CPAPtalk.com

CapnLoki wrote:
If you can afford it, more power to you.

You're punny!

Our budget is $50K to be road ready - so the (used) RV itself, trailer for the car, solar/batteries, satellite internet equipment, whatever devices we replace, whatever else we need to buy for or replace in the RV. We're not rich by any means (only one income stream), but we think it can be done on this budget without making HUGE sacrifices.

Thanks again. You've been a massive help in making my options more clear to me. I'll abandon the expensive battery backup and explore those other options. I still need to read a lot more about how solar (and electrical systems in general) work and what all the numbers and terms mean, but this is a great start.

Taking advantage any charge source is good, but it takes several hours to charge a computer and in the end you've only taken in a few amp hours. A big house bank can accept much more power so you should really focus on keeping that happy. If you want to think emergency backup, remember the cars alternator can put 30-50 amps into a deep cycle backup battery.

CapnLoki wrote:Taking advantage any charge source is good, but it takes several hours to charge a computer and in the end you've only taken in a few amp hours. A big house bank can accept much more power so you should really focus on keeping that happy. If you want to think emergency backup, remember the cars alternator can put 30-50 amps into a deep cycle backup battery.

Good point about how long it would take to charge a laptop. I just read that the average laptop draws 72 kwh, but mine plugged into the kill-a-watt only draws 18-20 kwh - with the fan on normal speed and an ssd. The fan only spins up high when I'm doing something graphics intensive like Youtube or Netflix and all of our hard drives are ssd's. Maybe I'm more concerned about the power draw of these devices than I should be.

Here's another question you might be able to answer: Would it be better to charge while not using the device and then unplug, turn on and drain the battery before charging again, or would it be better to continuously charge during use? I guess that question also applies to all the portable devices - three laptops, iphone, ipad, android phone and tablet. Luckily, our car will charge even with the engine off so a phone could be charged without draining the car battery or require the engine to run. Would charging the laptop drain the car's 12 v?

CapnLoki wrote:

Randy in Maine wrote:...
My "house battery" is a "29 series" (pretty big and 66 pounds 845 amp hours) should go 40 hours or so without any re-charging.

You mean 845 cranking amps. A Group 29 has about 120 amp hours.

You are correct. That is 845 "marine cranking amps" whatever that it.

One more question about the laptop. I looked up Dc laptops, but if I'm understanding what I'm reading correctly, all laptops run on DC power and the AC from the wall is converted to DC in the power brick. Is that right? So what I need is not a laptop that runs on DC, but a DC-DC converter to change from the incoming DC current to the proper current for the laptop. Is that correct?

I am coming to this party a little late.
I also lived full time in my RV for 5 years and half time for 5 years before that.
I was never able to justify the cost of solar, but the cost has been coming down.
Solar panels come in many sizes from 15 watts to at least 250 watts each. So counting the number of panels is almost meaningless. You need to know the total number of watts in the system.
Same with batteries. I had six 6 volt Lifeline AGM deep cycle batteries for a total of 660 amp hours.
I usually ran the generator about two hours twice a day while my wife used the microwave to prepare breakfast and dinner. A lot more if we choose to run the air conditioning. Don't forget you may want cooling or heating much of the time.
I used my Resmed S9 with H5i and heated tube and my Everflo oxygen concentrator every night on our 2800 watt pure sine wave Magnum Invertor. We also ran 2 satellite receivers and a 26" and 32" TV. I had my desktop computer with a 19" monitor that was seldom turned off, there were no SSDs yet.

So if you go solar you will need to match the solar capacity to the battery capacity. A good place to learn about solar is solar bob's blog. Just Google it.
I am guessing a good solar installation of about 1000 watts would cost between $2,500 and $4,000 today not including the batteries. That would pay for at least 1,000 gallons of fuel for the generator. I averaged about 3 hours per gallon. So that would cover about 2 years of generator use. When I was full time solar cost double what it does now and fuel was cheaper most of the time.

So to sum it up you should invest in good quality deep cycle batteries. Do not buy automotive starting batteries or marine batteries. Get as many as you can squeeze in. The CPAP, computers and phones are trivial, most can use cigarette lighter adapter for power if you want to economize on power consumption.

I do agree with your husband on the 50" TV.

bwexler wrote:

I do agree with your husband on the 50" TV.

LOL. In the last few years I have gone from a full size tv to a small monitor to the lap top. Now I mostly use the tablet to watch online shows while I am knitting. The occasional glance up is sufficient for most shows.

BlackSpinner wrote:

bwexler wrote:

I do agree with your husband on the 50" TV.

