One More Time: 6V or 12V?

[cal40john]

Originally Posted by paulw

Why do you say that it "is not possible" to switch to 12V batteries and increase the capacity of my house bank?


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It is possible, but what everyone is saying is that for the same size box you are going to have the same number of amp hours available. To double capacity you need to double the size of the space taken up by the batteries.

Your 4 6 volt batteries wired in series/parallel give you about 450 A-Hrs
Four 12 volt batteries close to the same physical size in parallel will be about 450 A-Hrs.

Four 12 volt 150 Amp-hr batteries have to be bigger and will not fit in the same space.

[JK n Smitty]

As others have pointed out, the golf cart batteries have thicker plates and are more robust and can handle abuse better than 12 volt deep cycle.

From a size to cost perspective they are also some of the best alternatives (priced using Duracell brand from Sam's Club):

-4X EGC2 Golf Cart Batteries gets you 460 Ah, in 292 square inches and 256 pounds for $450

-4X Group 31 12volt deep cycles gets you 420 Ah, in 351 square inches and 238 pounds for $380

So you end up with almost 10% more capacity in 20% less space for roughly the same weight for $70. All wrapped up in a more robust package.

My guess on your issue might be your practices. You said you are leaving the boat in the Caribbean for 3-6 months every year. Is the boat in the water or on land? Are you paying someone to check on the boat, top off the water in the batteries, run equalization charges, etc.?

[GrowleyMonster]

I just installed a 48v bank in my boat, and I am what could be described as economically challenged, so I wanted the biggest bang for the buck. The weight and space were not an issue, since I live alone on the boat and I just tossed about 450 lbs of engine and related tank, wire, piping, hoses, etc. Looking at kwh/$, the hands down leader of the pack was 6v gc2 golf cart batteries from Sams Club. They are much easier to lift and handle than 4D or 8D 12v batteries since they are only about 85lbs each and conveniently sized. The T105 isn't much different but it is a higher quality battery that should last longer, and it costs more too, naturally. You have a good setup. The only thing I might change is split it into two banks and use a 2 bank charger.

Like everyone else I agree that your real problem is probably your charging. You need a good trickle charge while the batteries are not getting a workout, and once in a while you should get an equaling charge. In simplest terms this is slightly overcharging each battery a couple of times, while monitoring temp and water level. This can bring back a sluggish cell... A cell that is not taking or holding a charge will bring down the whole bank. If you are having problems then you need to educate yourself in depth regarding batteries and their charging and use.

BUT... Every season, you should carefully check all cables and connections for looseness, corrosion, etc because a poorly connected bank can't do its job. It won't charge good, and it won't supply the current that it should. Heavy cables have lower resistance. I see a lot of banks hooked up with #6 or #4 cable. I would go with #2 or #0. My propulsion bank is wired with 2/0 cable.

[paulw]

Again, thanks for your input. Sailing in the Carib has at times meant making do with what's available. Locating T105s has been a problem (even in a the BVI!), and so I have mixed old & new once (and pairs of different brands). I'm reluctant to leave anything running on an unattended boat (on the hard), which may be moved at the yard's whim etc. Three years ago, a cockpit drain hose inexplicably disconnected and we came back to a flooded cabin sole. Most importantly, as you may have guessed, it's been a challenge learning to bend our demand & preferences to the capabilities of our electrical system. Over time, we added Solar & Wind, and it's all working pretty well today (when we're on the boat). On average, our house batteries have lasted 2-years. We were unable to go sailing this year and I'm expecting that my T105s, which I disconnected before leaving in 2013, will not have survived the neglect. That started me thinking about 12V batteries, which brought me to this forum.



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[btrayfors]

Paulw,

I apologize for my earlier quip. I can see now that you are not a troll, but a real person with a real problem. And, a situation which is VERY FAMILIAR to me because I kept my boat in the BVI for eleven years and, like you, had to be absent for 2-5 months or so while I worked overseas.

During those 11 years, I went thru 5 or 6 complete changes of Trojan T-105s. I had six of them: four in my house bank and two in a dedicated windlass bank. Very expensive lessons.

Since that time, I have become something of a battery specialist, having done rather extensive hands-on research and having designed and trouble-shot power problems on dozens of client boats, and having given seminars on battery care, installation, usage, etc.

