New Camper - Need Help Learning About Batteries

Hi folks,

I have not gone camping for six years, since I was diagnosed with sleep apnea. I used to love it and want to do it again. My partner (who also uses CPAP) and I would both like very much to go *car* camping with some friends who are going this month, but we need to be able to use our machines and the campground has no power. I'm okay with math, but I don't understand much about electricity and all the detailed posts talking about specific setups and volts, amp hours, percentages of power lost in conversion feels very overwhelming without some basic understanding on my part. I've spent a few hours muddling around on this site, and thought maybe it would get me somewhere if I asked for help.

Questions!

1. Is there a good primer somewhere that would help a total newbie understand enough about electricity to make decisions about CPAP batteries? I would love to read that blog / forum post / book / etc! For example, I can read the info on my machine (it tells me my 90% pressure is 12.5 / 10.5), but I don't know how to calculate how many amp-hours I need. I'd like to learn how to do this for myself.

2. Battery type: I understand there are different types of battery. I'm interested to choose something that balances cost and longevity so we can go camping a lot. Since I'm car camping for two machines, and hoping to go a few times a year, should I just go heavy and cheap? AGM sounds nice, since I don't want to worry about leaks or dangerous fumes in the tent around my 3-year-old son.

3. Recharging: If camping at our site for five days (with two machines), should I expect to recharge from my car? It seems like that would annoy everyone else in the campground--is that really what people do? Will I have to take my battery out for a drive? Or, is it reasonable to think we could recharge our batter(ies) using a solar panel?

4. How much energy do I need / what are the salient numbers to consider for purchasing a battery? I've seen the 100 amp-hour Walmart battery option mentioned here--would I need two of these? I don't live near a Walmart, but I'd look on Amazon or maybe at Fred Meyer.

5. If I can't figure it out, is there a business I can go to and receive help with this? Radioshack? Right now I feel like I'm pretty far out of my depth!

Go up to the Search line (above) and put in things like "batteries", "camping", etc.

MANY, MANY discussions of it in the past.


Den

.

1. Search the forum for threads on this, there are many.

2. I use AGM. More expensive than regular flooded lead acid car type battery, but allegedly provides more charge cycles, more tolerant if deep discharged (but avoid that anyways) and no leaking fluids. Overcharging will kill them quickly - they will vent hydrogen like any car battery when overcharged - so for home charging you should use a charger that has an AGM setting and is not oversized for the battery you're charging.

3. Solar panel might be enough but can be expensive, the sizes are all over the place, and you need sun. If you use a panel that is larger (output of like 40-50+ watts) you would probably want a charge controller with it which acts like the special battery charger in #2 above to avoid overcharging. It gets a bit more complicated.

4. Note that Amp Hours are not the same as "reserve capacity" with these batteries. Reserve capacity is how many minutes a perfect condition car battery will deliver 25 amps until it's dead. With no heated humidifier my PRS 560 machine draws no more than 10 watts at a pressure of 12 - less than one amp per hour. You can test your machine using a Kill-a-Watt to get the actual power draw of your machine(s).

5. Bottom line is you could get away with one decent sized battery without heated humidifiers, maybe 50-60 Amp Hour capacity if you can top off the charge every day or two or three. I use a smaller battery when camping but I am one person/one machine and I top off the battery daily in direct sunlight at the peak of summer with a 27 watt solar panel.

sleepynina wrote:Hi folks ...
1. Is there a good primer somewhere that would help a total newbie understand enough about electricity to make decisions about CPAP batteries? I would love to read that blog / forum post / book / etc! For example, I can read the info on my machine (it tells me my 90% pressure is 12.5 / 10.5), but I don't know how to calculate how many amp-hours I need. I'd like to learn how to do this for myself.

Read all of my posts! Most of them concern battery power, with the focus on lead-acid (as opposed to lithium) based on my experiance living off-grid for extended periods over the last 20 years.

