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Old 12-13-2017, 09:33 PM   #41
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This subject is also about space, that is getting the biggest amount of total power possible.

Not knowing every RV model, but guessing now they provide a larger space than a standard 12 v car battery. I have what looks like space for 2 regular sized car batteries but installed are 2 6v batteries.

As stated before do not parallel batteries, it is not safe to do that without isolators.

So work from your dimensions and find the biggest batteries that will fit. There are differences in amount of power for the same size. Basically the more they cost the higher power (more lead plate).

Math is math - Total voltage (adding batteries together) times the amp hours of (one battery) when in series gives you the watts (work).

Now another piece of battery 101
Batteries will deliver more total power when discharged slowly. The difference is big.
Also never use a battery below 75% as now you start to cause life limiting damage. Some 12 volt equipment will not operate at low voltages.
Last never leave a battery mostly discharged, charge it right away.

So for you inverter people to do it right you need LOTS of power to avoid deep discharging the battery at a rapid rate.

My suggestion is to have a 24v inverter with charger and 4 - 6v batteries just to operate the inverter.
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Old 12-13-2017, 09:37 PM   #42
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We ended up changing out our original 2. 12 volt, with in the first week we picked it up, CW failed to maintain them while it was on there lot. We opted for 2. 12 volt flooded golf cart deep cycle, they just fit in under the step on the 35sk. This spring will be installing a tray in the compartment next to the inverter compartment, for ease of maintaining. They do the job running the residential fridge over night plus.
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Old 12-14-2017, 12:05 AM   #43
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Originally Posted by groundpounder View Post
... That is paralleling batteries is never recommended. Batteries are never the same and do not age the same. The charging characteristics are mismatched, overcharging or undercharging becomes a problem. Overcharging can boil out the electrolyte, cause the battery to get hot and explode.
...
Quote:
Originally Posted by groundpounder View Post
...
As stated before do not parallel batteries, it is not safe to do that without isolators.
...
I'm sorry - but there is nothing wrong with running batteries in parallel... Many of our rigs are supplied that way - and it works fine when the batteries are cared for.
It is recommended to parallel identical (in age/specs) batteries for best life - but there is nothing 'dangerous' about a mismatch... It can hurt the life of the pair if one degrades - but that is about it...

Even mismatched in capacity batteries CAN be charged in parallel... I wouldn't view it as a best practice - but it can be done. Each battery will absorb what it needs.

Can 2 six volts in series outperform 2 12v in parallel? Sure - given the right batteries - but that isn't always the practical answer... Space and money and usage requirements can dictate what needs to be used...

Quote:
Originally Posted by groundpounder View Post
...
My suggestion is to have a 24v inverter with charger and 4 - 6v batteries just to operate the inverter.
Not a bad suggestion as the higher voltage would cut the amps required from the battery source in half... but likely not practical in many cases to carry 4 additional batteries just for the inverter.
Now I know Chance would like to see a 24V RV...
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Old 12-14-2017, 12:23 AM   #44
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Originally Posted by groundpounder View Post
This subject is also about space, that is getting the biggest amount of total power possible.

Not knowing every RV model, but guessing now they provide a larger space than a standard 12 v car battery. I have what looks like space for 2 regular sized car batteries but installed are 2 6v batteries.

As stated before do not parallel batteries, it is not safe to do that without isolators.

So work from your dimensions and find the biggest batteries that will fit. There are differences in amount of power for the same size. Basically the more they cost the higher power (more lead plate).

Math is math - Total voltage (adding batteries together) times the amp hours of (one battery) when in series gives you the watts (work).

Now another piece of battery 101
Batteries will deliver more total power when discharged slowly. The difference is big.
Also never use a battery below 75% as now you start to cause life limiting damage. Some 12 volt equipment will not operate at low voltages.
Last never leave a battery mostly discharged, charge it right away.

So for you inverter people to do it right you need LOTS of power to avoid deep discharging the battery at a rapid rate.

