6 volt batteries in series

[rgreenwell8962]

Ok, I know this is a forum for Maxum boats, and I have had the discussion on here about batteries for our boats, but I am hoping that somebody with some expertise in batteries can help me out here with regards to my motorhome.

This is off topic, so if this needs to be moved or removed, I understand, but I am not having any luck with the motorhome forums I participate in.

My motorhome has six, yes SIX 6 volt Deka Promaster GC25 in series. Every person I talk to in the rv world says this is absurd. Besides the fact that I am pushing over 350 pounds, I am curious if there is a better route to go. Do I really need SIX 6 volt batteries?? I really do not know what specifically I should ask. I am curious how long these batteries will provide power while not using a genset. I am also looking for an alternative to reduce weight without compensating the amount of battery I will have. I have a Xantrax Freedom 458 Invertor rated for 2500 watts if this helps.

I have heard about group 31's. What are these? How would they compare to the 6v Deka's I have.

Thanks for the input on this somewhat off topic question.
Rich

[Jerryh3]

Are you sure they are all in series? I looked at the datasheet for the Xantrax and it seems like it's just a 12V/120V inverter/charger. So, most likely, they are set up in a series/parellel combination. If my math is right, that setup should provide around 1400 minutes of reserve capacity at a 25A discharge. Group 31 is just a physical size. It's one of the bigger "standard" batteries that are sold. I really don't see any way to save weight and still maintain the capacity that you have.

[mmwjr]

I agree with Jerry there are probably set up to deliver 12V so there would be 3 parrallel banks of two 6V series batteries. Group 31 is a large case with more storage. In the end there is no free lunch and to get the same capacity that you have now will occupy the same volume and have the same weight. GasMat battery may help some but much higher $'s

[shrew]

It doesn't matter whether the 'Recreational Vehicle' rolls or floats, the same principle's apply equally to either vehicle. This is a good topic.

[shrew]

Incidentally, the 6V would need to be in Series/Parallel.

6V Series: 2 x 6V(100aH) batteries = 12V Bank (100aH)
6V Parrallel: 2 x 6v(100aH) batteries = 6V bank (200aH)
6V Series/Parallel: 4 x 6V(100aH) Batteries = 12VBank (200aH)

Series/Parallel means you would need a min. of 4 x 6V batteries. In order to properly scale up, you would need to add new 6V batteries in sets of 2 x 6V. Each 2 x 6V set would be wired in Series. Each Series would be wired together in Parallel in order to make a larger 12V bank.

They question is, is what is the cost per Amp Hour (aH)? How much is it going to cost to get how many amp hours?

[rgreenwell8962]

Originally Posted by shrew

6V Series: 2 x 6V(100aH) batteries = 12V Bank (100aH)
6V Parrallel: 2 x 6v(100aH) batteries = 6V bank (200aH)
6V Series/Parallel: 4 x 6V(100aH) Batteries = 12VBank (200aH)

Series/Parallel means you would need a min. of 4 x 6V batteries. In order to properly scale up, you would need to add new 6V batteries in sets of 2 x 6V. Each 2 x 6V set would be wired in Series. Each Series would be wired together in Parallel in order to make a larger 12V bank.

They question is, is what is the cost per Amp Hour (aH)? How much is it going to cost to get how many amp hours?

I currently have 3 sets of 6v batteries in series wired in parallel. The specs on the Deka Promaster GC25 are:
488 Min @25Amps, 132 Min @75Amps, 235Ah @20Amps, 67 Lbs
20AH capacity: 235
5AH capacity: 188

So with three sets of these wired in parallel, what exactly does that mean I am getting for the 350 pounds of batteries I am carrying? What I am getting at is, should I replace these with a different kind of 12v battery setup that will weigh less but give me comparable results? During the winter ski season, I will be utilizing only the battery bank and genset for 2-3 days and nights running the propane heater (with electrically driven fan) interior lights, electric head, water pump, microwave, tv, dvd, stereo....... you know, the usual stuff to make "camping" as glorious and as comfortable as possible.

Again, my main concern here is weight. I do not want to compromise quality and quantity I get from the batteries but weight is a bigger concern in my motorhome than it is is my boat.

Thanks for the input!

