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mr_andyj

Georgia

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Posted: 05/03/21 03:40pm Link  |  Quote  |  Print  |  Notify Moderator

batts dont typically just die. They start to die slowly. With two 6's one might be going bad, the other still is good. The two add together to still give you enough volts to do everything. 11.5 is low, but 5.75 plus 6 is 11.75 which is still pretty good. With one 12 volt batt only able to get to 11.5 and the other 12 then the total voltage available is still 11.5. The bad batt brings down the good one. when parallel, but not when in series. This is the big reason to go with two 6's. You can mis-match two 6's in series, but you really should only exactly match when in parallel (two 12s).
Nonsense? No. Good advice, but go do an easy forum search as there are many post on this same topic and easy easy to find with a few keystrokes....

Gdetrailer

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Posted: 05/03/21 04:18pm Link  |  Quote  |  Print  |  Notify Moderator

mr_andyj wrote:

batts dont typically just die. They start to die slowly. With two 6's one might be going bad, the other still is good. The two add together to still give you enough volts to do everything. 11.5 is low, but 5.75 plus 6 is 11.75 which is still pretty good. With one 12 volt batt only able to get to 11.5 and the other 12 then the total voltage available is still 11.5. The bad batt brings down the good one. when parallel, but not when in series. This is the big reason to go with two 6's. You can mis-match two 6's in series, but you really should only exactly match when in parallel (two 12s).
Nonsense? No. Good advice, but go do an easy forum search as there are many post on this same topic and easy easy to find with a few keystrokes....


You do realize that "lead acid" batteries are nominal 2V per cell, right?

To get a "12V" lead acid battery, it takes six 2V cells which are wired internally in series to arrive at nominal 12V. A "12V" battery just combines all 6 cells into one box.

To get a "6V" lead acid battery, it takes three 2V cells wired in series to arrive at nominal 6V. A "6V" battery combines 3 cells all in one box.

There is nothing "magical" about a "12V" battery compared to a "6V" battery other than the fact that it takes two "6V" batteries wired externally in series to achieve nominal 12V.

The sticking point many point to is using 6V batteries ends up with a higher "internal resistance" than if you used two "12V" batteries in parallel.

All battery cells have something call "internal resistance". Internal resistance causes a high voltage drop under high current draw.

So, to get around the internal resistance issue folks insist that 12V batteries are better because the internal resistance is reduced when in parallel, which is sort of true to some extent.

However, they do so at a loss of capacity when you compare the physical size, weight and Ahr capacity.

Not to mention 12V batteries actually have a higher internal resistance due to less plates, smaller plates and less surface area on those plates. But in electronics when you parallel resistors the overall resistance is reduced (Ohms law) so the end result may be a bit less voltage drop when paralleling two 12V batteries when using very high current draw devices.

A group 27 12V battery is roughly the same size as a 6V GC2 but the GC2 is a bit taller and weighs more than a group 27.

one group 27 has roughly 80Ahr of capacity and max usable capacity of 40Ahr (50%) for rated life.

6V GC2 has roughly 210 Ahr capacity and max usable capacity of 168Ahr (80%) for rated life.

Granted, you need two 6V GC2s (series wiring of 6V batteries does not increase Ahr capacity) but from my POV 168 Ahr is considerably much more usable capacity than three group 27 12V batteries wired in parallel.

Personally, if internal resistance bothers you, go with four 6V GCs and wire up as two series strings of batteries and parallel the two series strings. End result will be far more usable Ahr capacity with low enough internal resistance than using four 12V batteries in parallel.

stevenal

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Posted: 05/03/21 05:40pm Link  |  Quote  |  Print  |  Notify Moderator

Real world here: When running a single 12, twice we had sudden battery failures while traveling.Each time required an out of the way trip to a town to find a replacement. Not how I wanted to spend precious vacation time. The new camper has a pair of 12s. No failures yet, but when it occurs I’ll disconnect the bad one and deal with a replacement later. Do you suppose NAPA (or anyone) in Joseph, OR has a suitable 6 in stock?