It's clear from your posts that you have a lot to learn. If you only learn one thing, learn this:

ALL LEAD-ACID BATTERIES NEED TO BE KEPT AS FULLY CHARGED AS POSSIBLE.

Leaving them for weeks or months at a time will kill them. This is especially true in the tropics where high ambient temperatures result in high self-discharge rates.

Batteries which are not kept at a sufficiently high float voltage (13.4-13.6VDC for T-105s) AND which are not given a goose in the way of absorption voltages (13.8-15.0VDC) periodically WILL SULFATE and lose capacity.

Sulfation, the formation of lead sulfate (PbSO4) crystals on the batteries plates is a progressive process which literally eats away at the AREA of the plates which is needed for storage and delivery of energy. As this progresses over time, battery capacity (which is a different thing than battery voltage) deteriorates.

By the way, this is true of all LA batteries, no matter their chemical composition, type, or voltage.

OK. What to do if you have to leave the boat for longish periods?

I learned thru sad experience over 11 years that you cannot trust someone to turn on or plug in your charger regularly. And, if they don't, the batteries will deteriorate rapidly, particularly in the hot environment of the BVI.

Fortunately, there is a way to get over the problem. Technology has come a long way recently.

What you need is a system which is completely independent of shore power or of hands-on treatment.

The cheapest, most reliable source of power for this purpose is solar. You need to install a solar panel AND...very important....a good MPPT controller. These will maintain your batteries at full charge without any external attention.

All that's required in the way of maintenance is to have someone periodically check the fluid level in the batteries, and use ONLY distilled water to maintain the proper level. With T-105s, I've found that HydroCaps or WaterMiser caps reduce water loss and make it easier to check and refill battery cells. I use WaterMiser caps on all my 12 golf-cart batteries, both on the boat and in shore locations. These are available from Northern Arizona Wind and Sun.

So, next time you put in new batteries be sure to install a solar panel and MPPT controller to keep them charged while you're away. Good small controllers can be found at Genesun and Morningstar. A panel of 50-60 watts or so should be large enough to keep a bank of 4 T-105s fully charged in the BVI.

Hope this helps,

Bill

By the way, with proper treatment you should get 5-7 years or even more from the T-105s. I got almost 8 years on my last batch.

B.

[JK n Smitty]

Originally Posted by paulw

Again, thanks for your input. Sailing in the Carib has at times meant making do with what's available. Locating T105s has been a problem (even in a the BVI!), and so I have mixed old & new once (and pairs of different brands).

Well there is your problem. You can't mix different age or size batteries in the same bank. It will artificially age the new batteries and reduce the overall life of the batteries. You should be replacing the bank as a whole.

As far as availability in the BVI, what about St. Thomas or St. Marteen? There are some larger suppliers in those locations and they aren't that far of a sail.

I'm reluctant to leave anything running on an unattended boat (on the hard), which may be moved at the yard's whim etc. Three years ago, a cockpit drain hose inexplicably disconnected and we came back to a flooded cabin sole. Most importantly, as you may have guessed, it's been a challenge learning to bend our demand & preferences to the capabilities of our electrical system. Over time, we added Solar & Wind, and it's all working pretty well today (when we're on the boat).

If it were me, I would leave the wind and solar charging the system and leave the bilge pump on (probably wired direct to the batteries anyways). Solar should be able to handle the occasional load from that.

But the key part is you really need to have someone check on it and top off the batteries on a regular basis.

On average, our house batteries have lasted 2-years. We were unable to go sailing this year and I'm expecting that my T105s, which I disconnected before leaving in 2013, will not have survived the neglect. That started me thinking about 12V batteries, which brought me to this forum.

2 years?! Ouch. that is short. But I think the mixing of the bank may be your biggest problem. A couple of months being disconnected is bad but there are many banks up here in the NE US that get that kind of treatment during winter layup and last longer than 2 years.

[Stu Jackson]

For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

Link-series Charging Algorithms -- The "Gotcha" Factor!

DEFAULTS are factory settings that are made to be modified to suit your setup.

