Amp hours question

[Stargazer]

Appliance label says "6 amps".  Is that six amps per hour, assuming it runs continuously for that hour?

 

[skyl4rk]

Yes

 

[Stargazer]

Thank you!

 

[DLTooley]

That’s the maximum draw and may use less depending on particulars, not just run time.

Don’t forget to adjust for voltage. A 120v draw will be ten times that of a 12v and there will be an inverter loss.

 

[ckelly78z]

Some appliances that create heat with a heating element, will cycle on/off to prevent damage. The 6 amps would be when the element is under full power, obviously 0 amps when it is in cool down mode. It may cycle several times a minute (coffee pot, toaster, microwave, space heater).

 

[Trebor English]

Amps is the speed of the current flow.  A cruise ship leaves Miami on the way to Barbados traveling at 20 knots, the speed.  Twenty knots per hour doesn't make sense unless you mean after an hour it is going 40 knots and then an hour later it is going 60 knots.  So if the appliance takes 6 amps, it takes 6 amps. 

If a refrigerator compressor runs 6 minutes per hour (1 tenth on) and uses 5 amps while it is on then each day it will have run 2.4 hours at 5 amps for a total of 12.0 amp hours per day.  That's January but in August it will still take 5 amps during the time it is on.  It will run 12 minutes per hour, 2 tenths on, for a total of 4.8 hours per day.  Then it will be 24 amp hours per day at 5 amps.

 

[trailer-t]

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

 

[Trebor English]

I have an amp meter.  The cheapest red Harbor Freight meters that are sometimes free with a coupon can measure 5 amps, like what a fridge takes.  Actually it goes up to 10 amps.  You put the meter in series with the load.  The easy way is to pull a fuse and put the amp meter across the terminals where the fuse was.  It tells you how many amps are flowing at the moment.  If you watch the amp meter for a minute or for 5 minutes or an hour it only tells you the momentary speed of the current.  

Amazon sells a $12.39 amp meter, volt meter, watt meter and amp hour meter.  
https://www.amazon.com/Analyzer-Digital-Balance-Battery-Voltage/dp/B0753DPC2D/

When you connect it in a circuit it tells the amps flowing at the moment and the volts at the moment.  It also multiplies those two and displays the watts at the moment.  Over time it keeps track of the current.  It updates every few seconds.  While the fridge compressor is on the amp hour display increases.  When the compressor is off the display holds, doesn't increase.  

I have a small Haier 1.7 cubic foot dorm room fridge powered by an inverter.  I have an old timey electric clock, kitchen, hang on the wall style.  I connect that to the thermostat switched 120 volt supply to the fridge compressor.  While the compressor runs, so does the clock.  That way I can measure the compressor run time.  If you know that it ran 2 hours and 18 minutes and it took 5.2 amps while running then (2.3 * 5.2 = 11.96) it took about 12 amp hours.  During the 2 hour run the current varies.  As the temperature of the freon varies the pressure varies.  As the pressure varies the watts used to pump the freon varies.  If you write down the amps every tenth of an hour, every 6 minutes, and multiply the amps at the moment by 0.1 and add them up you will, as time passes, accumulate the amp hours used.  

Don't forget Doctor Peukert.  He figured out that a higher current has a disproportionately higher effect on a battery state of charge.  Ten amps for one hour has a greater effect than one amp for ten hours even though they are both ten amp hours.

 

[Tony's Dream]

I have seen the volt meters you are talking about. There should be a meter that not only displays it's current usage but logs and reports its use for a 24-48 hours period. That would allow us to look and see that over the past 4 hours I consumed 16 amp hours...….and knowing I have a 100 amp hour battery...…..I will know better when it's time to recharge the battery...…..and if I can't recharge it, about how much power I have left and when I will run out. Like our gas gauge in our car. When we drive 75 mph we know we are burning more gas then if we drive 55, the guage still shows us exactly how much gas we have left in the tank. In fact, my car calculates my gas usage and predicts how far I can drive based on my usage. We should not have to sit around and do math all day to determining what we use/need.

 

[trailer-t]

Thanks Trebor, That testing is a bit beyond my present (or future) abilities, but I understand what you are doing in measuring the actual amps by measuring the running time.

Let's say I have a 3.3 cubic foot Insignia fridge with an estimated annual usage of 258kw annually per the manufacturer disclosure if typically used. Could that give me a ballpark usage to start from if I divided the annual usage down from annually down to an hour?---I understand that the initial cool down will be a big drain and that actual usage will vary by user, contents, temperature etc. T

 

[highdesertranger]

"There should be a meter that not only displays it's current usage but logs and reports its use for a 24-48 hours period."

there are and there are a few of them I know one is the "Trimetric" by Bogart Engineering, it's like a fuel gauge for you batteries. hopefully others will chime in with some others.

highdesertranger

 

[Trebor English]

Thanks Trebor,  That testing is a bit beyond my present (or future) abilities, but I understand what you are doing in measuring the actual amps by measuring the running time.