In particular, in this post I measured the battery usage of various configurations of humidity:
viewtopic.php?t=102179
And this thread where I talk about the setup for a backup system, though I would use a different battery for this application
viewtopic.php?t=102775

You don't mention the model cpaps you're using - this is significant. If Respironics, you can use a 12V cable since it runs on that. Resmed uses 24V, so you should get a 12/24 converter which costs about $85. Otherwise, you'll need an inverter - 150 Watt will do (assuming you don't use humidity) but they run at about 60% efficiency so you'll need almost twice the battery!

For Resmed you could use this guide:
http://www.resmed.com/us/dam/documents/ ... lo_eng.pdf

sleepynina wrote:2. Battery type: I understand there are different types of battery. I'm interested to choose something that balances cost and longevity so we can go camping a lot. Since I'm car camping for two machines, and hoping to go a few times a year, should I just go heavy and cheap? AGM sounds nice, since I don't want to worry about leaks or dangerous fumes in the tent around my 3-year-old son.

Tough choice - I use flooded golf cart batteries on the boat (stashed in a locker and the most bang for the buck) but AGMs at home where they get moved around and live in the house. AGM's also have a low "self-discharge" making them ideal for occasional backup. New marine flooded deep cycle are sealed fairly well, but "maintenance-free" really means you can't maintain them, so they'll probably need replacement in 4-5 years regardless of usage.

Its a toss-up - you probably won't regret AGMs if they price doesn't kill you.

sleepynina wrote:3. Recharging: If camping at our site for five days (with two machines), should I expect to recharge from my car? It seems like that would annoy everyone else in the campground--is that really what people do? Will I have to take my battery out for a drive? Or, is it reasonable to think we could recharge our batter(ies) using a solar panel?

First on solar - as I write its overcast, so my solar panels are only putting out about half what they would on a sunny day. The rough rule of thumb is assume 4 hours worth of full power for average summer weather. So a 50 Watt panel would put out 200 watt-hours or about 16 amp-hours, assuming dawn to dusk sun exposure. So it depends on your location. In any case, on a rainy day you're screwed, so you need a backup.

Most car alternators will put out 30-50 Amps running at a high idle - that is reved up to around 1200 RPM. This would mean sitting with your foot lightly on the gas At low idle the regulator usually doesn't turn on. You should see a volt meter jump up from 12.5 to around 14 volts when you're charging. The nice thing about a large battery is that they can accept a high current, up to about 25% of the capacity. So in ideal conditions your 100 amp-hour battery would accept about 25 amps. Topping off the battery is tedious, however, and for maximum life you don't want to go below 50%, so the sweet spot for offgrid usage is to discharge down to 50%, then recharge to 85%. Occasionally going down to 30% won't hurt too much, and you should fully charge the battery every few weeks. You should be able to follow this regime by charging for about an hour every day or so, depending on usage. It shouldn't be too noisy to idle the car for an hour. If you can drive it around it will go a bit faster. If you need more than about a third of the battery capacity every night, you need a bigger battery, and maybe a bigger charger.

sleepynina wrote:4. How much energy do I need / what are the salient numbers to consider for purchasing a battery? I've seen the 100 amp-hour Walmart battery option mentioned here--would I need two of these? I don't live near a Walmart, but I'd look on Amazon or maybe at Fred Meyer.

Amp-hours is the important number. Also, make sure its a "Deep Cycle." "Marine" does not imply deep cycle as there are marine starting batteries. "Dual purpose" batteries are a bit of a scam - once you design for starting, its going to be more fragile for deep cycle - but that's what you get at Walmart. Still, at $80 for 100 AH its not bad.

The pump will use between 0.5 and 1 Amp but an inverter will almost double that. Humidity could triple that, and a heated hose also hurts. Unless you're in a desert, you shouldn't need the comfort features outdoors - I don't bother taking the humidifier on the boats or on trips to most locations.

sleepynina wrote:5. If I can't figure it out, is there a business I can go to and receive help with this? Radioshack? Right now I feel like I'm pretty far out of my depth!