[S/V Alchemy]

Originally Posted by transmitterdan

Because the 6V golf cart batteries already have very high power density. Going to 12V batteries will not increase the stored energy for a given space/weight. 6V golf cart batteries are about as good as you can do with lead acid batteries as far as power/weight/space is concerned.

Later today, I'll be crimping power lugs...because I concur!

I like T-105s...I had T-105s, but I do not think the Trojan premium price is worth it, and I will be getting Interstate or something similar L-16s, three pairs of two, to make up a house bank.

I concur that for a small bank it's hard to be a "maintenance" solar panel, appropriately fused and with a controller with proper set points and batteries with Hydrocaps or some other means of maintaining optimum SG.

[S/V Alchemy]

Originally Posted by btrayfors

By the way, with proper treatment you should get 5-7 years or even more from the T-105s. I got almost 8 years on my last batch.

B.

Bill, when we bought our custom steel cutter in 2006, it had the original pair of T-105s house batteries from its launch in 1988! Yes, 18 years. I noticed they were, to put it mildly, not great at holding a charge, and I have no idea if the boat was kept plugged in all winter (we haul five months out of seven in Southern Ontario), but I was mightily impressed. I have heard from loyal Trojan fans that "they aren't like they used to be", but the principle that a pair of 6Vs in P/S trumps a single, same sized 12V battery still holds.

Echo-charged windlass and starter batteries excepted, of course. I concur that seven or slightly more years for well-tended house batteries is reasonable. By well-tended, I mean temperature-sensored, hydrocapped, regular (like monthly) tests with the hydrometer, regular equalizations, and a charging/depletion regimen that stays at the higher end of the "useful" 50%-80% SOC band.

[btrayfors]

I haven't noticed any deterioration in build quality of T-105s over the past years, but I have noticed a major increase in price.

To my mind, Trojan has just about priced themselves out of the market. So much so, that last year when I replaced my six T-105 house batteries I chose Crown industrial golf-cart size batteries, the white 235AH version. So far, they've been great. We'll see about longevity.

Problem is with user reports of longevity, batteries tend to be replaced at very different stages of deterioration. For some folks who are mostly at dockside, this can be after the batteries have lost a whole lot -- or even most -- of their capacity.

For me, the replacement decision came after some years of careful treatment and testing and research. Two of my six house batteries -- then over seven years old -- began to lose capacity. In just a few months after testing like new for several years, they lost between 10% and 20% of original capacity. The remaining four still tested at near original capacity. I decided to replace them all and start afresh with the battery tests on a completely new set.

Most users wouldn't have noticed, and would have gone on using them, possibly for years. Thus, the statements you hear about "I got XX years from my batteries" mean next to nothing, without sophisticated tests of actual remaining capacity. Most users don't have the equipment, time, or knowledge to do such testing.

Take your car battery. These are "good" for five or six years, faithfully starting your car every time you turn the key. Until that fateful time they won't. These abused batteries (under the hood in hot and cold conditions, poorly charge controlled, etc.) are losing capacity from the day they leave the factory, but they hang in there for years because it takes only a tiny fraction of their AH capacity to start your engine. So, one morning your start battery which is 90% depleted in its capacity won't start your engine, even though it did the night before.

If you had measured the car battery's voltage the day before it no longer could start your car you might well have seen "normal" voltage. Why? Because -- and I need to shout here:

BATTERY VOLTAGE HAS ALMOST NOTHING TO DO WITH BATTERY CAPACITY.

A badly sulfated battery with 90% of its original capacity gone may still "hold a charge" and exhibit "normal" voltages. Battery voltage can be a decent indicator of state-of-charge (SOC), but not capacity.

Thus a 100% fully charged battery with most of its capacity gone thru sulfation and other problems may show "normal" voltages, but it won't start your engine.

Bill

[CaptTom]

One thing that tipped the scales in favor of 6V batteries for me was that they are taller than typical deep-cycle 12V batteries, at least the ones I was looking at. Thus more AH density in the same footprint. Since I had room to go "up" but not "out", this worked for me. Obviously if you have plenty of floor space but not height in your preferred battery location, it may be best to go with 12V batteries.

