Topping off batteries

Guest · Aug 9, 2009

House bank

Our boat has two 8D wet cell house bank batteries. I top both of them off with distilled water every two months and that schedule seems to work for our situation. I also keep shore power connected at all times while in the slip and both freezer and fridge running 24/7.

How old are your batteries? Awhile ago, when one of our 8Ds reached the end of its life, the first thing it did was to consume an increasing amount of water. The battery guy told me that when a battery reaches the end of its life usually a cell dies, shorts out and boils away the water quicker than normal.

I installed our current set of 8D batteries in 2003 and they continue to perform as new. I never let them go below 12.0 volts before charging. So far so good. Hope this helps.

Terry Cox

Don S/V ILLusion · Aug 9, 2009

Without checking internal resistance of each cell, it's a guess what is happening to the combined batteries. My suggestion is the proverbial "watchful waiting" to see why one is starting to cook the water out.

BobW · Aug 9, 2009

Water loss is usually related to charge/discharge cycles

The main cause of water loss is inefficiency of the charging process which, if I recall correctly, involves breaking the chemical bond of the H2O molecule when the SO3 molecule is 'pried' off the lead plate by the electrical current to become H2SO4, which is the 'charged' state of the sulfuric acid. In the ideal situation, ALL of the H20 attaches to the SO3, but that's not possible. Hence, if you had a battery made of clear acrylic, you'd see large oxygen and small hydrogen bubbles rising.

The same thing happens during the discharge cycle, but except under extreme discharge rates, is not as noticeable.

In your scenario, you're not discharging your batteries much, except when you put on an equalize charge, and perhaps when your refrigeration system runs.... which explains the general lack of water consumption (do you set your battery charger to 'equalize' every month or so?) and brings us to your unequally water-losing batteries.

First, your batteries should be reading approximately 12.8 volts when fully charged and disconnected from charger and load - I'm assuming 13.8 is a typo.

The unequal water consumption could be for any number of reasons, including different ages, makes or just the variation between 2 batteries, but you might check another reason:

Your batteries are connected in parallel, but unless the charger is connected directly to each battery, one of them will be 'farther' from the charger than the other - and farther from the load as well. If the charger is connected to the A/B switch, this is definitely the case. Otherwise, you can verify this by tracing the wires.

The effect of this different 'distance' is that the 'closer' battery will get used more - and charged more - due to the resistance in the wiring and, quite possibly, consume more water. Of course, the more distant battery could also be consuming more water, because this isn't the only factor, as I mentioned.

Is this a problem? Probably not, although the more used battery will fail sooner. You could swap the 2 batteries annually, or just replace each battery when it fails.

Another thing to check is the wiring between the two batteries - larger is better, and minimizes the difference in use.

Cheers,

Bob
s/v X SAIL R 8

Snotter · Aug 10, 2009

I run my 12v refrigeration every weekend. That requires me to add water to my group 27s (at least that is what I think they are) every other weekend. The batteries are 1 year old and the one bank of 27s I have are 3 deep. On the other hand, my semitractor batteries are not near as thirsty. I have a bank of semitractor batteries 2 wide in parallel with the bank of 3 27s. I run these banks in parallel because they are all new. I have a dedicated semitractor battery for starting the engine. That battery is over 2 years old and hardly ever needs water. I have a 60 amp ferrous resonant battery charger which is analog charging the 3 semi-tractor batteries and the 3 group 27s.

bodonovan · Aug 10, 2009

For what it's worth...

Yanmar Diesel School suggests charging only overnight, once a week. The caution is that lightning can strike any boat on the dock, and then spread to any boat that's plugged in.

Chuckbear · Aug 10, 2009

bodonovan said:
Yanmar Diesel School suggests charging only overnight, once a week. The caution is that lightning can strike any boat on the dock, and then spread to any boat that's plugged in.

I am not sure what Yanmar school you received this advise from, but you might want to post it so everyone else can avoid it. It is nonsense and does not make sense. Chuck

BobW · Aug 10, 2009

It's hard to figure lightening as a danger to batteries

All your other electronics, sure, they're pretty delicate, and the current of a lightening strike quickly develops voltage when it reaches wires. I'm not an expert on lightening strikes - they follow the laws of physics a lot more than electricity - but I'd worry about a LOT of things on my boat before being concerned with the chance of a lightening strike damaging my batteries. After all, they are actually nothing more than a current sponge, right?