No. This forum is the best place for real advice. You just have to remember that this is more of an art than a science, and half the advice is hearsay. Also, it helps us a lot if you would fill in the equipment info in your profile, and roughly the location you'll be camping in.

Sleepynina is showing a PR System One 60 series BiPap Auto in her signature line.

Thanks so much for the replies. I've been reading and reading and reading threads on here (maybe 16 hours of reading; I'm not joking), though I think I started with older threads. I have come across CapnLoki's setup and it looks like something I could modify for our needs. I'm sure I haven't understood everything I've read though!

As for cables, I've already ordered two Respironics cords from cpap.com, one for the 60-series I use, and one for the 50-Series PR System One that is my backup, but which my partner will use--adjusted to his pressure settings--while camping (he normally has Resmed, and he doesn't want to take it camping).

I understand that we won't be able to use humidity. I don't think that will be a big sacrifice, compared to the extended time outdoors I've been sacrificing for years now.

Here are my big questions that remain, unanswered by my reading thus far:

Double Access: How do I set this up for two people: can we both run our machines off the same battery? Would that cut the amps each of us draws in half or something, or does it not matter as long as the battery doesn't have a flow restriction on amps? (If this is a ridiculous question it is because I don't understand electricity).

Can I just plug each of our cables into a splitter like this? Car Mate http://www.amazon.com/Car-Mate-CZ206A-A ... e+splitter

Batteries: I'm looking hard for the least expensive AGM options around Seattle. I tried Costco and didn't find anything there, though maybe I just became faint from hunger before I found it. Tomorrow I'll call a scooter supply store to see if they have ideas.

What I've found online is these:

Schumacher SB 12350 '12V' 35Ah AGM Sealed Lead Acid Power Sport Battery - $61.75
http://www.amazon.com/gp/product/B009II ... PDKIKX0DER
I like these batteries because I could lift them myself--good if I don't want them in the living room forever after our trip. I thought I might get 3 or 4 of those. Then I need to wire them in parallel, I guess? I don't know what that means. I picture myself blowing up the tent. Assuming that didn't happen, at home would I be able to keep them charged as a bank by having them wired up together and attached to a single trickle charger? Or would I have to purchase as many trickle chargers as batteries?

Schumacher SB 12750 '12V' 75Ah AGM Sealed Lead Acid Power Sport Battery
http://www.amazon.com/Schumacher-SB-127 ... acher+75ah
I could get two of these, one for each sleeper, and just keep them separate. Maybe that is the simplest? I'm not sure whether I can lift the 50 pounds though.

Oh, and my campground will be in the Pacific Northwest, at 1,243 feet elevation.

Other details... since I'm just guessing energy needs, I got myself a KillAWatt. Tonight I'll see how much juice my machine uses without humidity.

OK - First with humidity - you probably won't miss it in the Pacific Northwest. Also, the Respironics pumps are the best: they run on 12V and are efficient. As a first guess I would say 6 Amp-hours a night.

I like the 35 Amp-hour AGM batteries. They are size "U1" and can commonly be found as scooter batteries. At 24 lbs they can be carried easily. Although the can be setup in parallel, this causes issues unless they are always used in the same configuration. If your plan would be to sometimes use one, sometimes two, etc, it might be better to just use them one at a time. Charging mismatched batteries together is not quite so bad, although ideally they should be at a similar charge level since the regulator is trying to match a charge voltage to the charge state.

If your two pumps use 12 AH a night, a 35 AH battery should go two nights. Using the "bottom third" of the battery would lead to a premature death. So three of these batteries should easily handle 5 nights. If you need to charge, you could recover one night's charge in a little over an hour. Actually, if your car has a reasonable sized alternator, it could probably handle two or maybe even three batteries at a time. Topping off the batteries is more of a problem, it can take several hours or more to get the last 15%. After a trip they should be left on a charger at least overnight so they will not sit partially charged for a long time.

