Opinion - Build it or Buy it

CactusBob

New Member
I found this forum and thought this might be a good place to ask a question or two and haven't found an answer while looking around.

I am looking at getting a power system to run a CPAP machine and a couple cell phones as necessary when away from power such as camping, etc.. I am looking at two different ideas.

First off the CPAP
On the power adapter from the wall it reads 12v 5A output. I haven’t picked up a killawatt yet, but I did find someone online with the same unit that said it used 8A at startup an .4 I believe throughout the rest of the night with a use of 40Wh total. Once I can get a killawatt I'll check mine. I wioll be getting a dc cord which should use less power than the ac adapter.

Option 1 - Purchased Power Station with this info
--Capacity: 300W/80000mAh
--9 Interfaces: 1x 110V AC Outlet, 3x DC Ports, 3x USB-A Ports, 1x USB-C Port, 1x Wireless Charging
--3 Charging Methods: solar panel, wall plug, car charger
--LED lighting, Built-in voltage regulator
-Input Recharging: Adapter 15V/3A; Solar panel 13V-22V/3A -Fully Charged Time: About 4-8 hours.
--USB Output: USB-A: 5V/2.1A; USB-A(QC 3.0): 5V-9V/2A; USB-C: 5V-9V/2A
--DC Output: DC55x21mm 12V/10A;DC55x25mm 24V/4A.
--AC output: 110V±10% frequency 60HZ ±5%
Rated 4.5 out of 5 by 49 people. Cost $175.09

Option2 - DIY build

7S 5P 24v battery pack using New Panasonic NCR18650B cells 3400mah 87.5Wh per series bank total 437.5 Wh
60A1400W BMS
DC to DC converter to get 12V, USB 3 outlet to provide 5v 3A output
Total cost roughly $275 after case, charge controller, etc

For charging I would be looking at solar for the most part and charging when they get to about 50%.
Is it better to purchase something prebuilt or to build it yourself?

My biggest concern is reliability and longevity. From the building cost it seems I would get twice the size system for less than double the cost. Am I missing something?

Should this be built as a 12v instead of a 24v system and are there better batteries for this use

Thanks

Bob
 

Hedges

Photon Sorcerer
I skimmed it.

Why DIY? Just get a 12V AGM battery. Forget an AC inverter, not needed for those loads.
AGM is good for 200 to 5000 discharge cycles, depending on brand and depth of discharge.

"I wioll be getting a dc cord which should use less power than the ac adapter."
Yes, CPAP runs on 12V, just get a fused cord. Do they have one that works off a cigarette lighter output?
Hook multiple such outlets to the battery. Cell chargers plug into the rest.

Want solar charging? Get a charge controller that has a "load" port with adjustable low-voltage shutdown; connecting the outlets to that you can stop discharging at 80% DoD or so.

Get a suitable AGM charger/maintainer for AC charging.
 

CactusBob

New Member
From what I understood, and I may be wrong, AGM's need venting and since this is where I would be sleeping I would rather not have it in a confined area. Putting it outside brings up other issues

Bob
 

Hedges

Photon Sorcerer
AGM is safe for airline transport.
Try THAT with a lithium battery.

AGM is non-hazardous unless you bust it open, short it out (will melt your screwdriver), or severely overcharge it (in which case your nose will warn you.)

Did you see the news item about a lawyer who was arguing the case regarding his client's smoking violation?
While he was speaking, the e-cigarette in his pocket caught fire.
Lawyer, Lawyer, Pants on Fire!
 

CactusBob

New Member
LOL, that sounds like a visit from Karma!
I see I was misunderstanding AGM's, what are some of the better quality ones to look for? A quick search shows comparable Ah rating with prices widely fluctuating. A few brands to look for would be a big help

Thanks
 

Hedges

Photon Sorcerer
I use SunXtender, parent company Concorde which makes batteries for Aerospace.
My 100 Ah 12V costs about $325.

Trojan has AGM as well as wet cell.
There are a few others. Some may have cycle life a multiple of what my batteries have. Some (cheap brands) a fraction.

lithium seems to be getting down to AGM prices, sometimes lower. They can offer several times as many deep cycle.
Of course they also require a quality BMS to monitor and balance individual cells, and bad things happen of one cell gets too. high or low.

