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Backup power options for CPAP machines
#31
(01-02-2018, 05:10 AM)Ockrocket Wrote: So just skip all the complications of technology and over priced commercial products... just hook the machine up permanently to the 12 volt battery, hook a trickle charger that will keep the battery topped up from the mains.

The Dreamstation is 12 volt to start with, it runs off a transformer that drops the mains power to the required 12 volts, so by running from a 12 volt battery you are actually supplying it with the correct current it runs on.

Leaving the battery on a mains power trickle charger will keep it charged up, and batteries on trickle charge have a longer life than batteries that are depleted and recharged.. you will get years of life from a battery. 

Another advantage is that if the mains power goes down there is no "switch over" lag where the pressure will drop and wake you up.

You should be able to set the whole thing up for $150 or less (that is in Australian money, depending what country you live in it may be cheaper) 
The genuine 12 volt DC cord for the machine cost me $50, the battery was about $80 (got discount because I buy my car and motorcycle batteries from the same place, and about $15 for the female socket and connecter terminals to wire the socket to the battery.. I also added an in line fuse just in case. 

And the bonus is that you can take it camping.  Cool

Just Mongo and I discussed this - the conclusion - didn't seem an optimal solution even if it runs (odd - for reference I went to check and all of our private messages seem to have disappeared from my PM mailbox?).  

If you have the charger on the battery all the time, and run the CPAP off of that, what you are in effect doing is running the CPAP off the charger (to the amperage limit of the charger).  If you have a smart charger (four charge modes - initialization, bulk, absorption, and float) it may have a difficult time figuring out what mode to properly run in while the machine is running, depending on the battery state.  Charge current to the battery is best isolated from the supply to the machine.  

That's the beauty of the powergate.  Power coming in from power supply?  Splits that off and powers the machine.  Keeps float charge going to the battery as needed.  Power supply interrupted?  Instant switchover to pull from battery, no lag, no drop, no interruption.  Power supply restored?  Powergate returns to supplying the machine with current and recharging the battery for what got used.    

Also, for maintenance, need to be careful to differentiate between a "trickle" charge (bad) and a "float" charge (good).  Trickle chargers constantly charge at a low amperage, but a higher voltage.  They will overcharge (kill) a battery if they are left on it.  Trickle chargers mean the user needs to monitor the state of the battery and remove it from the battery or turn it off.  Float chargers, on the other hand, have circuitry that will monitor/manage the battery's charge state and keep the battery charge within specs.
There.  I said it.

OMMOHY
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#32
(09-30-2017, 06:44 AM)OMyMyOHellYes Wrote: Then again, I do quite nicely on my homebrew CPAP UPS that consists of a 35 Ah battery, a powergate/charger (West Mountain specifically-the Astrons powergates don't have true smart charging capability) and a commercial power supply.

Would you be willing to share details of your setup?  Like, which West Mountain powergate model you use, which battery, etc.?  I looked at the Super PWRgate PG40S on westmountainradio.com and it looked like it could also work with a flooded lead acid or marine-type battery - very versatile.

Thanks--
WA
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#33
It is the WM Super PWRgate 40S, an Astron 12 A switching power supply, and I tend to gravitate towards the CSB (Hitachi) AGM batteries - 39 AH same size as the 35 AH format. I tend to try and stay with real name, known brand batteries (in additon to CSB I also have PowerSonic), there are a lot of folks out there slapping what looks like name brand stickers on batteries from who knows where in outer China where quality control may be more, um, inconsistent. The older brand names have a reputation to protect; the importer slapping the "Good, Best Giga Battery" labels on cheap imprts, may not so much.

For the most part, moving eelectorns are moving electrons. So yes, the SuperPWRgate should handle lead acid batteries with no problem (using with Gel requires opening the case and moving a jumper fuse, IIRC - easy instructions included) - but I wouldn't want a wet lead acid battery in my bedroom..... Seems AGM/SLA is ideally suited for this purpose.

West Mountain has introduced a new model SUPER DUPER powergate and so the PG40S units have come down in price now - I just ordered one for $115-120 to use with my radios.
There.  I said it.

OMMOHY
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#34
Note: this solution is useless if you need something light and portable.

My sister's step-son lives near them and has to have a backup because power failures can last a day or two (rural area) plus he needs it at the hunting cabin since there is only solar electric there (it's only enough for a couple of lightbulbs). He set up a backup using golf cart battery. It's on its own little cart in the closet. Leaving off the humidifier (with an Airsense, you need that panel to shut down the humidifier), he had more than adequate battery power for 3 days. If he was running the humidifier, he did not have enough power for 2 nights. This more or less matches Fisherman's information.
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#35
Important to remember about Lithium Batteries ... unlike Ni-Cad or NmH cells, Litihium cells do NOT like to be deep cycled. Lead batteries don't care one way or the other.
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#36
Yes, some Lithium batteries are very sensitive to being discharged too far. LiFePO4 batteries (Lithium Iron Phosphate) are more tolerant, and are what I would use over lead-acid.
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