Debating 2 6V vs 1 12V battery

[Iflyfish]

I will be using a 12V compatable CPAP, perhaps a portable 12V Cooler/Refrigerator and an LED light in my Teardrop. I am debating with myself whether I need to purchase 1 6V deep cycle golf cart batteries, at $87 apiece (providing the deepest and most long lasting charge) or a single 12V battery. I plan to use an Progressive Dynamic Charger and my TV Generator to power the battery(s).

Any ideas?

Anyone run your CPAP off of a 12V deep cycle battery? How many hours have you gotten out of a 12V?

Thanks,

Iflyfishscratchingmyhead

[Shadow Catcher]

TLI (too little information).
If the cooler is a peltiaer type it will draw about about 4.5 A continuously (really battery draining). The CPAP is open to question but 2.5A was given as one example.
Similar results can be had from either set up, it is a matter of amp hours. Our Lifeline AGM is 150 AH. The Golf-cart batteries work, and well reportedly and are less expensive but they must be maintained water level...

[Madmike8]

A good deep cycle 12v should work. If it does fall short of what you want, you could always add a second in parallel to double the run time. While not 100% accurate the amp hour battery ratings can be used to figure your runtime if you know your total amp draw. A 100AH DS battery will deliver 100 amps for 1 hour or 1 amp for 100 hours or 10 amps for 10 hours...

[Iflyfish]

A good deep cycle 12v should work. If it does fall short of what you want, you could always add a second in parallel to double the run time. While not 100% accurate the amp hour battery ratings can be used to figure your runtime if you know your total amp draw. A 100AH DS battery will deliver 100 amps for 1 hour or 1 amp for 100 hours or 10 amps for 10 hours...

Perhaps you might help me with this calculation:
My REMstar Auto seems to draw an average of approx. 0.6 amp under normal operating conditions. In terms of battery usage this translates to about 5 amp-hours (0.6 x 8 ) for an 8 hour night

I wonder if you could help me understand how many hours I might anticipate a 100AH battery would last using the cpap described above. This is challenging for me. My degree is in Social Work!

Iflyfishwithgratitude

[Iflyfish]

TLI (too little information).
If the cooler is a peltiaer type it will draw about about 4.5 A continuously (really battery draining). The CPAP is open to question but 2.5A was given as one example.
Similar results can be had from either set up, it is a matter of amp hours. Our Lifeline AGM is 150 AH. The Golf-cart batteries work, and well reportedly and are less expensive but they must be maintained water level...

Thanks, I'm narrowing in on the answer. I appreciate the input, this is no doubt way more simple than my complex brain makes it. I am What/Volt challenged!

Iflyfish

[Madmike8]

A good deep cycle 12v should work. If it does fall short of what you want, you could always add a second in parallel to double the run time. While not 100% accurate the amp hour battery ratings can be used to figure your runtime if you know your total amp draw. A 100AH DS battery will deliver 100 amps for 1 hour or 1 amp for 100 hours or 10 amps for 10 hours...

Perhaps you might help me with this calculation:
My REMstar Auto seems to draw an average of approx. 0.6 amp under normal operating conditions. In terms of battery usage this translates to about 5 amp-hours (0.6 x 8 ) for an 8 hour night

I wonder if you could help me understand how many hours I might anticipate a 100AH battery would last using the cpap described above. This is challenging for me. My degree is in Social Work!

Iflyfishwithgratitude

100/.06=166.667 hours...

6v batteries for golf carts are heavy, and you would need 2. I'd start with a good 12v deep cycle which will probably handle all your needs from the sounds of it, and you could always add a 2nd 12v in parallel if needed later.

[Iflyfish]

A good deep cycle 12v should work. If it does fall short of what you want, you could always add a second in parallel to double the run time. While not 100% accurate the amp hour battery ratings can be used to figure your runtime if you know your total amp draw. A 100AH DS battery will deliver 100 amps for 1 hour or 1 amp for 100 hours or 10 amps for 10 hours...

Perhaps you might help me with this calculation:
My REMstar Auto seems to draw an average of approx. 0.6 amp under normal operating conditions. In terms of battery usage this translates to about 5 amp-hours (0.6 x 8 ) for an 8 hour night

I wonder if you could help me understand how many hours I might anticipate a 100AH battery would last using the cpap described above. This is challenging for me. My degree is in Social Work!

