Battery setup

[Jrw1]

I am thinking about setting up uninterruptible power. I've read various threads on the subject, but I figured I'd post my proposed setup to see if there are any obvious issues. 

1. 2 x 12V AGM batteries 18 Ah hooked up in series to make 24V
2. 2.5 amp 24V trickle charger connected in parallel.
3. 1 resmed 90W 12/24V DC converter connected in parallel (24V).
4. Probably an inline fuse.

Using a kill-a-watt, it looks like the machine draws about an amp.

I would like to think the 2.5 amp trickle charger powers the machine until the power cuts out, at which point the batteries kick on and would last the night, and probably 2.

Thoughts?
thx,
Jay

[justMongo]

I'd do a search on "battery backup". There have been many lengthy threads on the subject; and rehashing old ground is sort of a waste.

Watch out for Trickle Charge. It means a constant current charger; and it will kill most batteries if left for any time.
"Float Charge" is a constant Voltage charge that is regulated for temperature and battery type (gel/agm or flooded).

The most elegant system I've seen, for backup in home, centers around the West Mountain PWRGATE PG40S BACKUP POWER SYSTEM. That's only one component -- basically a Schottky diode "switch" between charger/power supply and a SLA/AGM battery and the load (the ResMed converter attached to the PAP machine).

Read about what others have tried; then ask questions.

[Jrw1]

I'd do a search on "battery backup".  There have been many lengthy threads on the subject; and rehashing old ground is sort of a waste.

Watch out for Trickle Charge.  It means a constant current charger; and it will kill most batteries if left for any time.
"Float Charge" is a constant Voltage charge that is regulated for temperature and battery type (gel/agm or flooded).

The most elegant system I've seen, for backup in home, centers around the West Mountain PWRGATE PG40S BACKUP POWER SYSTEM.  That's only one component -- basically a Schottky diode "switch" between charger/power supply and a SLA/AGM battery and the load (the ResMed converter attached to the PAP machine).

Read about what others have tried; then ask questions.

I think I'm a little off the reservation with wanting to do a 24V system. 

...Will a 24V battery tender designed to shut off when "full" kill an AGM? This is a key component as I didn't see much for 24V. 

Thx

[justMongo]

Since your must use the ResMed 12/24 converter, why not go with a 12 V AGM battery in the 35 Amp-hour range.
The Deltran Battery Tenders are kind to Sealed AGM batteries.

There are folks who keep an AGM battery on a Battery Tender; and hook up manually during power outage.
There is also the crowd that wants to take their system camping.

It sounds like you'd like to rig up sort of a UPS system where the Cpap and converter run off 12 VDC. Pulling from a "Battery Charger" when the mains are live; and from the battery when the mains are down -- with automatic switch-over. For that, you will need a power supply like the Astron SS-25M, 12 V supply, a method of switching like the West Mountain Powergate, a Battery, and your converter.

You want to Float Charge for the above method. Not rely on a Battery Tender to power your CPAP when the mains are live.

You should talk with user OMyMyOHellYes. He used such a solution. You have to be electrically very handy. You'll need an accurate DVM to set the power supply Voltage. You'll need the tools to make up cabling using Anderson Power poles.

If you just want to go simple -- then check out this guys setup:
http://www.apneaboard.com/forums/Thread-...#pid106570

His is for off main use; and does not have automatic switch over.

[Jrw1]

Since your must use the ResMed 12/24 converter, why not go with a 12 V AGM battery in the 35 Amp-hour range.
The Deltran Battery Tenders are kind to Sealed AGM batteries.

There are folks who keep an AGM battery on a Battery Tender; and hook up manually during power outage.
There is also the crowd that wants to take their system camping.

It sounds like you'd like to rig up sort of a UPS system where the Cpap and converter run off 12 VDC.  Pulling from a "Battery Charger" when the mains are live; and from the battery when the mains are down -- with automatic switch-over.  For that, you will need a power supply like the Astron SS-25M, 12 V supply, a method of switching like the West Mountain Powergate, a Battery, and your converter.  

You want to Float Charge for the above method.  Not rely on a Battery Tender to power your CPAP when the mains are live.

