6V bank to replace 12V bank

[Group9]

Originally Posted by nigel1

The other advantage is that two 6V batteries are easier to handle than a single 12V battery

That's the truth. Who wouldn't rather haul two 6v's instead of a 4D or 8D up the companionway stairs?

[foggysail]

Originally Posted by savoir

You will need a whole new set of cables so buying a crimper might be a good idea. The good ones cost around $200+.

.

And then comes Ebay!

Heavy Duty Crimper 1 0 2 4 8 10 Gauge Hex Crimping Wire Lugs Terminals Large New | eBay

[Andina Marie]

Originally Posted by foggysail

I wonder! Have you considered the impact of parallel 12s where the internal resistances are different? So now it becomes a trade off between internal battery resistance for parallel banks and a series configuration where the analogy is similar to that of the weakest chain link.

NO THAT IS NOT A PROBLEM.

SERIES CONNECTIONS:
For batteries in series matching is essential (as stated above). If one cell fails before all the rest, the load on the battery becomes the equivalent of a jumper from + to - and the bad cell becomes the load. This will reverse the voltage on that cell and destroy it rapidly. By balancing and matching they all the cells discharge uniformly so when the lowest cell reaches zero charge the rest are too low to damage it and the user is hopefully aware of the low voltage.

PARALLEL CONNECTIONS:

I fail to understand you concern about different internal resistance of batteries in parallel. They are at the same voltage (in parallel) so there is no differential voltage. With no voltage difference there is no current (when idle). If there is zero current it doesn't matter what the resistance is.

Fortunately they are different. Having an internal resistance is fundamental to how batteries in parallel work and that resistance is related to the charge level. So strong batteries have a lower resistance and carry more of the load. Weaker batteries have a higher resistance and contribute in proportion to their capability.

It is a very common misunderstanding to think that if you draw 100 amps from 2 batteries in parallel that 50 amps will come from each battery. That is virtually never the case. You can parallel a 200 Ah battery with a small lawn mower starting battery and it will work fine with the big one supplying (and accepting) say 97% of the current and the small one 3%. The current supplied is the difference between charge level (say 12.6) and the load voltage (say 12.4). The difference divided by the internal resistance of the battery determines how much current each will supply.

[nigel1]

Originally Posted by foggysail

And then comes Ebay!

Heavy Duty Crimper 1 0 2 4 8 10 Gauge Hex Crimping Wire Lugs Terminals Large New | eBay

Something similar I bought from ebay last year when I re did all the charging and battery cables and fitted the solar panels
16mm- 300mm HYDRAULIC CABLE CRIMPING TOOL (CRIMPER) | eBay

[Cheechako]

I've done it, and the golf cart batteries are good batteries, but the complication of all the short fat cables, 2 x the connections.... etc... frankly I dont think it's worth it. You dont need to go to a 4D or 8D in 12v batteries.
If you do it, be sure to work out the bends etc in the heavy connecting cables prior to fabricating them... they dont bend well after crimping the ends. If you bend prior to crimping the strands in the cable slide along each other... then cut the ends and install the end fittings... the cable will stay in that approximate shape.

[jeremiason]

We switched from three 8D batteries to eight US Battery US 125XC 6v Batteries about 3 years ago and love them... This increased our house bank from 675 AH to 968 AH.

These batteries were slightly taller than the originals, so we used side connecting terminals instead of wing nuts.

The new batteries fit in the same foot print as the original 8Ds, with room to spare.

We went with the US Battery over Trojan at the recommendation of a friend who happened to own a Battery Store, which sold both.

In his opinion these were the best batteries for a marine application... According to him the plates on the US Batteries are much larger/heavier and will last longer, justifying the higher price. It also didn't hurt that we got a great discount!

[Maine Sail]

Originally Posted by Andina Marie

True except for one provision.

It is ESSENTIAL that batteries in series be matched for as many parameters as possible, age, chemistry, capacity, manufacturer etc.

This is AUTOMATIC when you purchase or replace a 12 volt battery.

