What does amp this test tell me?

[ladywendolyn]

I bought an power meter to figure out how many amps our fridge draws in the trailer. I am trying to determine if we can rig a solar system or possibly an inverter to keep the fridge cold while we are driving.
The device has very poor instructions that do not explain very well how to use it or read it.
So I basically plugged it in for 24 hours just to measure how many amps the fridge draws. It says at least from what I can see that it drew 117 amps over 24 hours.
Does this seem normal?
So then I take it I need to have a system in place that can support a draw of 4.8 amps per hour? (If I'm only talking about the fridge).

If I'm looking at keeping the fridge topped up while driving, I am guessing I need to figure out how much 12 volt energy the alternator supplies, and also how much the battery bank can hold?

Is there a 12 volt power for dummies book anyone can recommend that would help me understand this?
I feel like it's two different systems I'm needing to understand.
A solar system for offgrid, and an inverter that can work off the tow vehicle.
Anyway if there is a place to study this I need to know about it.
Thanks

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[jonyjoe303]

the 117 has a v next too it, thats the average voltage 117 volts. I think you need to cycle the display button so it shows an A, that would be the amps. The bottom display shows 24 hours 13 minutes 58 seconds.

117 amps would be quite alot for a fridge, maybe a full size fridge with icemaker might consume that much.

 

[ahh_me2]

That meter looks a little odd.
Can you post the model no of it? or a full picture of the meter?

It is reading 117 v, which is your input voltage, and shows it has been running for a little over 24 hours.

If you can cycle through the display you would be looking for A or Ah, as well as W or Wh, amp-hours or watt hours.

The graph seems to indicate it records 10 kw per bar, but no bars are shown, 1 kw = 1000 watts.

Again a model number would be more helpful as we could look up the specs or manual and then explain what you would need to do.

 

[highdesertranger]

what type of refrigerator? compressor or absorption? does it also run on propane? if it runs on propane it is an absorption unit. absorption units are very inefficient on electricity. on that meter it appears to be reading 117 volts not amps. give us some more info. highdesertranger

 

[tx2sturgis]

Lw, I think we need to back up a bit...

117 is the voltage not the amperage and I cant tell from the picture what the other number is...

This is a 120v fridge only? In other words will it run on 12v or propane or only shore power?

Can you take a nice clear picture of the display?

 

[ladywendolyn]

Ok so when we bought the trailer we thought this was a propane/110 fridge but then found out that it was 110 only. It is an absorption fridge. Only 3 ft high. I want to keep the fridge but would like to possibly run it off an inverter when traveling to keep it cold. We would also like to explore solar boondocking possibilities.
So to be honest because I could not understand the instructions I pushed all the buttons after the 24 hour period and took a photo of each screen. I have no idea what they mean. If you can help me interpret that would be great. On the amp one I think there is a decimal point, so I think it says 2.4 Amps max, not 244.

 

[ahh_me2]

1st pic : 117 v  is your power source, normal around 115 to 120 v,
            24:13:58 looks like total time elapsed in hr/min/sec

2nd pic ; 2.44 a is maximum peak current , meaning nothing consumed higher than 2.44 A at a given time
             24:14:20  new time total

3rd pic : 103.5 W  is current or average wattage drawn ?

4th pic : 60 Hz , the standard AC frequency in North America.

5th pic : I can't make out the sine wave at the top left, but the second line shows 2.49 kw/h, meaning you have used 2490 watts in a 24 hour period.

It all seems to point to: approx 1oo Watts per hour consumption,

24 hrs at 103 watts = approx 2472 watts, very close to the 2.49 kw in pic 5



Remember, this info is solely based on the pics provided.

 

[tx2sturgis]

OK!

Now we have something. 2.49 kwh and that was in 24 hours, right? Thats what we need.

For now disregard the Max A, the HZ and the V scales. Not really relevant to the calculations.

Absorption fridges run very inefficiently on shore power and 12v RV power.

Its burning thru a lot of energy...too much to power it with any reasonable solar array. Was the fridge 'pulling down' to temperature or was it already cooled when you started your test?

