LifePO4 vs AGM Batteries

[cdnred]

Since this seems to be a CPAP thread, I will chime in too. 156Ah LiFePO4 battery (soon to be 246 with the addition of a second 90Ah battery). My ResMed unit is 24 volt and runs at about 65 watts (about 5 amps at 13.2V) on its 120VAC power brick. I have an inverter that can run it easily, but I am wondering if anyone has any solutions for converting 12 to 24 volts to run a CPAP? There is no car charger for my unit because of the voltage difference. I know DC-DC converters exist, but would they be any more efficient than my Victron Phoenix inverter? I like the idea of getting a non heated hose to save power while camping.

That's interesting. I had the DreamStation for just about 5 years until they had the recall. At 5 years old, they refurbished the CPAP for me so it's like new again with no issues. My next CPAP that I got this past summer was the ResMed AirSense 11 which I love. It's the same as yours 24v but since my older DreamStation was rebuilt, I just use it solely for camping with the 12v adapter cord. I don't have a clue on how you could run the 24v on a 12v system other then going thru a 120v convertor. Have you tried contacting ResMed directly about this..?

The ResMed Technical Care Team can be reached at 1 (800) 424-0737

[cdnred]

Mine reads 12 VDC, 6.67A

Mine is the same, but it uses much less than that (I can't recall how much) when I dump the stock tubing.

Tony

It seems that even though it lists 6.67a, it must operate much lower. Since you can run it on your 70ah (35ah usable) battery with no issue then I shouldn't have any issues running mine off my 40ah LifePO4..

I was under the impression that I could connect my 40ah LifePO4 in parallel with a future 100ah LifePO4 down he road to give me 140ah. After contacting a couple dealers that sell them, they recommended against it claiming that I wouldn't be able to achieve the 140ah..

With your solar panel, did you need to add a separate MPPT Solar Charge Controller to the mix to be able to recharge your battery..? Gonna need another TD just to store and run all the electrical..

[RJ Howell]

I had been thinking about solar panels for awhile. They seem to be rather expensive right off but I'm sure that with some digging around better bargains can be found.

With the solar panels I'd need to install a separate DC/DC - MPPT Solar charger in addition to the 12v 20a DC-DC charger..?
Helmuth

I bought a suitcase style and love it for ~$100. If you want that charging on the road, then mount a panel like Tony shows. I'd still have the suitcase one as you can redirect it or park in the shade and put the panel only in the sun.

My Atempower is an all in one. Charges either way, solar/ or truck and switches according to power supplied. No additional hardware/electronic's required. It also well once the house battery is full, trickle charge the truck battery.
I mention the separate solar charger just as a less expensive means to charge as those are far less $$ than a DC/DC charger.

[RJ Howell]

I was under the impression that I could connect my 40ah LifePO4 in parallel with a future 100ah LifePO4 down he road to give me 140ah. After contacting a couple dealers that sell them, they recommended against it claiming that I wouldn't be able to achieve the 140ah..
:

Missed this.. Like all batteries, when daisy chaining the flow like the least capable. To obtain that 140ah you'd have to switch from one to another. That would be a PITA when it comes to charging!
Value for cost is 100ah and higher, but stay in the range you can afford and build up with the same size.

IMHO

[italianub]

I've seen lots of "car charger" cables for the airsense 11 (I also have this) but am not sure which one to get for when my build is done. This one I've seen has good reviews but not a lot of them. Anyone with the same machine have success with any specific adapter?

https://www.amazon.com/HKY-Replacement- ... B0BYJ7NKM4

I too, use a CPAP. I saved a lot of juice (roughly 20%) by getting rid of the 120-volt cord and going with a 12-volt adapter cord. The other thing, I leave the heated tube at home and have a tube with a fleece sleeve. That saves amps... lots of amps. As in a third the power needs.

I run a group 24 AGM in my teardrop but bought a Weize 50 amp LiPo for my drift boat trolling motor. When I bought the AGM, lithium batteries were too expensive. Financially, it didn't compute. Times have changed, when the AGM dies, I'll stick a LiPo in the 'drop.

Tony

Which brand do you have?

[tony.latham]

Which brand do you have?

The Philips Dreamstation.

Tony

[Pmullen503]

.........
I was under the impression that I could connect my 40ah LifePO4 in parallel with a future 100ah LifePO4 down he road to give me 140ah. After contacting a couple dealers that sell them, they recommended against it claiming that I wouldn't be able to achieve the 140ah..
.........

You can connect batteries in parallel if they are the same chemistry, even if they have different capacities. They should be in good condition, ie both charge and discharge normally to their rated capacity. Off grid home battery systems are often massively parallel with a dozen or more batteries.

[cdnred]

Went out shopping today and bought a Victron Tr Smart 24/12-Volt 20 amp 240-Watt DC-DC Charger ($169), Victron Smart Battery Sensor ($39) both with Bluetooth, fuses and cables. I was looking at the store's 100w solar panels which were at a good price ($139 each). The owner recommended getting one fixed flexible 100w panel to mount on the roof and one portable 100w panel that can be moved around similar to Tony's setup. He claimed panels to be roughly 70% efficient for their rated capacity. Having one panel being portable would help for greater efficiency by following the sun. I'd also need to get a MPPT Charge Controller (about $150-$160) to add to the battery setup..

For mounting everything on a panel, what kind of material did you use for a backing plate. If there's a lot of heat being generated, I'm think a plywood backing plate may not be a wise choice and the same would be for a sheet metal panel..