Blitz, it probably isn't a big thing, but you may want to look at having 2 outputs of the same battery charger hooked up to the same battery (having 2 batteries hooked in parallel effectively makes them 1 battery. That could be a problem, but probably not.

Snotter, keep in mind that water consumption is directly related to charge/discharge cycles, not battery size or capacity. So if your Group 27 bank is thirstier than your bank of big batteries (8Ds?), the most likely explanation is that the Group 27 bank is being used more because it is electrically 'closer' to the charger and load.

Being wired in parallel isn't enough to ensure equal charging or discharging. The wires connecting your battery banks to the charge or load, no matter how large, potentially have different resistances, which in turn can affect how they get used.

Cheers,

Bob
s/v X SAIL R 8

Ross · Aug 10, 2009

Re: It's hard to figure lightening as a danger to batteries

Bob, Ben Franklin determined that lightning is electricity a long time ago and that fact still remains undisputed.

ed fiss · Aug 11, 2009

running light oil

I was on a CG bouy tender and icebreaker and we would send the new guys below to
get red running oil for the port running light.

barcode readers · Aug 11, 2009

Not all batteries are equal

Blitz said:
I was curious how often does everyone who is at a dock have to top off the water in their wet batteries? I check them once during the season (April - Sept) and normally don't need much if any - is this good or bad?

Another reason I ask is that have a weird concern - The system and usage is as follows: I have one battery for my starting battery (sealed), two paralleled as my house bank. I'm at the dock most of the summer, hooked to shore power, battery charger on all the time, and the 12 volt refrig on all summer at the dock. My concern today is that when checking the water is that one of the house bank batteries had lower water in it than the other the other. Meaning I had to add water to one and not the other? It wasn't alarmingly low but lower.
Charger is hooked up so that the bank should be charged equally. Voltages seemed normal (13.8 after they settle or higher (14.2) when charger is on).
Can anyone explain this?

This happens all the time. The problem is simple. When both batteries are connected together to give you low volts. For some reason the readings are not real. The real reading is the lower volt battery. Now overheating can cause a battery to loose electrolite all the time. I have been boating a long time. Always check your batteries if you are going to get underway. Also always clean your batteries. Dirt draws down a battery. Make sure the batteries are also secure at all times. Batteries need to be changed or replaced every so many years. They do not last forever.

BobW · Aug 11, 2009

Ross, I was referring to the behavior of high energy pulses...

of electrons, which includes lightning. There are aspects of these pulses, including their formation, that can't be explained solely by the laws of electricity.

With all due respect to Ben Franklin, his 'observable universe' in 1752 was quite limited. It's obvious that lightning does a lot of what electricity does, but does that mean necessarily that it's the only laws it obeys?

As an example of a limited observable universe, let's suppose Ben Franklin saw a MinuteMan III missile on its side being pulled on wheels out of a barn. Would he have any chance of determining that this is an intercontinental ballistic missile with a range of 6,000 miles, capable of raining 10 MIRVed nuclear warheads of hundreds of kilotons each onto an enemy's cities? I reckon he'd think it was a new kind of wagon, whereas any kid of the 1960s would know all the things I just wrote immediately.

My experience with high energy pulses was back in the '80s, working on surge arrestor upgrades for the same MinuteMan III missiles I mentioned above. My company build a trailer mounted high energy pulser to test the surge arrestors we deployed in MinuteMan Launch Facilities (silos) and Launch Control Facilities. The pulse was delivered by a coax cable that was 6 inches thick (and rather difficult to move). As I recall, there were as many physicists on that project as electrical engineers...... and that pulser did some wierd stuff!

But I don't feel like arguing, Ross.... it's just my opinion, and not germane to the discussion at hand.

Cheers,

Bob
s/v X SAIL R 8

Topping off batteries

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bodonovan

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ed fiss

barcode readers

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