Cheapest way to measure this?

snipped-for-privacy@whidbey.com wrote on 6/1/2017 11:44 AM:

You don't provide much info on how it will be powered from batteries. Does the unit contain batteries? Will you be powering it by something like a UPS that generates AC line power?

If you can use a measurement of AC line power, there are any number of watt-hour meters available. They plug into an AC line socket and you plug your device into them. A display shows the current voltage, current and power. It accumulates the power to display energy in watt-hours.

If this is not good enough you will need to find a way to connect a multimeter to the batteries to figure out the power draw. I'm not aware of a universal solution for this. I have a small device that does the watt-hour measurement for a USB connection, but is likely limited in power and voltage.

Huh, fun. So you want to log data for ~8 hours.

(The cheapest way would be to find the max current draw and multiple by 8 hours.. or does the current vary widely?)

I've never used my DSO to log data to the computer. So no comment on that.

I've got a DMM with a data logger, I think I can set up the data rate. I've only used that a few times.

A DMM with an RS-232 output wouldbe nice... send data to your computer.

With a little work you can DC couple into the sound card on your computer and use that to record data.

Some Arduino thing maybe... Do you have an Arduino?

I've got a labjack, so I'd use that.

Hey there's a USB data logger there... that might work for you.

Or a cheap usb 'scope.

George H.

You did not mention what kind of power. If 120 volt AC, then one of the Kill-o-Watt meters for under @ 20 will do this.

Here is another from Amazon of a different brand.

There are some less expensive ones from China on ebay without a case, but by the time you get the plugs and case you will have a lot more in it.

I should have said that the CPAP machine will run directly from a 12 volt battery. But since it also plugs into the wall I could use a watt hour meter. I didn't even think of that. Thanks. Then whatever it shows will be more than if run directly from a battery so that would give me a little cushion. Cheers, Eric

Greetings George, I do have an Arduino. Rickman suggested using a watthour meter. I think that might be the best way because it will give me result that is higher than if I run the thing directly from a battery since the power supply uses some power. Thanks, Eric

Well, that was simple. I have a Kill-A-Watt ordered and on its way. Thanks everybody for your advice. Now I need to look for some good deals on LiIon batteries. Maybe a solar charger too. Eric

If you looking for batteries for extended laptop use check out these guys: It even says it might run a CPAP for 2-3 nights.

LiIons are expensive but it might be what your looking for. I'd forget about the solar charging, the panels would be huge.

Cheers

As a matter of fact, I didn't know anyone still used CPAC machines. I thought I saw a commercial for something called a "CPAP mouthpiece"