 2020 12:55 pm A picture is worth a thousand words.
../..
All those connections must be kept scrupulously clean and free of corrosion in order for all the cells to charge and discharge evenly. ../..
Yep, what stands out is the corrosion which may result in poor electrical connections.
The nuts of each connection also need to be tightened to the same torque.
Parallel banks can be problematic if the batteries are not well matched, (usually the main problem,) and there can also be problems with I2R losses in the wiring causing slightly different levels of charge between parallel strings, but that can be minimized by careful selection of wiring lengths, terminations and equipment.

If you do decide to tackle working on this bank, PLEASE wear protective gear and use INSULATED tools. Even wrapping a wrench with electrical tape can save you from a nasty surprise.

I would venture that each bank needs to be torn down, and all the connections cleaned and any corroded jumpers replaced.
I would further isolate all the batteries that are of the same manufacturer (and hopefully the same lot #) into one 'bank' if possible.

Number each battery to keep track of them and then start testing.

Even if you can 'group' them together by manufacturer, I still would be inclined to tear one bank out, break it apart and charge each battery string with an external charger. Yours are grouped as two 6v batteries in a string, so a regular 12v charger will work in a pinch.

If you have a 'smart charger,' run them through the bulk and absorption phase, and check the voltage and SG levels.

IF you don't have smart charger, use a regular 12v charger that can put out 10 to 20 amps, (if these are 200 a/h batteries,) and continue until they are reading 'green' SG levels. Keep an eye on the voltage and the temperature of the batteries and don't let them get too warm.

I would also look up the manufacturer recommendation as to what the actual specific gravity is for that battery to be considered charged.


Hopefully, the current level will drop down as they reach full charge and will fall to a fairly low level and stabilize. Most of the time, the battery will be considered to be fully charged if the voltage reaches the absorb voltage and the current drops off and stabilizes for about three hours. Specific gravity will also have come up to close to whatever that value is supposed to be.


THEN, disconnect that 'string' from any load and just let it sit for another 24 hours. (You can 'cheat' a bit here, but I wouldn't.)

Measure each battery voltage and record it along with the SG readings at the end of that 24 hours.

Then try to assemble a battery bank using a combination of 6v batteries whose resting open circuit voltages, SG# and manufacturer match as close as possible to each other. If you get wildly different open circuit voltages on a particular battery after 24 hours, I would be suspect that you have a damaged battery.

A lot of work?

Yes.

Pain in the rear?

Yes.

You will wind up with a bank that you know the condition of all the batteries and should be able to 'weed out' any ones that are causing issues.

You're better off with a smaller bank made up of properly matched batteries, than a large bank sprinkled with bad ones.

Anyone reading this who wants to chime in, have at it!
Information, you get not; if incorrect question, you ask..
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Re: 18.4V coming in but only 12.8V going into battery bank

Post by raysun »

sbrownian wrote: Tue Dec 22, 2020 7:28 pm
SandyP wrote: Tue Dec 22, 2020 1:39 pm
raysun wrote: Tue Dec 22, 2020 12:55 pm A picture is worth a thousand words.
../..
All those connections must be kept scrupulously clean and free of corrosion in order for all the cells to charge and discharge evenly. ../..
Yep, what stands out is the corrosion which may result in poor electrical connections.
The nuts of each connection also need to be tightened to the same torque.
Parallel banks can be problematic if the batteries are not well matched, (usually the main problem,) and there can also be problems with I2R losses in the wiring causing slightly different levels of charge between parallel strings, but that can be minimized by careful selection of wiring lengths, terminations and equipment.

If you do decide to tackle working on this bank, PLEASE wear protective gear and use INSULATED tools. Even wrapping a wrench with electrical tape can save you from a nasty surprise.

I would venture that each bank needs to be torn down, and all the connections cleaned and any corroded jumpers replaced.
I would further isolate all the batteries that are of the same manufacturer (and hopefully the same lot #) into one 'bank' if possible.

Number each battery to keep track of them and then start testing.

Even if you can 'group' them together by manufacturer, I still would be inclined to tear one bank out, break it apart and charge each battery string with an external charger. Yours are grouped as two 6v batteries in a string, so a regular 12v charger will work in a pinch.

If you have a 'smart charger,' run them through the bulk and absorption phase, and check the voltage and SG levels.

IF you don't have smart charger, use a regular 12v charger that can put out 10 to 20 amps, (if these are 200 a/h batteries,) and continue until they are reading 'green' SG levels. Keep an eye on the voltage and the temperature of the batteries and don't let them get too warm.

