Oh no, another battery question, specific gravity this time

[Rich Stidger]

I wouldn't think that flooded lead acid batteries would be so difficult to understand, but maybe they are really rocket science.

I currently have four golf cart batteries made by US Battery that were new in June 2006. Just used two seasons. I have a Link 20 that I obsess over to be sure my batteries are in better health that I me. I measure and record the specific gravity of all the cells several times per season and check the electrolyte level about once per month. I also have a Trojan starting battery that is six years old.

My sailboat lives on a mooring. It is almost never plugged into shore power. All recharging is done with a 70A charger and a 30A charger together driven by a genset. When motoring I have a 80A Balmar with an external regulator to replenish as much charge as possible. I also have a wind generator that pumps 5-10A if I have wind, but I usually see under 3A.

My problem is that it seems like my batteries are always undercharged. I put in the wind generator so that it would top off my batteries between uses of the boat. If the darn wind would just blow that might actually work.

Today I measured the specific gravity of all five batteries- four golf carts and one starting. Tomorrow I will install them all onboard. They have been kept in my basement, first fully charged and then on a float charge all winter.

I took the batteries off float 36 hours ago. Here are my measurements:

Six year old starting battery:

Voltage=12.91v
Specific gravity (corrected) 1.277, 1.282,1.277, 1.282,1.277, 1.277

The four two-year old golf carts:
#1-A, V=6.36, sg (corrected)= 1.257 (all three cells)
#1-B, V=6.36, sg (corrected)= 1.257 (all three cells)
#2-A, V=6.37, sg (corrected)= 1.257, 1.262, 1.262
#2-B, V=6.36, sg (corrected)= 1.257 (all three cells)

The combined voltage of these pairs is 12.72V, and I consider a corrected specific gravity of 1.260 to be 100% charged.

The golf carts were connected in pairs and paralleled together and also with the starting battery for charging and then float charging all winter.

What I see here is very typical of deep cycle and starting type batteries that I have observed over the years. The deep cycle batteries never reach the higher sg readings or the higher terminal voltage of a starting type battery.

When I have shown this discrepency to other electrical engineers, they have told me that my deep cycle batteries are simply not fully charged and that all flooded lead acid cells should charge to the same terminal voltage and the same specific gravity if they are good cells and are fully charged.

I have researched this topic and found no information that suggests that a deep cycle and a starting battery should have different endpoint readings. Yet I have always seen this difference.

Am I nuts? I won't ask my wife becasuse her answer has nothing to do with the charged state of my batteries. So the question goes to the techno-geeks here.

Are these sg readings normal? Are my deep cycle batteries undercharged? If the sg readings of the deep cycle are normal, why is the sg of the starting battery so much higher?

I'll be away for Sat and Sunday to uncover, wash, prep, and bottom paint. I'll check for your opinions on Sunday evening.

 

[Stu Jackson]

This could be challenging

Rick,

Your last question is very conclusive in itself: "Are these sg readings normal? Are my deep cycle batteries undercharged? If the sg readings of the deep cycle are normal, why is the sg of the starting battery so much higher?"

Hope you had a good weekend, I'm still dreaming of seeing my boat.

For starters:

1. What have your previous sg readings been on the house bank?

2. Did you break them in as the Ample Power Primer recommends?

3. Have you equalized the house bank regularly? (please note that I've heard that some 6V manufacturers suggest to NOT equalize their batteries)

4. Have you ever "over-discharged" the house bank? Like, done any inadvertant potential damage to them?

The reserve bank, hardly used and usually fully charged, often has a higher state of charge [i.e., sg] because while it's been cycled as many times, perhaps, based on how you're set up electrically, it has a much lower % of capacity discharge than the house bank. What does the Link 20 tell you in comparison to the house bank?

Given your "obsession" with your Link 20, whatzit tellin' ya? You didn't say what it is telling you, so I can't help you there without this critical piece of information. If you have recalibrated it recently, I'd suggest that you trust it, explicitly, as long as YOU trust your [this particular] instrument, based on me knowing how good you are with this stuff.

