Batteries Short...New Converter

[robandzoe]

I have to replace the two dead shorted batteries that are two years old from Sam's Club to put into my 34' Limited TT, 1985 model. My converter went bad and I hd a new one put in. Just wondering about the new batteries, and looking for advice on what should I buy, and from where, for the best deal? I need these for the upcoming Cherry Blossum Rally next month.
Thanks,
Rob

[markdoane]

What brand converter?

[Steve Heywood]

Originally Posted by robandzoe

I have to replace the two dead shorted batteries that are two years old from Sam's Club to put into my 34' Limited TT, 1985 model. My converter went bad and I hd a new one put in. Just wondering about the new batteries, and looking for advice on what should I buy, and from where, for the best deal? I need these for the upcoming Cherry Blossum Rally next month.
Thanks,
Rob

Since you're replacing both batteries at once consider going to two 6 volts "golf cart" batteries.

[TomW]

Originally Posted by Steve Heywood

Since you're replacing both batteries at once consider going to two 6 volts "golf cart" batteries.

I believe that would be four 6 volt batteries to better his present capability.

Tom

[Steve Heywood]

Originally Posted by TomW

I believe that would be four 6 volt batteries to better his present capability.

Tom

It takes two 6 volt batteries to equal the voltage of one 12 volt, but two 6 volt batteries will almost always have more reserve capacity than two 12 volts batteries.

[TomW]

Originally Posted by Steve Heywood

...but two 6 volt batteries will almost always have more reserve capacity than two 12 volts batteries.

I find that believable even though that was obviously not my first thought.

Believable is the key word; Hopefully others will chime in.

Tom

[john hd]

rob

go with marine starting batteries of the 650 cca range.

they will give you the best bang fer your buck.

john

[markdoane]

Unless we know what type of converter/charger you have, it's difficult to make a recommendation. If you have a three stage charger, it may be worth investing in good quality AGM batteries.

If not, then just get cheap wet cells (6V or 12V) because you'r just going to boil them out and need new ones in a couple of years anyway.

It would also help if we knew more about your type of camping. If you dry camp and don't have hookups or a generator, the type batteries you want will be different than if you always have electrical hookups.

[robandzoe]

I had a 7400 Series Parallax Converter / Battery Charger in. Which one in the 7400 series, I have to find out exactly. Don Mar here in SC put it in.

Rob

[robandzoe]

We usually are at a campground with hook ups or I have my generator. Hope this helps.

Rob

[Steve Heywood]

One thing I didn't consider was battery location. As long as the batteries are located next to each other it's very simple to replace two 12-volt batteries with two 6-volt batteries. However, if you have an Excella/Classic with the two seperate batteries compartments it would be difficult (at best) to use two 6-volt batteries.

If someone know a simple way (to use two 6-volt batteries in an Excella/Classic) I'd sure like to hear about it!

Thanks,

[Inland RV Center, In]

Generally speaking, replacing 12 volt batteries with two 6 volt batteries, is not recommended.

To use 2-6 volt batteries, they must be wired in series. Should one of them fail, or become weak, you will have no power.

In the case of 2-12 volt batteries wired in parallel, should one fail, simply disconnect it and your still in business.

Additionally, battery capacity is measured in watts. Therefore, of a given physical size, a 6 volt battery does not offer any more wattage, than a 12 volt battery.

Basic ohms law applies. Batteries in series, increases the voltage, not the current available. Batteries in parallel, keep the same voltage, but the current available increases.

Therefore the wattage stays the same, between the 6 and 12 volt setups.

Bottom line is there is no advantage to using 2-6 volt batteries in series, in fact you gain a disadvantage, since you have to rewire.

Golf carts are far removed from an RV when batteries are the topic.

Keep in mind what happens to simple Christmas tree lights that are wired in series, as opposed to parallel. In series, when one goes out, the entire string quits. In parallel, when one goes out, the rest of the lights still function.

And finally, again generally speaking, the cost for 2-6 volt batteries is greater then their equal in 12 volts. Simply supply and demand.

The formulas are simple E=IR I= E/R R=E/I

For wattage. W=EI

E=voltage
I=Current
R=Resistance
W=Wattage

As an example, take two 6 volt 200 amp batteries, (1200 watts) and wire them in series. You will have 12 volts at 200 amps, which also equals 2400 watts.

Then take two 12 volt batteries at 100 amps each (122 watts). Wire them in parallel and you then will have 12 volts at 200 amps, or 2400 watts.

The point being, you gain nothing by using 6 volt batteries. Practical experience, bears that out.

Andy

Andy

[markdoane]

Rob,

I am not familiar with the Parallax 7400, but I believe it is a single stage charger/converter. These chargers may overcharge the batteries if left hooked up continuously. That may be what ruined your previous batteries.

I would recommend you buy a pair of cheap deep cycle 12V batteries, based on Steve's observation. I wouldn't use marine starting batteries, or combination starting/deep cycle. Go straight deep cycle. They're inexpensive and you can replace them every year if you need to.

If you want to see a totally overboard analysis of battery selection and life cycle costing, look at this guy's analysis:http://www.vonwentzel.net/Battery/index.html

postscript: if you spend most of your time 'on grid' at a campground, you may not need two batteries. Just try one battery for awhile and see if it works.

[Inland RV Center, In]

Parallax 7400 charger, more specifically, the 7455 model, has been used by Airstream, in production, for several years.

The charger company name has changed, but the charger proper is the same.

If it overcharged, Airstream would have quit using it years ago.

It is a superior charger, therefore Airstream will continue to use it.

Andy

[markdoane]

Originally Posted by Inland RV Center, In

If it overcharged, Airstream would have quit using it years ago.

It is a superior charger, therefore Airstream will continue to use it.

Andy

There is a lot of disagreement about both those statements. Even a cheap Sam's Club charger is smarter than a Parallax.

[greg176]

A good info source for batteries and charging is at http://www.phrannie.org/phredex.html

I have to agree with Don if you are on grid all the time get one cheap 12 volt battery. You will have to replace it every two years as it will sulfide (see Battery poop sheet).

That Parallax charger is junk and is only suited for folks who run cheap batteries.

[robandzoe]

Having taken Electrical Engineering at Annapolis, I have to agree with Andy about the series and parallel thing...basic Ohms law. I'll go with my cheap Deep Cycle Batteries. Thanks everyone.

Rob

[john hd]

the reason i suggested the marine starting batteries, is because they closely match what is under the hood of your truck.

when driving down the road they are charged as a group with your trucks batteries.

john

[robandzoe]

I'm going to go for just some cheap deep cycle RV batteries for now. One thing, why would Airstream use junk, in refering to the Parallax charger....I find that hard to believe that they would use an inferior charger like that.

Rob

[markdoane]

The main reason is that half the people don't care because they run on shore power 95% of the time. The Parallax is a fine converter, it just isn't a very good charger.

The other half (boon-dockers) will throw out whatever is there and replace it with a custom designed system. They don't want to throw out a lot of expensive gear.