Charging large battery banks, such as this dedicated bow thruster set-up, can be problematic

One of our readers sent in a query just yesterday regarding a rather large battery bank on a Niad sailboat and the fact that some of the batteries keep going dead. Check this out:

Ed,

I have a customer with battery problems. The boat is a Niad 44, maybe 7 yrs old. There are 6 Lifeline Group 31 batteries in 3 banks of 24v. The 3 battery banks are each wired to a common bus bar of pos and neg. The pos, thru an on-off battery switch. 12 v needs are taken off a 24-12 convertor. There are no power drains off any battery. In each battery bank of 2 batteries, 1 battery is failing. Testing was done with a Midtronics tester, 250cca on a 600cca battery. Lifeline refused to accept the results (they say the tester is junk) so I confirmed the results with a full charge and resting voltage test. Charging is directly to the pos buss, with a Balmar 24v alt or Mastervolt charger. The batteries are only 1 year old. These are the 4th set of batteries. Like everyone, they probably don't get a regular full charge. Voltage drop is minimal. My question is would it be better to wire the 3 banks in parallel to make 1 large bank, with 1 single pos and neg to the bus bars. Would it promote more even charging? I don't want to replace the batteries without making some change to a system that's not working. What would you recommend, and why? Thanks for your help.

Alan

Well without actually seeing the set-up in person, I can't give a definative answer here, but experience certainly tells me that Alan is thinking on the right track when he says that maybe combining all the batteries into one singular bank might be better.

There are several things going on here that may be causing the problem, which I believe to be nothing more than an imbalanced charge regimen. The 24-12 volt converter, and multiple banks and switching complicate things considerably. 

In any application as complex as the one Alan describes, with many terminal connections and even a voltage shift going on, the risk of uneven draw and uneven charging is just too great. I believe that is what is actually going on here and the net result is that the batteries that are at the weakest point in the system are suffering from a continual undercharging situation, causing pre-mature failure of the otherwise great batteries. 

Oh, and I categorically do not agree with the "Midtronics" testers are junk statement either. I think they are the best available. Alan has confirmed that his tests aren't lying to him.

My advice? Apply the KISS principle here and I think the problem can be solved. 

First, let me apologize for not posting since last week. I've been traveling and really tied up with meetings and such. But I'm back at it. 

We received a scary message from one of our readers several days ago, and I need to share this because it is illustrating a super dangerous situation that you all need to know about.

First of all, the reader bought one of the reference cells I mentioned in my July 8th post. So, as all people curious about such things would do, he decided to check out his own boat. The reading on his meter is shown here:

So, you may ask what is our friend reading here? The electrode he purchased is in the water next to his boat and the other meter lead is connected to the boat's ground. It looks like the meter leads are actually hooked up backwards, but all that affects is the plus minus reading on the meter. To check for corrosion potential you would normally put the electrode lead in the meter's "com" socket and the + lead would be connected to the grounding bus or a really good ground on the boat. (that's with a digital meter like the one above). With an old style analogue meter you would do the opposite with the leads.

Anyhow, what this person is reading right now is a really, really big DC ground fault on thier boat that is entering the water around the boat. (The meter is set to the DC volts scale.) Yup, the boat is dumping almost 11 volts DC into the water around the boat. It has not blown a fuse or circuit breaker because there must not be enough amperage flowing to do so. Not an uncommon thing to occur.

Now, what this means is that if left unattended for more than about 24 hours some serious damage can occur to his boat and any boats near him in the marina.

What to do? I'd disconnect the battery(s) on this boat until an electrician can isolate the ground fault. I've seen this level of leakage destroy things like bow thruster drive legs in less that two days.

It's been a year and I've just heard from our friend Vincent regarding his Alerion/Mastervolt electric yacht. As discussed last summer one of the big questions that remained unanswered regarding the boat was the actual range with just battery power and limited regeneration capability. Well, as some of us expected, and the designer wisely anticipated, the second set of Mastervolt LION batteries has been installed. Vincent reports: " After a methodical 11 hour day yesterday, and some sore muscles, the second pair of MLI24/160's are in place, wired up and functioning. Considering the age difference of the original batteries and the new ones, I decided to move one of the old ones over and put it in parallel with its twin, and similarly parallel the two new batteries together. I left them all charging up last night, and will check on them later today (Saturday). I will then take the boat out and test its range a bit over the next few days.