LOL. In the last few years I have gone from a full size tv to a small monitor to the lap top. Now I mostly use the tablet to watch online shows while I am knitting. The occasional glance up is sufficient for most shows.

We literally only bought the TV last month before we hatched this hairbrain idea of going RV full time. I can't even think of where we would put it. Maybe if we were buying a massive class A, but we're thinking a 30-35' class C. So I think he's going to be disappointed... lol

bwexler wrote:I am coming to this party a little late.
I also lived full time in my RV for 5 years and half time for 5 years before that.
I was never able to justify the cost of solar, but the cost has been coming down.
Solar panels come in many sizes from 15 watts to at least 250 watts each. So counting the number of panels is almost meaningless. You need to know the total number of watts in the system.
Same with batteries. I had six 6 volt Lifeline AGM deep cycle batteries for a total of 660 amp hours.
I usually ran the generator about two hours twice a day while my wife used the microwave to prepare breakfast and dinner. A lot more if we choose to run the air conditioning. Don't forget you may want cooling or heating much of the time.
I used my Resmed S9 with H5i and heated tube and my Everflo oxygen concentrator every night on our 2800 watt pure sine wave Magnum Invertor. We also ran 2 satellite receivers and a 26" and 32" TV. I had my desktop computer with a 19" monitor that was seldom turned off, there were no SSDs yet.

So if you go solar you will need to match the solar capacity to the battery capacity. A good place to learn about solar is solar bob's blog. Just Google it.
I am guessing a good solar installation of about 1000 watts would cost between $2,500 and $4,000 today not including the batteries. That would pay for at least 1,000 gallons of fuel for the generator. I averaged about 3 hours per gallon. So that would cover about 2 years of generator use. When I was full time solar cost double what it does now and fuel was cheaper most of the time.

So to sum it up you should invest in good quality deep cycle batteries. Do not buy automotive starting batteries or marine batteries. Get as many as you can squeeze in. The CPAP, computers and phones are trivial, most can use cigarette lighter adapter for power if you want to economize on power consumption.

I do agree with your husband on the 50" TV.

Thanks for the blog suggestion. I will definitely look that up. There is a massive amount I don't yet know. My mom was an electrical engineer who designed her own solar power system, so I'm learning from her experience (and mistakes) as well. But all info is good right now as there is a lot to learn that I don't understand yet. I guess the fact that there are varying outputs per type of panel should have been obvious to me. lol

KatyDidAgain wrote: SNIP

I really know next to nothing at this point about power systems and feeling a little out of my depth. Do you run all those things at the same time on battery?

I could but usually didn't. Maybe one laptop, the wireless router, TV and sat receiver. That was pretty close to 180 watts which is about a 14 amp draw on the batteries. That is about 114 amp hours in 8 hours. I had two 6 volt (in series to = 12 volts) deep cycle Trojan batteries. 114 amp hours would drop the batteries to about 50 % which is the max amount of draw down for maximum battery life.

Dedicated boondockers often have as many as 6 or more batteries and 4 or more solar panels on the roof - sometimes with inclination remotely controlled so as to keep the panels at the best angle.

I would recommend that you join the following RV forums:
http://www.irv2.com/forums/f61/
http://www.rv.net/forum/
http://www.rvforum.net/joomla/index.php ... Itemid=104
http://www.rvnetwork.com/
http://rv-dreams.activeboard.com/forum.spark?aBID=91511

and visit this site - http://www.jackdanmayer.com/rv_electrical_and_solar.htm -
for a lot of info on solar by Jack Mayer. He frequents the irv2.com forum and is very knowledgeable.

ClayL wrote:

KatyDidAgain wrote: SNIP

I really know next to nothing at this point about power systems and feeling a little out of my depth. Do you run all those things at the same time on battery?

I could but usually didn't. Maybe one laptop, the wireless router, TV and sat receiver. That was pretty close to 180 watts which is about a 14 amp draw on the batteries. That is about 114 amp hours in 8 hours. I had two 6 volt (in series to = 12 volts) deep cycle Trojan batteries. 114 amp hours would drop the batteries to about 50 % which is the max amount of draw down for maximum battery life.

Dedicated boondockers often have as many as 6 or more batteries and 4 or more solar panels on the roof - sometimes with inclination remotely controlled so as to keep the panels at the best angle.

I would recommend that you join the following RV forums:
http://www.irv2.com/forums/f61/
http://www.rv.net/forum/
http://www.rvforum.net/joomla/index.php ... Itemid=104
http://www.rvnetwork.com/
http://rv-dreams.activeboard.com/forum.spark?aBID=91511

and visit this site - http://www.jackdanmayer.com/rv_electrical_and_solar.htm -
for a lot of info on solar by Jack Mayer. He frequents the irv2.com forum and is very knowledgeable.

