Dual 12v in parallel OR dual 6v in series???

[shay_mcquaid]

Hi.

I'm researching batteries for a new house bank.

Looks like the RV guys have an argument for running 6v's in series for a better price per amp hour.


The dual 6v sounds good.
Is a dual 6v setup suitable for the water?
Would a standard 12v charger work for dual 6v in series?

I tried to search the forum before posting.


Thanks for any input.

-Shay

 

[bruceb58]

Re: Dual 12v in parallel OR dual 6v in series???

If you had to pick two 12V batteries in parallel or two 6V batteries in series, you always want to go the 2 6V in series route. No different charging two 6V in series than a 12 V.

 

[achris]

Re: Dual 12v in parallel OR dual 6v in series???

If you had to pick two 12V batteries in parallel or two 6V batteries in series, you always want to go the 2 6V in series route. No different charging two 6V in series than a 12 V.

I would pick 2 x 12v in parallel.... double the capacity... 2 x 6v in series is the same as one 12v...

 

[q5ka]

Re: Dual 12v in parallel OR dual 6v in series???

The two 6v in series is not the same as one 12v unless you are talking about voltage only. Most tractor trailers (semi) along with some farm equipment uses two (or more) 6v in series instead of one 12v due to the quick discharge ability of the 6v batteries, quick recovery time, and amp hours. Tractor trailers can have as many as eight 6v starting batteries in their truck and the reason for so many is the cranking amps. A farm tractor is the same way.

Now take it to the other side, electric golf carts. Here it is important to have the amp hours. They are often filled with 6v deep cycle instead of 12v deep cycle batteries due to amp hours.

Would two 12v in parallel have more amp hours than two 6v in series? It all depends of the amp hours of each battery. Lets look at interstate batteries as an example since it is used by many. The GC2 U2200 (6v) has 232 amp hours. The Optima SC31DM (12V) has 75 amp hours. That would mean that the two 6v in series would have 314 more amp hours as two 12v in parallel. But look at the warranty and price. The 6v has 6 month warranty. The 12v has 18/36. The 6v cost about $100. The 12v cost about $250. So what do you get, less amp hours for more cost using 12v.
http://www.interstatebatteries.com/cs_eStore/content/product_info/marine_f.asp

Look for yourself at cost and amp hours and shop around. You can get a very good 12v battery from Walmart or such for about the same price or cheaper. You can also get the 12v in higher amp hours. You can also find 6v in lower amp hours or more expensive. It all depends on price/warranty/amp hours.

One big disadvantage of 6v system is if one battery starts going bad, it can often bring the whole system down with it. You will have to load test each battery to find the weak one and replace that one. It is not as dramatic with a 12v parallel system. You still notice the system as a whole show weakness with 12v, just not as dramatic.

If you have the room, I would recommend going with two (or more) 6v instead of two (or more) 12v. That is only if you have the room and can handle the weight. The negatives are easily masked by the advantages.

 

[bruceb58]

Re: Dual 12v in parallel OR dual 6v in series???

I would pick 2 x 12v in parallel.... double the capacity... 2 x 6v in series is the same as one 12v...

If you have 2 12V batteries that are 100 amphours each or 2 6V batteries that are 200 amphours each, the capacity ends up being the same. Remember that for the physical size battery, the 6V will have a higher capacity per cell since you only have 3 cells in the same volume.

 

[bruceb58]

Re: Dual 12v in parallel OR dual 6v in series???

One big disadvantage of 6v system is if one battery starts going bad, it can often bring the whole system down with it. You will have to load test each battery to find the weak one and replace that one. It is not as dramatic with a 12v parallel system. You still notice the system as a whole show weakness with 12v, just not as dramatic.

You have that backwards. With two 6V in series, one cell that starts getting weaker brings down the total voltage but only affects the one battery. With a parallel system, it brings down both batteries to the lower voltage of the two. No matter how good one of the batteries is, it will get pulled down to the lower voltage and over time will not allow it to fully charge so they both will end up going bad. No matter what you have to test both batteries but with the series connection you can test the voltage of each bank to determine which bank has the low cell.

 

[q5ka]

Re: Dual 12v in parallel OR dual 6v in series???

You have that backwards. With two 6V in series, one cell that starts getting weaker brings down the total voltage but only affects the one battery. With a parallel system, it brings down both batteries to the lower voltage of the two. No matter how good one of the batteries is, it will get pulled down to the lower voltage and over time will not allow it to fully charge so they both will end up going bad. No matter what you have to test both batteries but with the series connection you can test the voltage of each bank to determine which bank has the low cell.

You are correct. That is what my brain was saying but fingers doing their own thing.

