Which is better - (3) 12v batteries vs (2) 6v batteries

BFL13 wrote:

ktmrfs wrote:
I'd go with the GC IF your typical current draw is reasonably low like 25A or less. This sounds like your case.

If you typically are going to run an inverter with a heavy load (>75A), then the 12V may work better.

GC have an advantage of having very high cycle life even down to 30% SOC or more, (hundreds of cycles) taking abuse as long as they are kept watered and properly charged etc. However, every battery design has tradeoffs, and with GC it high load current. They have fewer but thicker plates so they have higher internal resistance which compromises high current use.

Since you can repeatedly draw GC down to 20-30% SOC and still get hundreds of useable cycles, the GC wins in the "useable" AH category compared to a 12V. For example a 12V combo of 250AH has realistically 125 Useable AH at 50% DOD, the max recomended for most 12V batteries. By comparison, a 250AH bank of T-125's will give you 250*.7= 175 "useable" AH, That "extra" 50AH could give you an extra day or two of camping.

My last set of Trojan GC were quite often discharged to about 30%SOC, probably about 20 times/year and 50% another 30 times year. After 8 years they went to in-laws and are still running strong for him, better than his bank of 3 year old 12V by far. SG after 8 years is still 1.275 on each cell.

Another thing is how often will you boondock?? If it's only a few times/year, 12V may end up being the lowest cost/year choice. If in a pinch not worrying about discharging the batteries down to 20-30% SOC is important, then GC win hands down. The trojan GC have a higher cycle life at 30% SOC than the trojan true 12V deep discharge do at 50% SOC.

But in either choice the key to longevity is getting a quality battery and properly recharging them as soon as you return from a trip. And unfortunetly, the common WFCO charger in many trailers will seldom do anything near a proper recharge since they seldom go above 13.6V. And you need to get into the 14.5+ V range to properly recharge a flooded cell battery. So you need an iota or Progressive dynamics charger or better yet, the B&D Vector portable charger to get them recharged.

This post has opened my eyes to something that should have been obvious. There is a mismatch between 6s and inverters for two reasons:
- they have a large voltage drop under high amp draw
- the inverter has an 11v loaded voltage alarm you try to stay above.

Which means you can't exploit the advantage of 6s in going to a lower SOC to get more AH before you need to recharge them.

Using the 12s for inverter matches in that you want to stay above 50
% SOC anyway, so the inverter alarm is not itself a restriction on your DOD, and the 12s have less voltage drop under high amp draw, so you can get away with those inverter loads longer.

I am currently trying out a new arrangement with the big inverter on my 12s and the small inverter for TV etc on the 6s with the rig on the 6s too for furnace etc.

But the quoted post has just hit me that I am missing a trick here, by not putting all my inverters on the 12s, leaving the furnace etc on the 6s.

It is possible with some juggling that would allow the 6s to go longer to 30% before a recharge is needed and that the 12s would still be good at 50% till then too, if the AH draw from inverter use was managed right. That would depend on a whole bunch of situational things of course.

Some other folks here have a mix of 6s and 12s, so it might be worth a look.

(BTW, my 12s are Trojan golf car batts (T-1275s) so I find the quoted post confusing. I don't know if they come under the not below 50% rule or not. They do have less voltage drop than my 6s under high amp load though, so that part of being 12s applies ok.)

EDIT--now I am wondering about any advantage in putting the pair of 12s as a 24 and using a 24v inverter, since there is no "ordinary" rig draw on the 12s. My solar controller will do 24 batts or 12v batts too. Hmmmm. But I don't have a 24v inverter.

BFL:

yup, The 6V drop will get ya. When I had two GC, my 1000W inverter would cut out before 75% SOC. Now that I have 4GC, it will run down close to 50% SOC, then the undervoltage gets ya. 12V wins here by a landslide.

From the trojan web site, the trojan 12's are a true deep discharge but won't give the cycle life of the 6's. about 1/2 for same DOD . When I talked to a trojan rep at length at a show he stated that the 12's won't handle the less than 50% SOC near as well as the 6's and suggested with 12's to try to stay at or above 50%. With the 6's he stated keep them above 30%SOC for even heavy dry camping use and you'll get lots of life. Everyday GC use, then stay above 50%.

but he also mentioned folks using a 12V for GC to get more acceleration, (guys driving them around town) tradeoff is cycle life and run time.

