Posted: 4/3/2013 1:50:05 PM EDT
|
Ok, I am looking to get a backup battery for my CPAP (breathing machine ) I have sleep issues, so I use this at night and feel like crap if I don't. I am going to go camping for 6 nights and do have access to a place to charge a battery if needed. I also want a set up to run if the power goes out. I do have a generator, but don't want to run it all night just for a CPAP. I currently have used a jump starter pack with a DC outlet. This is good for a night or 2. From what I have researched my CPAP draws 2 amps per hr without heat and a humidifier. I got that from some testing done by someone on a CPAP forum. So if I sleep 8 hr I would need 16 AH per night, I think?
There look to be two options there is a company that makes Lithium Ion battery packs. http://www.batterypowersolutions.net/C-222_Power_Pack.shtml They list it as having 222 WH for capacity. This is lightweight but made in China. I would plug into it with DC cord from CPAP. The other option is a marine Battery. I am leaning towards an AMG battery since it is sealed and if I need to run it in the house I don't want to have acid leak. I would connect to it with alligator clips to a 12V plug and then plug in the DC cord to that. I have looked at a Optimum Blue top with 75 AH rating. http://www.optimabatteries.com/us/en/shop/bluetop/bluetop-group-31-dual-purpose-deep-cycle-and-starting/ or http://www.lifelinebatteries.com/marineflyerprint.php?id=2 a lifeline batter that has 100 AH of capacity Am I correct that you should run the battery down to only 1/2 of its life so I could get 3 nights of sleep with this set up? (100 AH / 2 / 16 amps per night) For a charger I was looking at a CTEC 7002 http://smartercharger.com/products/batterychargers/ctek-multi-us-7002/ Can someone help with the math on the WH vs AH. Are the Lithium Ions batteries that much better and smaller? Any thoughts? |
|
You're better off with the sealed lead-acid, both cost and durability wise, so you're leaning is good there.
Flooded lead acid is probably the most durable and cheapest, but obviously a big issue for indoor use. You are correct that the depth-of-discharge for lead-acid batteries shouldb't be more than 50% for maximum battery life. You can go to 90% DOD a few times, but it's not something you want to do routinely. To convert from Watt-hours to Amp-hours, you essentially divide by the voltage of the battery (there are other considerations, but that's good enough for this.) So that 222Wh battery is probably about 15 Amp hours or so. Lithium batteries are smaller and lighter, but they're not as rugged and can fail in very spectacular ways (vent and burst into flames, not common but scary as hell when it happens.) The charger looks like a well-built high-end unit, but you can get a very good one for less. The charging amperage isn't very high (7A) so it would take most of the day to recharge the battery. You might want to look at something with a higher current capability. |
| If you want to get spendy, Lithionics is manufacturing lithium-ion batteries in most of the traditional deep-cycle lead-acid battery sizes. Some folks are now using them as direct replacements for the LA batteries that were originally installed in their boats and RVs. |
|
Quoted:
The charging amperage isn't very high (7A) so it would take most of the day to recharge the battery. You might want to look at something with a higher current capability. High amperage charging is hard on deep cycle batteries. In general you want to keep the amperage as low as you can get away with. Battery Minder has a great computer controlled charger with selectable 2, 4 or 6 amp charge rates plus will do long term float and desulfating, it's about $100. |