Two 6-volt vs. one 12-volt battery

[Ed-Sommers]

[QUOTE=scgator;698849]Combining batteries in series provides you with the combined amperage of both, versus amperage of a single battery;


NO! - Series adds voltage, not amperage. Parallel wiring combines amperage.

Ed

[RJay]

I would recommend 2 6 volt deep cycle batteries. Six volt batteries have thicker plates and if not discharged more than 50% you can expect to get about 550 charge cycles, which is typically more than a 12 volt battery. By the largest size batteries that will fit in your battery compartment. As a general rule the battery charger capacity should be about 10% of the 20 amp hour rating of the battery so if you do go bigger check you charger output. You get what you pay for so buy from a reputable dealer. Some companies that sell to discount stores skimp on plate thickness so look at the weights of the batteries and compare.

I almost forgot. After the new batteries are charged be sure to equalize them, then take specific gravity tests and record the readings. These will serve as a reference and a base point for future readings to determine battery condition.

[TQ60]

I touched a nerve with some...that was not the intent.

The intent of my post was to drive folks to do their homework before spending their money.

My reference to Walmart was to point out that because it is Walmart does not mean it is the best buy.

Sure a 27 group battery that they sell a lot of will most likely be fresh and well priced, but in my case, the 8D batteries on the shelf were dated 1 year old, and the warranty based on the manufacturer stamp was only 1 year or so.

A local battery supply had a battery manufactured by the same manufacturer with a higher capacity that was fresh, date code on the battery was the month we purchased them, and each one was $15.00 less, so we got batter product that was fresh and saved $45.00.

Regarding all of the other arguments aboult plate thickness, deep cycle and hour rating, these are all valid considerations that must be included in the design of any battery plant, it also must be considered that not every battery plant has the same requirements so each are different.

If one is building a telcom battery plant (my other job) the batteries used are designed for an installed life of 10 to 20 years, the power supply (rectifiers) are designed to both properly supply the energy required for the equipment supported as well as float charging the batteries in such a manner to insure they last as designed.

Golf carts have requirements that are different than starting truck motors, the batteries are designed to meet this need.

They need to supply varying currents for a day's worth of golf, and the currents may not be excessive for anything more than short periods of time, similar to the average MH user.

Depending on the need of the battery the type of battery will be different, just do your homework to insure you design your battery plant to meet your needs.

[BryanL]

wow. what a mess. so much misinformation.

The size of the plates in a battery depends upon the case in which you put them, not on the voltage. Thickness of plates in modern batteries as available for RV's only vary over a small range and is not an issue of any significance.

If you are looking for weight savings, you are looking for a smaller battery. Again, voltage is not at issue.

One should be careful not to confuse entities like power (watts), energy (watt hours), and current (amps). In series configurations, current is shared between all devices and voltage adds. In parallel, voltage is shared and current adds. There are very few circumstances where this makes much of a difference in RV applications. It is related to why the diesel engines often use parallel batteries and why you might want to use a parallel situation if you have a high power inverter and it is a factor in the wire sizes you use inside the bank, but these considerations are usually overwhelmed by other factors.

Again, look at the 'hard data' - the specifications for a manufacturer's battery line will demonstrate the trade-offs between cost, capacity, and life and just how much they can be pushed in each direction and how little of an impact battery voltage makes on things as asserted in some of the myth pounding going on in this thread.

[scgator]

[QUOTE=Ed-Sommers;698871]

Originally Posted by scgator

Combining batteries in series provides you with the combined amperage of both, versus amperage of a single battery;


NO! - Series adds voltage, not amperage. Parallel wiring combines amperage.

Ed

My apologies for the typo; you are correct it is parallel and not series if you are trying to gain more amperage AND still maintain 6 volts. But if you want 12 volts AND wire them in series, you will still end up with more ampere hours; and that is in practical application. You will not increase total amperage, but you will increase the length of time it is available

Second thought: being a little more diplomatic would have been nicer than "NO".
fa47e2db-796e-4d17-9672-8a2e620a563a
1.03.01

[SL1966]

Wait, I didn't know that Trojan made more than just prophylactics. I'm kidding.

I was not aware that wiring in series would only increase voltage and not also amperage. Good to find this out now before I installed everything. Thanks!

[wa8yxm]

Originally Posted by TQ60

I touched a nerve with some...
Sure a 27 group battery that they sell a lot of will most likely be fresh and well priced, but in my case, the 8D batteries on the shelf were dated 1 year old, and the warranty based on the manufacturer stamp was only 1 year or so.

It gets worse TQ, it gets worse.

In another thread, I don't know if here or on rv.net.. It was mentioned that Wall-Mart no longer honors any battery warranty... You have to go the the manufacturer.

At least, that is, till some smart consumer who knows the consumer protection act in his state, sues the batteries off them.

Cause that "you may have other rights which vary from state to state" ...

Well.. Learn them.