[nigel1]

My vote would be to keep to the 6 Volt batteries, as explained by all the excellent preceding posts.
It is my intention to switch from 12V batteries to 6 V batteries as soon as they need replacing. I presently have 12V Varta batteries which are in their 5th year at the moment, which is pretty good, but I still want to go with the 6 V batteries.
On big advantage with the 6 V system is that it is a lot easier to move a 6 v battery than a 12 v battery.

[S/V Alchemy]

Originally Posted by btrayfors

A badly sulfated battery with 90% of its original capacity gone may still "hold a charge" and exhibit "normal" voltages. Battery voltage can be a decent indicator of state-of-charge (SOC), but not capacity.

Thus a 100% fully charged battery with most of its capacity gone thru sulfation and other problems may show "normal" voltages, but it won't start your engine.

Bill

Bill, I concur and just factor in a full replacement every six or seven years as the cost of doing sailing. And I do realize that the actual capacity of the elderly T-105s I mentioned was likely similar to that of nine or 10 D-cells in series and parallel. The few months we had them, we never spent much time both off shore power and off alternator, so they were never truly tested for duration.

That said, it strikes me that the variable of "keep 'em topped up" (and watered and cool and properly cabled and monitored and all the other good habits one should have) is a function less of battery construction and more of maintenance, usage patterns and "right sizing" the battery bank. We are going for a six L16 house bank (around 1100 Ah) because a) we can have that weight close to the boat's CG/CE and therefore we can avoid excessive cabling runs and putting us out of trim, and b) because a seemingly vast bank with relatively low draws and plenty of charge sources (externally regulated alts, 4 x 135W panels and 400W wind, plus a pair of Honda 2000s if needs be) give us the best shot at keeping the bank not in the typical "50-80% SOC", but in a "70-95% SOC" that is more likely to give us the maximum pop in terms of time and capacity.

Trojans and their (probably reputation-based) price premium don't enter into this equation. Any adequately plotted out and maintained bank can last closer to stated capacity if the drawdown is kept modest and the charging regime is very rarely "off". Trojans may just tolerate bad habits somewhat better than "stock" 6V units.

Please tell me, Bill, if you think I'm on the wrong track here, but that's where my researches are pointing: get the biggest bank you can carry, watch your watering and charge regimens, and draw down from the highest SOC you can feasibly maintain. I realize not everyone can do this, but I have a steel full keeler. An extra half-tonne of batteries is not a hardship for me to carry, and if put in the middle of the boat, actually stiffens us up.

[S/V Alchemy]

Originally Posted by CaptTom

One thing that tipped the scales in favor of 6V batteries for me was that they are taller than typical deep-cycle 12V batteries, at least the ones I was looking at. Thus more AH density in the same footprint. Since I had room to go "up" but not "out", this worked for me. Obviously if you have plenty of floor space but not height in your preferred battery location, it may be best to go with 12V batteries.

If I had a flat-bottomed performance cruiser, I would consider the sort of AGMs used in telecom backup battery banks under the floorboards for this reason, because you can lay 'em down and they are only five inches or so tall. We plan on having two tall rows of three L16s and building new saloon stairs over them. They will sit in a fibreglassed vented box bolted to a welded L-bar frame. Access will be from the stair treads.

[btrayfors]

S/V Alchemy,

I think you're on the right track in terms of a battery system which is right for you!

But, as you said, it might not be right for every situation.

Having a huge battery bank and drawing only a relatively smallish load from it has the added benefits of:

1. having a real AH capacity greater than the rated one, since the drawdown is less than C/20 and thus real AH capacity is larger; and

2. the charge acceptance rate in the latter stages of charging is greater than with a smaller bank, i.e., at any given SOC you can put more amps back faster than you could with a smaller bank.

However, and quite apart from cost and weight considerations, remember that you'll be operating in the upper regions of battery SOC where charge acceptance is progressively lower and lower. This is true no matter the size of the charging source.

Put another way, it will cost a lot more to replenish 20AH when the batteries are at a 90% SOC than it will when they are at a 50% SOC. If the charging source is engine or generator-driven, this is a consideration since you'll not likely want to "top off" the charging of your batteries with mechanical means. Much better (more economical) is solar, shore-power, or wind-power.

Bottom line: each situation is different and the choice of battery and charging systems needs to be tailored to spacific individual requirements.

There's no one-size-fits-all solution!

Bill