Amp hours question

[Ticklebellly]

trailer-t, my example was about running a 40 litre Engel on 12 volts. My intent was to show that the fridge cycles at a high rate in warm weather and not so much in cold weather and that time is only included when you want to calculate Amp Hours. Going on what you describe (120V and 3.3 Cu Ft, drawing 6 Amps at 120 Volts, and estimating what Solar you might need) you would be putting about 70 Amps from a 12 Volt battery into an inverter to run the fridge. There a lot of variables in any estimate.

I suggest a way to get some proper data, cheap, is to get a Bluetooth battery monitor (like amazon.com.au/Wireless-Battery-Monitor-Bluetooth-Android/dp/B07SJ3SCJR/ref=asc_df_B07SJ3SCJR/?tag=googleshopdsk-22&linkCode=df0&hvadid=341793265826&hvpos=1o4&hvnetw=g&hvrand=6033416394793200341&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9069008&hvtargid=pla-844860331118&psc=1) and an Ammeter and do some real world testing. The current drawn by the inverter will frighten you a bit, both when the fridge is not running and when the compressor is running. Just turned on and idling, an inverter can draw quite a lot of current. The Blue tooth monitor I linked to will give you history. How to use the history is to watch when the compressor turns on and off (the graph will jump up and down as the fridge cycles), to calculate duty cycle. That duty cycle will vary as the ambient temperature varies. You can now do some real world estimates using data you collected on your setup and in your conditions.

 

[Trebor English]

For a 120 volt fridge get a $25 "Kill A Watt" and measure the actual watts used.  Let it run a full 24 hours and read the kilowatt hours, multiply by 1000 to get watt hours then divide by 12 volts to get a good estimate of 12 volt amp hours.  Add 20% for inverter loss.  That 24 hour number will reflect the portion of time that it is off and on.

https://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU/

Without that you have no clue.  6 amps at 120 volts is 720 watts.  That's a wrong number.  That is the sort of power level of an air conditioner.  For that  you would need a thousand watts of solar and a huge battery.

 

[Stargazer]

Ticklebelly,

Your posts are exactly addressing my question in that if it's labeled that it draws 6 amps, that "may be" every time it is on and immediately, but time running etc  Then my brain just sorta jumbles up.  I will have to really study all these responses.  Downside is this is not my system, owner knows less than I do and doesn't seem to want to know so I am blind to what is actually there. And cannot get ammeters et al to do what you detail.  Damn.  But I really want to learn this!  Please don't give up on me.

As for the outlet being GFCI, I am told all the outlets in the house are GFCI.  None look like the standard ones I have had, with the labels and buttons.  A google search does show new ones that look like regular outlets.  Electrician told owner they are all wired to a main GFCI switch "at the panel".  I don't trust this info but the inspector apparently didn't mention this so okay. 

It is a touchy situation for me but I really do want to learn this.  If I had my own system, it would be so much easier.  I am very thankful for the kindness of strangers!

 

[Stargazer]

To all who are responding here, THANK YOU! I am determined to get this.

 

[highdesertranger]

I am not sure of the exact number but you only need one GFCI outlet per X number of regular outlets. you wire them in parallel and the one GFCI protects all the outlets. highdesertranger

 

[B and C]

Your local library might have a kill-o-watt to lend.

 

[wayne49]

I used GFCI at the panel for wiring in a new garage.
If you plan on ever using florescent lights, they require a non-GFCI circuit.
Maybe florescent lights are illegal and/or immoral now.
If you find out what the separate circuit issue is about, please post the info.

 

[Stargazer]

Wayne49,

Will do. But why does a fluorescent light require non-GFCI? I guess I should google that.

 

[tx2sturgis]

Yeah cuz bathroom florescent fixtures often specify GFCI wiring....

:huh:

 

[Tom_M]

A word of caution about a Kill-A-Watt. I had mine plugged into a modified sine wave inverter. It got very hot and blew an internal fuse.

 

[maki2]

Trebor,  Thanks for your explanation.  I have never quite understood this.  From your post the Fridge is amp "rated" by the manufacturer based upon the compressor running continuously for an hour--is that correct?  Is there any way to obtaine an estimate on how much the Fridge compressor would actually run per hour to estimate the real world amp hour draw on the batteries per hour?  I understand the external temperature would make a significant difference as explained your post.  A light bulb seems easier to determine than an appliance that stays plugged in 24 hours a day but runs only a fraction of the time.  Thanks T

I have seen a graph from Engel showing the amps used per hour at various temperatures for a couple of their units. It don't think it was done recently but their units still are using the same compressor they have had for many years. I don't know if other companies have that type of graphed information available.  With refrigerators much depends on the volume of space, the type of compressor and the amount of insulation as well as factoring in the variations of temperature.  But usually they just give a ball park estimate of Maximum and Minimum conditions in their literature. The Engel graph/chart is the only one of its type that I have come across.

 

[future_vandweller]

I have been watching this thread for a while. There seems to be a general misunderstanding of Amps, Amp-hrs and would like to correct this.