I would also look up the manufacturer recommendation as to what the actual specific gravity is for that battery to be considered charged.


Hopefully, the current level will drop down as they reach full charge and will fall to a fairly low level and stabilize. Most of the time, the battery will be considered to be fully charged if the voltage reaches the absorb voltage and the current drops off and stabilizes for about three hours. Specific gravity will also have come up to close to whatever that value is supposed to be.


THEN, disconnect that 'string' from any load and just let it sit for another 24 hours. (You can 'cheat' a bit here, but I wouldn't.)

Measure each battery voltage and record it along with the SG readings at the end of that 24 hours.

Then try to assemble a battery bank using a combination of 6v batteries whose resting open circuit voltages, SG# and manufacturer match as close as possible to each other. If you get wildly different open circuit voltages on a particular battery after 24 hours, I would be suspect that you have a damaged battery.

A lot of work?

Yes.

Pain in the rear?

Yes.

You will wind up with a bank that you know the condition of all the batteries and should be able to 'weed out' any ones that are causing issues.

You're better off with a smaller bank made up of properly matched batteries, than a large bank sprinkled with bad ones.

Anyone reading this who wants to chime in, have at it!
Pretty much wrote the gospel for battery rehabilitation there.

I can only add "Amen".

The "smoking gun" on the state of the battery is the amount of electrical "effort" its taking to charge it - large size not withstanding - and the short discharge duration until the working voltage drops too low. Both of these speak to failed cells.

Following the (admittedly arduous) steps above will help cull the bad blocks from the battery, and identify the good ones.

The saving grace of having so many parallel strings is one (or two) of the strings can be removed at a time without materially affecting the overall battery. As the two-block (12V) strings are removed, they can be tested, and charged, independently of the main battery.

Once 6 or so healthy blocks are selected out, they can be put back into service, while removing the remainder of the as-yet rehabilitated blocks.

All the bus bars and connecting cables should be thoroughly cleaned of corrosion.

A box of baking soda, rubber gloves, protective eyewear, and a sacrificial long-sleeved shirt will be helpful during the rehab.

Dielectric grease, a torque wrench, and a good multi-meter will help with the reassembly.
sbrownian
Forum Czar
Posts: 538
Joined: Mon Nov 30, 2020 9:23 am
My RE system: GS8048 FM80 FNDC Mate3
4kw solar
7kw Kubota propane gen
Had 1200 Ahr FLA Locomotive batts
Just replaced with
2 x 300 Ah ReLion Lithium packs
MUCH more efficient!!
Location: Central Washington State

Re: 18.4V coming in but only 12.8V going into battery bank

Post by sbrownian »

Just for comparison, this is what a commercial grade, 120v UPS bank looks like using VRLA cells.

This is a series connected bank, despite the parallel strapping.

Each of the 60 cells are 2 volts nominal, (the usual 1.8 to 2.3v per cell,) for a stack voltage of '120' vdc which supplies a three phase ferro resonant inverter.
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20140627_125002.jpg
Information, you get not; if incorrect question, you ask..
sbrownian
Forum Czar
Posts: 538
Joined: Mon Nov 30, 2020 9:23 am
My RE system: GS8048 FM80 FNDC Mate3
4kw solar
7kw Kubota propane gen
Had 1200 Ahr FLA Locomotive batts
Just replaced with
2 x 300 Ah ReLion Lithium packs
MUCH more efficient!!
Location: Central Washington State

Re: 18.4V coming in but only 12.8V going into battery bank

Post by sbrownian »

And here is a shot of a 12v parallel bank installed on a mountain top for the local 911 dispatch center.
The outfit that put this in did a very nice job..
Attachments
20150910_142044.jpg
Information, you get not; if incorrect question, you ask..
pioneerMan
Forum Virtuoso
Posts: 90
Joined: Wed Jan 09, 2019 3:40 pm
My RE system: 12 volt system
26 lead acid batteries, 6V, each rated at 210 amp hours
12 solar panels (Mitsubishi 125 Watt)
Outback VFX2812 inverter and two FLEXmax 60 inverters
Trimetric 2030A battery monitor
Mate 3d
Dual fuel 4500 watt AC generator
Location: Northern Utah

Re: 18.4V coming in but only 12.8V going into battery bank

Post by pioneerMan »

I appreciate all of this advice. It seems so time consuming, however, that it almost makes more sense to run a propane generator 24/7.

Ugh.

:sad:
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