A large battery - 75 to 100 AH (50 to 60 lbs) simplifies everything. You might not need to charge at all, and the large size means it can accept a lot of amps quickly. If your tent is near the car you could leave it in the trunk and run a wire to the tent for both pumps.

Running two pumps off one power source is no problem at all. The double socket would work, but I've found stacking up sockets like that leads to flaky connections. If you wire the BatteryTender cables you can get a 1-5 splitter and put several sockets on it, or even a few USB chargers. When you want to charge at home, plug in a BatteryTender to one of the outlets - it can charge while you're running a pump so it acts as an Uninterupltible Power Supply! However, if you have several small batteries with the BatteryTender cables, make real sure you don't connect them together - that would pop a fuse faster than you can say OOOPS! And on the subject of safety, although the AGM batteries are very safe, if you short one out, say with a screwdriver across the terminals, they will instantly pass a HUGE amount of current - enough to melt said screwdriver! Ideally they should be kept in a box, but at the very least rubber "booties" or even electrical tape over the terminals is needed.

Once you decide on the battery setup, I can advise on wiring details. I will be travelling a a lot over the next few days and my marginal wifi on the boat frequently goes to zero, so you might have wait a day or so for a reply.

Thank you CapnLoki, from the bottom of my heart. I have been feeling pretty lost and bewildered, while scrambling to get the hang of this. I hope you enjoy your next few days of travel!

I like the 35AH, less heavy batteries. I'm not sure we'll be parked very close to our tent on this trip, and for another, I don't want to throw my back out carrying these! I think I'll order the Schumachers today. I'll be getting a box for each battery, as I'm a little terrified of the batteries and want them as safe as possible. If I didn't, it's entirely possible that my 3-yo would try to hammer them, especially if I told him not to.

But, how many Ah of batteries do I really need? I had been assuming that I needed to plan 2 amp-hours per hour of use, 16 Ah a night to cover me and my partner sleeping eight hours each, x 4 nights = 64 Ah of combined use, with a larger Ah amount in battery needed to avoid over-draining without a recharge. This is probably the longest camping trip we'll take together--the longest time I'd need to go without a recharge. If we go longer, we'll probably try to figure out a recharge option.

To get more info, I used my KillAWatt last night with passover humidity (I feel fine!) and got 0.04 kWh for 8 hours of use (unlikely that I'll sleep that much while camping with a 3yo though).

I found a formula that says:
kWh = Amp hours x voltage / 1000

I solved this to
1000 x 0.04 kWh / 12v = 3.33 amp hours (for a whole night of sleep!)

I rounded up my kWh to 0.05 for a safety margin and got 4.17 amp hours. That suggests I alone might go 4 nights and use about 17 Ah, safely discharging a single 35Ah battery only half way. Doubling this for my partner, we'd use 34 Ah, or two 35Ah batteries for our 4 nights. (His pressure is lower than mine, so maybe uses even less juice). Do my numbers look right?

Might we truly handle the 4-night camping trip with just two 35 Ah batteries? That would be great news to me, if true, but I'm wondering if I made a mistake somewhere.

The idea of recharging my batteries off my car alternator, or recharging them simultaneously, is the most intimidating to me. I just have no idea how to set that up, and I'd be worried I might somehow overcharge my AGMs too. Would I need to sit with my foot lightly on the gas pedal for an hour, to keep the car at 1200 rpm? My car is a 1999 Buick LeSabre; I don't know its alternator size but I know someone I can ask.

I think the 3.3 AH per night is a bit optimistic. I consistently measure about 4 AH for my PRS1 560 at pressure 9, so I would have to think your BiPAP takes more. However, even at 6 AH one 35 AH battery should go 4 nights with a reserve. To be conservative, you would want to run both pumps off of one battery. If it goes 2 nights, you can be fairly sure the other one will do the same. This also gives you the option to charge the first during the third or forth day. If you run both simultaneously, they could both die in the forth night!

