Battery Life?

[Tightwadted]

Camped for years, but never without power. Going to a family campout this summer with no hookups, I've got the water issues solved, but I need advice on the electrical. DW needs an oxygen concentrator to sleep with, it draws 3.4 amps (120 volt) so 408 watts. I have a 1500/3000 watt pure sine wave inverter. Planning on using the group 24 battery in my camper, plus 2 group 29 batteries pulled from my boat. all batteries deep cycle. the grp 24 battery says RC 140, the 29's say RC 210. I am assuming that means reserve capacity amps? So if I hook them all up parallel I should have 560 AH? I am using formula AH x V = W divided by 408 so I come up with 560 x 12 = 6720 divided by 408 = 16 hours. that seems like a long time, I have a generator to charge them back up every day. Need some input if my thinking is off or if it is close to right. Thanks

[1bigmess]

Since someone's health depends on your batteries, I would read part one and two of the following link and make sure you understand what you will need, how to do it, and why.

The 12volt Side of Life (Part 1)

[wardy]

Originally Posted by Tightwadted

Camped for years, but never without power. Going to a family campout this summer with no hookups, I've got the water issues solved, but I need advice on the electrical. DW needs an oxygen concentrator to sleep with, it draws 3.4 amps (120 volt) so 408 watts. I have a 1500/3000 watt pure sine wave inverter. Planning on using the group 24 battery in my camper, plus 2 group 29 batteries pulled from my boat. all batteries deep cycle. the grp 24 battery says RC 140, the 29's say RC 210. I am assuming that means reserve capacity amps? So if I hook them all up parallel I should have 560 AH? I am using formula AH x V = W divided by 408 so I come up with 560 x 12 = 6720 divided by 408 = 16 hours. that seems like a long time, I have a generator to charge them back up every day. Need some input if my thinking is off or if it is close to right. Thanks

You also have to look at the efficiency of the inverter. A very high-quality inverter can approach 95% but many are closer to 85% and it is load dependent. Then what is the actual amp hours available. If they are new and have been treated well then they should be close to capacity (560AH). But I would de-rate that depending on their age brand and are they TRUE deep cycle batteries or dual purpose? Let say they are true deep cycle (best case scenario). So fully charged starting at 95% of avertised rating or 532 AH then figure only 92% is available after the inverter inefficiencies are factored so 532 X .92 = leaves about 490 AH. Now how deep of a discharge are you willing to take these? If they are true deep cycle you can take them comfortably down about 80% or 490 X .80 = 392 AH first day use. Why do I say 1st day use? Well the following days you would have to run the genny a long time to top them off. But getting them back up to 80% is more realistic so the following days leave you with about 314 AH of which only about 216 AH is available before discharging below 20%, that won't do it. And, since you gave RC numbers I'm guessing these batteries are dual purpose so my numbers are overly optimistic.

I would take the advise of the previous comment from "1bigmess" and read up more.

[Tightwadted]

Thanks Wardy and 1Bigmess, read up on the info, looks like I should get 1 more battery to take along and also my regular battery charger to charge them quicker. I appreciate the responses! Rather have too much than have to cut trip short. DW can sleep without the O2 concentrator, but she feels better with it.

[charles tuit]

Originally Posted by 1bigmess

Since someone's health depends on your batteries, I would read part one and two of the following link and make sure you understand what you will need, how to do it, and why.

The 12volt Side of Life (Part 1)

I cannot say it better. The "12 volt side of life, parts 1 & 2" should be mandatory reading for every RV'er. It will explain everything you need to know.

[JohnBoyToo]

While you COULD run your genny a lot,
have you thought of supplementing it with a portable solar panel ?
something like this might help..

just a thought and even though it's one event, you can always use it later...

[Twilightzone]

>"it draws 3.4 amps (120 volt) so 408 watts. I have a 1500/3000 watt pure sine wave inverter. Planning on using the group 24 battery in my camper, plus 2 group 29 batteries pulled from my boat."

IMHO: Can you go out and camp in your 'driveway' ?
If so, you can see how it does.

What are you using to re-charge your batteries? That load might be too much for your internal inverter/charger. You might need to bring a bigger battery charger to run off of AC (generator) power.

[OLYLEN]

Think you need more research. You will not be in the 500 amp hour range. 4- T105 batteries, true deep cycle are in he 450 AH range and at 50% you have 225 AH use. At your stated use rate near 40 per hour with overhead you will have less than 5 hours on a good battery bank. Maybe tank rental would work for quiet time.

LEN

[757driver]

Originally Posted by Tightwadted

Camped for years, but never without power. Going to a family campout this summer with no hookups, I've got the water issues solved, but I need advice on the electrical. DW needs an oxygen concentrator to sleep with, it draws 3.4 amps (120 volt) so 408 watts. I have a 1500/3000 watt pure sine wave inverter. Planning on using the group 24 battery in my camper, plus 2 group 29 batteries pulled from my boat. all batteries deep cycle. the grp 24 battery says RC 140, the 29's say RC 210. I am assuming that means reserve capacity amps? So if I hook them all up parallel I should have 560 AH? I am using formula AH x V = W divided by 408 so I come up with 560 x 12 = 6720 divided by 408 = 16 hours. that seems like a long time, I have a generator to charge them back up every day. Need some input if my thinking is off or if it is close to right. Thanks

RC stands for reserve capacity as you said but it is the number of minutes at a 25 amp load to discharge to 10.5 volts. To convert to amp hours multiply the RC minutes by 0.4167. You actually only have a total of 233 AH and so as not to destroy your batteries consider only 1/2 of that AH total usable or 116 AH.

You will need more batteries to have a decent chance of making it through the night without running the generator.

[John Hilley]

Your batteries are probably not true Deep Cycle batteries, but Marine/RV batteries. They are meant to start the boat engine as well as provide power for accessories. The cells are designed to provide more short term power when cranking. You might find that there is a 12 volt device to power the oxygen concentrator. I'm surprised you don't have one for your car.

[Twilightzone]

Interesting... Looking at oxygen concentrator.
This one has 'internal batteries'... that are good for 10 hours.

Battery Duration:
Single Battery: Up to 5 hours, Double Battery: up to 10 hours
Has a DC Power supply (less wasted current).
DC Power Supply (G2) Inogen One G2 Universal Power Supply

(Am nosing the web around trying to find the power required)

Yup.

Found one with a DC power supply.
DC Power: Input 12 to 19 VDC 8.0 A max (96 watts @ 12V)
AC power and recharging.
Power Consumption 120 watts and 150 watts during AC charging

Maybe you need to get a new O2 concentrator ?

[Tightwadted]

Thanks everyone for your input and advice, I did follow the advice of using the system in the driveway, I pulled my 2 boat batteries (grp 29) and purchased 2 more 29's 122 ah each. took my 2 battery chargers and borrowed 2 more, was able to get 9 hours of use each night and took about 6 hours of gennie time to get them back up each day. kept the camper battery separate for just running the lights, frig fan, water pump, etc. All worked out well and I now have 2 spare batteries for my trolling motor!