Question for battery experts: proper inverter?

I've got a major 4x4 camping trip coming up in a couple of weeks. I have a deep cycle 50aH battery and one of those 18aH jump starters with ac outlet. I'd rather save the jump starter in case I need to do some actual jump starting, so I'm trying to make sure I have a suitable rig to run my cpap (without humidifier) off the deep cycle battery for maybe one, definitely not more than two, nights between charges.

I've already spent a ton on equipment and I'd rather not spend any more. Soooo ... what I have lying around the house is:

- the 50aH deep cycle battery
- a cable that has clips to attach to the battery on one end and a cigarette lighter-style outlet on the other
- a cigarette lighter inverter that claims to be rated 200w
- a trickle charger to charge the battery (and that I can plug into the ac outlets on my much larger inverter in my truck)
- AC adapter only for my APAP

I may try to mod a normal plastic battery box to make a pretty package, or I may just leave it as is.

My question is, can someone who understands batteries tell me if this set-up will work? I know I lose about 10% efficiency with the inverter as opposed to ordering a DC adapter, but will I still have enough juice to last a couple of nights? Finally, will a 200w inverter provide enough power to run the apap w/o humidifier?

That should work ... For atleast one night ... Not knowing what preasure you are running at ... 20 cm/h20 is a lot more of an electrical load than only 10 ...

ResMed has a chart about how much ahr's are needed per setting, which I presume would be simular to the PR useage ...

I've run mine WITH the humidifier on a 300w inverter without any problems ...

I know you said you didn't want to spend more money but consider these items. It will wrap everything up in one neat package. If you bump up to a larger battery you could possibly run the humidifier as well.

DC cable - no need for an inverter. https://www.cpap.com/productpage/respir ... -cord.html

Battery box w/cig adapter, fuse, and power gauge - http://www.walmart.com/ip/Minn-Kota-Tro ... r/20511018

Chris

Some people get 2-3 nights off those jump packs alone ... So you should be fine ...

Best sugestion is bring the battery and inverter into your bedroom tonight ... And try it! See how long you can go, then you will KNOW!

Great, thanks both of you for the answers. Sounds like I've got something that will work, even if not ideal.

Chris, you said:

ChrisD wrote: DC cable - no need for an inverter. https://www.cpap.com/productpage/respir ... -cord.html

Battery box w/cig adapter, fuse, and power gauge - http://www.walmart.com/ip/Minn-Kota-Tro ... r/20511018

Chris

My problem is timing as much as not wanting to spend. I'm American, but I'm on a two-year assignment in South Africa (the offroad trip is through South Africa and Mozambique). Through my work, I can have stuff sent from Amazon or eBay, but there's not enough time before the trip for me to get the DC adapter, and that kind of thing can be a real pain to find down here. Same with the Minn-Kota box - it looks awesome, and I really, really want one, but there's not time before my trip. I'll probably order both for the future though. The Minn-Kota box has got me thinking that with all the separate components I've got, there's probably a way to make a decent-looking box myself that would do the same thing - maybe from a mid-sized plastic tool box or something ...

Anyway, you've got me thinking. And thanks again for the answers - at least I know I've got something that will allow me to breath when I'm out in the middle of nowhere.

123.Shawn T.W. wrote:Some people get 2-3 nights off those jump packs alone ... So you should be fine ...

Best sugestion is bring the battery and inverter into your bedroom tonight ... And try it! See how long you can go, then you will KNOW!

Yeah, good point. I will test run it tonight.

BTW, do you think I could use another 12v cigarette lighter adapter to plug directly into the APAP (without inverter)? The one I have for my jump starter is the same size - but I'm afraid of burning something if I try it. I mean, they're both 12v, right? Are there certain specs for the official Respironics adapter that would have to be duplicated? Bad idea to even try?

The DC cable is very cheap insurance that you've got it right:
https://www.cpap.com/productpage/dc-pow ... hines.html
or the one previously linked, depending on the series of your machine.

Ziggy,

Read this thread viewtopic.php?f=1&t=37668&st=0&sk=t&sd=a I join in on the second page ...

If you have the right plug, you can put 12vdc right into the PRS1, that is what I do with my Semi-truck ... Been using it that way for 6 months!

ziggytosh wrote: The Minn-Kota box has got me thinking that with all the separate components I've got, there's probably a way to make a decent-looking box myself that would do the same thing - maybe from a mid-sized plastic tool box or something ...

The 4x4 trip sounds like the experience of a life time.

Look into this thread about building your own battery box. It has some great information. viewtopic.php?f=1&t=49115&st=0&sk=t&sd=a&hilit=battery

Chris

I am going to "third" the battery cable. Here's why: An inverter has it's own losses ... if you can run directly from the battery you'll get much more out of it.