I think AGM is a good deal if it will be cycled either shallow enough or infrequently enough to last 10 years, so on par with lithium. If you expect to replace it several times in a decade, then lithium can save you money.
Size/cost of battery is another factor. For small stuff, keep it simple even if that costs more.
Portable tools (and cars) are going lithium for weight and fast charging. I have some, also a drill that is AGM.
 

Pnw_steve

Solar Enthusiast
The pre-built powerstation sounds like it is priced reasonably for what it is. If you have more money than time I would buy it.

If you are anything like me, with a little time available and a love of tinkering, then build it.

If I were going to build it for what you mentioned then I would forego the inverter. I would use four LFP prismatic cells in series with a basic bms and charger. If your budget allows, the 280A/H cells are a great value. Add a Daly BMS and a couple of $5 12v USB charging jacks and a couple of Anderson connectors for your 12v loads.

Wait a minute...... I am building one like that...... Whodathunkit?
 

Pnw_steve

Solar Enthusiast
I just saw 4 x 25A/H Lifepo4 prismatic cells on eBay for $100 and you can probably get 4 x the 280A/H from the gent running the group buy. I can't quote but I would guess that you can probably have them delivered for less than $500. Check with Michael for the straight scoop.
 

Pnw_steve

Solar Enthusiast
AGM is safe for airline transport.
Try THAT with a lithium battery.

AGM is non-hazardous unless you bust it open, short it out (will melt your screwdriver), or severely overcharge it (in which case your nose will warn you.)

Did you see the news item about a lawyer who was arguing the case regarding his client's smoking violation?
While he was speaking, the e-cigarette in his pocket caught fire.
Lawyer, Lawyer, Pants on Fire!

I believe that the FAA breaks it down to specific chemistries. Some are allowed with conditions.
 

BoloMKXXVIII

Fully Charged
I think most here are suggesting batteries bigger than you need. I use a 12v, 20Ah lifepo4 battery for my CPAP when camping and for power outages. Get the OEM 12v cord, not the after market one. A folding 100w solar panel and PWM charge controller should keep it charged if your usage is anything near mine. Remember folks, he is camping so it needs to be portable.
 

Rocketman

Solar Addict
If you decide to build it - this is what I am doing:
Case - harbor freight “pelican” case
From electric car parts.com - eight 25ah fortune lithium cells in 2p4s for a 50ah 12 v battery ( or only four for a 25ah battery).
Anderson plugs, 12v light on the side cig plug.
And some meters...
 

MrNatural22

🌞SW sunshine =⚡️⚡️lit up thru the darkness✌️
Another thing on Cpap use, many users agree, if you don’t use the humidifier it will use a lot less battery power. Just a heads up. ✌️
 

Pnw_steve

Solar Enthusiast
I think most here are suggesting batteries bigger than you need. I use a 12v, 20Ah lifepo4 battery for my CPAP when camping and for power outages. Get the OEM 12v cord, not the after market one. A folding 100w solar panel and PWM charge controller should keep it charged if your usage is anything near mine. Remember folks, he is camping so it needs to be portable

For just the CPAP 280A/H may be significant overkill for short trips. If you wanted to go longer without charging or have other load you want to support the additional capacity may be handy.

A 12v 280A/H pack by itself is roughly 5"x6"x8". You could fit the cells and BMS in a roughly 6"x6"x10" enclosure. I am considering an ammo can for mine.
 

CactusBob

New Member
I think most here are suggesting batteries bigger than you need. I use a 12v, 20Ah lifepo4 battery for my CPAP when camping and for power outages. Get the OEM 12v cord, not the after market one. A folding 100w solar panel and PWM charge controller should keep it charged if your usage is anything near mine. Remember folks, he is camping so it needs to be portable.
Nothing wrong with bigger, I had figured that the 18650's I was looking at should last almost 11 days, if I recharged every 5 days min I should be good. since the cost would be close is there a difference between using the Fortune cells and 18650's if the cost and AH is relatively the same?

Bob
 
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