Rich

[Jerryh3]

Originally Posted by rgreenwell8962

I currently have 3 sets of 6v batteries in series wired in parallel. The specs on the Deka Promaster GC25 are:
488 Min @25Amps, 132 Min @75Amps, 235Ah @20Amps, 67 Lbs
20AH capacity: 235
5AH capacity: 188

So with three sets of these wired in parallel, what exactly does that mean I am getting for the 350 pounds of batteries I am carrying? What I am getting at is, should I replace these with a different kind of 12v battery setup that will weigh less but give me comparable results? During the winter ski season, I will be utilizing only the battery bank and genset for 2-3 days and nights running the propane heater (with electrically driven fan) interior lights, electric head, water pump, microwave, tv, dvd, stereo....... you know, the usual stuff to make "camping" as glorious and as comfortable as possible.

Again, my main concern here is weight. I do not want to compromise quality and quantity I get from the batteries but weight is a bigger concern in my motorhome than it is is my boat.

Thanks for the input!

Rich

Bottom line: You have a decent capacity/weight setup. I don't see how you could improve on it much. You could unhook one pair of batteries and see if you make it through a typical trip. If so, you could remove one of the pairs to lighten the load.

[rgreenwell8962]

Thanks Jerry. I guess I am just concerned with the weight. One more thing on the to do list.

[pascavone]

6v batteries are common in car prior to 1957, as I have several.

The 6v work fine, and die a slow death as they age. They have less top end cranking capacity, but last six years plus.

12v batteries, at the end of there life just nose dive and are done.

So, for long slow electrical draws, 6v combined like a German U-boat, they are a cheaper option in the long run.

But, as a fellow camper, I don't want any more lead/accide in my living space, so I go with the rechargeable battery packs until that have a build in trickle charger.

[rgreenwell8962]

I have learned that the 6v in series is in fact a better option for off the grid camping and long life of the batteries. I have an enclosed battery tray in the basement of my motorhome so they are not in the living space. My main concern is the weight limit of the battery tray since I have 402 pounds of batteries on it. I need to figure out the weight limit of this tray. The original one that came with it was a slide out rated at 130 or so. I believe it has been replaced with a non slide version, so I have no idea what the spec are.

Good input from all. Thanks!

[CaptJerry]

Originally Posted by rgreenwell8962

I currently have 3 sets of 6v batteries in series wired in parallel. The specs on the Deka Promaster GC25 are:
488 Min @25Amps, 132 Min @75Amps, 235Ah @20Amps, 67 Lbs
20AH capacity: 235
5AH capacity: 188

So with three sets of these wired in parallel, what exactly does that mean I am getting for the 350 pounds of batteries I am carrying? What I am getting at is, should I replace these with a different kind of 12v battery setup that will weigh less but give me comparable results? During the winter ski season, I will be utilizing only the battery bank and genset for 2-3 days and nights running the propane heater (with electrically driven fan) interior lights, electric head, water pump, microwave, tv, dvd, stereo....... you know, the usual stuff to make "camping" as glorious and as comfortable as possible.

Again, my main concern here is weight. I do not want to compromise quality and quantity I get from the batteries but weight is a bigger concern in my motorhome than it is is my boat.

Thanks for the input!

Rich

In the same type of battery (AGM, Wet, etc.) it is all about plate capacity, so two 6V batteries in series will provide the same number of 12V amp hours as two similar size/weight (and type) 12V batteries in parallel. Li is higher energy density than AGM, which in turn is higher than Wet, so if you are trying to save weight, the more exotic batteries might be your choice, but at a premium price.

Also, the other benefit of the 6V series/parallel setup vs all 12V in parallel is that it minimizes the number of parallel connections to the common points (+ and -), which aids in keeping the bank balanced. Eight 6V batteries will have four parallel connections to each bank + and -, while eight 12V batteries will have eight connections to each. The connections should also be "homeruned" instead of daisy chained to minimize preferrential discharging.

[mmwjr]

CaptJerry welcome aboard

Thanks for your input, being that this is a 2 year old thread the OP has probably already made a decision. None the less your input will be helpful to others.

[CaptJerry]

I recognize that, but as a real Capt with a real MSEE, I thought some basic physics might contribute to the discussion for future inquiries.

[mmwjr]

Originally Posted by CaptJerry

I recognize that, but as a real Capt with a real MSEE, I thought some basic physics might contribute to the discussion for future inquiries.

Which is why I said you input will be helpful to others

[CaptJerry]

And yet you were compelled to point it out.

[Kevlar7r]

Ooh!!!! A REAL captain! And yet so humble and professional!