Your generator usage and your Link should tell you if you have ever really FULLY charged your house bank. With your NON-windy wind generator ("wg"), you may, just recently, have actually been undercharged. Your input in-your-head "calculations" (and your Link 20) should clearly tell you if what you're putting back in eventually overcomes the acceptance of the batteries for that very rough looong charging time between 80% to 85% to a REAL full charge.

That FULL [really up-to-the-absolute-TOP] charge often requires 24 hours or more on shorepower. We've linked this before from our C34 'site as a result of some very helpful discussions right here on this forum: "Battery Acceptance" http://c34.org/bbs/index.php/topic,4787.0.html

As you know, float is NOT full.

What went back in has always been a lot less than I'd ever thought, based on charging time and knowing the maximum and minimum charging amperage from each of my charging devices. These inputs get completely "whacked" by the battery acceptance reality after the 85% level is reached, and thus the importance of the reliability of the Link instruments we both have.

Understanding your battery condition from your description, you may well have to consider how to get plugged into shorepower more often [or at least for what I would consider you start planning to be a minimum of 36 hours, straight - like, you could visit a marina during an upcoming cruise ], or run your generator longer, or go solar. Solar, without wind on your wg, is the silent option, and is "traditionally" and, perhaps usually, the first choice of the "you-guys-on-the-mooring-blokes" before wgs.
When the wind comes up again, you should be just fine.

If it was my boat, I'd agree with your initial assessment. You're undercharging and undercharged, and need to top off and consider the other issues here. And primarily because of no wind lately.

Ready for the ultimate BUT???

All that said, Rick, you could well consider yourself a "true cruiser" who uses his house bank between 50% and 85% and rarely ever gets a chance to get to 100% because the cost-benefit ratio of fossil fuel [engine run time & generator] combined with lack of solar and no wind, simply puts you in that position.

Remember the very important information that Maine Sail has provided us regarding alternator and regulator charging. For instance, as a kinda parallel example or analogy, he suggests, with great merit, that the three stage regulators may well be overkill on our weekend warrior recreational boats, since the internal regulation on his new-to-him boat worked just fine for his PO's on their cruise, because they ran the 50% to 85% curve on their house bank for the duration of their cruise. He also made some very other important points in his well presented discussion of alternator regulator charging; it was that post of his with the "back of the alternator" great pictures; it may be on his website, too.

You wrote: "My problem is that it seems like my batteries are always undercharged."

At the risk of closing the loop, or starting again from the beginning right here at the end, what does "seems like" mean? What prompted you to start thinking this? Dim bulbs, hard starting, flickering candles, no mention of voltage [thanks goodness]???

Welcome Home, skipper.

Stu

 

[Rich Stidger]

OK, Stu, give me a day or so to digest your answer and dig up any other info that I have.

A few answers to your first questions:

1. My previous sg readings are in line with my current ones for fully charged batteries. I will look for the actual data, maybe I will find slightly different readings. But for sure, the sg of my deep cycles have NEVER been as high as my starting battery. And this observation has been true for all the deep cycle golf carts that I've had. Prior to this set of US Battery, I have had Trojan T-105 and Excide CG-4. In all sets, the sg has always been lower than any starting battery in either my boat or car.

2. I am totally ignorant of any "break-in" procedure. What does Ample Power recommend?

3. I equalize at home at the end of the season. If I happen to be at a dock with power I will equalize during the season, but the hours using a genset to equalize is just too much.

4. Over-discharged- well yes, the first year. While on a month-long Maine cruise, I was running both refer and freezer as well as all the other house loads. The refrigeration is the biggest power hog I have and when I run both systems I suffer about 120Ah/day just for the total refrigeration.

The Link 20 has an "gotcha" that isn't real obvious. When charging, the Link 20 considers the battery to be fully charged when two conditions are met. First the charging voltage must be at or above the entered parameter and the charging current must be below the percentage of the bank capacity that is also an entered parameter. In my case those parameters were 13.2V and 2%. 2% is about 9.2A for my bank of 460Ah. When these two parameters are met, the Link 20 blinks the top green LED indicating full charge, resets the AH used to zero, and recalculates and stores the charge efficiency factor for future charging. This can happen even if the used AH are not counted down to zero.

