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  View original topic: How much electricity is actually used?
uther Tue Aug 20, 2013 5:35 pm

I have a couple of medical devices I need to run from battery power while my wife and I camp. We have been staying only in places with power but would like to stop doing so. How can I determine the actual electrical usage over a night. Is there something I can plug into the wall and then plug her O2 concentrator, for example, into when she goes to bed that will tell the overnight usage?

I intend to add house batteries and solar panels but need to understand how much I need.

r

Syncronoid Tue Aug 20, 2013 5:50 pm

The device itself should list power consumption on it, either in watts or amps. There must be a label somewhere. You could also look up the device online; I did that for a small coffee maker before purchasing for my Syncro.

uther Tue Aug 20, 2013 6:10 pm

Syncronoid wrote: The device itself should list power consumption on it, either in watts or amps. There must be a label somewhere. You could also look up the device online; I did that for a small coffee maker before purchasing for my Syncro.

Sorta. But the number is not very meaningful. One of the devices lists 120 watts but I can run it for three nights (8-10 hours/night) on a old, tired, 60 amp/hr battery through a 400 watt inverter. This should be 10 amps per hr times 27 hours = 270 amps!

I want something that will measure the actual usage.

Ahwahnee Tue Aug 20, 2013 6:28 pm

uther wrote: ...I want something that will measure the actual usage.

An ammeter in series with the device will measure what it is drawing. A cheap (sometimes free) one from Harbor Freight would be enough to give you a rough idea (I suppose the accuracy of these is suspect but like I said - a rough idea).

If you know the draw then you can work out what it will do vis a vis your battery capacity over a period of time.

I've never tried it but seems you would put the ammeter between the battery and the inverter for the best measurement.

nocreditnodebt Tue Aug 20, 2013 6:30 pm

Kill a watt

http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU

The listed power consumption on the back of devices is the maximum they can pull, not the average that they pull. While this will be the same on some devices, not all.

Plug the appliance into a Kill a watt, get a reading over a certain amount of time, then do some math, adding 15% for inverter inefficiency

SSWesty Tue Aug 20, 2013 6:36 pm

The 120 watt figure may represent the maximum surge at start up. I agree a good way to go would be to test it with an amp meter and the cheap one from harbor freight should get the job done.

http://www.harborfreight.com/7-function-digital-multimeter-92020.html

dobryan Tue Aug 20, 2013 6:41 pm

http://www.ebay.com/itm/BATTERY-MONITOR-DC-LCD-DIG...vi-content

Or something similar....

uther Tue Aug 20, 2013 7:05 pm

dobryan wrote: http://www.ebay.com/itm/BATTERY-MONITOR-DC-LCD-DIG...vi-content

Or something similar....

This is WAYYY out of my league. What I know about electricity is that you plug some widget or the other in, turn it on and it works. If not you try turning it on/off a few times, plug it in somewhere else and if both of those fail, buy a new widget. I have no idea how to use a battery monitor or honestly any electrical tools. I was hoping there was something out there that measured the total amount of electricity used by whatever was plugged into it... and was cheap!

uther Tue Aug 20, 2013 7:23 pm

nocreditnodebt wrote: Kill a watt

http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU

Plug the appliance into a Kill a watt, get a reading over a certain amount of time, then do some math, adding 15% for inverter inefficiency

This is exactly what I'm looking for - assuming that I understand what it does. I just ordered one.

Thanks so much...

r

r39o Tue Aug 20, 2013 8:56 pm

Here's the real killer. Many people discharge their batteries to death via over optimistic guesses at how much power you can pull out of them.

You need to determine your true needs and balance that against just how much energy you can safely pull from a given configuration.

You will likely find you needs quite high actually.

You may consider spots with shore power to be the safe thing to do and hence limit yourself to those places.

For the true story on batteries: http:www.batteryuniversity.com

This energy topic comes up frequently around here, and from an engineers stand point, I see many people who are not nice to their power sources, unless you consider new batteries every year to be OK.

uther Tue Aug 20, 2013 9:40 pm

r39o wrote: Here's the real killer. Many people discharge their batteries to death via over optimistic guesses at how much power you can pull out of them.

You need to determine your true needs and balance that against just how much energy you can safely pull from a given configuration.


I agree. It's the "determine your true needs" part that I can't figure out. O2 generators, CPAPs, and BiPAPs are not the sort of things that are listed on the usual "how much battery power do you need" charts. I can find lots of info about the fridge, various heating options, TVs, radio, laptops, phones, and such.

Does anyone use an O2 generator while camping? Surely we're not the only people who still want to camp with breathing problems.

joseph928 Wed Aug 21, 2013 7:21 am

uther wrote: I agree. It's the "determine your true needs" part that I can't figure out. O2 generators, CPAPs, and BiPAPs are not the sort of things that are listed on the usual "how much battery power do you need" charts. I can find lots of info about the fridge, various heating options, TVs, radio, laptops, phones, and such.

Does anyone use an O2 generator while camping? Surely we're not the only people who still want to camp with breathing problems.

:bay_blue: X-2 on the kill a watt, use one all the time. Works great when you are on shore power or hooked up to an inverter. Not so much on 12 volt. Use my solar MPPT charge controller for keeping tabs on my 12 volt system. http://www.ebay.com/itm/20A-MPPT-solar-charge-cont...417601ca97 Been camping in a VW bus-van since 1966 and never heard of someone using a O2 generator. So keep it up, keep camping, and good luck. :D

PDXWesty Wed Aug 21, 2013 8:07 am

For devices like you list, given the important nature of them, I would certainly purchase a small generator and not rely soley on battery power. A Honda EUI 1000 can be had for $500 used and would be a wise investment.



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