battery hook up and charging

[hmtyson]

I have two series 27 batteries hooked up in parallel, and when charge by the 3 stage electronic charger, #2 drops the electolyte level much faster than #1. #1 has the refrigerator on it but that is the only difference. Any thoughts on why this occurs?

[hellosailor]

Yeah, because when batteries are hooked up in parallel, they always will charge and discharge unevenly. That's why it is simply not recommended, by all the battery makers.

No two batteries are identical--even if they come of the same line in the same lot. So whichever battery you have the charge sensor hooked up to, is controlling the charge. And the other battery is being charged randomly and incorrectly.

Any difference in cable lengths, corrosion or quality of the battery terminals and fittings, etc. could also change how #1 charges /vs/ #2. If they have been set up with automobile grade cables, odds are there is green crud corroding the cables inside, and that's also changing the resistance of the cables, and affecting the charging.

If they really are in parallel--you can't have the reefer hooked up to #1 only. It will be drawing from both, although in theory it will draw more heavily on #1.

[dave.verry]

Parallel batteries are the only practical way to get the required capacity on a sailboat. If they are truly in parallel and both batteries use the same charge voltage. It is obvious you have a problem if they are not both charging equally. With all respect to hellosailor, they should charge and discharge evenly, even if they are different sizes (which I do NOT recommend).

A list of the possible problems are as follows;

They are not parrelled.
The connections between the batteries are made with too small of gauge of wire.
The wires have corroded internally increasing the cable resistance between batteries. (always use marine grade cable)
The connections are corroded and are imposing a high resistance between batteries.
The connections are loose and imposing a high resistance.
The crimp of the battery lugs is corroded.
The one battery boiling off water has a shorted cell which over charges the other cells. (is one cell not loosing water?)

If the charge voltage is correct, you should not be boiling off water. Check the charge voltage at both batteries. Make sure the float voltage is between 13.3V to 14.1V (13.3 is the preferred float voltage for wet cells). If it is higher that is the reason for boiling. Measure the voltage of both batteries during a heavy charge (or discharge), they should be the same measured with a 3 ½ digit voltmeter.

If your charger has a remote sense wire, measure the voltage of both batteries. Perhaps the charger is overcharging the one battery because of one of the problems listed above. A resistance between batteries, if the battery at the end is the one beings sensed, will overvoltage the near battery.

The best thing you can do at this time it to replace the cables between the batteries, cleaning the terminals thoroughly. Do not use abrasives.

[hellosailor]

Dave-
I'm not saying parallel installations can't be used--only that they shouldn't. Even GE, in their commercial battery manuals, says that if you are going to parallel cells/batteries the preferred method is to parallel the CELLS and then stack the parallel cells in series, rather than paralleling the assembled batteries. This is because there will still be real potential for problems associated with charging and discharging if there is any one bad cell, or any voltage/resistance variation in each battery.

But when you say paralleling is NECESSARY for boats...what kind of boats do you have in mind? I can get you 12V batteries rated for over 1600AH @ 12V from commercial vendors, such as:

Item # Ah@20hrs Weight (lbs) Size (inches) (L x W x H)
15-799 627 498 30.75 x 7.78 x 23.25
15-800 732 558 17.89 x 12.96 x 25.0
15-801 836 630 20.16 x 13.0 x 25.0
15-802 941 696 22.38 x 12.97 x 25.0
15-803 1046 762 38.96 x 9.01 x 24.88
15-804 1150 840 27.12 x 12.97 x 25.0
15-805 1255 918 29.82 x 13.48 x 25.0
15-806 1359 984 31.58 x 13.0 x 25.0
15-807 1464 1068 33.65 x 13.0 x 25.0
15-808 1568 1128 35.95 x 13.0 x 25.0

15-809 1673 1260 38.96 x 13.51 x 25.0
List Price: US$2,649.00 includes free motor freight delivery within the US to a business address.

from the first hit on Google at:
http://www.realgoods.com/renew/shop/...401/ts/2015799 claiming "With proper maintenance, these cells will last 15 to 20 years. Cycle life expectancy is 1500 cycles to 80% depth of discharge, or 5000 cycles to 20% depth of discharge." The vendor, "Real Goods" has a good rep but they are NOT battery manufacturers or commercial vendors, prices will be deeply discounted for similar batteries at your local industrial park.

and they DO come bigger than that. Incidentally, if you buy these batteries UNassembled, they are built from standard 2.2V cells that can be lifted by a single human and configured into odd spaces/forms as well.

How many of use really sail with more than a 1600AH combined battery capacity? (Now now, submariners don't count!<G>)

With a parallel setup, you simply have the opportunity for more new problems that just don't exist in serial installations. Sure, it's an EASY way to buy your batteries at the local K-Mart...its just not "best of breed" practice.

"If the charge voltage is correct, you should not be boiling off water." Assuming that the whole boat is at 70F or there is a temperature compensation lead or sensing in the alternator. Normal charging, deep charging, without temperature compensation may occassionally boil off water.

"Measure the voltage of both batteries during a heavy charge (or discharge), they should be the same measured with a 3 ½ digit voltmeter."
Yes, but unless he has a Fluke-quality DMM...Typical numbers from a "consumer" grade DMM are +-2% with a float of 2LSD on the DCV scales.
That means 12.60 volts "displayed" can be off by 2% either way, plus or minus a float of 2 digits in the last column. So 12.60 on the meter can mean 12.32 to 12.87 volts is actually being measured. 12.34-12.85 more probably.

