How can I run a CPAP in my tiny van?

[BigT]

Thanks, Bob, found it! http://www.renogy-store.com/200W-Mo...pEz2qlQ0yfcz5zdup7MqH-7OiPzrX-_zNcaAuLz8P8HAQ

 

[highpsiguy]

I have a Resmed cpap machine. I have used 1 AGM 96ah battery for 5 nights in a row with a single charge. Did not check before and after voltage. I did not run the humidifier. Thats my real world experience. Now I have solar and also charge off the alternator and can keep up with my voltages. The 5 nights were before I had a way of checking voltages easily.

 

[offroad]

Thanks highpsiguy. That the straight answer needed. Am going to buy a battery like yours and a charger, and a 12v adapter for the resmed.

 

[offroad]

I have a Resmed cpap machine. I have used 1 AGM 96ah battery for 5 nights in a row with a single charge. Did not check before and after voltage. I did not run the humidifier. Thats my real world experience. Now I have solar and also charge off the alternator and can keep up with my voltages. The 5 nights were before I had a way of checking voltages easily.

The 96ah size costs $150 or more. Ouch!! Plus a charger costs $30. And 12v adapter for cpap costs $50. --- guess I better budget $300 for this solution.

 

[LeeRevell]

My local Wally's has a 120AH Marine Cycle battery for about $80. Should work okay.

 

[offroad]

My local Wally's has a 120AH Marine Cycle battery for about $80. Should work okay.

If I use that 120ah battery for a three day weekend, it's likely the battery will not be recharged for three days. Not sure how that will effect he longevity of the battery but understand these batteries last only three years. Point is, may need to budget $100 battery replacement every three years.

Plus that battery is heavy to haul. And it likely needs venting, storage outside. Am going to investigate other battery tech in addition to the classic lead acid deep cycle. Maybe find something lighter weight that can handle being deep discharged for a couple days. Will need to study lithium ion batteries.

 

[BigT]

Will need to study lithium ion batteries.

What's the advantage to that type of battery vs an AGM?  I'd like something I don't have to vent to the outside or mount under the van.  
It would also be nice if it wasn't huge and heavy either.  
Since I'm not living in my van but simply using it for camping, a battery and 120V charger might be a good and simple way to start.  

I found this during a quick search.  https://www.batterybusiness.com.au/store/product_detail/lion-batteries-standard-882

Battery prices are insane! 

 

[BigT]

Will need to study lithium ion batteries.

Not sure how this got posted twice. I was trying to edit the original.


What's the advantage to that type of battery vs an AGM?  I'd like something I don't have to vent to the outside or mount under the van.  
It would also be nice if it wasn't huge and heavy either.  
Since I'm not living in my van but simply using it for camping, a battery and 120V charger might be a good and simple way to start.  

I found this during a quick search.  https://www.batterybusiness.com.au/store/product_detail/lion-batteries-standard-882

The one I linked to is only 12" wide by 6" wide by 8" tall, but it says it weighs 25kg (55lbs!)  Can that be right?!  :huh:  
That seems like an awful lot of weight from such a small package. 

Battery prices are insane!    

 

[BigT]

After doing a little searching it seems that the LiIon battery is slightly lighter than the AGM, but about $100 more expensive.  
The size seems to be about the same as does the weight.  (AGM = 58 lbs/LiIon - 50 lbs).  They're both about 12" X 6" by 8".  

I'm hoping to find something I don't need to vent to the outside because I'd like to avoid cutting holes in my van.  

 

[blars]

Conventional Lithium ion batteries are a fire hazard and loose capacity whether you use them or not.

Lithium iorn phosphate (LiFePO4) have long life if treated as they like (not the same as lead-acid) and you only need about half as many amp-hours as lead-acid (including AGM). Technomadia has a series of blog articles about them, as do I. Some people still consider them "bleeding edge".

 

[BigT]

I have used 1 AGM 96ah battery for 5 nights in a row with a single charge. Did not check before and after voltage. I did not run the humidifier. Thats my real world experience.

Optimistic Paranoid


The rule of thumb is that you never discharge a deep cycle battery below 50%. 
____________________________________________________________________________________________________

Hmmm....  I like the idea of being able to run a single AGM for multiple days, but given what Optimistic Paranoid states, I sure would like to know how far down highpsiguy ran the battery.  

My device being 6.67 Amps, it would use 53.3 Amps in a single 8-hour night.  If the 50% rule is accurate, I would need a 106.6 Ah battery for just a single night's sleep, and a 112.12 Ah for the full weekend.  

My head is starting to spin from all the number swirling around in it. 

 

[offroad]

No way you need that kind of Amps for a Cpap. Look a little more closely at that device. What brand and model Cpap?

See if you can disconnect the humidifier as they use the most current-amps.

 

[BigT]

No way you need that kind of Amps for a Cpap. Look a little more closely at that device. What brand and model Cpap?

See if you can disconnect the humidifier as they use the most current-amps.

It's a Respironics System One (REMstar Auto A-Flex) and it doesn't have the humidifier.  

It says 6.67 A on the back.  

 

[offroad]

My condolences about the power needs of that. That's rather large. Mine is 24V and 1.25A and a resperonics also. That's a lot of power to be supplied continuous for several hours. That much current will cause heating of the connections I fear. Can not think of a solution yet.

 

[BigT]

Odd. When I read the reviews on the CPAP sites, people give high praise to the 12 Volt system. Nobody mentioned overheating terminals.
Oh goodie, one more thing to think about before pulling the trigger on this project.

