6 volt vs 12 volt?

[bill good]

Often the batteries are split into starting type of batts & storage type. It sounds like this is the reason for what you have. Check to see if the two 12v are the starting & the golf batteries are the house batteries.

Regards Bill Gooward

[Whimsical]

Originally Posted by Alan Wheeler

I do however, have one fridge/freezer that consumes a total of 17A @ 12V continuosely.

400 AH/day
Must be as big as your holding tank

Out of curiosity I converted the daily consumption for my land dwelling back to 12V and it is 660 AH per day for the entire house.
Mike

[ssullivan]

Originally Posted by Whimsical

Out of curiosity I converted the daily consumption for my land dwelling back to 12V and it is 660 AH per day for the entire house.
Mike

Wow... if your cacls are correct, you have designed a great house.

[Whimsical]

Last bill just in is 12 Kw per day so if you work on 14V that is 850 Ah so I am up a fair bit this time.
Not really great, a lot of people I know use a lot less power than I do. House is 200 square meters well insulated. 500 liter fridge freezer, 140 ltr freezer, small fridge in shed, big TV that is on probably 8 hours with lots of hifi etc on standby. Computer would be a consumer being on 10 hours. Lights are all fluro but usually only 80 W
I am hoping to keep the energy budget on the boat down to 200 Ah.

Mike

[hellosailor]

Wheels, he posted that he runs his batteries down to 12.5V and then runs the gennie for an hour to get them back up again. Since 12.6V is "all the way up" for most batteries...he may only be cycling them 10%, from 90% to 100%. Not too hard to put a 10% C charge into batteries in one hour, they'll take that. (Most conservative charging regimen I've ever heard of.[g])

[forsailbyowner]

Dropping the bank to 12.5 is definately not 50% charge. I figure the fridge uses about 50 amp hrs and 10 are to the intermittent water pump usage and maybe a little reading lamp after dark. The promariner converter is rated at 60 amps, so with a little diffused light to the solar panel array I should be almost replacing the power used, I realize it takes 10 hrs to get the last saturation charge to get 100% but an hour gets the best usage of the converter at a higher amperage.

[44'cruisingcat]

[quote=Alan Wheeler;103365]
I do however, have one fridge/freezer that consumes a total of 17A @ 12V continuosely. It does not cycle. [quote]

Are you sure? That's massive power use. Esp in NZ, where it's not even really hot. How long can you last off shore power?

[Alan Wheeler]

Yeah it's one of theose stupid three way systems that use a heater element to heat the coolant and cycle it. When I purchased it, I was a bit nieve to fridges and no one told me the issues with these systems. I have certainly not had any issues with heeling like these can be prone to, but I can't use gas when sailing. The flame goes out for no reason. So I run it on AC when underway and Gas when moored/anchored. Gas consumption is 330g/24hrs.
But oops, I am getting of the subject.
No, 12.2V is 50% charge. Once again, just using No's, randomly plucked from the fact that the bank is big, to give the general idea.
Because it now begs to ask, if you are using so little power, why such a big bank of batteries. You would be better dropping the bank size dramaticaly.
50% is not a "criticle" charge point. The 50% mark was determined as the most economical point of running a battery to, based on it's cost, charge cycles and demise once it is in a state of discharge. Above 50 and below 50 are considered to be either side of the balance of cost versus life.
However, having a charge systme that can not fully recharge the banks to max, means that the case of running the bank to only 50% is futile anyway. Not fully charging the bank is the same as running the bank waaay below 50%. So you would be far better decreasing the size of the bank and ensuring the bank is recharged fully. Or you need to dramaticly increase your charger size or charging time.

[Ex-Calif]

Originally Posted by Alan Wheeler

What ever the actual actually is, the main concern I am trying to show is that 24hrs of discharge can not be rectified by one hr of charge, or...400Ahr or even significantly less, can not be replenished in 1 hr.

Agree 100% - Even my example (100amps/day) @ 60 amp alternator can't be done in 1 hour...

[David M]

Originally Posted by hellosailor

"I am saying that TWO 6 volt batteries have more amp hours than one 12 volt marine grade deep cycle battery. "
David, something is lost in translation. Two six volt batteries bolted up make one twelve volt battery. Volts and amps have nothing to do with each other, if you lash up two 100-AH 6V batteries you'll simply get one 100-AH 12V battery.

But if you buy one 12V battery instead of two 6V batteries, you'll have one less set of cables and terminals, and less space and weight wasted by the physical cases. All else being equal, IF you can find the 12V battery in a physical form factor that fits the boat (and you can lift) it should be cheaper and higher capacity than two 6V batteries. If only because it is one product instead of two, and one set of case walls instead of two.

West Marine is convenient but hardly the best place to go for batteries, there are all sorts of physical standards for size and capacity and some manufacturers offer a far larger choice than others. West only carries the most popular conventional sizes.