Amps - [font=Tahoma, Verdana, Arial, sans-serif][size=small][size=small][font=Tahoma, Verdana, Arial, sans-serif] [/font][/size][/font][/size][font=Tahoma, Verdana, Arial, sans-serif]the *rate* of charge flow.  [/font][font=Tahoma, Verdana, Arial, sans-serif]1 Amp = 1 Coulomb per second.[/font] Amps is similar to other common rate measurements like gallons per min or miles per hour.

Amp-hrs = amount of electric charge = 3600 Coulombs.  This similar to gallons, miles, etc; a measurement of quantity.

When Amp-hrs is multiplied by the voltage of the source, you get the energy consumed by the appliance, measured in Watt-hrs.

A 12 Volt 6 Amp appliance will draw 6 Amps from a 12 Volt electrical supply.  In one hour, 6 Amp-hrs of electrical charge will flow thru this appliance.  The power consumption of this appliance is 12 Volts x 6 Amps = 72 Watts.  The appliance will consume 72 Watt-hrs in one hour or 1728 Watt-hrs (72*24) in one day.  The charge flow during this time is 6x24 = 144 Amp-hrs.

 

[Trebor English]

I have been watching this thread for a while. There seems to be a general misunderstanding of Amps, Amp-hrs and would like to correct this.

You will fail.  Pulling out your hair over this will leave you a bald failure.  You deserve to keep your hair.  Your failure here is not a reflection on you but rather an indictment of the education blah, blah, blah, nobody cares.

For some people there is no such thing as a mile.  There are only miles per hour.  There are no amps, just amps per hour.  I used to work with a kid who was raised in a commune by a den of hippies and could only tell time with a digital watch.  So what's an hour?  A quarter till four didn't make sense but three forty five he knew about.  So what's an amp forty five? 

The impression I get is that I, author, shouldn't have to use words with specific meanings.  They should mean what I want them to mean and you, reader, should figure out what I mean without regard to my choice of words.  As the author I want to put that effort off to you, the reader.  I am not to be bothered by trivia and details.  You, reader, are not worth my time and effort.  

I commend your valiant attempt.  Thank you for your effort.

 

[highest_vision]

So what's an amp forty five? 

I remember getting results like this in college chemistry. Chemistry I wasn't supposed to be in! Nice teacher gave me a C. But can you convert amp-minutes into meter-joules?

 

[wayne49]

These were hanging fixtures with dual 48 inch tubes with a sizable ballast, a type usually found in a garage or workshop back in 1989. The kind that always started with a buzz and a flicker. Beyond the observed behavior, I know nothing.
Since the thread's subject house was later revealed to be GFCI at the panel, my original comment was useless to the thread.

 

[tx2sturgis]

Yeah, you cant fix the pervasive, global, universal, misunderstanding of amps vs amp-hours.

I've tried, Trebor has tried, others too. Then someone with a good reputation or forum 'cred' will come along and mis-state it all over again. Or someone here will watch a youtube and see it stated wrongly, then tell us 'well so and so said blah blah, etc'

The worst offenders, in my opinion, are the DC fridge manufacturers websites, when they print something like:

"DC current: 4 amps per hour (or amps/hour)" (which is amps DIVIDED by an hour) 

There is absolutely NO SUCH MEASUREMENT. (its amps TIMES one hour, or amp-hour or ah)

But since some web designer typed it up that way, (amps per hour) then rest of us have to play 'wack a mole' with this stuff.

Arrrgh...

 

[tx2sturgis]

I should add this part, just for clarity:

Yes, you can measure, or quantify, amp-hours per (x) hours, such as 20 amp-hours per 24 hours (or 20ah/24hr)(in this case meaning 20ah consumed within the stated time, rather than divided by it)

Yes I know, that seems to be a bit of inconsistency but that is the way it is commonly written or stated.

This is a common and acceptable unit of total "amperage" consumed...and can be used as a statement of power usage if we know the voltage, and usually, we do, when talking about mobile electronics especially.

 

[Trebor English]

 
. . .
misunderstanding of amps vs amp-hours.
. . .

The original post in this thread, post #1, asked the question:
"Is that six amps per hour, assuming it runs continuously for that hour?"   

That's a reasonable and fair question.  The original poster asked a question and deserves a respectful answer. 

On the other hand, responses using "amps per hour" are like "Celsius gallons" in that they do not help to clarify what was asked.  Derision is earned but best avoided. 

I think the people who might know better just don't bother.  I mean "amp hours" is eight letters to type while "amps" takes only four and "ah" takes only two.  After a while common usage follows laziness and we become less able to communicate.

If you go back to the original question and substitute "amp hours" where the word "amps" is used it makes sense.  For example:
"Is that six amp hours per hour, assuming it runs continuously for that hour?"   The answer then is simply yes.

 

[tx2sturgis]

Trebor, no disrespect was intended to the OP...I was addressing the later sub-topic of trying to 'fix' the general mis-use of the terms.

As you said, it can't really be done....fixing it, that is. 

If someone (who wants to understand this) asks about this topic (amp hours question) we should help explain it, I agree. It's when the so-called experts get it wrong...thats when I feel the need to point it out...educate the educators...that's all I am trying to do.