Reminder on CPAP Battery Safety

Just supplied this post to a question about indoor U1 size lead-acid agm battery safety and realized there is a broader audience that can benefit from it. Applies to anyone who is buying/building their own CPAP battery system based on either lead-acid agm or lithium technology. My experience is with agm lead-acid batteries. Anyone with direct lithium battery experience should chime in given the fire hazard from a battery management system failure.

For background I've posted multiple times on this based on my experience in building CPAP battery packs based on half-U1 size agm lead-acid batteries. Added my experience to CapnLoki's extensive set of posts that you can see via the link below. Good detailed explanations across these posts on how to scope and build battery packs of various sizes/designs.

https://www.cpaptalk.com/viewtopic/t114 ... ?start=150

While agm batteries are one of the safest type of lead-acid cell for use they can still be dangerous if not used correctly as they store a lot of power. Drop a wrench across the terminals of one of these (even my half-U1 size 20ah batteries) and hundreds of amps will go across the short circuit welding the wrench to the battery terminals. The keys to a safer design include:

1) Make sure your wiring is of a sufficient gauge to handle the expected current. Also, see details in the posts above, make sure the gauge will be sufficient to prevent voltage drop or you CPAP won't work. (see dialogue on voltage drop issues experienced by one user in the posts above)

2) Ensure that there is no exposed metal in your circuits that could result in an accidental short circuit. This means no use of alligator clip connectors on other than a short term emergency basis. All connections need to be covered by an insulator such as heat shrink tubing or at least a couple layers of electrical tape. Even better use off the shelf connectors, such as Anderson Poles, that also help eliminate the possibility of accidentally connecting a short circuit.

3) Install the correct level of fusing in your circuit. For 12 volt batteries this means your typical auto type fuses. Fuse to protect the circuit/wiring. For CPAPs used remotely without a humidifier the current required is often a lot less than the machine specs that are set to cover humidifier use and the maximum therapy pressure (typically 20cm). You can look these up for many machines or test with a multimeter. My devices only use between .5 and .65 amps at my therapy pressures which is why only half-U1 size batteries were chosen as these easily support two nights of therapy. Based on my wiring, and sometimes review of manufacturer DC cord specs, I've fused my CPAP connectors at just 5 amps with just one nuisance blow in 10 years.

4) Consider a batter box/bag for added safety. My half-U1 size batteries are placed in the bottom part of a plastic ammo box that is then placed in at heavy duty tool bag. For larger batteries the recommendation would be to place the battery and fusing inside the correct size battery box. Provides an added layer of protection to your battery set up. Lots of blogs/videos on how various folks have done this. Have seen one that converted a small igloo cooler.

Hope this helps.

P.S. As I sometimes use my batteries to power other devices via an inverter my design evolved into one with two fuses. A 15 amp main fuse right on the battery with a appropriate lower value fuse on a second fuse on a connector for specific uses. This varies from 3 amps for a 30 watt solar panel, 5 amps for my cpaps and 7.5 amps for my batterytender chargers. Inverter is protected my the main fuse.

Yep. Battery boxes and SAE connectors are your friends.