Battery voltages

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ericmcgrandle

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New to the forum so hopefully this is in the correct place.


I am having some problems with my deep cycle batteries on my RV. Here is some quick information about the system:

2 x 130AH Crown Lead acid, flooded batteries.
2 x 100 W Renogy Solar panels
Renogy Rover 30a mppt charge controller

Currently my batteries voltage's never stay at 12.7V, instead they will drop to about 12.5V with no load on them. To test this I charged them to 100% using 1 nights full charge with a 7.2a charger, and then 2 full days of solar charge with the batteries not connected to any load. I then disconnected all of the chargers and let the batteries sit over night, no load, no charging, and in the morning the batteries voltage was at 12.42 and 12.45. However, the SG reading was 1.275 for all of the cells.

I have tried to equalize the batteries but I do not have a big enough charger to reach the 15.5V recommended for equalization. As such I used the solar panels to push in 14.2-14.4V for about 8 hours.

Any thoughts on why the batteries won't hold a 12.7V charge?

Cheers
 

Kevin Means

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Hi Eric, and welcome to the RVForum. I'm assuming the water levels are good. How old are the batteries, and how were they used? The first thing I'd do is test the voltage with another volt meter to rule out a bad indication. If it's the same, I'd suspect sulfation. It occurs when the batteries sit for extended periods of time in a not fully charged state. If caught early, sulfation can often be reversed by equalizing them. You're going to need a charger that's capable of getting the voltage up higher. 

Another possibility is, they're just worn out. When lead/acid batteries are repeatedly deeply discharged, they lose their ability to hold a charge.

Kev
 

Gary RV_Wizard

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Lead-acid batteries that have been frequently discharged to low levels, roughly 50% or less, will lose capacity. Ditto if heavily discharged just a few times, say to 20% or less.

Could also be low on electrolyte in one or more cells (add distilled water if needed), or some contamination may have got into the electrolyte when the cell cap was off (dirt or chemical).

12.4v is only about 80% charge level, so you are definitely taking a substantial loss.  You said the chargers were removed before resting overnight, but were the batteries disconnected from the house circuits altogether? In other words, are you sure there was no phantom power draw?  Merely turning off all the power switches does nt generally stop all power consumption - most circuit boards retain power. They use only tiny amounts, but they can add up.
 

ericmcgrandle

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Kevin Means said:
Hi Eric, and welcome to the RVForum. I'm assuming the water levels are good. How old are the batteries, and how were they used? The first thing I'd do is test the voltage with another volt meter to rule out a bad indication. If it's the same, I'd suspect sulfation. It occurs when the batteries sit for extended periods of time in a not fully charged state. If caught early, sulfation can often be reversed by equalizing them. You're going to need a charger that's capable of getting the voltage up higher. 

Another possibility is, they're just worn out. When lead/acid batteries are repeatedly deeply discharged, they lose their ability to hold a charge.

Kev

I made the mistake of not watering the batteries for a couple months (which I am sure caused some of the problems), but the water levels are now good.
Batteries are 6 months old.
The charge controller reads the same voltage as my voltmeter.
I do not believe the batteries were ever discharged below 50% however, I did not check them very frequently in the first couple months so I cannot be sure.

Cheers for the response.

Gary RV_Wizard said:
Lead-acid batteries that have been frequently discharged to low levels, roughly 50% or less, will lose capacity. Ditto if heavily discharged just a few times, say to 20% or less.

Could also be low on electrolyte in one or more cells (add distilled water if needed), or some contamination may have got into the electrolyte when the cell cap was off (dirt or chemical).

12.4v is only about 80% charge level, so you are definitely taking a substantial loss.  You said the chargers were removed before resting overnight, but were the batteries disconnected from the house circuits altogether? In other words, are you sure there was no phantom power draw?  Merely turning off all the power switches does nt generally stop all power consumption - most circuit boards retain power. They use only tiny amounts, but they can add up.