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Gdetrailer

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Posted: 05/03/21 06:11pm Link  |  Quote  |  Print  |  Notify Moderator

stevenal wrote:

Real world here: When running a single 12, twice we had sudden battery failures while traveling.Each time required an out of the way trip to a town to find a replacement. Not how I wanted to spend precious vacation time. The new camper has a pair of 12s. No failures yet, but when it occurs I’ll disconnect the bad one and deal with a replacement later. Do you suppose NAPA (or anyone) in Joseph, OR has a suitable 6 in stock?


Batteries rarely "just quit", degrade, sure, but just quit not so much.

Most battery sudden failures are more from ignoring the maintenance things like checking and adding water. More dead batteries are caused by ignoring the water level and using the batteries through normal charging cycles will eventually boil off enough water tot dry out the battery..

Parallel operation however while it makes you "feel good" in reality will ultimately hide a weak battery and the weaker battery will end up zapping the life of the other battery and eventually you will end up in the exact same boat you found yourself in.

Paralleling sounds great on paper, but in real life, not one battery ever made is 100% perfect and the same as the next on off the line even in the same day batch. They all have different characteristics from charging current, to discharging current. In reality each 12V battery will charge or discharge at slightly different amounts/rates.

It is for that reason auto manufactures like Ford highly recommend on their Diesel trucks which have two starting batteries that when you replace the batteries you should replace both at the same time. Those batteries are connected in parallel but yet a weak battery can cause issues.

ktmrfs

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Posted: 05/03/21 07:04pm Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:

mr_andyj wrote:

batts dont typically just die. They start to die slowly. With two 6's one might be going bad, the other still is good. The two add together to still give you enough volts to do everything. 11.5 is low, but 5.75 plus 6 is 11.75 which is still pretty good. With one 12 volt batt only able to get to 11.5 and the other 12 then the total voltage available is still 11.5. The bad batt brings down the good one. when parallel, but not when in series. This is the big reason to go with two 6's. You can mis-match two 6's in series, but you really should only exactly match when in parallel (two 12s).
Nonsense? No. Good advice, but go do an easy forum search as there are many post on this same topic and easy easy to find with a few keystrokes....


You do realize that "lead acid" batteries are nominal 2V per cell, right?

To get a "12V" lead acid battery, it takes six 2V cells which are wired internally in series to arrive at nominal 12V. A "12V" battery just combines all 6 cells into one box.

To get a "6V" lead acid battery, it takes three 2V cells wired in series to arrive at nominal 6V. A "6V" battery combines 3 cells all in one box.

There is nothing "magical" about a "12V" battery compared to a "6V" battery other than the fact that it takes two "6V" batteries wired externally in series to achieve nominal 12V.

The sticking point many point to is using 6V batteries ends up with a higher "internal resistance" than if you used two "12V" batteries in parallel.

All battery cells have something call "internal resistance". Internal resistance causes a high voltage drop under high current draw.

So, to get around the internal resistance issue folks insist that 12V batteries are better because the internal resistance is reduced when in parallel, which is sort of true to some extent.

However, they do so at a loss of capacity when you compare the physical size, weight and Ahr capacity.

Not to mention 12V batteries actually have a higher internal resistance due to less plates, smaller plates and less surface area on those plates. But in electronics when you parallel resistors the overall resistance is reduced (Ohms law) so the end result may be a bit less voltage drop when paralleling two 12V batteries when using very high current draw devices.

A group 27 12V battery is roughly the same size as a 6V GC2 but the GC2 is a bit taller and weighs more than a group 27.

one group 27 has roughly 80Ahr of capacity and max usable capacity of 40Ahr (50%) for rated life.

6V GC2 has roughly 210 Ahr capacity and max usable capacity of 168Ahr (80%) for rated life.

Granted, you need two 6V GC2s (series wiring of 6V batteries does not increase Ahr capacity) but from my POV 168 Ahr is considerably much more usable capacity than three group 27 12V batteries wired in parallel.