Iflyfishwithgratitude

100/.06=166.667 hours...

6v batteries for golf carts are heavy, and you would need 2. I'd start with a good 12v deep cycle which will probably handle all your needs from the sounds of it, and you could always add a 2nd 12v in parallel if needed later.

Madmike8 wrote:No problem. Just remember you need to add up all your electrical draws. So if you run LED lights that draw 2amp and you run them for 5 hours that's 10 amp hours. You have a Cooler that draws 6amps and you run it 12 hours, that's 72 amp hours. You have your Cpap that you run 10 hours at .6 amps that's 6 amp hours. So in this example you would need at an 88 amp hour deep cycle battery to meet your needs. . To make your battery last longer try not to discharge it down below 20% of it's capacity. So 88AH plus 20% is 105AH. Like I said the battery formula is not accurate as all batteries are different and wiring causes losses... So always round up... So a 115 amp hour batter should be good. If later you decide you need more power you can add a second battery in parallel to get more amp hours. So, 2x115ah battery will give you 230 amp hours. Also battles tend to loose their ability to deliever power in near freezing temps. So an insulated battery box works well if you plan camping in those conditions.

Hope that helps.

Mike



This is great stuff and exactly what I need.

I like to figure conservatively.

So if I ran a CPAP each night for 10 hours at .7 amps that's 7 amp hours. If in addition I used
2 amp LED lights each night for 5 hours that's 10 amp hours. So if I get this right then I would draw a total of 17 Amp Hours per night. Then I would need to recharge the battery. Is that right?

If that is right then I theoretically would discharge a 100 AH battery to 80% in 4.7 days. Did I calculate that right? 80/17=4.7

I think I'm getting there.

Iflyfish

[Thawley]

Maybe time to bump this poll again...

viewtopic.php?f=6&t=53830&hilit=battery

[eamarquardt]

All batteries are not created equal. Few batteries are built to take an 80% discharge on a regular basis and live to tell about it. Before buying any battery double check its specifications (call the manufacturer). Also, the specifications will apply to a new battery and your battery won't be new for long. I'd add at least a 50% margin for good measure. Overkill in moderation.

Cheers,

Gus

[Iflyfish]

Maybe time to bump this poll again...

viewtopic.php?f=6&t=53830&hilit=battery

Good one! Thanks

Iflyfish

[Bogo]

First off, the faster you drain a lead acid battery, the fewer Amp hours you can get out of it. Batteries are usually rated for a 20 hour rate. Second, you never want to deplete a deep cycle battery more than 80%, but 50% is much better for long life. An average car battery should never be discharged more than 25% to 30%. They have sacrificed deep discharge ability for the ability to output high starting current.

Second: If you add a second 12V battery in parallel to an already existing one, during periods when the battery are idle, not charging or being draw on, the newer battery will end up charging the older one. Eventually this will lead to early death for both. If they are always being charged or discharged, they will share the load, and it will be OK. One will do slightly more of the work, but eventually they will mostly even out. The problem comes when they aren't being used. If you think you will need more battery power, it is better to buy it from the start. When paralleling lead-acid batteries, always use the same type and capacity. Preferably get them from the same manufacturing batch, but sometimes it can be hard to tell that.

Third: The thermoelectric coolers draw to much power, and don't really keep stuff cool enough. They have a rough maximum of 35F lower than ambient. So on a 90F degree day, the inside of the cooler will be 55F. Cool enough for drinks, but not food like meat. For each day of use, you will basically need more than a Group 31 Deep cycle battery (110 Amp Hour) can supply. Very quickly you will have the cost of a compressor based cooler in the battery bank, the solar array, or generator to recharge daily. Either get a compressor based cooler or use ice. Coleman Extreme 5 day coolers are a low cost long ice life cooler. They work great and are under $100.

BTW, my Coleman thermoelectric cooler draws 4.5 Amps continuous so it uses 108 Amp hours in 24 hours. A 110 Amp hour Group 31 deep cycle battery would be depleted down to 80% DOD in only 19.5 hours.

[GuitarPhotog]

So if I ran a CPAP each night for 10 hours at .7 amps that's 7 amp hours. If in addition I used
2 amp LED lights each night for 5 hours that's 10 amp hours. So if I get this right then I would draw a total of 17 Amp Hours per night. Then I would need to recharge the battery. Is that right?