Electrolyte levels are all good as per the hydrometer tests.
Water levels are good (now).
There is some contamination in one of the cells (has produced a slightly brown, murky colour) but the SG reading for that cell is still 1.275. The batteries were completely disconnected from all chargers and from the house. There was 0 load on them. There is a very slight possibility that the batteries were discharging due to dirt + a little bit of water that was dripped from taking SG readings but that's very unlikely in my mind as the batteries are pretty clean.

Cheers for the response.
 

Lou Schneider

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If you have the 31DC130 commercial deep cycle battery, it may have a slightly lower than normal resting voltage on account of it being a true deep cycle battery with different plate chemistry and structure than a starting or dual purpose battery.

In any case, 12.75 specific gravity is great.  If all the cells are at that level the battery is fully charged and healthy.  If you had sulfation or other problems the SG would be lower in one or more cells.

Crown doesn't give the fully charged resting voltage on their data sheet, but it does have a Depth of Discharge vs. Voltage table that starts at 12.3 volts after a 20% DOD:

https://cdn.shopify.com/s/files/1/1579/5179/files/31DC130_PowerSheet_D12130_0213.pdf

In short, you're probably fine even with the slightly lower full charge resting voltage.  If the batteries are otherwise working OK I wouldn't worry about it.
 

Gary RV_Wizard

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That murky color in one cell seems ominous, but if the SG is 1.275, it must be ok.  Most home & shop hydrometers aren't that accurate, though, and there is only a few hundredth of SG between 80% and 100% SOC.  Well, all you can do is use them and see how well they hold up in use. If they seem to discharge rapidly, then the probably are only at 80% despite the SOG. But if they a yield the expected amp-hours, then they are fine.

I've not heard or read that a deep cycle has a lower voltage than a starting battery. The difference is in the plate thickness and spacing, not cell chemistry. AGM and Gel type batteries exhibit slightly higher voltages, but from what I read flooded lead acids should read the same and total 12.6v.
https://deepcyclebatterystore.com/how-to-maintain-batteries/
Be aware that a battery can have good voltage and SG and still have few usable amp-hours. If the lead plates are damaged or crusted with unusable lead alloys, the amp capacity is decreased even though the remaining plate is sufficient to produce the desired voltage.
 

ericmcgrandle

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Lou Schneider said:
If you have the 31DC130 commercial deep cycle battery, it may have a slightly lower than normal resting voltage on account of it being a true deep cycle battery with different plate chemistry and structure than a starting or dual purpose battery.

I have the 31HDC130 (presumably the same?). I?ve never heard of the lower voltage but I?ll look into that. Thanks
John From Detroit said:
12.5 Well  Is your meter calibrated?  I mean 12.6 is normal resting and self discharge happens too.

As far as I can tell. It?s the same reading as the charge controller.
Lou Schneider said:

Yup. Although I do not have a thermometer so I am guessing a little bit (a lot). But I am in 90+ weather at the moment and the SG readings (without compensation) is around 1.270 so safe to assume the batteries are at least 90 degrees plus a little bit. All in all, 1.275 SG reading.

Gary RV_Wizard said:
That murky color in one cell seems ominous, but if the SG is 1.275, it must be ok.  Most home & shop hydrometers aren't that accurate, though, and there is only a few hundredth of SG between 80% and 100% SOC.  Well, all you can do is use them and see how well they hold up in use. If they seem to discharge rapidly, then the probably are only at 80% despite the SOG. But if they a yield the expected amp-hours, then they are fine.

I believe I got a little dirt in the one cell when I was cleaning the battery. I completely agree about the hydrometer. Not the most accurate at all but good enough for my purposes I guess.
 

Gary RV_Wizard

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The point about hydrometer accuracy is that you cannot rely much on small differences in the readings.  1.265 is 100% while 1.225 is only 75%, so only 0.04 difference.