You should talk with user OMyMyOHellYes.  He used such a solution.  You have to be electrically very handy.  You'll need an accurate DVM to set the power supply Voltage.  You'll need the tools to make up cabling using Anderson Power poles.

If you just want to go simple -- then check out this guys setup:
http://www.apneaboard.com/forums/Thread-...#pid106570

His is for off main use; and does not have automatic switch over.

Thx! That setup is exactly what I'm trying to do, just with 2 12 V 18AH batteries and a little more juice in the battery tender.

I think what the setup is actually doing is running off battery all the time. When the voltage drops below the battery tender's threshold it kicks on and the required current will go to the cpap, and the remainder to re-charge the batteries.

I guess I was thinking that being at 24 volts would be more efficient than trying to step up 12V in the power supply, but comparing the setups they are almost identical 24V/18 Ah vs 12/35 Ah.

[OMyMyOHellYes]

Since you can't go directly from a 24 V battery to your S-10 - which would be ideal in an ideal world where ResMed hadn't fornicated things up by locking their machines down to only using their power supplies - you may as well save some bucks and simply go with the 12 V system. They're just way more common. And I don't think you lose much in the 12 to 24 step-up. I use 35-39 AH batteries, but that gets me through several nights if needed (first night would continue with whatever humidification I had going with auto switch over to battery, after than I would kill humidification and just go straight from the flow generator or pull out my new old stock Respironics passive humidificator.) If I was only concerned about one night, a single 18 AH would be more than sufficient for me.

And yes, fusing is required for your system. Well, not REQUIRED - nobody is gonna arrest you or anything, but it is the prudent thing .....

Kill a Watt may not be the best measuring device to get your power draw from. Have you checked ResMed's latest version of their battery guide? I give them points for publishing that. It gives a good estimation of current draw and battery size requirement for their machines used at different settings and humidification configurations.

OMMOHY

[OMyMyOHellYes]

Oh, and if you didn't care to make your own, you can buy PowerPole lines in most needed configurations pre-made (Powerwerx) , but you likely end up with lots of excess wire and will spend a ton of extra money and have some wonky looking connections (I cut off all the cigar lighter connections off of everything and replace with Power Poles. It might be very well cheaper to buy a PowerPole crimper tool and the components. They are easy to use after a few learning attempts and I have sometimes found myself inventing projects just to get to use them. I started rigging up a portable battery system for handheld comm radio and GPS in my 70 year old airplane that didn't have an electrical system. Tinkering with PowerPole systems was probably one of the factors that drew me into hamateur radio.

OMMOHY

[Jrw1]

My Aircurve and Airsense are both 24 volt systems. They currently are running off an expensive as all get out 24V Lithium Ion FAA approved battery. It needed to be used 1 time and when it runs out of juice it beeps so loud you can hear it up the street. It's actually 2 batteries to barely get you to 8 hours some of the time (Medistrom Pilot and Co-pilot 24). They'll be useful for the occasional road trip, but not much else. 

Basically I'm looking for a sustainable setup that won't break the bank every 3-5 years when the battery needs to be replaced. Batteries were $34.99 each, and the charger was $80 (fully potted waterproof fused...all stuff I like to see if I'm going to sleep next to enough power to blow a hole in the wall or burn the house down) 

I really didn't see a price difference between running 24V vs 12V. I think the 35 Ah battery might be the 2 18s in parallel I just bought. I did see where Deltron suggested using two 12V chargers instead of the 24V charger to make sure each battery is full, but I suspect that's a loosing battle and the batteries will more or less lose capacity in lock step in a series configuration.  I went ahead and pulled the trigger. When I get it all setup I'll take some pictures and let ya'll know if I blow the fuse in the power supply 

Jay

[Jrw1]

when it runs out of juice it beeps so loud you can hear it up the street. 

Fixed that problem.

http://imgur.com/ndnswSY

[Jrw1]

I got it setup.  Predictably the voltage is a little high while charging 29.5V, but the resmed power supply seemed to handle it. Long term I'm not sure if that will cause me to burn up power supplies or not. Maybe it's made for it    

http://imgur.com/I6EjH9R