My suggestion is to have a 24v inverter with charger and 4 - 6v batteries just to operate the inverter.
Quote:
Originally Posted by gmc View Post
I'm sorry - but there is nothing wrong with running batteries in parallel... Many of our rigs are supplied that way - and it works fine when the batteries are cared for.
It is recommended to parallel identical (in age/specs) batteries for best life - but there is nothing 'dangerous' about a mismatch... It can hurt the life of the pair if one degrades - but that is about it...

Even mismatched in capacity batteries CAN be charged in parallel... I wouldn't view it as a best practice - but it can be done. Each battery will absorb what it needs.

Can 2 six volts in series outperform 2 12v in parallel? Sure - given the right batteries - but that isn't always the practical answer... Space and money and usage requirements can dictate what needs to be used...



Not a bad suggestion as the higher voltage would cut the amps required from the battery source in half... but likely not practical in many cases to carry 4 additional batteries just for the inverter.
Now I know Chance would like to see a 24V RV...
Groundpounder: Every place you said "Power" you should have said "Energy". If you're gonna lecture "Battery 101" you need to get yor terms right.

And as GMC said there is no danger to connecting batteries in parallel. How many 100s of thousands of motorhomes have 2 batteries in parallel without an isolator? How many battery powered toys have batteries in parallel? Danger is not a concern for parallel batteries.
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Old 12-14-2017, 04:59 AM   #45
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I disagree, just because some coaches are built with parallel batteries it is still bad practice (done for a price point). Yes it can be done, yes match new battery with new battery.

There are three parts to this, drawing power, charging and idle state. I have no issue while drawing power, the batteries can be mismatched and still operate safely as the power will be divided according to available charge.

The problem occurs during charging, yes each battery will absorb its own charge according to internal resistance of the chemical state of the cells. At some point the battery will reach its charged state partially reflected by the voltage. The other battery may not be at the same state. This sets the stage for either a overcharged or undercharged battery. An overcharged battery can be damaged and can get hot and cause it to lose water more so than the other battery. An undercharged battery is wasted.

At idle the batteries charge and discharge each other looking for middle ground, still you have a loss efficiency.

BTW the word "power" is usually referred in electrical circuits, "energy" covers everything. I could have used watts or work to be more specific.

Even batteries in series are not perfect because any cell can be different.

But when given a choice go with batteries in series is safer more efficient and may last longer.
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Old 12-14-2017, 07:44 AM   #46
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Interesting comments with most bearing merit.
Sometimes design engineers use an algorithm dependent on some factor(s). Cost, redundancy, frequency of cycle, lowering transmission losses with increased potential.
Perhaps the general availability of GC batteries can keep cost down.
A parallel configuration allows one to use one battery in an array to be used in limp mode should another battery (cell) fail. Series, not so much.
Ever been in a POTS Plain old telephone system exchange? Large rooms of commercial heavy wet cell batteries wired in parallel doing little or nothing just in case they might be required to provide 48V for phone service in an outage. May only happen once or twice in their entire lifetime.
GC golf cart batteries wired in series, cause they are relied upon to be taken to a low state of charge, generally daily. Frequent cycling.
High end coach or tactical equipment might have parallel cells wired with ability to be hot swapped, or have redundancy at a higher cost.
Some maintenance free, spill proof, you bet. AGM, LiFePO4 (Lithium) ...$$$ Check out aircraft arrays.
Higher voltages can allow lighter gauge wiring and switch / fuse gear. Perhaps less line loss.
Ultimately many arrays are a combination of multiple configurations.
I'm waiting to be able to afford a LiFePO4 array, half the weight twice the wattage. Sigh!
Be well.
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Old 12-14-2017, 01:15 PM   #47
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Originally Posted by groundpounder View Post
I disagree, just because some coaches are built with parallel batteries it is still bad practice (done for a price point). Yes it can be done, yes match new battery with new battery.

There are three parts to this, drawing power, charging and idle state. I have no issue while drawing power, the batteries can be mismatched and still operate safely as the power will be divided according to available charge.

The problem occurs during charging, yes each battery will absorb its own charge according to internal resistance of the chemical state of the cells. At some point the battery will reach its charged state partially reflected by the voltage. The other battery may not be at the same state. This sets the stage for either a overcharged or undercharged battery. An overcharged battery can be damaged and can get hot and cause it to lose water more so than the other battery. An undercharged battery is wasted.