If that is right then I theoretically would discharge a 100 AH battery to 80% in 4.7 days. Did I calculate that right? 80/17=4.7

No, your math is backwards. That would deplete your battery to 20% in 4.7 days. You will use about 21% of your 80% capacity each day.

<Chas>

[Iflyfish]

So if I ran a CPAP each night for 10 hours at .7 amps that's 7 amp hours. If in addition I used
2 amp LED lights each night for 5 hours that's 10 amp hours. So if I get this right then I would draw a total of 17 Amp Hours per night. Then I would need to recharge the battery. Is that right?

If that is right then I theoretically would discharge a 100 AH battery to 80% in 4.7 days. Did I calculate that right? 80/17=4.7

No, your math is backwards. That would deplete your battery to 20% in 4.7 days. You will use about 21% of your 80% capacity each day.

<Chas>

Thank you, I reversed the numbers...math never a strong suit for me. Thanks for reading and commenting. It looks like a single 100Ah Battery would suit my purposes, 4 nites of boondocking with out a shower would probably be enough! and certainly would be enough for anyone unlucky enough to be camping beside me!

[bdosborn]

I like to figure conservatively.

So if I ran a CPAP each night for 10 hours at .7 amps that's 7 amp hours. If in addition I used
2 amp LED lights each night for 5 hours that's 10 amp hours. So if I get this right then I would draw a total of 17 Amp Hours per night. Then I would need to recharge the battery. Is that right?

If that is right then I theoretically would discharge a 100 AH battery to 80% in 4.7 days. Did I calculate that right? 80/17=4.7

Not quite, as Bogo stated, you shouldn't discharge a deep cycle battery below 50%, that's the best compromise between depth of discharge (DOD) and total battery cycles. You won't get many cycles as 80% DOD. Here's a graph showing how the total number of cycles goes down with increased DOD. The graph is for a golf cart battery, which is the only type of easily available battery you can reasonably expect to withstand an 80% DOD. A start or marine battery won't take the abuse of an 80% DOD for many cycles at all.



Here's what I would figure for your battery capacity:

100 amp-hrs*0.5=50 amp-hrs real capacity.

50amp-hrs/17amp-hr/night=2.9 nights of use before you should recharge. I'd get a 20 or 30 amp battery charger, a trickle charger is going to take days to recharge from a 50% level.

Bruce

[Bogo]

For recharging at home between weekends. For each 100 Amp hour battery, I'd have 5 Amps recharge rate. Less chance of damaging batteries if the charger fails to cut off. Also less damage to the plates will be done at a nice slow charge rate. In two days a totally discharged battery bank will be fully recharged.

If you want to recharge from a generator, then get a charger capable of 20 or so amps per 100 amp hours of battery, but obviously not larger than the watt output of the generator. Then only recharge to 80% to 90% of full. The last 10% of the recharge will take allot longer to do, and will be expensive fuel wise. Skip it, and just recharge more often.

If you want to recharge from your car alternator, use jumper cables and turn all lights, radios, etc,, off in the car. The wire in the trailer wiring connector isn't large enough for a fast recharge rate. Monitor the battery voltage, and cut off recharge when it gets to 80 to 90% recharged. Again, that last 10% is expensive fuel wise. Skip it, and just recharge more often. A note on recharging from a vehicle. When you decide to stop recharging, disconnect the jumper cables, then wait a couple minutes for the TV battery to top off a bit more, and then shut down.

On depth of discharge vs. cycle life: From that Trojan battery spec. Note 80% DOD is well over 500 cycles. 50 weekend trips a year times 10 years is only 500 cycles. Chances are the battery will be killed by winter neglect, or simply die of old age before it cycle lives out for the average TD user. Note: the chart is for that Trojan battery. A typical AGM deep cycle/starting will only have 250 to 400 cycle life at 80% DOD. Still a long time for an occasional use RV.

If you really want proven long life, get Saft NiCd traction batteries. They have been in use in electric cars for over 30 years. Many in use in cars have well over 3000 cycles to >80% DOD and are still going strong. At 50 cycles a year, that is 60 years. About the only things that kills them are accidents, and letting the plates get exposed to air. The main thing with them is keeping them topped off with deionized distilled water. They make this easy with a filling system that is easy to use. All the batteries in a bank are hooked together with tubes. When you pour water in the funnel, the cells are topped off one by one. When water flows out the exit tube, refilling is done.