BTW Trojan defines cycle life as to when capacity is 50% of initial. So the 1200 cycles @50%SOC 700@20%SOC for GC spec says to me expect maybe 500 mixed discharge cycles before capacity is to the point I'd notice a drop.

The trojan site data sheet shows about 1/2 the cycle life for their line of 12V deep discharge batteries.

using a 24V inverter with the 12's may make sense, however not sure if it is gaining much. with 24V, current gets cut in half. with 12V each battery (in theory) supplies 1/2 the current, so the net draw from each battery stays the same. What you gain is less IR drop between the battery bank and inverter, which depending on run length may or may not be a noticeable net gain.

However, for those that want high inverter draw and long life, the idea of a pair of 12's and a pair of 6's makes perfect sense!! Great idea.

64thunderbolt wrote:

ktmrfs wrote:
I'd go with the GC IF your typical current draw is reasonably low like 25A or less. This sounds like your case.

If you typically are going to run an inverter with a heavy load (>75A), then the 12V may work better.

GC have an advantage of having very high cycle life even down to 30% SOC or more, (hundreds of cycles) taking abuse as long as they are kept watered and properly charged etc. However, every battery design has tradeoffs, and with GC it high load current. They have fewer but thicker plates so they have higher internal resistance which compromises high current use.

Since you can repeatedly draw GC down to 20-30% SOC and still get hundreds of useable cycles, the GC wins in the "useable" AH category compared to a 12V. For example a 12V combo of 250AH has realistically 125 Useable AH at 50% DOD, the max recomended for most 12V batteries. By comparison, a 250AH bank of T-125's will give you 250*.7= 175 "useable" AH, That "extra" 50AH could give you an extra day or two of camping.

My last set of Trojan GC were quite often discharged to about 30%SOC, probably about 20 times/year and 50% another 30 times year. After 8 years they went to in-laws and are still running strong for him, better than his bank of 3 year old 12V by far. SG after 8 years is still 1.275 on each cell.

Another thing is how often will you boondock?? If it's only a few times/year, 12V may end up being the lowest cost/year choice. If in a pinch not worrying about discharging the batteries down to 20-30% SOC is important, then GC win hands down. The trojan GC have a higher cycle life at 30% SOC than the trojan true 12V deep discharge do at 50% SOC.

But in either choice the key to longevity is getting a quality battery and properly recharging them as soon as you return from a trip. And unfortunetly, the common WFCO charger in many trailers will seldom do anything near a proper recharge since they seldom go above 13.6V. And you need to get into the 14.5+ V range to properly recharge a flooded cell battery. So you need an iota or Progressive dynamics charger or better yet, the B&D Vector portable charger to get them recharged.

My WFCO 55a will charge @ 14.4 when checked @ the batt with voltmeter. I dry camp exclusively. Been in a camp ground 1 time in 13 yrs and was in a dry site. Last set of 27's lasted 8 yrs. Current toyhauler has 24's and I added a small solar maintainer. No problems staying out 5/6 days with min gen use. Maybe 2 hrs per day total. But we always have sun in Az.

your one of the few lucky guys with the WFCO. Most folks can't get them to go to the "bulk mode" charging, due to the WFCO algorithm and wire size length. If it does, your in good shape and the WFCO is closer to constant current than PD so your actually in good shape.

ktmrfs wrote:
I'd go with the GC IF your typical current draw is reasonably low like 25A or less. This sounds like your case.

If you typically are going to run an inverter with a heavy load (>75A), then the 12V may work better.

GC have an advantage of having very high cycle life even down to 30% SOC or more, (hundreds of cycles) taking abuse as long as they are kept watered and properly charged etc. However, every battery design has tradeoffs, and with GC it high load current. They have fewer but thicker plates so they have higher internal resistance which compromises high current use.

Since you can repeatedly draw GC down to 20-30% SOC and still get hundreds of useable cycles, the GC wins in the "useable" AH category compared to a 12V. For example a 12V combo of 250AH has realistically 125 Useable AH at 50% DOD, the max recomended for most 12V batteries. By comparison, a 250AH bank of T-125's will give you 250*.7= 175 "useable" AH, That "extra" 50AH could give you an extra day or two of camping.

My last set of Trojan GC were quite often discharged to about 30%SOC, probably about 20 times/year and 50% another 30 times year. After 8 years they went to in-laws and are still running strong for him, better than his bank of 3 year old 12V by far. SG after 8 years is still 1.275 on each cell.

