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Open Roads Forum  >  Tech Issues

 > Why 6V battery instead of 12V?

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mena661

Southern California

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Posted: 04/19/13 10:29am Link  |  Print  |  Notify Moderator

RJ, there's less voltage drop under heavy inverter loads with 12V than 6V. But that doesn't make 6V any less suitable for inverter use in practice. Considering that most off grid home applications use 6V's and not 12V (only the big money setups use 2V's generally), that crowd isn't concerned to much.


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HiTech

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Posted: 04/19/13 10:30am Link  |  Print  |  Notify Moderator

RJsfishin wrote:

Quote:
My system was designed using 12 volt jars because I use my inverter LOTS! Six volt jars would not work well for me at all.
---------------------------------------------------------------------
I am curious, why would using an inverter a lot not work well at all on 6 volt batteries. Could you please explain that ?


Surface area and Acid starvation. Heavier duty plates are better for abuse and durability, but for not maintaining voltage at a high current draw.

"In general, a 20 year design will have thicker grids, thicker plates, more dense active material, wider plate spacing, etc., all designed to maximize life. Unfortunately ..., these features all reduce the high-rate efficiency of the cell."

Plate thickness vs. lost efficiency at high amp rate draws (Peukert)

6V will work very well, you just need more of them generally to support a given heavy inverter draw than you would 12V batteries (with all kinds of disclaimers about the types of 6v or 12v batteries - typical example being 6v golf cart vs 12v hybrid/marine).

Jim

wa8yxm

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Posted: 04/19/13 10:36am Link  |  Print  |  Notify Moderator

The first thing you need to understand is there are only 12 volt batteries in RV's. (Yes, I knwo, you ask about six volt) With six volt batteries you use two, in series which makes one BIG (key word there BIG) 12 volt battery, roughly somewhere between a 4-D and an 8D, 230 amp hours of which you can safely use 1/2 or 115 amp hours.

These are true DEEP CYCLE golf car batteries

Most 12 volt batteries are "Marine/Deep Cycle" which in truth are closer to starting batteries than DEEP CYCLE, they do not like 50 percent state of charge , they like to be "Bette fed" this means they tend to have shorter lifes unless you double up on the capacity.

They also cost more per amp hour, The reason for this is that the GC-2 Golf car battery is quite possibly the most popular lead acid battery in the world, with thousands and thousands of golf cars using them, many golf courses buy 'em by the pallet load.

Means lower per unit production cost.

Now.. Today, you can get 12 volt DEEP CYCLE Golf Car batteries, somewhere around a group 29 or 31, (I've seen 'em never measured them) this is due to at least one golf car company going to a 12 volt battery and a higher voltage motor.

And as more and more golf cars go to this set up, the price on those 12 volt batteries is coming down. But Six volt are still cheaper.


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sh410

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Posted: 04/19/13 10:49am Link  |  Print  |  Notify Moderator

Good answers to the OP question. I think that the majority of RV'rs are weekenders who go to full hookup CG and occasionaly dry camp can get by with a single 12v battery.

Next up are those who dry camp for a weekend several times a year and they will find benefit with 2 6v batteries if they maintain them and fully recharge when they get home (same for 12v). Many get 6-8 years of life. Whereas the 12V users seem to get fewer years use. The failure rate on 6V's, although possible, is very low.

Then there are the high amp users with inverters to power their coffee pots, microwaves etc. and they are better served by multiple 12V batteries.

Each have an application, and is up to each of us to determined what works for us.

We are working on year 7 for our 6v'ters and are still OK. Hope to get this year in before replacing.





tenbear

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Posted: 04/19/13 11:07am Link  |  Print  |  Notify Moderator

I think that possibly one reason for the longer life of 6v batteries may be the users.

RVs come from the factory with 12v batteries. Many RVers don't know much about the electrical system in RVs. People who have made the effort to change their batteries to 6v golf car batteries probably know more about batteries than many RVers and monitor the batteries better than the average RVer, thus getting longer life from their batteries.

In my case, my first battery lasted about 3 years and failed while on the road. I just replaced its replacement after 6 years, not because it failed but because I didn't want it to fail while on the road. Both were/are 12v marine batteries. I think I learned quite a bit in the past few years, and I have added meters so I don't have to depend on the idiot lights.


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elkhornsun

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Posted: 04/19/13 11:08am Link  |  Print  |  Notify Moderator

It is simply a matter of weight. 6v are industrial batteries and designed for heavy use in forklifts and golf carts and similar applications. With 6v batteries you split the weight of a 12v battery into two halves. Industrial batteries can provide 6v, 4v, and even 2v of power and are coupled together to provide then required voltage.

