BigT said:
My CPAP is rated at 6.67 Amps. At 8 hours of use each night, that would be 53.36 Amp hours per night. I was told in earlier posts that I don't want to discharge the AGM batteries more than 50% (30% would be optimum). Given this information, I figured a 150 Ah AGM would be perfect. Did I miss something?
I was also told that a general rule of thumb is 1 Watt of solar for every 1 Ah of battery, thus my plan to run a 160W panel to a 150 Ah battery.
I would gladly buy a "smaller" battery, but I was told that doing so would greatly reduce the lifespan of the unit.
Maybe I should go back to the first page of this thread and read it all over again.
1 watt per 1AH of storage capacity is a bit light for an AGM battery. These act better when recharged at higher rates. You can't have enough solar. you can't have too much in most every situation. It is far too easy to have too little.
Deeper cycles reduce the total amount of cycles, however, too little solar for too much battery capacity can be just as detrimental, especially with AGMs.
I happen to be getting the best $ per cycle of any of my previous batteries, and it is the smallest amount of capacity I have cycled. I stepped down to 130 AH from 230, and with 200 watts of solar, this only approaches the 'recommended' 10% rate in summertime. Quality AGM's like lifeline recommend a 20 % rate, and Odyssey say no less than a 40% rate on a deeply cycled battery.
Cycle depth and rate of recharge are kind of a trade off with AGM's. Yes the deeper the cycle the more detrimental, but also the slower the recharge rate, the more detrimental, and if the battery is not recharged fully by the end of the day, it is more detrimental.
If one can charge via alternator with higher amps, even relatively briefly, and then let the solar finish the job, the AGM will last significantly longer than just low and slow solar cycle after cycle. This goes for flooded batteries too, but with AGMs, higher currents applied regularly are much more beneficial.
AGM's biggest possible performance advantage over Flooded, is the ability to accept huge recharge currents when depleted. but not all AGM's say they can handle huge currents. Many say no more than 30% of capacity.
Anyway, a well balanced system is best done initially. If you need 150 AH of AGM, I'd say no less than 200 watts of solar, and preferably 300 if Solar is to be the only recharging source. If you already have 160 watts of solar then get no more then 110AH of AGM.
Not the end of the world if you cant meet these recommendations, just expect the battery to lose capacity faster than hoped for. And remember, systems work just fine, until that day when the battery does not have enough capacity left and No longer seems to 'take a charge'. How soon that day comes is dependent on how well the battery is recharged each cycle. Occasionally dipping below 50% is not as damaging as 2 weeks of cycling, never getting to 100%.
Go for more solar. It can pay for itself in lead.
