CPAP machine w/ inverter. How much power?
Hi Folks, A little background. Not new to RVing, but starting to deal with battery issues more, now that I have a week long music festival coming up w/ no hookups. I decided that after last year, n...
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Hi bgrass,
Capacity matters only when folks camp in locations where there is no shore power. Most rv's don't do that.
They cycle their banks too low--and get poor lifespan. They use items for 20 minutes not 20 hours.
The ones who realize what is going on, often add a solar system. The ones who don't may end up doubling capacity but that is still not enough to run a serious load for long.
I've always felt that the RV makers short change us with the size of the battery bank.
The charger amperage matters below 85% state of charge. Above that flooded batteries may only accept about 12.5 amps. Of course if you have lots of batteries then 8 X 12.5 = 100 amps for a charger.
Since you have two group 27 jars, a 25 amp unit above 85% would be good. I'm sorry I do not know the acceptance rate at 50% but some folks do charge at 100 amps. On a generator that would require about 2500 watts continuous. (based on a 1000 watt genny being able to reliably power a 40 amp PD converter with wizard).
Capacity matters only when folks camp in locations where there is no shore power. Most rv's don't do that.
They cycle their banks too low--and get poor lifespan. They use items for 20 minutes not 20 hours.
The ones who realize what is going on, often add a solar system. The ones who don't may end up doubling capacity but that is still not enough to run a serious load for long.
I've always felt that the RV makers short change us with the size of the battery bank.
The charger amperage matters below 85% state of charge. Above that flooded batteries may only accept about 12.5 amps. Of course if you have lots of batteries then 8 X 12.5 = 100 amps for a charger.
Since you have two group 27 jars, a 25 amp unit above 85% would be good. I'm sorry I do not know the acceptance rate at 50% but some folks do charge at 100 amps. On a generator that would require about 2500 watts continuous. (based on a 1000 watt genny being able to reliably power a 40 amp PD converter with wizard).
bgrasspkr wrote:
So, more for curiosity's sake, rather than needing hard answers, some responses just don't make sense. PianoTuna, I have gained a lot of info reading your posts this these past few months, so thanks again, but in regards to your statement "2 amps @ 120 volts via an inverter may translate to 20 amps @ 12 volts", OK, I guess I see the math, but if so, how the hell does anyone run anything in an RV with a converter? If a 2 amp cpap kills( brings below 30 or 40%)2 Group 27 bats (approx 190 AH correct?) in about 5 hours, how are people using other things that draw a boatload more current? Never mind all the people who successfully use their CPAPs?
I also have seen you post that graph, and I find it interesting. It would be nice if they spread out the x axis more, so I could see differences between 0 and 20 hours better, and also if they started with a higher SOC on the battery, say somewhere between 35-50%, where I would bet a lot of RVers take their bats down to before topping off.
Also, as the curve is so steep the first few hours or so, does it matter so much whether my charger is 20 amps, instead of 40 or 50, or even 70? Does the 20 amp setting on my Schumacher charger mean that 20 amps is the max, or does it go higher at the start, then settle down at 20, then gradually to trickle as it gets closer to full?
I have read hundreds of posts of most people bringing their bats from 50 to 90 percent with their gens, with run times approx 3 hrs a day. Your chart says that is improbable, if not impossible with even a 55 amp charger/converter.
Something's not adding up. What am I not seeing?