Oh, thank you. Great info. I've already joined rvforum.com but didn't know of the others.

KatyDidAgain wrote:
Good point about how long it would take to charge a laptop. I just read that the average laptop draws 72 kwh, but mine plugged into the kill-a-watt only draws 18-20 kwh - with the fan on normal speed and an ssd. The fan only spins up high when I'm doing something graphics intensive like Youtube or Netflix and all of our hard drives are ssd's. Maybe I'm more concerned about the power draw of these devices than I should be.

Your numbers are off - laptops will take roughly 5 amps at 12V which is around 60 watts. The Dell XPS 13 I'm typing on now claims to use about 48 watts but the exact number will vary a lot. "72 kwh" is huge - equal to 72000 watt-hours or 6000 amp-hours at 12 volts. The would run my fridge for 3 months!

KatyDidAgain wrote:
Here's another question you might be able to answer: Would it be better to charge while not using the device and then unplug, turn on and drain the battery before charging again, or would it be better to continuously charge during use? I guess that question also applies to all the portable devices - three laptops, iphone, ipad, android phone and tablet. Luckily, our car will charge even with the engine off so a phone could be charged without draining the car battery or require the engine to run. Would charging the laptop drain the car's 12 v?

Good question. The process of recharging is only 85-90% efficient so I generally try to keep things charged which really means running off the supply, not the battery. Also, when there is a good charge source (genset or bright sun) I try to charge everything, figuring that there is probably juice being wasted. My teenage daughter, who is so much smarter than her ancient dad, insists that running the battery down keeps it healthier.

BTW, there is a new generation of high efficiency computers now - a mini form factor, about 5 inches square and an inch thick. They use laptop style processors and come in a range of powers. I got a Dell for my 95 year old father that is a simple browser at $129. But I built an Intel NUC version for my wife that has a i5 (also comes with i7), 16 gig memory, and a large ssd, with WiFi, cat5, hdmi+displayport. A very credible machine that runs off a 65 watt supply, but probably uses half that or less.

KatyDidAgain wrote:Good point about how long it would take to charge a laptop. I just read that the average laptop draws 72 kwh, but mine plugged into the kill-a-watt only draws 18-20 kwh -

while trying to figure all this out, it helps to make sure you understand, and use the terms right. else it can be very confusing.

I *think* you're meaning 72 watts, and 18-20 watts. a kwh is a KiloWattHour, a WattHour is a measure of total power used over time, one watt, pulled for one hour. so if you had your laptop on for an hour, it would use 18-20 WattHours, or .018-.020 KiloWattHours, since Kilo means 1000.

Volts electrical pressure, amps is the amount of electricity flowing, more needs bigger wires... watts is roughly amps times volts, so it's a measure of electrical power. and WattHours is a measure of electricity used, or, capacity, in the case of batteries. often times, batteries are specified as "amp hours" so to get watt hours, you have to multiply amp hours by the voltage of the battery, to get watt hours.

that's why amp hours of those little lithium battery packs can be so deceiving, since they're saying it's 10 amp hours, but they often mean at something around 3.5 volts, (the voltage of the internal lithium battery) not 12v which is what you really care about when trying to power a cpap.... so 10 amp hours at 3.5 volts is 35 watt hours, but if you compare that to a 12v battery, it's only 2.9 amp hours@12v. not enough for a cpap. (they often use marketing and say that the battery has 10,000 milliamphours, just to be able to use a bigger number, but that's 10,000 thousandths of an amp hour... or, 10.

KatyDidAgain wrote:Here's another question you might be able to answer: Would it be better to charge while not using the device and then unplug, turn on and drain the battery before charging again, or would it be better to continuously charge during use? I guess that question also applies to all the portable devices - three laptops, iphone, ipad, android phone and tablet. Luckily, our car will charge even with the engine off so a phone could be charged without draining the car battery or require the engine to run. Would charging the laptop drain the car's 12 v?

every time you discharge and recharge a battery, you eat away at it's life a little.

running lithium batteries down below half way takes way more out of their life than running them down half and charging them up again. last time I checked, for instance, a battery that said it's good for 500 full charge cycles would last for 1500 half charge cycles.

so, in the long run, it's better to charge while in use, so you're not running down the batteries and using up their life unnecessarily.

Full time RV you need a generator so just use your house batteries via 12v or an inverter. Add solar and you'll run the generator less often but you will still need it.