 

[offroad]

If you make sure that you have good connections (solder-crimp-mechanical) and you have the right size (gage) wire, you should be okay. No heating will occur.

 

[BigT]

OK, I'm a little confused.  What's the difference between these two kits?
http://www.amazon.com/Renogy-Solar-...8&qid=1426748727&sr=8-8&keywords=solar+panels

http://www.amazon.com/dp/B00BCRG22A?psc=1

I'm just days away from pulling the trigger on this project, and now I see this.. :huh:  Is one a better idea than the other?
I'm hoping to run a single 12V AGM battery with somewhere in the neighborhood of 100-125 Ah.  

While I'm posting this I might as well add that I'm planning to mount the panels to my Yakima roof rack via two pieces of aluminum channel, in the hope that this will increase cooling.  
Does this sound like a suitable mounting idea?  

 

[AuricTech]

It looks like the only difference is that one has Z-brackets for mounting the panels.

After a derating factor of .77, 200W of PV panel would give you a charge rate of about 10.6% for a 100Ah battery, and about 8.5% for a 125Ah battery. 10%-13% is considered optimal for a full-time off-grid system. Here's the formula I used (which I found on the forum to which my sig file links):

.77w/vh = r

v=charging volts (for 12V system, use 14.5)
h=battery capacity in Amp-hours
r=rate of charge (decimal fraction)
w=Array size in Watts

 

[SternWake]

It looks like the only difference is that one has Z-brackets for mounting the panels.

After a derating factor of .77, 200W of PV panel would give you a charge rate of about 10.6% for a 100Ah battery, and about 8.5% for a 125Ah battery.  10%-13% is considered optimal for a full-time off-grid system.  Here's the formula I used (which I found on the forum to which my sig file links):

.77w/vh = r

v=charging volts (for 12V system, use 14.5)
h=battery capacity in Amp-hours
r=rate of charge (decimal fraction)
w=Array size in Watts

I've not visited the NAWS forums for a while, but a while back 5 to 13% of capacity was stated as the ideal for an off grid system.  Good to see they bumped up this rate.

While any solar is better than no solar, having too little for the amount of battery capacity is detrimental to the batteries compared to more for less.

I used to have 130 watts feeding 230 AH of storage, then 198 watts feeding 230AH of storage, and now 198 watts feeding 130AH of storage.

I am getting the best lifespan out of the single 130 amp hour battery, despite it being cycled deeper each night and I can only barely touch the 10% rate via solar.

Beware that some High$$ AGM batteries recommend extreme minimum recharge rates when deeply cycled.  Odyssey  recommends a minimum of 40 amps for 100 AH of storage, Lifeline says a minimum of 20AH per 100AH of storage.  Both these batteries say more is better, and that pretty much no charging source available to a consumer is going to charge at too high a rate for the battery to handle, as long as the voltage is controlled to no more than 14.7 for Odyssey and 14.4 for lifeline. 

Lower$$ AGMS can say no more than 30 amps per 100 amp hours of storage, which might mean they make a better solar only battery.  but a battery requiring a 40% rate minimum surely does not make for a good solar only deeply cycled battery.

As always, find the battery manufacturer charging recommendations and make an attempt to meet them.  If the charge rate via solar is well below the 10 to 13% recommendation, but there are other higher amp charging sources employed when the batteries are depleted, then this is better for the batteries and solar rates below 10% are more acceptable, but still far from ideal.

It is not just a matter of replacing the amp hours used plus some percentage, but meeting a minimum charge rate.

Some people act like the solar controller going into float mode before noon is wasteful, but this is actually best for the batteries, as it leaves a bigger buffer for worse weather, and Since most unprogrammable controllers are Timid in their charge algorithms, with absorption voltages too low and applied for too short a duration.  Amps required to hold float voltages are a mere fraction of what they are to hold absorption voltages.  So the batteries are screaming for more time at 14.X, and the controller ignores this chanting 'I know what's best for you' and allows 13.2v only. 

Almost all automatic charging sources, whether they be super 'smart' grid powered 11 stage chargers, or a 200+$ MPPT solar controller, Stop applying Absorption voltages well before the battery has reached the 99%+ range.

The person who can change the absorption duration and voltage has the happiest batteries, and this absorption duration is different among different batteries, and this also changes as they age, So No one size fits all charging algorithm will perfectly recharge any given battery.  The controller setpoints from the factory are timid, designed to not overcharge any given  battery.

Do not believe the flashing green light.  It lies to soothe you.

It is very easy to undercharge a battery, and then flash a green light to sooth the human, but actually fully charging a lead acid battery requires more for longer and a skeptical human, with a hydrometer, or an ammeter and a voltmeter to know when the batteries themselves would allow the soothing green light to flash.  

With Solar, more is Better, and just enough, only is, on the best days.  Less than Ideal starves batteries and can greatly impact their cycle life.

All charging sources possible should be employed/utilized to return lead acid batteries to the highest possible state of charge at all times, for best battery lifespan.  Alternator, Solar, and grid powered charging sources should all be utilized, and all can work together towards this goal of 100% state of charge, as often as possible.

This would be ideal, but the world is not, and few systems are, so don't stress achieving perfection, it is not as if the batteries will die in 5 cycles if not recharged ideally.  What one wants to avoid is chronic daily undercharging, and just believing the soothing but lying green light.

 

[AuricTech]

IIRC, the consensus over there is that the 5% charge rate is fine for a system that isn't used full-time. A weekend-use RV can easily get by for several days at that rate, but a full-time off-grid system needs more.