Another thing is how often will you boondock?? If it's only a few times/year, 12V may end up being the lowest cost/year choice. If in a pinch not worrying about discharging the batteries down to 20-30% SOC is important, then GC win hands down. The trojan GC have a higher cycle life at 30% SOC than the trojan true 12V deep discharge do at 50% SOC.

But in either choice the key to longevity is getting a quality battery and properly recharging them as soon as you return from a trip. And unfortunetly, the common WFCO charger in many trailers will seldom do anything near a proper recharge since they seldom go above 13.6V. And you need to get into the 14.5+ V range to properly recharge a flooded cell battery. So you need an iota or Progressive dynamics charger or better yet, the B&D Vector portable charger to get them recharged.

This post has opened my eyes to something that should have been obvious. There is a mismatch between 6s and inverters for two reasons:
- they have a large voltage drop under high amp draw
- the inverter has an 11v loaded voltage alarm you try to stay above.

Which means you can't exploit the advantage of 6s in going to a lower SOC to get more AH before you need to recharge them.

Using the 12s for inverter matches in that you want to stay above 50
% SOC anyway, so the inverter alarm is not itself a restriction on your DOD, and the 12s have less voltage drop under high amp draw, so you can get away with those inverter loads longer.

I am currently trying out a new arrangement with the big inverter on my 12s and the small inverter for TV etc on the 6s with the rig on the 6s too for furnace etc.

But the quoted post has just hit me that I am missing a trick here, by not putting all my inverters on the 12s, leaving the furnace etc on the 6s.

It is possible with some juggling that would allow the 6s to go longer to 30% before a recharge is needed and that the 12s would still be good at 50% till then too, if the AH draw from inverter use was managed right. That would depend on a whole bunch of situational things of course.

Some other folks here have a mix of 6s and 12s, so it might be worth a look.

(BTW, my 12s are Trojan golf car batts (T-1275s) so I find the quoted post confusing. I don't know if they come under the not below 50% rule or not. They do have less voltage drop than my 6s under high amp load though, so that part of being 12s applies ok.)

EDIT--now I am wondering about any advantage in putting the pair of 12s as a 24 and using a 24v inverter, since there is no "ordinary" rig draw on the 12s. My solar controller will do 24 batts or 12v batts too. Hmmmm. But I don't have a 24v inverter.

ktmrfs wrote:
I'd go with the GC IF your typical current draw is reasonably low like 25A or less. This sounds like your case.

If you typically are going to run an inverter with a heavy load (>75A), then the 12V may work better.

GC have an advantage of having very high cycle life even down to 30% SOC or more, (hundreds of cycles) taking abuse as long as they are kept watered and properly charged etc. However, every battery design has tradeoffs, and with GC it high load current. They have fewer but thicker plates so they have higher internal resistance which compromises high current use.

Since you can repeatedly draw GC down to 20-30% SOC and still get hundreds of useable cycles, the GC wins in the "useable" AH category compared to a 12V. For example a 12V combo of 250AH has realistically 125 Useable AH at 50% DOD, the max recomended for most 12V batteries. By comparison, a 250AH bank of T-125's will give you 250*.7= 175 "useable" AH, That "extra" 50AH could give you an extra day or two of camping.

My last set of Trojan GC were quite often discharged to about 30%SOC, probably about 20 times/year and 50% another 30 times year. After 8 years they went to in-laws and are still running strong for him, better than his bank of 3 year old 12V by far. SG after 8 years is still 1.275 on each cell.

Another thing is how often will you boondock?? If it's only a few times/year, 12V may end up being the lowest cost/year choice. If in a pinch not worrying about discharging the batteries down to 20-30% SOC is important, then GC win hands down. The trojan GC have a higher cycle life at 30% SOC than the trojan true 12V deep discharge do at 50% SOC.

But in either choice the key to longevity is getting a quality battery and properly recharging them as soon as you return from a trip. And unfortunetly, the common WFCO charger in many trailers will seldom do anything near a proper recharge since they seldom go above 13.6V. And you need to get into the 14.5+ V range to properly recharge a flooded cell battery. So you need an iota or Progressive dynamics charger or better yet, the B&D Vector portable charger to get them recharged.

My WFCO 55a will charge @ 14.4 when checked @ the batt with voltmeter. I dry camp exclusively. Been in a camp ground 1 time in 13 yrs and was in a dry site. Last set of 27's lasted 8 yrs. Current toyhauler has 24's and I added a small solar maintainer. No problems staying out 5/6 days with min gen use. Maybe 2 hrs per day total. But we always have sun in Az.