To achieve this with 6 volt batteries in series, ALWAYS replace both batteries with matched pairs when one of them dies.

I go one step further when buying new 6V batteries. I wire them in parallel to "balance" them by charging them to full at 6V and leaving them parallel wired for a couple of days. I then install them on the boat and wire them in series or series parallel, if more than two, and the bank seems to stay very well balanced. Is this 100% necessary? Often not, but it certainly does not hurt either...

They would eventually balance out on their own especially if you pushed an equalization voltage but at the low "ish" charging voltages we often see it can take a while for them to become fully charged if they were out when new.

[AnchorageGuy]

We have used golf cart batteries for many years on both of our boats. Here is some info on our current installation...

The Trawler Beach House: Batteries and Battery Chargers For The Boat
The Trawler Beach House: Moving The Starting Battery
The Trawler Beach House: Relocating The House Batteries

Chuck

[Andina Marie]

Originally Posted by Maine Sail

I go one step further when buying new 6V batteries. I wire them in parallel to "balance" them by charging them to full at 6V and leaving them parallel wired for a couple of days. I then install them on the boat and wire them in series or series parallel, if more than two, and the bank seems to stay very well balanced. Is this 100% necessary? Often not, but it certainly does not hurt either...

They would eventually balance out on their own especially if you pushed an equalization voltage but at the low "ish" charging voltages we often see it can take a while for them to become fully charged if they were out when new.

It is certainly helpful to equalize them if they don't have identical history, but probably not necessary when buying new batteries off the shelf.

Connecting the 6 volt jumpers together in parallel banks would help to even out differences in the individual batteries. This is a slow process and doesn't require much current so the jumpers could be a light gauge, say #10 which will make installation considerably easier and cheaper.

[sww914]

The biggest reason to switch is the life. About 700 cycles for T105's or similar VS about 300 for most 12v deep cycle batteries. Rolls Surettes last twice as long and cost twice as much.

[thomm225]

Originally Posted by boat_alexandra

better to put 2 6 volt in series than 2 12 volt in parallel. Fewer cells to keep watered, and too many strings in parallel is a bad idea.

What is wrong with two 12's in parallel? I have mine hooked up that way to power my 850watt inverter. The inverter needed the extra umph when I run my 650 watt drip coffee maker.

Plus, I charge both batteries simultaneously from my 60 watt solar panel through a small Jameco controller. Works great!

[onestepcsy37]

thomm225 - i think the comment was that, with two golf cart batts you have 6 'watering holes'; with two 12v batts you have 12 watering holes.

but to me the big advantage of the golf carts is that they are truly designed for many deep discharges/recharges. i've yet to find a 12v batt that is REALLY deep cycle - doesn't just say it on the label...

since you already own the 12 volts, i'd just keep them till they die. then give serious thought to golf cart batts.

[thomm225]

Originally Posted by onestepcsy37

thomm225 - i think the comment was that, with two golf cart batts you have 6 'watering holes'; with two 12v batts you have 12 watering holes.

but to me the big advantage of the golf carts is that they are truly designed for many deep discharges/recharges. i've yet to find a 12v batt that is REALLY deep cycle - doesn't just say it on the label...

since you already own the 12 volts, i'd just keep them till they die. then give serious thought to golf cart batts.

Okay, thanks. I've heard a lot about the golf cart batteries. How large are they? I have removed my diesel so I could probably fix up a space there for lots of batteries..................

and maybe even run a large trolling motor off them that can be stored after use. I really don't like having motors hanging off the stern.

[silversailor]

Thanks all for your thoughtful comment. Chick, if you are in the vacinity of South Haven, MI, I would love your hands on assistance. I'll buy the beer. I do have a height limitation so I'll go measure my battery box. If anyone has a handle on a short 6V please let me know. I'll be replacing a house bank of (3)12volt batteries plus a starter.

[savoir]

All brands of battery are pretty much the same size. The regular 12 volt ones are roughly 9 1/2" high and the golf carts are 10 1/2" - 11" high depending on the brand. 4D and 8D batteries are usually 10" high