Cheapest way to measure this?

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I have to use a CPAP to sleep well. I'm going camping and will need to
bring battery power for the thing. So I would like to measure the
power draw over several nights to see what the highest power draw is.
The machine changes the air pressure depending on my particular needs
so I can't just plug it in and measure the current draw.   I was
wondering if perhaps one of those cheap DSOs would be adequate. Any
advice?
Thanks,
Eric

Re: Cheapest way to measure this?
snipped-for-privacy@whidbey.com wrote on 6/1/2017 11:44 AM:
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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.

--  

Rick C

Re: Cheapest way to measure this?

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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


Re: Cheapest way to measure this?
On Thursday, June 1, 2017 at 11:38:35 AM UTC-4, snipped-for-privacy@whidbey.com wrote:
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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.
https://labjack.com/

Hey there's a USB data logger there... that might work for you.  
https://labjack.com/products/digit

Or a cheap usb 'scope.  

George H.  

Re: Cheapest way to measure this?
On Thu, 1 Jun 2017 10:16:27 -0700 (PDT), George Herold

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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

Re: Cheapest way to measure this?
snipped-for-privacy@whidbey.com says...
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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.

https://www.amazon.com/dp/B00E1E1XA2?psc=1

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.



Re: Cheapest way to measure this?
On Thu, 1 Jun 2017 14:02:47 -0400, Ralph Mowery

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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

Re: Cheapest way to measure this?
On Thu, 01 Jun 2017 14:14:42 -0700, snipped-for-privacy@whidbey.com wrote:

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If you looking for batteries for extended laptop use check out these
guys:
<http://www.bixpower.com/product-p/bat-cp170-s10.htm
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

Re: Cheapest way to measure this?
On Thu, 01 Jun 2017 14:14:42 -0700, snipped-for-privacy@whidbey.com wrote:  

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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"

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