Hi,

Generally speaking, Optima are not as high a capacity in amp-hours "regular" AGM units such as Lifeline.

tplife wrote:
Rock My RV with Bret Michael's crews install these solar/battery setups with multiple 12V group 24 Optima Blue-Tops. As tent campers, we only need one. Here's the view from above, double fused, crimp connectors (no soldering for quick repairs), shrink wrap, and quick-disconnect fittings:




Some useful data for considering costs/Ah:Battery Types

Rock My RV with Bret Michael's crews install these solar/battery setups with multiple 12V group 24 Optima Blue-Tops. As tent campers, we only need one. Here's the view from above, double fused, crimp connectors (no soldering for quick repairs), shrink wrap, and quick-disconnect fittings:




Some useful data for considering costs/Ah:Battery Types

I am running 3 12v agm's, There was room in the battery tray for 3, I could have gotten 2 6's, and left open space - but for the volume 3 12's have 50% more capacity. I have a 3kw inverter/charger so the extra amp output helps - the 5C charging rate (1000 amps combined) give the 150 amp charger a workout. FWIW I can 50-90 in about an hour on the generator. When I get solar, the last 10% will be done without shore power.

I'd go with the GC IF your typical current draw is reasonably low like 25A or less. This sounds like your case.

If you typically are going to run an inverter with a heavy load (>75A), then the 12V may work better.

GC have an advantage of having very high cycle life even down to 30% SOC or more, (hundreds of cycles) taking abuse as long as they are kept watered and properly charged etc. However, every battery design has tradeoffs, and with GC it high load current. They have fewer but thicker plates so they have higher internal resistance which compromises high current use.

Since you can repeatedly draw GC down to 20-30% SOC and still get hundreds of useable cycles, the GC wins in the "useable" AH category compared to a 12V. For example a 12V combo of 250AH has realistically 125 Useable AH at 50% DOD, the max recomended for most 12V batteries. By comparison, a 250AH bank of T-125's will give you 250*.7= 175 "useable" AH, That "extra" 50AH could give you an extra day or two of camping.

My last set of Trojan GC were quite often discharged to about 30%SOC, probably about 20 times/year and 50% another 30 times year. After 8 years they went to in-laws and are still running strong for him, better than his bank of 3 year old 12V by far. SG after 8 years is still 1.275 on each cell.

Another thing is how often will you boondock?? If it's only a few times/year, 12V may end up being the lowest cost/year choice. If in a pinch not worrying about discharging the batteries down to 20-30% SOC is important, then GC win hands down. The trojan GC have a higher cycle life at 30% SOC than the trojan true 12V deep discharge do at 50% SOC.

But in either choice the key to longevity is getting a quality battery and properly recharging them as soon as you return from a trip. And unfortunetly, the common WFCO charger in many trailers will seldom do anything near a proper recharge since they seldom go above 13.6V. And you need to get into the 14.5+ V range to properly recharge a flooded cell battery. So you need an iota or Progressive dynamics charger or better yet, the B&D Vector portable charger to get them recharged.

10 years from now, the group 24 85 amp hour batteries will have been recycled perhaps twice, while the golf cart battery will still be about 200 amp hours. My original Trojan T-105's lasted 13 years and where still somewhat strong, but my replacement, I did not keep them full of water all the time, and they only lasted 6.5 years.

For solar check out this place. SunElec.com

I bought a controller from this place. Did a search for 10 amp PWM solar controller, found one for $13. AliExpress.com

I also bought 24 LED 5050 panels from the same place.

For heating, I use a Olympic Catalytic safety heater that has a leg kit, dust cover, and quick connect fitting for the gas line that I mounted under the oven.


Fred.

pianotuna wrote:
Hi,

The answer partly depends on the intended use. If you wish to use a large inverter (1500 watts and up) the 12 volt solution, wired in a balanced manner may outperform twin six volt jars.

The 12 volts MUST be wired in a balanced manner for them to work in an optimal manner.

Here is a simple flow chart.

Budget-->Energy Audit-->Battery bank size-->number of watts-->PWM or MPPT.

Here is a link to the rather special spreadsheet that N8GS has created to help size solar battery charging systems!
Solar Spread Sheet N8GS

I do recommend between 60 and 150 watts of panels per 100 amp-hours of storage.

Here are two sites worth reading:

http://rvroadtrip.us/library/12v_system.php

http://rvroadtrip.us/library/solar_install.php

Well I was close Don! I shouldn't post late at night! :S