Personally, if internal resistance bothers you, go with four 6V GCs and wire up as two series strings of batteries and parallel the two series strings. End result will be far more usable Ahr capacity with low enough internal resistance than using four 12V batteries in parallel.


actually most 12V batteries have lower internal resistance than a comparable AH 6V because they have more and thinner plates per 2V cell than 6V. But the thinner cells and associated tradeoffs means lower cycle life and not likeing deep discharges.

But yes, using four 6 volt will give about 500AH capacity and suitability for reasonably high current draw. But four 12V in parallel will still give lower voltage drop due to lower internal resistance and load sharing amongst four batteries instead of two.


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Vintage465

Prunedale CA.

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Posted: 05/03/21 08:12pm Link  |  Quote  |  Print  |  Notify Moderator

JimK-NY wrote:

After 4 pages of opinions, it is interesting that there does not seem to be any data or studies cited which show proven advantages for 6 volt batteries. The closest was someone mentioning that Trojan considered 6 volt batteries to be more durable.


I think if you went for a comparison chart that showed pounds of battery per amp/hour you'd find that 6v golf cart batteries have the advantage. If I added up 4 100ah 12v batteries vs 4 235ah 6v batteries you'll be ahead with the 6's and also use less space and right at the same weight.


V-465
2013 GMC 2500HD Duramax Denali. 2015 CreekSide 20fq w/450 watts solar and 465 amp/hour of batteries. Retiring in 2021, then look-out road, here we come!

Gdetrailer

PA

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Posted: 05/03/21 08:49pm Link  |  Quote  |  Print  |  Notify Moderator

ktmrfs wrote:



actually most 12V batteries have lower internal resistance than a comparable AH 6V because they have more and thinner plates per 2V cell than 6V. But the thinner cells and associated tradeoffs means lower cycle life and not likeing deep discharges.

But yes, using four 6 volt will give about 500AH capacity and suitability for reasonably high current draw. But four 12V in parallel will still give lower voltage drop due to lower internal resistance and load sharing amongst four batteries instead of two.


4 "12V" batteries will net you considerably less Ahr capacity when comparing similar square inches of space in comparable battery size.

For instance group 27 has foot print of one 6V GC2 and Ahr capacity of 80Ahr. Of that 80Ahr it is rated for only half of the capacity for the cycle life. Cycle life improves drastically if you only use 20% of the capacity.

GC2s cycle life are rated at 80% of the capacity, don't try that with group 27, you will degrade a group 27 very quickly if you try..

So, in reality, if you want max life, max draw with max capacity the GC2s are the better choice even with high current draw.

I don't know what folks are doing to bother an inverter with high current draw on GC2s, so far I have not had any issue. I know for a fact that my home fridge conversion does indeed spike 100A draw on the compressor startup surge. Even draining my GC2s down to 50% discharge I have never had any issue with my inverter low voltage alarm or shut down.

I do know this, I can easily go 24hrs without recharging my one pair of GC2s. In fact, I typically will travel 800 miles over two days, overnighting one night without power to get to my camping spot all without any commercial power or stopping for generator. As you know, vehicle charge lines provide very minimal charge support.

To get that kind of run time with group 27s I would need better than 4 of them, most likely 8 and then I would be replacing batteries every few yrs because I would be discharging very deeply..

So far the first set of GC2 batteries lasted me 9 yrs, could have gone 10, maybe 11 yrs but I did notice they didn't have as much capacity as they did when new and they were using twice the water as new.

You can continue using group24/27 in parallel, myself I am more than satisfied with the long, long battery life I am getting with GC2s in series..

ktmrfs

Portland, Oregon

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Posted: 05/03/21 09:05pm Link  |  Quote  |  Print  |  Notify Moderator

Gdetrailer wrote:

ktmrfs wrote:



actually most 12V batteries have lower internal resistance than a comparable AH 6V because they have more and thinner plates per 2V cell than 6V. But the thinner cells and associated tradeoffs means lower cycle life and not likeing deep discharges.

But yes, using four 6 volt will give about 500AH capacity and suitability for reasonably high current draw. But four 12V in parallel will still give lower voltage drop due to lower internal resistance and load sharing amongst four batteries instead of two.