I understand the math and the equation. Volts times Amps equals Watts (power) for DC. What got lost in the translation is that golf cart batteries have beefier cells and more storage of energy per cell than your typical 12 volt marine grade deep cycle battery of the same volume. By putting two golf cart batteries in series, you can store more energy in the same amount of space than you can with one 12 volt marine grade deep cycle battery. Yes you will need twice as many battery terminals to do this but you will have stored more energy in the same space...which is the bottom line for a battery. The more stored energy per amount of volume the better. BTW, the way to stop battery terminal corrosion completely is Tef-Gel.

The only downside is two 6 volt golf cart batterys are going to weigh more than one 12 volt battery for the same amount of volume because the golf cart batteries contain more lead for the same volume.

Whether or not you look in the West Marine catalog or where ever, you will find this to be true. Yes I know that labeling "marine grade" on a battery is kind of a joke and that Port Supply/West Marine is rarely the best deal going. Defender Industries has better deals.

[Pblais]

David,

If you compare one group 4 12 volt to twin 6 volt golf carts then the amp hours match pretty close. You need the weights to be about equal before the numbers fall in place. Battery deals are best from a local batery supplier that stocks many types of batteries. Defender isn't bad but locally I can buy better that are cheaper. two group 4 12 volt batteries make a nice house bank. 4 golf carts do too.

[rleslie]

There is one major advantage to 6v batts....their weight per battery. When we replaced our bank three years ago, I found that our battery compartment could hold either 6-6v or 3-12v. When I looked at the weight of the batteries, I decided that I preferred to move aboard 2 - 72 lb batteries as opposed to 1 - 135 lb battery!!!!!!!!!

[forsailbyowner]

No, 12.2V is 50% charge. Once again, just using No's, randomly plucked from the fact that the bank is big, to give the general idea.
Because it now begs to ask, if you are using so little power, why such a big bank of batteries. You would be better dropping the bank size dramaticaly.



I like such a big bank because when im under sail using the autohelm I can also run the fridge and cabin ,running lights and dont have to worry about starting the engine or genset to recharge the battery for quite some time. With some breeze and sun my bank doesnt drop below 12.8 volts running the fridge full time in 90 degree weather days and high 70s at night. The only time I would have to run the genset is if im doing a lot of sewing and mother nature isnt giving much uvs or wind. I actually have 3 banks one 8d for starting one with 2, 6 volts and one with 6 ,6volts currently im running one diversion regulator for regulating the main house bank, ive been toying with the idea of using 3, diversion regulators , one on each bank . So when one is fully charged it diverts current to second house, when it hits 14.1 it would divert to starting to top it off then one on starting to divert to water heater 12v element. Am gonna run it by Mike at Mikes windmills who has been helping me out with my system to see if the regulators will work well together that way. He makes the regulators himself and they seem to work well. Steve

[hellosailor]

"By putting two golf cart batteries in series, you can store more energy in the same amount of space than you can with one 12 volt marine grade deep cycle battery. "
Still got to disagree. Wtice as many Amps is still just amps, not "energy". Twice the amps at half the voltage--is the same wattage, the same "energy", the same "power".

Golf cart batteries are what are considered "traction" batteries in the business. Not marine, not SLI, but "traction". And not surprisingly they are built a bit differently, in terms of plate count and thickness.

But there are still other kinds of batteries, including "commercial grade" deep cycle batteries sold for marine use (like Rolls and Surette) that have plates which make your golf cart battery plates look like...well, Bart Simpson trying to play Arnold Schwarzenegger. <G>

Your rule of thumb only works for the particular brand and size of the batteries you have chosen. That's like saying "Apples are rotten, oranges are not" based on what you picked up at one small fruit store one day.

If you look at the wider range of what is available, from all sources, you'll still find out that "volts" in a battery is inconsequential. Any maker can build battery with any kind of plate, thick or thin, and any number of plates, to build a battery for any target market. And when all else is equal--there's still no reason for them to build two six volts instead of one twelve volt. Except, one mortal can't lift one battery once it gets to a certain size. Six volts is no answer to that either--because they'll gladly sell you single 2.2 volt cells that weight over a hundred pounds apiece.

Is it easier to buy high amperage 6v batteries at WalMart than 12v batteries in the same amperage? Perhaps. That's just 'cause the stick boys can only lift so many pounds, not because that's the best place to buy batteries.<G>

[Alan Wheeler]

Just to affirm Hellosailors comments and rephrase slightly.
Just because a battery is 6V or 12V or 2V or what ever, has nothing to do with the weight, size or capacity. That is due to design and the materials it is made from.

2 x 6V batts does not automaticly mean more storage capacity, especially when compared to 1 x 12V batt.
1 x 6V 200Amphr batt = 200Ahr
2 x 6v 200Ahr connected in series to provide 12V still = 200Ahr
2 x 6v 200Ahr connected in parrelell = 6V @ 400Ahr
1 x 12V 200 Ahr = 200Ahr
2 x 12V 200 Ahr in parrelell = 12V @ 400Ahr.