That's not to say the DMM isn't valuable...but when it can be reading "12.6" while the actual battery voltage is 12.34-12.85....a grain of salt is needed in analyzing the results. The meter can't be taken at face value, unless it is calibrated or checked on something else. The variation of 0.6 volts is HUGE when we consider that a nominal 12V battery only supplies useful power over a 1-volt range.

I think we can both agree there are better and worse ways to do things...with variations in how we each decide what 'better' and worse mean.<G> And that there's alot of room for practicality versus finesse in 12V systems.

Paralleled banks work, sure. Most of the time. And when one battery goes bad--everything goes bad. I just don't trust them to be left alone, working in the dark, skulking under the quarterberth, without human supervision that way.<G>

[dave.verry]

Hellosailor,

Agreed, you can get 12V batteries in the size you described. If I get one, will you come over and lift into my boat?

I think we’ll have to agree to disagree. I routinely parallel battery banks in my work, telecommunications power, from 100 AH to 9200 AH. I’m familiar with 2V cell configurations.

Care must be taken in making connections, maintaining connections, cleaning connections. When paralleling batteries the connections are the most likely cause of problems after the electronics (charger). If the correct charging voltage is applied and batteries are outgassing and drying out, there is a bad cell in the string (correct voltage based on temperature, of course).

I own several 4 ½ digit voltmeters and sometime forget that not everybody has access to one, although if you’re going to do your own electrical work it would be the first item in my troubleshooting bag. If a poor quality meter is off by 2%, it should be off by the same 2% for successive readings. What we are looking for here is relative differences, not necessarily absolute values.

We can debate the merits of paralleling later, so as not to hijack this thread, I suspect hmtyson’s problem is in the cable connections (or cable) between the paralleled batteries. Measuring voltages across the batteries and/or connections during a high current condition can help find the poor connection.

Hmtyson, a poor connection has high resistance and will have a large voltage drop across it. This will heat the problem area which can cause the problem to get worse, or may expand the metal and improve the contact, until it cools off. Your cable and connections should tie the battery terminals together so you should not be able to measure voltage differences without very good instruments. If you can measure a difference you need to trace it until you find the problem. If you can’t measure a difference, then I’m all wet and have to start from square one.

[hellosailor]

"Agreed, you can get 12V batteries in the size you described. If I get one, will you come over and lift into my boat? "
Gladly, Dave. Just remember, I'm endorsing the *cells* not the premade battery. For 600+Ah each cell will still be a mere 50#, about the same as a good Group31 car battery.

"...there is a bad cell in the string ..." Another advantage to buying fork lift cells, you can replace just one bad cell. Which is what they routinely do, versus a battery costing over two grand.

"I own several 4 ½ digit voltmeters" I used to own a lab grade B&K, but accidentally sent it via express to silicon heaven some time ago and haven't felt the *need* to drop the price of a good Fluke today. (Even on the used market, they really keep their value.) But even with a cheapier, he'll be able to measure *differences* very nicely. If there's a 0.2v difference someplace, it doesn't matter what the measured voltages are, the difference itself will still be relevant.

[cardiacpaul]

Almost all of the class 8 over the road trucks in the US, almost all of the heavy agricultural farm equipment, and heavy construction equipment (not 24 volt system, those have 2 8D's in series) that I've seen have had either 2 4D, or 8D in parallel. If its good enough for Peterbuilt, International and John Deere, its good enough for me.

[hellosailor]

Paul, I'd suggest that trucks, with almost constantly running engines and alternators, do not reflect on the power needs of sailboats. Truckers are using SLI (Starting ignition lighting) batteries, not deep cycle. Their primary use is just the starter on the engine.

Sailboats are more akin to fork lifts--where the batteries are deep cycled on a regular basis. And *that's* the industry that doesn't use parallel batteries, because they're just not as good for this application.

Heck, the vast majority of boat builders still use an automotive alternator with integral regulator and no charging lead. Even auto makers progressed beyond that long ago, but boat makers still build "cheap" because it is 'good enough' to get the sales. Like parallel batteries..."good enough", just not best practice.

[cardiacpaul]

"Like parallel batteries..."good enough", just not best practice."...
"List Price: US$2,649.00 includes free motor freight delivery within the US to a business address. "


"I'm not saying parallel installations can't be used--only that they shouldn't. Even GE, in their commercial battery manuals, says that if you are going to parallel cells/batteries the preferred method is to parallel the CELLS and then stack the parallel cells in series, rather than paralleling the assembled batteries. "

Cat, JD, Paccar, Hatteras, Carver, Silverton... all parallel. It may not be optimum, may not be "best practice", but I can see a substantial price/performance difference between two 4D, or 8D's in parallel vs the latest and greatest. 250.00 vs over 2500. for very few amp hrs. Sometimes in life you need opitmum.. oh, pacemakers, airframes, PFD's for example. Batteries and women... good enough is good enough. (unless you're heading out on a round the globe singlehanded voyage)

In over 10 yrs of surveying, I can count on one hand the number of boats that have had what you suggest, 2 in the last year, and one of those was a dock queen, the other had been from Kemah to Belize and back. once.

[hellosailor]

Paul-
" two 4D, or 8D's in parallel vs the latest and greatest. 250.00 vs over 2500. " I'm not sure what you're comparing. The first hit I got on 8D's was for Concorde AGM's, $415 each at 255AH. Two of them would be $800 and 500AH, If you simply triple that and put three of them in parallel to get a COMPARABLE 1500AH, you'd pay $2400. Also comparable.

Without doing a whole bunch of price comparisons...your "$250/vs/$2500" example is totally out of the ballpark. Show me how you're going to get 1600Ah from a $250 battery, including shipping anywhere in the continental US. And bear in mind, as I said, that $2500 is "double retail" price, the highest not the typical price to be paid.