I mentioned that I was planning to mount everything near the battery in the front tongue box. He recommended installing a couple of vents on each side plus 2 more in the lid to ventilate the heat that's generated with the vents being about 3x3 in size. Have other run into heat issues where they've mounted their chargers and controllers..? Do you feel that with the heat generated that vents are a necessity to have..? If you did add vents, did you notice a big improvement..?

Helmuth

[tony.latham]

If you did add vents, did you notice a big improvement..?

My PWM controller is in the galley. It's never felt warm. He's right on the 70%.

For mounting everything on a panel...

My rigid (glass) panel is mounted on the surface of my tongue box with aluminum angle iron. The flexible is also on the surface of the roof. The glass panel gets hot, and the flexible is just slightly warmer than the roof surface, probably because it's darker.

The problem with adding roof-top solar panels is running the cables after the fact.



I designed a solar system into my build for the book. Note the space behind the panel that's left open for the cables.



You might consider a 200-watt folding solar system that incorporates the controller. You'll have to figure out where to carry it, but on the bed will work. There are several out there. It's an easy deal to install a connector to plug one in.

Tony

[cdnred]

The problem with adding roof-top solar panels is running the cables after the fact.

That's a good point..!! To incorporate solar panels into a new design and build would make the install much easier and more efficient. With a retrofit like mine it maybe better and easier just to get a 200w portable solar panel setup that could be easily moved around then put away when not used. I hate the thought of having loose wires or cutting holes that could cause issues.

Thanks for pointing that out.. I'll need to look into that further and see what I can come up with..

[Tom&Shelly]

The problem with adding roof-top solar panels is running the cables after the fact.

That's a good point..!! To incorporate solar panels into a new design and build would make the install much easier and more efficient. With a retrofit like mine it maybe better and easier just to get a 200w portable solar panel setup that could be easily moved around then put away when not used. I hate the thought of having loose wires or cutting holes that could cause issues.

Thanks for pointing that out.. I'll need to look into that further and see what I can come up with..

If we put a solar panel on our roof, I'll probably run the cable down the outside, and then up from underneath. I'll come up with some sort of conduit (homemade?, 3D printed?) that won't look too bad.

Tom

[lfhoward]

I've seen lots of "car charger" cables for the airsense 11 (I also have this) but am not sure which one to get for when my build is done. This one I've seen has good reviews but not a lot of them. Anyone with the same machine have success with any specific adapter?

https://www.amazon.com/HKY-Replacement- ... B0BYJ7NKM4

Which brand do you have?

I have the same one, AirSense 11. This adapter you linked to looks great. I had talked to ResMed on the phone and they don’t make 12 volt adapters for the AirSense 11. Luckily this aftermarket company does! Reading the reviews on Amazon, it looks like people save 1/3 to 1/2 the number of watt hours during the night vs. using a 120VAC inverter with the wall plug unit. I will probably get one of these.

[lfhoward]

To the OP, sorry for the thread-jack about CPAP 12 volt adapters. To your original question, LiFePO4 is so much better than AGM, and you get 90% capacity vs. 50% with AGM of the same amp hour rating. Also the voltage stays relatively high ~13.2 volts until it is close to the bottom, which means lights don’t dim and motors don’t run slower. LiFePO4 are pretty expensive, but you can build your own for half the cost or less using raw cells and a battery management system (BMS). Both of mine are DIY and it was a lot of fun to learn about them and build them.

[cdnred]

To the OP, sorry for the thread-jack about CPAP 12 volt adapters

No worries, I'm a CPAP user myself and it's always informative to learn on best ways to run them in the field. This posting has turned in partial LifePO4 vs AGM and CPAP usage..

I agree with regards to the LifePO4 being the best route to go. I was always under the impression that connecting a 40ah in parallel with a 100ah would give me 140ah. I bought the 40ah last year for about $150, today it's priced at $130 mind you it's a cheap Chinese made. The company I bought it from claims there is too much ah difference between the 40ah and 100ah to give me the 140ah I desired. I'd really prefer to have 100ah in case of higher battery usage..

My CPAP uses 6.67a so for 7 hours use means it could come to approx 47a per nite. Tony mentioned that he used the same CPAP that I have, Philips DreamStation without worries and he was running a 12v 70ah AGM giving him 35ah of usage, So the 6.67a rating or 47a nightly might be at the extreme end. I'd feel safer with using a 100ah so I have some cushion and could run 2 or 3 nites before requiring a recharge..

I can pickup a 100ah LifePO4 with BMS and charger for $198 minus a further 5% rebate including free shipping. It may not be the best performance wise but compared to another similar 100ah made in the US priced at $799 plus, it's more affordable to me. I'd rather buy US or EU made but the price difference is staggering. Everything on the shelf today seems to be coming out of China which is bad news down the road for our economy..

[tony.latham]

I can pickup a 100ah LifePO4 with BMS and charger for $198 ...

I'd be leery of a 100 amp LiPo that cheap. Does it have a low-temp cutoff?

I've learned a lot from Will Prowse's Youtube channel where he tears down LiPos. A lot are junk, but he comes up with some that are not and still inexpensive.

https://www.youtube.com/@WillProwse

Another good battery tear-down channel is this one:

https://www.youtube.com/@iceholepower8012

But he's usually taking the smaller ones apart.



As long as I don't use the heated hose, I use 8-10 amps per night (If I recall correctly). I assume you have a battery monitor in your teardrop you can test it with?

Tony