A typical 200 watt solar array, flat roof mounted, might (in theory) be able to provide about 600-800 watt hours avg in a full sunny day, which is .6 to .8  kwh per day.

Your fridge is using about 3-4 times that much...

I'm sorry to say its not gonna be a good match for solar power. Unless you are willing to spend a great amount of money on solar and batteries. But it would make much more sense to buy an efficient 12v compressor fridge like an Indel-B and then sell the old one on craigslist.

Now you can still run yours with an inverter, but the batteries the inverter is powered from will need a constant supply from shore power charging, or generator charging, or a fairly heavy 12v line from the vehicle...and that might be what you need.

It would be able to keep your food cold while in transit, but would drain the batteries pretty quickly if they are not on a charger.

 

[ahh_me2]

I had forgotten you said it was only running on 117v and that you would like to run it off an inverter.

So I edited my post as it had some confusing 12 volt numbers.

But if we want to run it off an inverter, assuming 10 per cent loss: 10 per cent of 2490 is around 250, so we have close to 2750 watts

Power =E(volts) X I(current) so 2750= 12 X (x) or 2750/12= 229 Amps total consumption.

This is at whatever duty cycle the fridge uses, as it is a total according to your meter over a 24 hr period.

Either way , it seems like a rather high current draw that will drain batteries in no time.

You need big batteries, and or big solar, or, a different fridge.

 

[ladywendolyn]

Ok that is great information to have. I basically am going to run it on 110 when we are at a campground and I may try to rig an inverter while underway to keep the fridge cold. We can always grab a bag of ice for boondocking.


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[ladywendolyn]

So if I want to run this fridge off an inverter plugged into my van, is there a specific size of inverter that would be best to handle this draw amount while we are underway?
I currently have a deep cycle battery from Costco, like this one.

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[tx2sturgis]

We can always grab a bag of ice for boondocking.

If you are only boondocking occasionally, its not that expensive to just buy a block of dry ice when you stop at the grocery store and stock up with frozen food on the way out...

 

[ahh_me2]

To find an inverter size, we need the numbers:

<<<1st pic : 117 v  is your power source, normal around 115 to 120 v,
           24:13:58 looks like total time elapsed in hr/min/sec

2nd pic ; 2.44 a is maximum peak current , meaning nothing consumed higher than 2.44 A at a given time
            24:14:20  new time total>>>

Power = Volts X current

so 117 V X 2.44 A = 285.5 Watts

Compressor motors often have a surge of almost double or more of their running current,  so we say
285.5 w X 2.5 = 713 starting watts
and around 250 running watts.

A 600 watt inverter should be able to start and run the unit, but it could depend on the brand.

An 800 watt inverter would probably be just right,
and a 1000 w inverter is probably overkill.

 

[ladywendolyn]

Ok 1000 it is.. lol Thanks!
Also... would my fridge have a compressor if it's an vintage absorption style?


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[tx2sturgis]

Also... would my fridge have a compressor if it's an vintage absorption style?

Nope.

They are two different systems. But it is unusual to have an ONLY 120v absorption fridge. Are you SURE its an absorption fridge? Does it have a finned metal plate in the back of the fridge compartment?

If you also have a wall vent outside and a vent on the roof of the RV, over the fridge, you probably DO have an absorption fridge.

 

[ahh_me2]

Well, a 1000w inverter also requires larger power cables and brings out other issues.
Try and always use the smallest possible inverter..

As for having a compressor, an absorption fridge doesn't have a compressor as it relies on heat to perform part of the cooling process, typically propane is used as the heat source, but when operating off of power it uses an element, like in your toaster or stove and generates the heat from there.

That is in part why your fridge is very inefficient on power as opposed to propane

 

[ladywendolyn]

It does have a vent out the back and on top of the roof, but I thought that might have been for a propane fridge, which this one is not. We think the first fridge was 3 way and it died and it was replaced by the one in the photo. There is a capped propane line next to the fridge in the wall.

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[ladywendolyn]

This is an original broshure for the fridge. It says something about evaporation but does not use the word absorption so I'm not sure.

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[tx2sturgis]

Babe, thats an old compressor fridge!

 

[ladywendolyn]

Ok.. good to know. It's from England. Late 1950's I believe


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