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CPAP gets 18650ed.
(08-22-2019, 05:38 AM)rebelrider.mike Wrote: Korishan: Ok, that makes sense. My (theoretical) battery as it is now could handle 6.5A continuously, so the boost converter would be the limiting factor more than the battery.

Yes, the converter is the limiting factor, that's what I'm referring to Wink
Depending on which one you get, it could be burned out from constant current load. The one Lucan is referring to actually might be the best route, especially considering that it also sends the authenticating signal to the CPAP to make sure it works.
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I've been thinking...
I'm sold on the 12/24V adapter rather than using my own regulator. I also really like the ABS box idea. I'm going to try to find one that will hold the battery and the cpap both. And since I won't be using a booster, I can make a 6s battery instead of a 5s, and be within the Voltage range of the adapter. That means more Volts, less Amps, and can still be balanced by my iMax charger.

I've got cells coming from Battery Hookup, and I've priced everything but the box. I'll have to get everything together and see what size I need.
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-Mike G
Batteries arrived!

I had to clean up a bit, because the testing station has been buried in other project stuff. These are modem batteries made by Pegatron. Never heard of them before, but they've used legit LG cells.

Dug out my favorite tools for cell harvesting, but after the first box, I found I didn't need the mallet.

These are pretty easy to open without destroying, and since they're compact, they may be useful for future project.

The first 4 cells came in at just under 2600 mAh. And it's so helpful to have the cat sit on top of the tester instead of trying to steal my tools as I'm using them!

I've added a couple features to the testing station since I last used it. I got a UPS just for the station; mostly to make sure the Opus doesn't lose power during the discharge test. Also, I discovered that there is such a thing as a GFCI adaptor that works just like the outlet, but you don't have to change out the outlet. Inexpensive, and just too cool not to get one!

Next thing is, I want to get the DC-DC adaptor made for the cpap, and test the output under different input Voltages to see exactly how it behaves. Then I can nail down exactly how I want to make the battery.
-Mike G
If you regulate to 24V, there is a simple way to use a Thevenin resistor equivalent for the center pin. I have the values somewhere if you want them.  That connector is unique even though it looks standard. I just cut it off the power pack as I had a spare.
For my UPS solution for the Opus, and my other chargers, I use an old lead acid battery. A car battery that is no good for starting anymore usually still holds a substantial amount of power. I pick them up for scrap price, and when I have used all the useful life from them, I sell them as scrap. Cost of ownership is $0. (last time I even made small profit, as the price of lead had risen) I usually get several years out of them. They are also great for running LED lights in a blackout.
I plan to get the DC-DC adaptor that's made specifically for the cpap. I've devised a way to test the output Voltages of the two + pins while I change the input Voltage. This should tell me if it really is acting as a boost/buck regulator or not.

The UPS was second hand. Usually, I pick them up for cheap and the battery needs replacing. In this case, the battery was in perfect condition, and so is the rest of the UPS. So rather than modify it, I left it as-is. Around here, we rarely get long outages, but we to get a lot of brief interruptions that are long enough to reset electronics. Only problem I have is the cat likes to walk across it and step on the power button. LOL.

I've discovered that TP4056 boards, buck converters, and small bms boards fit in the little space above the cells in those gray boxes. I've got 9 of them apart now, and only one broke during disassembly.
-Mike G
You need one of these. Stop unwanted button pressing.
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To power the center pin from 24V to make it look like a 85W pack use a 22K resistor to the +24V and a 3.3K for the bottom leg of the voltage divider. This is the Theveninof a 2.7K resistor sourced from 3.3V for the center pin. Actual values are 19.6K and 3.16K if you used 1% resistors, but the other values of standard resistance are close enough. DO NOT USE ANYTHING ELSE YOU MAY HAVE SEEN ON THE INTERNET. This information comes directly from the patent and will not damage your machine. I in the day. just use a car battery and a boost converter. Typical usage is between 100 and 120WH a night. I have mine on a timer so I don't forget to turn it off when I get up. It acts like a very rude alarm clock if I sleep late.
The DC-DC adapter is here! Finally get to experiment a little.

here is the DIY adapter I made to test the output.

A simple loop for the outer ground ring. Inner ring is a wire wrapped around another wire and held in place with the insulated wire with tape around it to get the width right. That will contact the inner 24V ring. Finally, the center pin connects with a short insulated wire, where I've taken a few strands out to make room for the pin. That would be 3.3V.

With that in place, I made a temporary 3s battery to test the adapter's ability to boost Voltage and keep it at 24V under a lode. The battery connects to the adapter, which connects to a CV CC regulator, which connects to a 12V 21W light bulb.

With the battery at just under 11V, the output is at 24V without a load. Not pictured is the center pin at 3.2V.

Under a load of about 20W, the battery drops to around 9V, and yet the adapter's output remains at 24V, and 3.2v.

So the adapter is a good boost regulator and can go as low as 9V input, maybe even lower.

Next I put together a 7s battery to test the adapter's ability to reduce Voltage. Same setup as last time, but with the bigger battery.

With no load, the battery is about 26V, and the adapter still outputs 24V and 3.2V.

Again, under a 21W load, The battery drops in voltage, but is still above 24V. The adapter's output remains at 24V, and 3.2V.

So between this and Lucan's experience, with a fully charged 29.4V battery, I'm convinced that this adapter is also a buck/boost regulator. Which means I don't have to install one on the battery.

I just ordered a bunch of stuff to start building the permanent battery. In the meantime, I'm charging up a temporary 6s battery to actually run the cpap off it for a couple hours.
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-Mike G
Glad to hear it is working out for you!

The center pin (3.3v) does some handshaking with the CPAP to tell it that it is a authentic power supply, so you might not be able to catch the signal with a multi meter. I know there was someone on the CPAP board that was reverse engineering the supplies, and was able to catch the signal and timing. I don't know much more than it is required for the CPAP to start up.

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