Without realizing this was happening, my golf carts were being cheated of 10-20Ah at various recharge cycles during the month. Thus I thought my batteries were being fully recharged but actually they were reported to be full but were short. Over the month I calculated that they were about 140Ah down out of the 460Ah capacity. Thus I had a chronic undercharge.

This undercharge showed itself as a low terminal voltage in the morning, sometimes as low as 11.9V when the voltage was 12.4-12.5 or so when retiring for the night.

The senerio for the Link 20 gotcha is this: The charging current has tapered down to about 13A with 20Ah still to go with the charging voltage at 14.4V. Now one of the refridgeration units turns on drawing 5A. This causes the battery charge current to drop below the 2% threshold and after 6 minutes the Link 20 thinks the batteries are fully charged because the charge voltage is over 13.2V, the charge current is below 2% or 9.2A, and these conditions have been met for 6 minutes. Then to make matters worse, the recharge efficiency factor is recalculated to a higher value (ex. 0.97 vs 0.95) so the at the next charge cycle the Link 20 thinks that the batteries require fewer input AH for the used AH. This is not true of course, but it makes the under-charge condition worse.

The fix for this gotcha is to set the Link 20 parameters to 15v and 1%. These parameters are not ever going to be met, so that means that the Link 20 will never think the batteries are fully charged until the AH used are fully counted down to zero. Also set the recharge efficency factor to manual of 0.94 instead of the automatic setting of 0.95. This will stop the automatic recalculation and fix the recharge efficency to be 0.94.

 

[tommays]

I do charge a lot of batterys and many 6 volt

1. 12.97 is really on the high side ?

2. A load test is really the ONLY way to check a batterys abilty to delivery is amp-hours as i have seen many that will charge up but give short run times as they age or are damaged buy deep discharge

 

[texas sailor]

Battery question

As a 20+ year sub EM, if you want to know battery cap then the only way to do it is with a test discharge. Keeping a battery on a positive float is not the best way to keep it healthy and at full capacity. You actually want to trickle discharge it down to say 40 to 60% dischage then conduct a normal charge, then once a month or so do an extended or equalizer charge. Once a year conduct a test discharge. You will always have variation on cell SG, give or take 5 to 10 pts. SG will tell you how effective your charge was (ions driven into solution), battery voltage really tells you very little after a charge, ICV would tell more. If you have one cell that loses SG quickly after charge then you have an issue.

 

[Stu Jackson]

Pretty much what I figured you'd say

Rich,

Your story about the link gotcha is part of my Link manual material in our logbooks. I thought it was a classic when we visited that subject with Donalex last year or the year before. That's why I said "recalibrate." Those of us who understand our Link equipment and the way the algorithm works know that. Oddly enough, I rarely shorepower charge only to the zero "full" mark, but usually well beyond it. I haven't reset mine yet, and have detailed instructions plus your input from the earlier discussions in my boat Electrical System book.

Download and save the Ample Power Primer from here: http://www.amplepower.com/technical_documents/index.html

Wow, I thought you'd have this already and have it memorized by now given all the times I've mentioned it.

I must admit I have NO CLUE about your different sg's and am eager to learn more from others here. I'm running 1.225 to 1.250 sg on all my 18 cells [3 batteries, 130 ah each, 12V, American Battery, Hayward, CA], but have been chronically undercharging my house bank since I bought it in 2006.

How'd I know? The Link 2000 and my suggestions on people learning about battery acceptance, and your invaluable assistance with this issue on the Link recharging parameters. The more I've read some older written electrical and battery material, and the Link manual, the more I realized how wrong I'd been about recharging, even though it was all there staring me in the face! That's why I do the SOAPBOX routine so often and provide a link to my acceptance thread on our C34 website: http://c34.org/bbs/index.php/topic,4787.0.html . [Hey, Phil, where'd the "soapbox" simile go?]

More later when you get back to this. I did get to see my boat yesterday, first time in 3 months, 4 days, 2 hours and 22.56798 minutes!