My jump starter has a built in inverter. If your's does, you can get an IDEA (they're not super-accurate) of how many watts your machine is drawing. That's at 120V, so divide watts by 120 to get amps. Let's say it shows 120 Watts (that is probably a little high but it is an easy number to work with). 120 (watts) divided by 120 (volts) is 1, so 1 amp. On 12V (DC doesn't matter much to this), that 1 amp turns in to 10. (120 / 12 = 10.) So a 10 amp draw from a 50Ah battery should last 5 hours. (All of this is theoretical in that it assumes perfect efficiency, which is never the case).

If memory serves, my aPAP at around 16cm draws around 50-90 watts (it jumps up and down as I breathe ... very hard to get a fixed number). My jump starter lasts almost 8 hours. The battery in the jump starter is a 22ah battery. I used it overnight and it lasted just about 6 hours. So you're 50Ah battery should do the job for a night, possibly more depending on current draw.

Just out of curiosity I ran it with the humidifier to see what the extra draw was. That was over 400 Watts (!!), so 3+ amps at 120V, or over 30 amps at 12V (!!!!)

So humidifier and battery means BIG battery.

One last note: The jump starter takes 3 days to recharge, with a trickle charger as you are planning. That means you're not going to get a full recharge unless you use a more aggressive charger. In fact, I would prioritize a better charger over the DC cable.
-Kevin

Yeah, but ... My PR S1 Auto w/A Flex (model 550) Same as OP has ... Only draws a maximum of 5 amps at 12vdc, and the power brick says 2.1 amps at 100/240vac

My power cord has a 5 amp fuse in it, and it never has been a problem, so load is less than 5 amps, I'm using 10.5 cm H2O and humidifier set at 5 (highest)

On the back of the 560 with heated hose is only 6.67 amps at 12vdc

I'm not sure if that was in reply to my message, but 50 watts@120 volts is .42 amps, and would be about 5 amps at 12 volts ...

khauser wrote:I'm not sure if that was in reply to my message, but 50 watts@120 volts is .42 amps, and would be about 5 amps at 12 volts ...

Yeah it was ... Your math is a bit off ... Re-read this:

khauser wrote:I am going to "third" the battery cable. Here's why: An inverter has it's own losses ... if you can run directly from the battery you'll get much more out of it.

My jump starter has a built in inverter. If your's does, you can get an IDEA (they're not super-accurate) of how many watts your machine is drawing. That's at 120V, so divide watts by 120 to get amps. Let's say it shows 120 Watts (that is probably a little high but it is an easy number to work with). 120 (watts) divided by 120 (volts) is 1, so 1 amp. On 12V (DC doesn't matter much to this), that 1 amp turns in to 10. (120 / 12 = 10.) So a 10 amp draw from a 50Ah battery should last 5 hours. (All of this is theoretical in that it assumes perfect efficiency, which is never the case).

If memory serves, my aPAP at around 16cm draws around 50-90 watts (it jumps up and down as I breathe ... very hard to get a fixed number). My jump starter lasts almost 8 hours. The battery in the jump starter is a 22ah battery. I used it overnight and it lasted just about 6 hours. So you're 50Ah battery should do the job for a night, possibly more depending on current draw.

Just out of curiosity I ran it with the humidifier to see what the extra draw was. That was over 400 Watts (!!), so 3+ amps at 120V, or over 30 amps at 12V (!!!!)

So humidifier and battery means BIG battery.

One last note: The jump starter takes 3 days to recharge, with a trickle charger as you are planning. That means you're not going to get a full recharge unless you use a more aggressive charger. In fact, I would prioritize a better charger over the DC cable.
-Kevin

You will be hard pressed to find a PRS1 that draws 30 amp of 12vdc! Mine has been running with a 5 amp fuse for over 6 months ... 10.5 cm H2O and humidifier set at 5 (highest) never blown the fuse ...

PR tech told me to use a 300w power inverter for my 550 model ...

ziggytosh wrote: - a cigarette lighter inverter that claims to be rated 200w
- a trickle charger to charge the battery (and that I can plug into the ac outlets on my much larger inverter in my truck)

As has been said, the trickle charger won't be enough. You need a real charger.

You need to check to see if your 200w inverter is square wave or modified sine wave, and what your CPAP power supply requires. If the inverter is square wave and the CPAP needs true sine wave or at least MSW, you've got a problem. In that case the DC power cord is the better choice. You should be able to find one in S Africa. Respironics are sold world wide.

I called PR about using my PRS1 in my truck with an invertor, the tech told MSW (modified sine wave) was fine recomendd s a 300w ... But if your not using a humidifier ... The 200 should do, as long as it is not square wave.

The power brick only draws 2.1 amps, so a tad more than 250 w, and that I'd able to power the humidifier too.

Best thing is to just try it.