The Buick certainly has a big enough alternator; the only way to tell about the gas pedal is to put a volt meter on the battery (or the socket) and measure it. Perhaps you have a neighborhood nerd who is handy with a meter? Or maybe you should get something like this:
http://www.amazon.com/Cigarette-Lighter ... B00UCEAKYU
If you have to rev the gas to get the voltage up to 14 (14.4 is ideal) perhaps on the third day you drive to an ice cream stand!

If we setup the wires properly, it should be fool proof. You want it so if you have to swap batteries in the middle of the night, there is no wrong way to plug it in. Again, the neighborhood nerd could be a handy resource!

Something like this should do the trick for charging:
http://www.amazon.com/SOLAR-ESA1-Male-O ... title_auto
I don't think you would over charge with an hour or two on the alternator. Overcharging is a problem when it continues for days. This is why I use a trickle charger like the BatteryTender if I want to leave it on for a long time.

Got it CapnLoki; I won't rely on my one-night estimate, and will go with yours instead. For the future, would a week's average measured with the KillAWatt likely be accurate, or should I just abandon the KillAWatt for energy-use calculation purposes?

I ordered my first 35Ah battery today, but Amazon won't let me get two with Prime, so I might have to find another source for the second one this week. The scooter store I called today was no help, but I'm sure there are others I can try on Monday.

Stuff I have ordered so far:
Respironics 50-series cigarette adaptor https://www.cpap.com/productpage/respir ... -cord.html
Respironics 60-series shielded cigarette adaptor https://www.cpap.com/productpage/dc-pow ... hines.html
Battery Tender Junior https://www.amazon.com/gp/product/B000C ... UTF8&psc=1
Battery Tender-style 5-Way Adapter Connector http://www.amazon.com/gp/product/B003L6 ... ge_o00_s00
Battery Tender Female Cigarette Adaptor (x 2, for 2 machines) https://www.amazon.com/gp/product/B0041 ... UTF8&psc=1
Voltmeter / Multimeter https://www.amazon.com/gp/product/B00TW ... UTF8&psc=1
Male to Male 12V Charger Outlet Cord (for car recharging) https://www.amazon.com/gp/product/B000G ... UTF8&psc=1
Schumacher 12350 35Ah Deep Cycle AGM Power Sport Battery (still need another) http://www.amazon.com/gp/product/B009II ... ge_o01_s00

Yet to buy:
2 x Battery Boxes
2 x Pairs of battery terminal covers
Faster charger (??)

Charger Question: If my battery arrives only the day before I need to leave, and I need to charge it up, should I buy a faster charger with which to do this? I bought that Battery Tender Jr. a few days ago as I began this process, but now I'm concerned it won't charge my battery fast enough. I have never experienced a power outage in Seattle, let alone repeated outages, so I guessed the Jr would be enough for me to charge up between trips. Could I realistically expect to charge my batteries on car cigarette outlet during the 2-hour drive to the campground?

Alas, I don't have a friendly neighborhood electrical/mechanical nerd to call on for any of this (all my nerds are the code-writing kind). I feel extra thankful to receive this support here!

Make sure you have spare fuses of correct type and amperage for anything that has fuses in it, like the cigarette lighter adapters for example.

Your batteries should arrive with plenty of charge, I would think 80% or more. If they discharge below 50% either on the shelf in a warehouse or during use their capacity will be diminished and life span shortened. You should have no problem if you put them on the charger to top off the day they arrive. An important thing when purchasing an automotive type battery is the date it was manufactured. There's a date stamp somewhere on the battery case. I don't accept any that are more than a few months old because there's a greater chance they've discharged or gone dead on the shelf at some point. AGM are better in this regard since they discharge more slowly when in storage. I have been sold a dead battery before and won't let that happen again!

