Homemade Resmed A10 camping battery

Good stuff here!

I like the outside the box thinking.

I've just realized that I used up all my copper wire on other projects! I'll have to get more before I can start building the battery.

Some good news though, I've finally finished testing all 99 cells, and they're all good! There's something very satisfying about seeing all the cells lined up together.


Anyway, I've chosen the best 66 to be in the CPAP battery. They'll range from 2661-2545mAh. That should give me some nice Watt-hours.


I think it's about time to go get that box and see how much I can fit.

rebelrider.mike, Very cool!! Excellent valuable post.

BTW, the Resmed Airsense S10 dc connector has outside 0.3" and inside cylinder (24v) 0.2" (measured with a caliper). Cannot measure the pin diameter.

1. Do you know the electronic part number of the above connector, and its mating connector you have shown in your photos? Where can I buy them from? Any suggestions or help is highly appreciated!

2. Do you know how much variation is allowed on the 3.3v tag line? Will it take 4v ? How low, 3v? I am thinking of using a 3 x LiIo batteries and feeding the tag line from one of the cells with the series resister. My plan is to have a simple floating battery, the resmed oc voltage is safely below the max (full charge) voltage of the 3 x LiIo. Any comments.

BTW, I had a rude awakening with the destructive power shutdown of PGE in Northern California, for no real reason than to extort pge customers and the state. In the last 50 yrs living here we may had only a few very brief shutdowns.

Sorry, something unexpected happened with my last post. rebelrider.mike, I thought I was posting to your thread where you have many photos of your backup power supply project. But I see now I ended up on another thread. Just FYI, I am referring to items in your slightly earlier another thread.

Sorry to hear that you've been affected by the blackouts. I sent a DM to answer part of your question. As far as the 3.3V pin, I've been told that it is more of a signal line than a power line. I think there is a special resistor that could be used to replicate the signal, but that's just what I've been told. I don't understand any of it. But after pricing the various part needed to build my own regulator/adapter, it turns out the one from Amazon was cheaper, and a whole lot less to worry about.

If you were to go with the adapter, I've tested it down to 9V, and it still delivers a constant 24V, 3.2V weather under load or not. Another fellow on a different forum had his all the way up to 29V with the same results. When you make your battery though, make sure the cells can handle the Amps as well as the Volts. It's common to forget that, and end up with a battery that gets hot. Lithium cells of any kind should never do that.

I hope all this helps.

I think you mean you should never permit lithium cells to get hot. There have been many documented instances if fires caused by lithium batteries.

Right. Normal healthy lithium based cells don't get hot either while charging or discharging. If they do, there's either an internal fault, or some external abuse is happening. Usually from faulty charge control electronics. Any home-made battery from lithium based cells should have several layers of safety built in. I prefer the 18650 cells as they have several safety bits in them already. Of course, safety is never guaranteed, and there is always some risk.

rebelrider.mike, Very cool!! Excellent valuable post.

BTW, the Resmed Airsense S10 dc connector has outside 0.3" and inside cylinder (24v) 0.2" (measured with a caliper). Cannot measure the pin diameter.

1. Do you know the electronic part number of the above connector, and its mating connector you have shown in your photos? Where can I buy them from? Any suggestions or help is highly appreciated!

2. Do you know how much variation is allowed on the 3.3v tag line? Will it take 4v ? How low, 3v? I am thinking of using a 3 x LiIo batteries (any number of sets in parallel to get the required capacity. But there are problems with simply connecting batteries in parallel, the slight differnes in voltages tends to cause leakage and run downs) and feeding the tag line from one of the cells with the series resister. My plan is to have a simple floating battery, the resmed oc voltage is safely below the max (full charge) voltage of the 3 x LiIo. Any comments.

BTW, I had a rude awakening with the destructive power shutdown of PGE in Northern California, for no real reason than to extort pge customers and the state. In the last 50 yrs living here we may had only a few very brief shutdowns.

Got my computer 95% up and running.

Now that all the cells are tested, I got them cataloged and arranged by similar capacity.


I ran out of the wires I normally use, so I had to scavenge some from a box of junk wires I've got laying around. Took one multi-stranded wire apart to use individual strands to connect the bottom half of the battery to each cell. Another multi-stranded wire was the right size for the bus, but insulated. I just cut a little insulation off at each solder site, and it seems to work fine. Each cell on the top of the battery is connected to the bus wire through a glass axial fuse.


BMS is installed. I guess it's working. At least it's not smoking, and the power out Voltage is right.


This particular BMS has the option to add a thermocouple switch. So I added one that is normally closed until 113F. Still need to add a cable for balancing and a main fuse, then some outer physical protection. But it's shaping up!

Are those single strands joining each battery sufficiently thick enough they strike me as fairly thin gauge. I know nothing just my thoughts each wire should be the same gauge your controller battery out cables are much thicker

Yep, they are fine. Each cell only has a draw of less than 0.32A, so the 0.3mm wire is more than sufficient. The bus wires, being insulated, and able to move up to 3.5A, needed to be bigger. So for that I chose the 16 AWG wire. If I were to be using more current from each cell, the wire size would have to increase. But this battery isn't designed for high current. It's going to be delivering small current over a long period of time. (3-4 night's sleep, I hope.)

Started fitting all the parts into the case:


Unfortunately, there's no room for the charging hardware, so that will have to stay out. Not a huge loss, just would have been nice.

The power meter and switch still need a box to hold their wires and position in the case. And there's still wiring and other details to sort out. But it's nearing completion!

rebelrider.mike wrote: ↑

Wed Dec 04, 2019 2:06 pm

Started fitting all the parts into the case:

Are you planning to fly with this?
I wonder if you will get grief going through security.

No, I'm planning to camp with it.