Wet Cell Batteries


Duane Siegfri
 

I'm trying to understand the condition of our house battery bank.  I'm definitely not a battery expert.  We have the original Dolphin Battery Chargers (100A and 30A).  We use the 30A at the dock and the 100A with the generator.  We also have a Victron Blue Solar 100/30 with 630 watts of solar panels.  The installer set it at 28.8V Absorption and 27.6V Float (Position 2).


First:  The 12 Group 31 house batteries use about 0.5 gallons/month...is that excessive?  I'm wondering if the MPPT controller is overcharging the batteries.


Second:  How close to replacement are we?

I checked the specific gravity of all cells recently (see the attached spreadsheet).  I read that a new, fully charged cell should be at 1.265, and is discharged at a SG of 1.120.  The best cell tested at 1.265 and the weakest cell at 1.145 (corrected for temperature).  The average SG of all cells was 1.226.  This SG corresponds to 75% state of charge from what I read.  At SG of 1.190 the battery is at 50% SOC and battery #3 has three cells in that range.


Third:  Should I just replace Battery #3?


Fourth:  I've read that when the difference between cells in a battery is greater than 0.03,0 the batteries would benefit from equalization.  My Dolphin chargers are not adjustable (at least as far as I can tell).  The MPPT has an equalization function that will run for an hour.  Will that be sufficient?


Thanks for your input,

Duane 

Wanderer, SM#477


greatketch@...
 




---In amelyachtowners@..., <sailor63109@...> wrote :

I'm trying to understand the condition of our house battery bank.  I'm definitely not a battery expert.  We have the original Dolphin Battery Chargers (100A and 30A).  We use the 30A at the dock and the 100A with the generator.  We also have a Victron Blue Solar 100/30 with 630 watts of solar panels.  The installer set it at 28.8V Absorption and 27.6V Float (Position 2).


First:  The 12 Group 31 house batteries use about 0.5 gallons/month...is that excessive?  I'm wondering if the MPPT controller is overcharging the batteries.


Second:  How close to replacement are we?

I checked the specific gravity of all cells recently (see the attached spreadsheet).  I read that a new, fully charged cell should be at 1.265, and is discharged at a SG of 1.120.  The best cell tested at 1.265 and the weakest cell at 1.145 (corrected for temperature).  The average SG of all cells was 1.226.  This SG corresponds to 75% state of charge from what I read.  At SG of 1.190 the battery is at 50% SOC and battery #3 has three cells in that range.


Third:  Should I just replace Battery #3?


Fourth:  I've read that when the difference between cells in a battery is greater than 0.03,0 the batteries would benefit from equalization.  My Dolphin chargers are not adjustable (at least as far as I can tell).  The MPPT has an equalization function that will run for an hour.  Will that be sufficient?


Thanks for your input,

Duane 

Wanderer, SM#477


greatketch@...
 

Duane,

You didn't mention how old your batteries are, or who made them.  With any voltage setting questions I always go to the manufacturer's literature as the primary source since different batteries are... well... different.  Not all flooded batteries are exactly the same.  A half gallon of water into 12 batteries over a month doesn't sound very excessive to me.  that's less than 30 ml/cell/month.

Equalization is an important part of getting certain types of batteries (especially flooded cell batteries) to live out their full life span. This is sometimes called "desulfateing."  It can be tough to get a good equalization charge using a solar system, but it can be done by bring them up to full before the brightest part of the day with the genset.  Again, your battery maker is a good source for what an equalization charge should look like and how to know how much is enough.  If one hour is not sufficient, you can just start another cycle right away.

Some battery makers recommend monitoring SG as a way of determining when the equalization charge is complete rather than using a time based recipe.

It is generally accepted that replacing one battery out of a set is bad practice.  Having batteries of significantly different ages means they are being charged very differently, and that it bad for the whole string.  Sometimes it can't be avoided, but in general it is a bad idea.

Check the connections, make sure they are all clean and tight.  Then do a full equalization charge, as per the makers recommendation, and see if those SG values come closer together. Then think about running an equalization as part of your standard maintenance program. 

Bill Kinney
SM160, Harmonie
Little Harbor, Abaco, Bahamas

---In amelyachtowners@..., <sailor63109@...> wrote :

I'm trying to understand the condition of our house battery bank.  I'm definitely not a battery expert.  We have the original Dolphin Battery Chargers (100A and 30A).  We use the 30A at the dock and the 100A with the generator.  We also have a Victron Blue Solar 100/30 with 630 watts of solar panels.  The installer set it at 28.8V Absorption and 27.6V Float (Position 2).


First:  The 12 Group 31 house batteries use about 0.5 gallons/month...is that excessive?  I'm wondering if the MPPT controller is overcharging the batteries.


Second:  How close to replacement are we?

I checked the specific gravity of all cells recently (see the attached spreadsheet).  I read that a new, fully charged cell should be at 1.265, and is discharged at a SG of 1.120.  The best cell tested at 1.265 and the weakest cell at 1.145 (corrected for temperature).  The average SG of all cells was 1.226.  This SG corresponds to 75% state of charge from what I read.  At SG of 1.190 the battery is at 50% SOC and battery #3 has three cells in that range.


Third:  Should I just replace Battery #3?


Fourth:  I've read that when the difference between cells in a battery is greater than 0.03,0 the batteries would benefit from equalization.  My Dolphin chargers are not adjustable (at least as far as I can tell).  The MPPT has an equalization function that will run for an hour.  Will that be sufficient?


Thanks for your input,

Duane 

Wanderer, SM#477


Ian Park
 

My battery knowledge is limited also. Personally I think it would be better to remove the weak battery rather than replace it. I only have 4 house batteries on my Santorin, but I had one poor one in Mindelo prior to crossing the Atlantic. I removed it ( to a grateful fisherman) and crossed with just 3. The although the notional capacity was less they charged up fully (and more quickly less amp hours). I bought 4 new ones in Martinique. Your bank will only charge up to the acceptance level of the weakest battery.

Ian

Ocean Hobo SN96


kwzy6vgkpvtfohjddjsrotobzwf2pjeafjwalhur@...
 

How old is your battery bank?
How budget conscious are you?
Are you about to go on a long voyage away from chandleries?
After fully charging how long and how many amps does it take to get to 50% charge measured by specific gravity?

Assuming that the answer to the last question is acceptable and:


Assuming you really want to maximise the life from your battery bank.  I would consider disconnecting the two worst offending batteries. So your bank is 10 batteries wired up as pairs to give 24v. Then see how the rest of the bank performs. If the remaining bank holds it's charge well then you must decide what to do with the two dead ones. Maybe equalise/replace them or do without.

As for equalisation. You could try it before changing the dud batteries.  If you fully charge the bank with your Dolphin chargers until they accept no more charge and then turn all load off and on a sunny day use the solar regulator to equalise. The batteries should gas and boil, this stirs up the electrolyte and hopefully cleans off the plates. One hour is not enough you could reset it several times.

The main advantage of wet cell batteries is that you can boil them and refill with distilled water. 

Nick Amelia (54) with a new bank of Lifeline AGM, new chargers as the old Dolphins died and 530w solar and two wind generators.