UPS - uninterrupted power source

timbalionguy wrote:Besides the extra load from the heaters, you have conversion losses in the inverter and in the machine's AC power supply."

Contemporary inverters and switched mode power supplies are typically 90% to 95% efficent, so conversion losses are a negligable factor.

timbalionguy wrote:I will also emphasize the importance of using a 'pure sine wave' inverter with ResMed machines. Unfortunately, these inverters (or UPS'es) are heavier, less efficient and cost more.

True sinewave inverters cost more but are generally not less efficent or significantly heavier, for the sort of power levels likely to be useful for xPAP purposes.

The Resmed flow generators will work fine off modified sine wave AC, it is the Resmed heated humidifiers, which use a phase control approach for setting the humidification level, that require true sine wave power.

Cheers,

Bill

pb5927317 wrote:http://www.tigerdirect.com/applications ... &CatId=234

Check out the cyberpower units...more reasonable then the APC, and I have had very good luck with them.

This sounds good as a one night backup in case of power outage. According to the reviews on the website, it will last for only a few minutes with a couple of computers and permit you just enough time to turn off safely.

Have you actually used the cyberpower with your xpap for an entire night?

billbolton wrote:

timbalionguy wrote:Besides the extra load from the heaters, you have conversion losses in the inverter and in the machine's AC power supply."

Contemporary inverters and switched mode power supplies are typically 90% to 95% efficent, so conversion losses are a negligable factor.

The losses in the inverter per se might be low. But when added to the losses in the power supply, and losses due to things like low power factor, the overall efficiency is probably closer to 70-75 percent.

billbolton wrote:

timbalionguy wrote:I will also emphasize the importance of using a 'pure sine wave' inverter with ResMed machines. Unfortunately, these inverters (or UPS'es) are heavier, less efficient and cost more.

True sinewave inverters cost more but are generally not less efficent or significantly heavier, for the sort of power levels likely to be useful for xPAP purposes.

I haven't shopped these devices lately. I agree they can be made lighter, and more efficient. But this drives up both complexity, and therefore the cost (as well as lowering the reliability).

billbolton wrote:The Resmed flow generators will work fine off modified sine wave AC, it is the Resmed heated humidifiers, which use a phase control approach for setting the humidification level, that require true sine wave power.

Cheers,

Bill

That is true. But most people use the companion humidifier, which is powered through the machine. So for all practical intents and purposes, a ResMed machine requires a sine wave inverter, unless the machine is being used standalone.

timbalionguy wrote:The losses in the inverter per se might be low. But when added to the losses in the power supply, and losses due to things like low power factor, the overall efficiency is probably closer to 70-75 percent.

That's a big claim. Can you please produce some evidence to support it.

timbalionguy wrote:(as well as lowering the reliability).

There is no evidence that I am aware of, from the extensive deployment of inverters in solar power systems, that suggests that true sine wave inverters have any different reliability profiles in practice to modified sine wave inverters at similar quality levels. Again if you have specific evidence to support your assertion, please provide it.

Cheers,

Bill

My plan is to connect the auto inverter I have to either tractor or car battery in the garage and run an 50' extension cord to the bedroom. Turn off the humidifier. Comments?

A ResMed machine and humidifier can easily be powered with a 300 watt true sine wave inverter.

A deep cell battery can be float charged with a small battery maintainer, they are automatic and just clip onto the battery posts. I have two stage-2-1 amp battery charger to float my AGM deep cell battery (I also have a three stage 12-4-2 amp battery charger in case it has to be charged). The 2 amp charger is designed for either Gel Cell or AGM batteries and the 12 amp charger has a setting for AGM batteries.

Humidifiers draw an average of about two or three times the current of a flow generator, so a battery that would power a CPAP machine for nine hours will power a CPAP machine and humidifier for about 2 or 3 hours. Powering a CPAP machine with an inverter will draw 10% or so more than powering the CPAP directly from the battery -- this could make a difference if you are not using a humidifier. If you are using an inverter to power a humidifier it will be easier to just plug the CPAP machine into the inverter and the ~10% or so loss is negligible compared to the humidifier's current draw.