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Battery usage, while camping
(05-11-2017, 04:03 PM)BrassCat Wrote: Hello Hank, lets say you did draw 6.67h for 9 hours (how long do you sleep).
That wound be 60 amp hours per night. A 105AH 12V would be a very good battery, perhaps 90AH would be OK.'
You say you can recharge once a say? I take that to mean you can get the battery to a 120VAC outlet somewhere.
You might want to be able to put 65 to ~70AH back in. How many hours can you have the battery on a charger each day??

If you have a charger that can charge at a 10a rate, then 6 1/2  to 7 hours a day charging. Its hours times rate (amps). If you can only charge 4 hours a day you would need to charge rate of 17.5 amps, the higher the amps the lower the efficiency. 12 hours of charge at 5.8A. So it depends on how long can you charge it each day.

So, going to an auto parts store, you would need to pick a charger that will put out the current you will determine that you need. You can see a little 3A trickle charger is not going to have enough power.

Thanks for the reply. I can literally have it plugged in, all day, except when I'm sleeping. I'll check out some chargers that can put out more power. So you think that 105AH would be adequate?  I sleep around 7 hours, per night
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(05-11-2017, 04:05 PM)justMongo Wrote: The battery type is typically an SLA/AGM battery.  (Sealed Lead Acid / Absorbed Glass Mat)
I wouldn't discharge it deeper than 60%.  So, you'd need around 90 AMP hours.  That's a heavy battery.
That weight penalty is why most people run without humidity when off the mains.
You turn off humidity and you can use a 35 A-Hr battery.

If you have access to 110 VAC during the day.  You'll need a charger in the 6 to 12 Amp range.
6 Amps, means a 10 hour charge time.

You need to re-think the humidity question...  You'll probably pull about 2 Amps at 12 Volts for 8 hours running the blower only.  That's 24 A-Hr; and within scope for a 35 Amp-Hr scooter battery.
You can get down to 35 A-Hours and use a 5 Amp Deltran Battery Tender during the day.
The camping that I'm doing isn't any type of backwoods camping, so the weight isn't a big concern.

My fear, without the humidifier, is that for about two week, that would be a while running such dry air in. I've honestly never not used the humidifier, so I don't know how comfortable it is
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I've used passive humidification for 3 days and it wasn't too bad at all. A little dryer in the nasal passages than with full humidification, but tolerable.
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Hello justMongo, the SLA/AGM batteries are really nice sealed cells. With plain deep cycle batteries water might/will need be added with deep cycling for two weeks. But some SLA/AGM batteries have been injured by over charging, at least according to reports I have heard at a local auto supplier.  Seems they are most sensitive to that. Nonetheless, no out gasing, being sealed.

Hansk, sometimes I don't run the humidifier, until later at night when/if I feel dry mouth. It would be nice if the cpap /bipap only required 30% of max current without the humidifier running. I just have not measure it, I don't know how much the humidifier draws. but the higher the humidifier setting, the higher the amps.

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I made my own battery pack from one of my old motorcycle batteries, the battery didn't have the oomph to start my bike anymore, but it does run my Dreamstation with heated hose and humidifier for 5 hours before going flat. [in the near future I will get a slightly larger brand new AGM bike battery to get a full night's use on CPAP, the current one is for a smaller mid sized bike.. I am making a lead that will allow me to recharge the battery from the bike's alternator while it is in a saddlebag when I'm riding]

You could get any reasonable sized motorcycle battery [from a Honda Goldwing/Can-Am Spyder, or similar] or a small car battery to do the job.

Seeing as you won't be flattening the battery each time between recharges I'd go for a sealed AGM battery rather than a deep cycle battery.

The large motorcycle/small car battery will get you through a night without a problem using humidifier and heated hose.

You should be able to get the correct 12 volt DC cable from any good CPAP supplier, I paid $50 Au for mine from a company down in Victoria [Australia].

One of the great things about the PR Dreamstation is that they run on 12 volt, so no need for a 24 volt step up or 110-240V inverter as is needed to run the Resmed machines when camping or "off the grid" ..

You can also split the Dreamstation in half, thus removing the humidifier completely, and plug the hose direct to the back of the machine, it then disables the heating to the hose and runs without trying to activate the humidification.

I'd stay away from the Lithium batteries, if they are not charged with a specific charger for the individual type and size of the battery they can be prone to catching fire, as seen with the cases of hoverboards and mobile phones in news reports over the last year or so.
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Hi hansk,
WELCOME! to the forum.!
You could use humidity in passover mode by just turning your humidifier off and putting water into the water chamber. It won’t be full humidification, but it will be better than nothing, and you could use a smaller battery.
I hope your trip gose well and good luck to you as you continue CPAP therapy.
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I have been running solar & battery systems in vehicles for the past 15 or so years. Assuming the figure of 6.67 amps includes the level of humidification you want, then your choice of a 105 Ah battery is good. Essentially a 105 Ah battery has around 50 *useable* amp hour capacity if you want it to last a long time. You need a multi stage ‘smart’ charger with a ‘float’ function to bring it back to 100% charged each day. The minimum size of charger will be determined by the length of time you have available to have the battery on charge each day. Eg. if you know you can have it on charge for 6 hours a day, divide the (approx) 50Ah you need to put back in the battery by 6 = 8.3amps. In that scenario a 10 amp charger would do the job. A 7 amp would be undersized.

Ignore any advice which suggests deep cycle batteries are intended to be fully drained before recharging, it’s a persistent but damaging myth. Any discharge below 50% on a regular basis will shorten the battery life considerably. I recently sold a vehicle with deep cycle batteries still going strong at 10 years old. They had never been discharged below 70%. Regularly going below 50% can reduce this to 18 months.
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Most of the above responses assume that you are using the humidifier. The actual amperage draw is much lower if you do not use a heated humidifier and hose, and use a direct 12 volt DC input rather than an inverter. Without additional loads the actual current draw is:

P............amp dry.......amp wet (humidity 4)
6 cm ..... 0.7 ..... 1.73
8 cm ..... 0.79 ..... 2.00
10 cm ..... 0.93 ..... 2.30
12 cm ..... 1.06 ..... 2.61
16 cm ..... 1.23 ..... 2.33
20 cm ..... 1.66 ..... 3.44

As you can see, even with the humidifier, and maximum pressure you can use a 42 a-hr battery and still have a 50% safety margin. I think most of the above answers are including the inefficiency of an inverter, or assuming the AC power rating has a relation to DC power requirements.
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I used the 6.67 Amperes in the OP. I now assume the OP inferred that from 12 Volts, 80 Watts.
Sleeprider's current tables are much more realistic as to the current that will be drawn.

Admin Note:
JustMongo passed away in August 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
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(05-12-2017, 09:18 AM)justMongo Wrote: I used the 6.67 Amperes in the OP.  I now assume the OP inferred that from 12 Volts, 80 Watts.
Sleeprider's current tables are much more realistic as to the current that will be drawn.

12V 6.67A and 80W are on the back of the machine. No math involved, on my part

In a side note, thanks to everyone, for the advice. I now have some info to work with
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