I have a few of the Die Hard batteries below around in case of power failure or whatever. They are kind of dual use since I have vehicles that use this same size Group 35 battery.

http://www.craftsman.com/diehard-platin ... ckType=G29

I'm not going to get into this thread again as it's posted monthly or more, and the mis-information presented is huge. I'll just add one thing everything you put in your car that isn't secured properly, becomes a projectile in the event of a wreck. Jim

Goofproof wrote:I'm not going to get into this thread again as it's posted monthly or more, and the mis-information presented is huge. I'll just add one thing everything you put in your car that isn't secured properly, becomes a projectile in the event of a wreck. Jim

I'm not seeing the huge misinformation in this thread, but I do agree about the projectile thing.

1. The math

2. Comparing Apples and Oranges

3. Confusing A/C and D/C, wattage and the power to run each

4. The fact you are running two machines and what they draw on d/c

5. A battery tender is to final charge batteries (top off) keep at full charge safely when stored.

6. A real battery charger is needed to recharge batteries, using a car isn't efficent, as the voltage is limited to 14 to 14.8 volts, to charge a battery fast takes higher volts. A small gas generator running a 110 volt battery charger of the correct size, is the way to recharge, but even that will take time, as the last 1/4 of the charge is slower. If used you bring another whole can of worms to the picknik. (Gas oil, bother ect.) They make storage alu 2 wheel carts, that are nice to carry the load.

The good thing you are power friendly machines.Resmed's aren't camping frendly. Jim

Goofproof wrote:1. The math

You'll have to be more specific.

Goofproof wrote:2. Comparing Apples and Oranges

You'll have to be more specific. I saw no mention of either Apples or Oranges

Goofproof wrote:3. Confusing A/C and D/C, wattage and the power to run each

There was no mention in my posts about A/C - this is all D/C.

Goofproof wrote:4. The fact you are running two machines and what they draw on d/c

If one machine draw 4 AmpHours a night, two will draw 8. Its really that simple. I've measured mine with AmpHour meters many time. We can only guess what the other units use, but they shouldn't be too far off.

Goofproof wrote:5. A battery tender is to final charge batteries (top off) keep at full charge safely when stored.

Its true that the primary design of BatteryTender is as a maintenance charger for larger batteries. This means that they can be left connected for a long time and will not overcharge. However they are a well designed multistage charger that put out the full voltage at their full current until the battery is near full so they can charge a battery, albeit slowly. If these were large flooded batteries, the self-discharge might overcome the low output of the BatteryTender Junior, but with small AGM's with low self discharge it will just take time. That said, I usually recommend (and have) the medium size BT that puts out 1.25 Amps, and it works just fine.

Goofproof wrote:6. A real battery charger is needed to recharge batteries, using a car isn't efficent, as the voltage is limited to 14 to 14.8 volts, to charge a battery fast takes higher volts. A small gas generator running a 110 volt battery charger of the correct size, is the way to recharge, but even that will take time, as the last 1/4 of the charge is slower. If used you bring another whole can of worms to the picknik. (Gas oil, bother ect.) They make storage alu 2 wheel carts, that are nice to carry the load.

What total NONSENSE!!! Are you actually claiming that the charging system used on over a billion cars doesn't work?? First of all, a 35 AH battery can only accept at most 10 amps while recharging, so using a Buick or a small generator is by definition "not efficient" and is huge overkill. Second, AGM batteries should not be charged at much over 14.8. Check out the specs for these two AGM batteries:

http://www.trojanbattery.com/pdf/datash ... Sheets.pdf
http://upgi.com/Themes/leanandgreen/ima ... /D5722.pdf

As I said several times, the goal when recharging deep cycle batteries in the field is to bring a battery up to about 85% charge. The can be done in about an hour to an 1.5 hours, depending on where you start. Going above 85% is tedious, and can take overnight or longer with any charger. The little "Junior" charger will take several days to bring up a U1 battery, but it will get there. There is plenty of time after the trip to top off.

Goofproof wrote:The good thing you are power friendly machines.Resmed's aren't camping frendly. Jim

True that.