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Old 02-10-2014, 18:55   #1
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How to Measure Daily Amp Consumption?

I've recently built and installed a freezer with a danfoss 35 compressor and I want to work out how many amps (12v) it's using in a 24hr period. I can use my multimeter to measure how many amps it's using whilst running and I also have a battery monitor which shows total amp usage but in order to find my freezer usage, I'd have to turn off all my other DC loads for 24hrs which isn't really practical as I liveaboard. Does anyone know of an easy (cheap) way of doing this? Thanks.
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Old 02-10-2014, 19:36   #2
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Re: How to Measure Daily Amp Consumption?

Sure, do an energy budget for all the rest of the easy stuff, then it will be the difference.

Or, if you haven't loaded the freezer yet, read a daily use, then turn it on for a few days and see the difference.
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Old 02-10-2014, 20:01   #3
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Re: How to Measure Daily Amp Consumption?

Don't sweat the nuance of the freezer, as long as you have enough power to cruise and anchor in between charging. But if you must know how much the freezer uses. Turn the freezer off for 48 hours, not the 24 hr usage of everything used as normal, then turn the freezer back on and run for 48 hrs, using the same house loads as before, then deduce the difference.

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I've recently built and installed a freezer with a danfoss 35 compressor and I want to work out how many amps (12v) it's using in a 24hr period. I can use my multimeter to measure how many amps it's using whilst running and I also have a battery monitor which shows total amp usage but in order to find my freezer usage, I'd have to turn off all my other DC loads for 24hrs which isn't really practical as I liveaboard. Does anyone know of an easy (cheap) way of doing this? Thanks.
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Old 02-10-2014, 20:11   #4
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Re: How to Measure Daily Amp Consumption?

Not too hard if you're willing to spend some time.

1) you can measure how many amps it draws when running with a simple ammeter, probably the one on your vom meter.

2) keep an eye on it for a few hours at different times of the day. record how long it's on and how long it's off. although it sounds like a fools errand you will see that the on/off periods tend to remain fairly constant once it's been running for a few days/weeks. my adler barbour runs 14 minutes on and 20 minutes off. so i figure its running about ten hours a day. at 4 amps. so 40 amps a day.

or you can buy a recording amp meter. google them. but they're pretty expensive for this one time use.....
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Old 02-10-2014, 20:53   #5
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Re: How to Measure Daily Amp Consumption?

We did ours using one of these purchase from JayCar in OZ but lots of similar metters around. This has the ability to monitor and save for 99 hours. Download to a PC using a USB interface and these pdf's are the result. Cost about $80 AUD but I use it on most of the other circuts. Just put it in series. Also used to measure input from my Solars as good for 30 amps
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Old 02-10-2014, 22:08   #6
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Re: How to Measure Daily Amp Consumption?

you could move the battery monitor shunt to the freezer line for a few days. saves buying other stuff. might need a bit of wire though
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Old 02-10-2014, 23:55   #7
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Re: How to Measure Daily Amp Consumption?

Amazon has these for about $25.

GT Power Watt Meter

You can see a review of it on Youtube at
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Old 03-10-2014, 05:05   #8
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Re: How to Measure Daily Amp Consumption?

Thanks to all, especially Dod42 and Roetter...those are perfect.
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Old 03-10-2014, 09:01   #9
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Re: How to Measure Daily Amp Consumption?

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or you can buy a recording amp meter. google them. but they're pretty expensive for this one time use.....
I take back everything I said. Think I'll get one too...
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Old 03-10-2014, 09:58   #10
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Re: How to Measure Daily Amp Consumption?

Nice video. I have a watts up on my solar panel. Good to see it performing well.


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Old 03-10-2014, 11:03   #11
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Re: How to Measure Daily Amp Consumption?

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Originally Posted by Privilege View Post
I've recently built and installed a freezer with a danfoss 35 compressor and I want to work out how many amps (12v) it's using in a 24hr period. I can use my multimeter to measure how many amps it's using whilst running and I also have a battery monitor which shows total amp usage but in order to find my freezer usage, I'd have to turn off all my other DC loads for 24hrs which isn't really practical as I liveaboard. Does anyone know of an easy (cheap) way of doing this? Thanks.
I think it would depend on how many cold beers are needed in 24hrs?
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Old 04-10-2014, 01:06   #12
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Re: How to Measure Daily Amp Consumption?

If you know how much it draws when the compressor is running, then just sit and time how long it runs and how many times it goes on in an hour. It will vary with significant outside air temperature changes.
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Old 04-10-2014, 01:58   #13
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Re: How to Measure Daily Amp Consumption?

I would throw in a 25% fudge factor if you are using the result for electrical usage planning.

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