At idle the batteries charge and discharge each other looking for middle ground, still you have a loss efficiency.

BTW the word "power" is usually referred in electrical circuits, "energy" covers everything. I could have used watts or work to be more specific.

Even batteries in series are not perfect because any cell can be different.

But when given a choice go with batteries in series is safer more efficient and may last longer.
Watt is power, work is energy. You store energy in a battery. You can't store power. Both terms are used in electrical circuits as well as any system doing work.

And you didn't disagree as much as change your original statement: "bad practice" is not the same as "dangerous".

Could the bad practice lead to one of the parallel batteries being overcharged? Sure, if the batteries were grossly mismatched. But you can do the same thing with batteries in series as well since all the batteries are experiencing the exact same charging current regardless of it's own voltage. So the good batteries can all be overcharged because a bad battery will not come up to voltage. In submarines where they use 128 lead acid cells in series they monitor each cell for voltage and specific gravity for this very reason. If a cell is not up to snuff it is jumpered around so it doesn't affect the rest of the cells. And in case you're wondering, each cell is bigger than a person, so each cell stores a lot of energy.

At least in parallel the charged battery with the highest voltage resists the flow of charging current so it is more difficult to overcharge it.
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Old 12-14-2017, 02:35 PM   #48
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.....cut....

Not a bad suggestion as the higher voltage would cut the amps required from the battery source in half... but likely not practical in many cases to carry 4 additional batteries just for the inverter.
Now I know Chance would like to see a 24V RV...

GMC, not at all. The right answer is 48 Volts.


Seriously though, as RVs become more dependent on electrical power, it will make sense to have a dedicated higher-voltage battery bank to power larger loads (most things from inverter) like refrigerator, air conditioners, microwave, coffee maker, hair dryers, etc. In the interim since some loads will still require 12-Volts, it will be necessary to have at least one small battery to power lights, water pump, 12-Volt control circuits, etc. In time once 48-Volt is adopted in large volume, manufacturers will start making water pumps and the like to run directly off 48-Volts.

This same problem is happening in the Auto industry, where 48-Volt is starting to be integrated to power large loads, but the old 12-Volt is still kept to power radios, instruments, etc.

For RVs switching to 48-Volts will also help lower current from solar panels, and reduce current through chargers and inverters.

Volta went to 48-Volt stand-alone system, but Xantrex appears to have stayed with 12-Volts (smaller system), even though I don't see how they can power 3,000-watt inverters with 6,000-watt surge (required to start air conditioners). That's so much current at 12 Volts, but I guess Xantrex may not have 48-Volt inverters (at least not listed in Xantrex site) so they may have not had a choice anyway.
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Old 12-14-2017, 03:01 PM   #49
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Originally Posted by mtntrek View Post

....cut...

Ever been in a POTS Plain old telephone system exchange? Large rooms of commercial heavy wet cell batteries wired in parallel doing little or nothing just in case they might be required to provide 48V for phone service in an outage. May only happen once or twice in their entire lifetime.
.....cut....
There was an interesting article discussing large 48-Volt battery banks assembled from 24 X 2-Volt cells which started out with an extra cell (25 total), making it literally a 50-Volt system. The idea is that if one cell fails, you remove it and keep going. Furthermore, if another cell fails, the system can still operate at 23 X 2-Volts, or 46 Volts. This was for solar homes and or buildings, but sounds similar to submarine procedure mentioned above.

The premise was that 48-Volt inverters can function adequately within the higher and lower ranges, so the only requirement from the owner/operator is to reset charging voltages to adjust for 50, 48, or 46 nominal Volts.

This idea wouldn't be practical for most RVs because that many 2-Volt flooded or AGM cells would be too large/heavy; but it does get around rare problem of individual cell failures.

The funny thing is that lithium batteries often connect tiny cells in series to make higher voltages, and then in parallel to increase capacity. It's the same principle but they can get away with it because lithium cells can be so small while remaining practical.
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