I bring this question up because your SG readings are suspiciously high. The expected SG for a 100% charged lead-acid battery at 90 F. is 1.261, yet you are showing 1.275, even without temperature compensation. The temperature comp factor is +0.004 per 10 degrees F., so your compensated reading is 1.279.. Either the battery is 120% of full or the hydrometer is somewhat off spec.

http://all-about-lead-acid-batteries.capnfatz.com/all-about-lead-acid-batteries/lead-acid-battery-maintenance/battery-hydrometer-temperature-correction-chart/
 

solarman

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ericmcgrandle said:
New to the forum so hopefully this is in the correct place.


I am having some problems with my deep cycle batteries on my RV. Here is some quick information about the system:

2 x 130AH Crown Lead acid, flooded batteries.
2 x 100 W Renogy Solar panels
Renogy Rover 30a mppt charge controller

Currently my batteries voltage's never stay at 12.7V, instead they will drop to about 12.5V with no load on them. To test this I charged them to 100% using 1 nights full charge with a 7.2a charger, and then 2 full days of solar charge with the batteries not connected to any load. I then disconnected all of the chargers and let the batteries sit over night, no load, no charging, and in the morning the batteries voltage was at 12.42 and 12.45. However, the SG reading was 1.275 for all of the cells.

I have tried to equalize the batteries but I do not have a big enough charger to reach the 15.5V recommended for equalization. As such I used the solar panels to push in 14.2-14.4V for about 8 hours.

Any thoughts on why the batteries won't hold a 12.7V charge?

Cheers


good chance of sulfation, especially as you have insufficient solar panels for that amount of storage.
you need at least 312 Watts to make the C/10 minimum charge rate and that equates to approx 400 watts of panels.

C/10 here assumes you have those batteries in parallel. ( 130 Ah * 2 / 10 = 26 Amps @ 12 V )


also you don't get 8 hours of sunshine to do that equalization cycle unless you live on the equator..



 

ericmcgrandle

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Arch Hoagland said:
Have you thought about taking the 6 month old batteries back to where you bought them and have them test the batteries?

Currently in Mexico far away from where I bought them (Canada). I have thought about bringing them to a shop down here but thought I'd find out a little more information first.

Thanks.

Gary RV_Wizard said:
The point about hydrometer accuracy is that you cannot rely much on small differences in the readings.  1.265 is 100% while 1.225 is only 75%, so only 0.04 difference.

I bring this question up because your SG readings are suspiciously high. The expected SG for a 100% charged lead-acid battery at 90 F. is 1.261, yet you are showing 1.275, even without temperature compensation. The temperature comp factor is +0.004 per 10 degrees F., so your compensated reading is 1.279.. Either the battery is 120% of full or the hydrometer is somewhat off spec.

http://all-about-lead-acid-batteries.capnfatz.com/all-about-lead-acid-batteries/lead-acid-battery-maintenance/battery-hydrometer-temperature-correction-chart/

It is a very cheap hydrometer with a large arrow pointing to where the level should sit. Not very accurate at all. However, the 1.275 reading is with temp compensation. No matter what, I agree with you, it's not the most accurate reading.

Cheers.

solarman said:
good chance of sulfation, especially as you have insufficient solar panels for that amount of storage.
you need at least 312 Watts to make the C/10 minimum charge rate and that equates to approx 400 watts of panels.

C/10 here assumes you have those batteries in parallel. ( 130 Ah * 2 / 10 = 26 Amps @ 12 V )


also you don't get 8 hours of sunshine to do that equalization cycle unless you live on the equator..

I definitely should have gotten more solar panels but that's a future job now. The batteries are also charged from the alternator, but I do not know the specs of that so I didn't include it.
I'm currently in Cancun, Mexico so the sun is up at 6:20am and sets at 7:30pm. Granted if I account for the angle then maybe I do not get perfect sun for 8 hours. In any case, the charge controller does not properly equalize as it doesn't produce 15.5V.

Thanks for the reply.
 

Mark_K5LXP

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ericmcgrandle said:
There is some contamination in one of the cells (has produced a slightly brown, murky colour)

That's usually due to paste shedding, indicating a cell that's damaged.  Have you done a capacity test on this set?

Mark B.
Albuquerque, NM
 

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