Two 12v in parallel or two 6v in series...

[oldsgg]

This is a 3-part question I hope someone has experience with....

[note: I'm speaking in a language (battery speak) I know VERY little about]

We are about to own a 2015 Bigfoot 25B25FB travel trailer. It has installed two 12v deep cycle batteries wired in parallel, each produce 100 a/h. They still hold a good charge.

We are considering upgrading to two 6v deep cycle AGM batteries wired in series. They are rated at 220 a/h.

The trailer is pre-wired for solar so we are also considering adding either a 120w or 160w portable Zamp solar panel.

Questions:
1. Does it make sense to upgrade now to two 6v deep cycle AGM series batteries when the two 12v deep cycle parallel batteries still hold a good charge?

2. Would a conventional charger installed in the Bigfoot be compatible with two 6v deep cycle AGM batteries wired in series?

3. Would either a 120w or 160w portable Zamp solar panel be compatible (and efficient) with either choice of battery setup---two 12v deep cycle in parallel and two 6v deep cycle AGM in series?

Thanks for your help.
Gary

[Wayne Collins]

Two batteries in series effectivly doubles the voltage: 2 x 6 = 12
Others can check me on this:
Two batteries in parallel increases the available amperage. As long as the load you put on them is the same, they should go twice as song as one battery.

Amperage is like flow or volume in a water line.
Voltage is like the pressure that pushes the water through the line.
Volts x Amps = Watts, the measure of "power"

High amps in a wire creates heat. That's why we use LED lamps, to keep the amps low,

[panhead_mike]

Questions:
1. Does it make sense to upgrade now to two 6v deep cycle AGM series batteries when the two 12v deep cycle parallel batteries still hold a good charge?

2. Would a conventional charger installed in the Bigfoot be compatible with two 6v deep cycle AGM batteries wired in series?

3. Would either a 120w or 160w portable Zamp solar panel be compatible (and efficient) with either choice of battery setup---two 12v deep cycle in parallel and two 6v deep cycle AGM in series?


My quick answer is No, yes, and yes...lol

I'd like to see you wire 2 6's and stay away from the 12 volt batteries. Your power is based on the weaker of the two when wired in parallel.

You may have your own reasons for the AGM batteries but I prefer the Trojan deep cycle..the biggest you can afford... identical and wired in series.

I'm not familiar with the Zamp system, but I would guess it would be fine with 2 6's in series.

I suspect others will add to this........

Mike in NS

[Carl V]

Two 6V in series and two 12V in parallel should both give you 12V and approximately the same amp capacity, if the batteries are of similar size.

The advantage with the 6V is since there is only 3 cells on the each battery (vs 6 in a 12V), the lead plates are bigger and thicker, this makes them more resistant to deep discharges and more durable.

I would not replace the two 12V if they are still good. In a few years, when you'll have to replace them, you could then consider dual 6Vs. And they don't have to be AGMs. You need AGMs if you install them inside the trailer (as they don't produce explosive hydrogen - or very little of it), or if you need to mount them sideways (or even upside down) for some reason. Otherwise, regular lead-acid batts will do a very good job.

No personal experience with a solar charger and dual 6Vs, but I don't see why it wouldn't work. Note that AGMs usually need a slightly different charge voltage than standard lead-acid, and some charger have a specific charge mode for AGM, so one more reason to pass on the AGM unless you really need them.

[BradBev]

Agree with most of above. Your two 12 volt in parallel are providing 200 a/h. I'd retain until the need to be replaced.
I use to have the same trailer and loved it. Tried to buy it back recently and the owner told me to get lost.
I'm not a big fan of agm's outside. I just ordered a new trailer and opted for the standard wet cell rather than the agm option that cost over twice as much. Save the agms for difficult venting situations.

[C&G in FL]

I agree on question 1. Keep and replace when they die, and go to dual 6s due to the thicker plates. Remember, in Donna D's words, a trailer is a rolling earthquake.

On question 2, very few of the converters installed in travel trailers put out the charging voltages specified by the manufacturers nor can they provide the voltage specified for equalization. But they will charge either flooded or AGM batteries adequately. That is where changing the curves on your solar controller omes into play. And I disagree with the general consensus on AGM batteries. They recharge faster and can be discharged deeper than flooded lead acid batteries, and they never have to be topped off with distilled water. I switched to AGM and will not go back to flooded.

As to question 3, yes. Two 12s in parallel equals two 6s wired in series. In either case, a "two part" higher capacity 12 v battery. Either will be fine with whatever brand of solar controller you choose.

[Civilguy]

Oh no, you are getting terrible advice.

You should send the existing batteries to me postpaid and then get whatever you want to replace them!

Actually, what I wanted to say was how much I like the bicycle built for two in your signature!

[John in Santa Cruz]

the advantage of serial over parallel is, when parallel batteries start to age, they inevitably do it unequally, and the stronger battery will discharge into the weaker one. series batteries, all the current has to go through all the cells, so this can't happen.

that said, if it ain't broke, don't fix it til it IS broke what the other guys said, don't replace what you got until you need to.

[rick in arvada]

I agree, use your current batteries until they need replacing, then go with twin golf cart batteries (flooded). That will give you approximately 220 Amp Hours, and accordingly, the optimum solar panel configuration would be in the 220+ watt range. So, the 160 watt panel will be a very good start. It will work great on "good sun" days and need help on overcast days. The Zamp ZS-30A charge controller will work perfectly with the golf cart batteries if set on the calcium flooded setting. In the mean-time, the ZS-30A will work fine with your current batteries.
Rick

[Johnny M]

With the 2 12v batteries in parallel you are doubling the amp hours of each battery but keeping the voltage the same. With the 2 6v batteries its just the opposite, you are doubling the voltage but the amp hours stays the same...In other words you have about the same amp hours with the 2 12v batteries producing a total of about 200 a/h as if you bought 2 Trojan 6v 200 a/h batteries and wired them in a series. So from that viewpoint I would use the 12v batteries you have as long as possible to get your monies worth out of them and then switch to the 2 6v. The advantage with the 6 volts is like mentioned above they each have 3 large cells and are able to handle deeper discharges better than the 12v ones. But you should try to never let either setup deplete below 50% capacity to maximize the life of the batteries. Hope this helps you better understand the difference.

[Joe Romas]

Originally Posted by John in Santa Cruz

the advantage of serial over parallel is, when parallel batteries start to age, they inevitably do it unequally, and the stronger battery will discharge into the weaker one. series batteries, all the current has to go through all the cells, so this can't happen.

that said, if it ain't broke, don't fix it til it IS broke what the other guys said, don't replace what you got until you need to.

X2
I was hoping someone would mention what happens to batteries in parallel.

Joe