[BryanL]

re: "you will still end up with more ampere hours; and that is in practical application." -- The 'practical application' is watt hours or available energy capacity, not amp-hours or current (a common source of error in comparing battery capacities of differing voltages). Available energy does not depend upon the voltage of the battery bank components but rather on the total weight of batteries you have. Plan on about 10 to 15 usable watt hours per pound of battery in your RV.

As for retail batteries (such as from Walmart) -- no matter where you purchase your batteries you should always check that they are fresh according to manufacture date on the battery, that you know the warranty and how it is expressed and honored, and that the batteries you purchase are in good condition with a proper charge. Don't buy anything blind.

Do be aware (again) that there is a significant amount of disinformation out there and you need to be very careful about individual stories and blanket assertions not supported with appropriate measure or resource.

Cause that "you may have other rights which vary from state to state" ...

Well.. Learn them.

knowledge is the first step towards effective consumerism!

[TQ60]

Regarding battery warranty, ALWAYS check with your point of purchase how the warranty on the prouduct you are purchasing will be processed.

If you are out of state you may be up a creek.

Many require testing with specific equipment, others may require testing of the installation, that is difficult if you are dead on the road and take the dead one in with your toad.

Amp-Hours add when in parallel, WATT-Hours add either way, Watts are AMPS*VOLTS, so adding volts by series connection of batteries makes for (VOLTSx2)*AMPS=WATTSx2, where batteries in parallel = VOLTSx(AMPSx2)=WATTSx2, one must be careful how they do their math.

It is easy to get confused, either convert everything to amps or watts, try to avoid using both.

Some battery manufacturers use both on their rate sheet, this is usually for UPS use, for other use amp-hours and amps load are used.

If an inverter is involved then the overhead of the inverter needs to be included in calculations.

Spreadsheets are great for this as everything can be included, and regardless of the unit of measurement on the device it can be converted to common units and the design created.

It boils down to simple tasks.
Check the original design, many manufacturers make assumptions on what will be in the unit, or in older ones, the needs have changed. Batteries certianly have changed over the years, past devices that were the current product were not as good for the batteries as current devices so the original designs may not be the optimum for todays equipment or your personal configuration.

Consider the needs first, what are the loads. This needs to include all devices and the amount of tiem that you need to operate them.

Also consider combined loads, this will give a better image of what the batery needs to provide in periods of time as well as durations.

Next is duty cycle, what is the time available for restoring the charge to the batteries, if the time is short then a battery system that will withstand a higher rate of charge is needed, this may require a charger with active feedback to insure the rate of charge is within the limits of the batteries. If longer duratio for recharge then the battery type is more open to choices.

Now that the capacity of the battery plant is known as well as the duty cycle the size and type of battery can then be selected.

VRLA batteries are great for domestic loads but they hate being near heat, these are safe to carry on an airplane, so they are safe to install inside the MH, under the bed or other unused space on the floor would allow for these to be installed inside and a few in parallel to increase the capacity, inside also increases their expected life as long as they are treated properly.

2x6 volt in series, 12 volt in parallel, or ???, these are controlled by product availability and limitations of space.

When the final design is completed then one searches out the providor of the product, price matters, but service matters more.

Work with a vendor who will provide a product that will honor their warranty wherever you go, and verify what it takes to file a claim, make sure a claim can be filed with the battery in hand and not in the MH.

This may require taking some measurements while still installed, the dealer can confirm this, take notes and possibly a claim form to check, again, your call when making your selection of product.

If you are working with a battery supplier show them your design calculations as they may be able to assist in selecting the best battery to support your design, this will both improve the performance of the system and make the warranty easier to process as the battery was selected by the dealer.

The short point is simple...
Always do your homework to insure you know what the heck is going on...

[SSteve]

I hope I can revive this thread...

BrianL,

Far and away you impress me as an expert in this area. No kidding!

I have been looking for the last year or so for good information on what would be best to replace my bulging T-105s. It seems I shouldn't have worried so much. The "hair splitting" concerning the virtues of the 6V over the 12V has made me crazy. I love it when opinions and hearsay are banished by knowledge.

In my experience, in the stores, 12V "Deep Cycles" are easier to come by than 6V. With the information you've provided, I'm going to buy 4 12V batteries.

I know I'll have to reconfigure the cabling for 4x12V vs 4x6V. I promise I won't do a "Tim, the Tool Man, Taylor" re-wiring job. Well, I hope I won't.

It happens frequently but is often overlooked. It's good to have the experts here to debunk the myths. One has only to open one's eyes...

Thanks dude!

Steve

[scoutmstr]

try this link

Battery Types: Flooded versus AGM and Gel

I 've used 12v, 6v golf cart but the best I've ever found is Lifeline AGM. Charges like wet battery, never outgasses or corrodes connection and last four days on dry camping without any charging at all.
Not cheap but troublefree and maintenance free.