4 "12V" batteries will net you considerably less Ahr capacity when comparing similar square inches of space in comparable battery size.

For instance group 27 has foot print of one 6V GC2 and Ahr capacity of 80Ahr. Of that 80Ahr it is rated for only half of the capacity for the cycle life. Cycle life improves drastically if you only use 20% of the capacity.

GC2s cycle life are rated at 80% of the capacity, don't try that with group 27, you will degrade a group 27 very quickly if you try..

So, in reality, if you want max life, max draw with max capacity the GC2s are the better choice even with high current draw.

I don't know what folks are doing to bother an inverter with high current draw on GC2s, so far I have not had any issue. I know for a fact that my home fridge conversion does indeed spike 100A draw on the compressor startup surge. Even draining my GC2s down to 50% discharge I have never had any issue with my inverter low voltage alarm or shut down.

I do know this, I can easily go 24hrs without recharging my one pair of GC2s. In fact, I typically will travel 800 miles over two days, overnighting one night without power to get to my camping spot all without any commercial power or stopping for generator. As you know, vehicle charge lines provide very minimal charge support.

To get that kind of run time with group 27s I would need better than 4 of them, most likely 8 and then I would be replacing batteries every few yrs because I would be discharging very deeply..

So far the first set of GC2 batteries lasted me 9 yrs, could have gone 10, maybe 11 yrs but I did notice they didn't have as much capacity as they did when new and they were using twice the water as new.

You can continue using group24/27 in parallel, myself I am more than satisfied with the long, long battery life I am getting with GC2s in series..


I'll agree with GC2 for cycle life, ability to do hundreds of really deep discharges, and long life. And even 100A or so spikes in current draw from GC2's. That's why I like them.

where I had trouble with a pair of GC2's was running my panasonic true inverter variable output microwave for long periods (5-10 minutes) . it doesn't cycle between 0 and 100% but stays at a fixed %. On my 1000VA inverter with very short (18 inches) of 4/0 cable between the batteries and inverter it would run the microwave just fine at 50% input (90A 12V draw) as long as the battery bank was at 80% or more. much below that and it would shut down due to low input voltage after 30-60 seconds.

Keep current draw below 30A-40A or so and they perform wonderfully.

On one trailer I have a pair of GC2's running a small fridge on a MSW inverter. Like you mentioned current can spike, in my case in the 75A range, but then settles down to 15A or less. A pair of GC2's will do this all the way down to 50% SOC or less no problem.

I think BL13 and some others experienced the same thing at very high continous current draw (100A or so). I since switched to a bank of 4 GC2's, and no issues down to 50% SOC.

And I've run two sets of batteries on different trailers for 10 years on a bank of GC2, often averaging 60 days or so off grid so the batteries will last a decade if properly cared for.

JimK-NY

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Posted: 05/03/21 09:20pm Link  |  Quote  |  Print  |  Notify Moderator

Vintage465 wrote:



I think if you went for a comparison chart that showed pounds of battery per amp/hour you'd find that 6v golf cart batteries have the advantage. If I added up 4 100ah 12v batteries vs 4 235ah 6v batteries you'll be ahead with the 6's and also use less space and right at the same weight.


Sorry but that is a common fallacy. Looking at specs it seems that for batteries of roughly the same size and weight, the 6 v seems much better. That is because the amp draw is based on 6 v, not 12v. If in your example you have 2 235 AH 6 volt batteries, you only get 235 AH total for both batteries wired for 12 volts.

If you compare size of batteries, typically 6 v batteries will take up much more space than the equivalent 12 v batteries. The weight will be about the same.

JimK-NY

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Posted: 05/03/21 09:25pm Link  |  Quote  |  Print  |  Notify Moderator

mr_andyj wrote:

.....
Nonsense? No. Good advice, but go do an easy forum search as there are many post on this same topic and easy easy to find with a few keystrokes....


I am still trying to locate some facts and studies, not just opinions. Forum searches have not been any better. Instead I have seen even more myths, fallacies and unfounded opinions.

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