The golf cart 6v batteries are industrial type batteries and they are naturally going to last longer than a standard 12v battery. The industrial battery will have thicker plates which in turn makes it heavier for its size. Check out the Trojan industrial battery lineup and the weight difference is obvious.

A J150 battery is the largest size made in 12v form and these provide 150 AH at 12 volts and each one weighs 84 pounds. Group 921 size batteries provide up 225 AH at 12v and each weighs from 114 to 128 pounds.

It is not difficult to understand that as the AH capacity of a battery so does its size and its weight. At a certain point it makes sense to break a battery into smaller segments. Two 6v ones or six 2v batteries are individually easier to handle than a single 12v battery providing the same amount of amp hours. The greatest capacity battery produced by Trojan is nearly 4 cubic feet in size and weighs 465 lbs. It takes three of these 4v batteries for a total weight 1,395 lbs. to provide 12 volts. Plus side is that these batteries are rated at 1570 AH over a 20 hour period.

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Posted: 04/19/13 11:12am Link  |  Print  |  Notify Moderator

RJsfishin wrote:

Quote:
My system was designed using 12 volt jars because I use my inverter LOTS! Six volt jars would not work well for me at all.
---------------------------------------------------------------------
I am curious, why would using an inverter a lot not work well at all on 6 volt batteries. Could you please explain that ?


It takes a larger weight bank of 6Vs to run a high wattage inverter load like a microwave for the same minutes.

The sweet spot for a 'useful' amount of microwave time is 4 x 6Vs. Of course, the same weight 4 x 12V will run the microwave longer, but somewhere up the line, there is no 12V advantage when you reach the size where you can run the microwave more than needed. After that point, the 6Vs are better.

It depends on your definition of 'useful'.

HTH;
John

mkirsch

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Posted: 04/19/13 11:19am Link  |  Print  |  Notify Moderator

Whether you use 6V batteries, or 12V batteries, the SYSTEM itself will still be 12V...

In many cases, you are replacing one 12V "deep cycle marine" battery with *TWO* 6V golf cart batteries, wired in series to make 12V.

There is an obvious, distinct advantage here: TWO batteries versus one. TWO. Double. Twice as much battery capacity.

If you replace two 12V in parallel with two 6V in series, the advantages aren't quite as significant. You are still getting bit better capacity, and better durability from the golf cart batteries, but you're only getting 5-10% more capacity, not double the capacity, not 5 times the capacity.

Of course, if you replace your old worn mostly-dead 12V batteries with brand new batteries of any flavor, you're going to see a HUGE improvement! That's because your old batteries were old, not because the new batteries have magical properties.

Volts are Volts. Amp-hours are Amp-hours.


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Kevin J

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Posted: 04/19/13 11:42am Link  |  Print  |  Notify Moderator

This is why I asked the original question (especially the last sentence): "Volts are volts, amp hours are amp hours".
I understand that all systems are ultimately 12V, and since I have (2) 12V batteries in parallel in my existing setup and little room to increase the number of batteries, I questioned the advantage of replacing (2) 12V batteries in parallel with (2) 6v batteries in series (and I guess I still do to some extent).
Right now, this is just for curiosity, since I don't dry camp often, but, in the future, I may want to dry camp more and I'll eventually have to replace batteries anyway. Interesting replies.

mkirsch wrote:

Whether you use 6V batteries, or 12V batteries, the SYSTEM itself will still be 12V...

In many cases, you are replacing one 12V "deep cycle marine" battery with *TWO* 6V golf cart batteries, wired in series to make 12V.

There is an obvious, distinct advantage here: TWO batteries versus one. TWO. Double. Twice as much battery capacity.

If you replace two 12V in parallel with two 6V in series, the advantages aren't quite as significant. You are still getting bit better capacity, and better durability from the golf cart batteries, but you're only getting 5-10% more capacity, not double the capacity, not 5 times the capacity.

Of course, if you replace your old worn mostly-dead 12V batteries with brand new batteries of any flavor, you're going to see a HUGE improvement! That's because your old batteries were old, not because the new batteries have magical properties.

Volts are Volts. Amp-hours are Amp-hours.



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HiTech

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Posted: 04/19/13 01:40pm Link  |  Print  |  Notify Moderator

Volts are volts. Amps are amps.

Amp hours are at a fixed draw for a given number of minutes. 2 batteries with the same 20a amp hour rating will have a different 10a or 75a or 200a amp hour rating. Sometimes very different. And the only voltage that is a given in the amp hour rating is 10.5v at the end. When two batteries with the same amp hour rating hit 11v can be very different as well.

Jim

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