 

[shay_mcquaid]

Re: Dual 12v in parallel OR dual 6v in series???

Thanks all for your time.



Okay. Ive decided to go with dual 6v's.

Heres why:

My 6v Choice

• NAPA 8146 6v
• 242Ah
• $111.00 x2

OR


My 12v Choice

• Walmart Maxx Series 29 (biggest one)
• 125 Ah
• $87.00 x2 (I think)

And note...The NAPA battery is AGM!!!



The Dual 6v's seems to be a better set up to me considering the AGM construction and the reported capacity and durability of the golf cart type battries.

yes? no?


thanks again


-Shay

 

[fishrdan]

Re: Dual 12v in parallel OR dual 6v in series???

Thanks all for your time.



Okay. Ive decided to go with dual 6v's.

Heres why:

My 6v Choice

• NAPA 8146 6v
• 242Ah
• $111.00 x2

OR


My 12v Choice

• Walmart Maxx Series 29 (biggest one)
• 125 Ah X2 = 250AH
• $87.00 x2 (I think)

And note...The NAPA battery is AGM!!!

If you are considering sheer battery capacity the dual 12V batteries have the 6V's beat, barely. The 12V's are cheaper too. The 6V's being AGM is a huge bonus though and I would pay $110 for an AGM over $87 for a flooded battery. Be aware, WalMart no longer has a warranty on their deep cycle marine batteries, so the NAPA's are looking even better.

Things to consider; if one of the 6V's dies that bank is dead, if one of the 12V's dies just take the bad battery out temporarily and you will still have power. If one of the 12V's goes bad it can make the other 12V go bad by draining it, or if one of them is marginal it will bring the good battery down. How easy is it going to be to find a 6V battery in a pinch, if you need one ASAP to get on the water. If your start battery goes dead how easy will it be to use the other batteries, do you have a battery switch, will you need to swap a batteries.

I went with 12V batteries as they are easy to find and swap around if needed. If I was in your position and the 6V AGM's were that cheap,,, I think I would be going with the 6V's. The dependability of the AGM's should out weight the problem of one 6V going dead.

BTW, the G29 batteries are about $75, I just bought one from Sams and it was around $83 total.

 

[JustJason]

Re: Dual 12v in parallel OR dual 6v in series???

Uhmm.. fisherdan... you didn't multiply the 6V batterys amps times 2 as you did with the 12v batts.

I wrote this in another battery thread. But when doing your battery shopping, if you buy a cheap battery you can usually get by with a cheap charger (like sears/craftsman) If you go with pricier, Gel, or AGM batteries, you need a better charger. If your going by price, you need to factor in the cost of a quality charger into the overall picture.

 

[fishrdan]

Re: Dual 12v in parallel OR dual 6v in series???

Uhmm.. fisherdan... you didn't multiply the 6V batterys amps times 2 as you did with the 12v batts.

Well, no,,, the voltage is multiplied. 2 x 6V = 12V

 

[JustJason]

Re: Dual 12v in parallel OR dual 6v in series???

Okay. Ive decided to go with dual 6v's.

Heres why:

My 6v Choice
NAPA 8146 6v
242Ah each... or X2 = 484 amp hours <-------
$111.00 x2
OR


My 12v Choice
Walmart Maxx Series 29 (biggest one)
125 Ah X2 = 250AH
$87.00 x2 (I think)

And note...The NAPA battery is AGM!!!

I said amps.... not volts buddy

 

[achris]

Re: Dual 12v in parallel OR dual 6v in series???

Uhmm.. fisherdan... you didn't multiply the 6V batterys amps times 2 as you did with the 12v batts.....

That's because he's only using 2 6v batteries in series. Doubles the voltage, but doesn't increase the capacity.... To double the capacity and have 12 volts he'd need 4 x 6v batteries.

Chris......

 

[JustJason]

Re: Dual 12v in parallel OR dual 6v in series???

Just a bit confused Chris.
Your saying if you have 2 6V batts, which are 242 amp hours each, and wire them in series that you would not essentially have 1 12V battery with a total amp hour capacity of 484ah? I thought you added the ah of each battery to get a total when wired in series.

 

[achris]

Re: Dual 12v in parallel OR dual 6v in series???

Just a bit confused Chris.
Your saying if you have 2 6V batts, which are 242 amp hours each, and wire them in series that you would not essentially have 1 12V battery with a total amp hour capacity of 484ah? I thought you added the ah of each battery to get a total when wired in series.

If you series two 6V, 242 AHr batteries, you'll have a 12V, 242AHr battery. If you want double the capacity, you need to parallel them, but then you would only have 6V. If you want double the capacity and double the voltage, you would need 4 of the 6V batteries.

Chris.........