It was a challenging job to lower those 121 lb. bricks into the seat lockers, and position them into the mounts, but I did it (alone) with no incidents!

Wayne Burkett's original judgement call to mount the second pair longitudinally was a great one. Not only did that keep space in the locker much better preserved, but it also puts the additional weight closer to the center line, which seems better for ballast placement. I mocked up the arrangement in the garage, and pre-planned and built the bonding cables there, which made the installation much easier with the limited maneuvering room in the lockers. Much of the wiring had to be done blind and by feel, but patience and perseverance won the day.

What Vincent is talking about is the pre-molded mounting pads for a second set of batteries already part of the inner hull liner. Good thinking Wayne!

I'll keep you all posted after Vincent gets a feel for his increased range. I think he's nailed it this time.

Love it. We're internationally famous! I received a nice note from a reader in Switzerland yesterday. I'm sharing this as I know his is a question that many folks have. Here's the note:

Dear Ed

I'm Silvio from Switzerland, work as you in the marine electronic / electric business here in Switzerland. We are Distributor for the Navico Brands and MasterVolt.
I will start very soon with my own project, a online support service.

I read your article about galvanic corrosion in Cruising World some month ago. And now meet your site. Very interesting what you’re doing.

Its a very interesting and important topic and its really hard to get good information, at least in German.
I was looking for this silver- cell to measure the insulation. I think there are not a lot of people who do that over here, so I'm interested. Can you give me some information about this cell, and were I can buy it or what manufacturer you use?

Looking forward to hearing from you.

Best regards.

Silvio

I strongly recommend one company to get this problem solved.  Go to: www.BoatZincs.com What Silvio is talking about here is the cell attachment you need for your multi-meter if you want to do some reference checks for the protection level of your boat's anodes. The unit Boat Zincs sells looks like this:

For those of you with questions about all of this, the BoatZinks.com website is loaded with answers. Check it out or shoot me a specific question. We'll get an answer. 

Should battery cells be equalized?

The July 4th holiday weekend sent me into super busy mode so sorry for not posting in a few days. I received an email from a reader today though that asks a good question that I'll bet a few of you may have.

Dave writes in:

Ed,

I saw a product advertized as "Battery Equaliser 12 Ounce # BE12oz" which is to increase battery longevity... what do you think?

I have two four year old 8D wet cell batteries and these things are expensive! Cat 3208

120 amp alternator with internal regulator...
Dual Pro 4 stage charger when on shore power...

Thanks!

Dave

Well I'm not familiar with the specific product that Dave mentions but I can certainly answer the question about battery cell equalization in a general sense.

Battery cell equalization is one of those maintenance items that where if a little bit is good, more is NOT necessarily better. In fact, this is someting that if overdone, can destroy your batteries. Also, it is something that should never be done with sealed batteries of any type.

Battery equalization is a controlled overcharge of the battery that induces a really violent electrochemical reaction inside the battery's individual cells. The purpose of this is to literally rattle sulfate particles that accumulate on your battery's cell plates over time, off the plates and back into the liquid electrolyte. By doing this, you effectively remove these unwanted particles, which act as insulators on the cell plates and reduce the plate's effective surface area. This reduces the battery's potential capacity. So, cell equalization is done periodically to maintain what amounts to parity among the cells inside your battery. I don't recommend doing this any more than once or twice during a typical boating season. Any more frequent than that and you risk damaging the cell plates.

Modern battery chargers will often have this function as a manual selection or automatic function that requires user intervention to activate. Read the manual for the charger to make sure you get it right and do not do it too often! 

Personally, I prefer using the PulseTech products I discussed last week over this functionality. It does exactly the same thing in an on-going manner and does not induce the violent reaction that can be damaging to the cell plate material. Each to his own on that count.