Let's say I have a 3.3 cubic foot Insignia fridge with an estimated annual usage of 258kw annually per the manufacturer disclosure if typically used.  Could that give me a ballpark usage to start from if I divided the annual usage down from annually down to an hour?---I understand that the initial cool down will be a big drain and that actual usage will vary by user, contents, temperature etc.  T

The yellow sticker on refrigerators has the annual energy consumption.  That is based on a specified test that is repeatable but not necessarily realistic for use in a van.  It is based on a specific ambient temperature that is, as I recall, constant.  

258 kilowatt hours per year, 258,000 watt hours per year divided by 365 days per year is 706.8 watt hours per day.  Divided by 24 hours per day it is 29.4 watt hours per hour.  It is not 29.4 watts as it is on some of the time, off some of the time.  If the actual watts while it is on is 60 watts then 29.4 / 60 = 0.49 means it runs 49% of the time.  At 12 volts, 706.8 watt hours per day / 12 volts = 58.9 amp hours per day.  

As they say, your mileage may vary.

 

[Trebor English]

"There should be a meter that not only displays it's current usage but logs and reports its use for a 24-48 hours period."

there are and there are a few of them I know one is the "Trimetric"  by Bogart Engineering,  it's like a fuel gauge for you batteries.  hopefully others will chime in with some others.

highdesertranger

The one I linked accumulates as long as it is plugged in.  If you want to know the 24 hour use, read it at 24 hours, unplug it to reset it, then plug it back in.  If you want to know the 48 hour consumption do that twice and add the use for the two days or just let it run two days. 

At the bottom of the barrel cheapest of all time price point you don't get Peukert coefficient compensation or automatic resetting at the time of day you are thinking about.

 

[Stargazer]

Woah!  I thought this was a simple question.  I see i will have to go over this a few times to understand it well.

A friend has built a tiny house, off grid.  Don't know detaiils on her six panels, batteries are lithium ion labeled "800 AH".  When the inspector was there, he told her the Code disallowed two appliances being plugged into the same standard 120V 15A outlet.  Her water heater (tankless) is labeled 2A (propane with electric starter) and she has a small portable washer that is labeled 6A.  I think that outlet will easily support those two items.  The space was designed and built to run these two items on that same outlet.

Thanks to all!

 

[AuricTech]

At what voltage are those lithium ion batteries rated for 800 AH?

 

[Almost There]

Woah!  I thought this was a simple question.  I see i will have to go over this a few times to understand it well.

A friend has built a tiny house, off grid.  Don't know detaiils on her six panels, batteries are lithium ion labeled "800 AH".  When the inspector was there, he told her the Code disallowed two appliances being plugged into the same standard 120V 15A outlet.  Her water heater (tankless) is labeled 2A (propane with electric starter) and she has a small portable washer that is labeled 6A.  I think that outlet will easily support those two items.  The space was designed and built to run these two items on that same outlet.



Thanks to all!

Might be way off base but I suspect that the code violation he is referring to is that each of the top and bottom outlets on the duplex are supposed to be on different circuits. It's standard in kitchens and with a tiny home the outlet she is using may very well be in the kitchen area. Building codes don't take in to consideration WHAT is going to be plugged in, don't matter, don't care type deal!

 

[Stargazer]

Auruc Tech: I don't know. She purchased the entire system from a solar company. They asked the right questions (I think) and made this recommendation.

Almost There: That makes sense. It is in the bathroom.

I will see her tomorrow. We are doing some finishing work (baseboards and trim, easy). I will pass this info on and see about the batteries.


Later...

 

[Ticklebellly]

From your post the Fridge is amp "rated" by the manufacturer based upon the compressor running continuously for an hour--is that correct? 

Amps is an instantaneous measurement.   Nothing to do with time.   The device when running draws X Amps.   In the case of a fridge, the compressor motor when running will draw X Amps.   Time enters the equation when we measure the time of a cycle, of time compressor runs to time the compressor is off.   An example - my fridge draws 2.5 Amps when the compressor runs.   Recently, in 17 Degrees C ambient, the compressor would run for 3 minutes, to drop cabinet temperate, then sit idle for 6 minutes until the thermostat triggered another compressor start up.   In round figures, about a 30% duty cycle; 33% on to 66 % off.  That same fridge in 42 Degrees C ambient runs a 82% duty cycle.   The ambient temp a fridge is exposed to mostly varies over a day/night situation so the AH a fridge might use over a day is very difficult to calculate or predict.   I am most concerned about how much energy my fridge draws overnight when Sun is not available to charge the battery.   Experience has had me settle on 12 AH overnight draw.   You will see that my numbers equate to working on an average draw of 1AH per hour.   If you do not have access to a coulomb meter, I suggest you start by timing a cycle and link that cycle time to an ambient temperature.  Do it a couple of times over the day and you will have some real data to work with.

 

[wayne49]

Bathroom would require a GFCI outlet, maybe that is the confusion about a "separate" circuit.

A solar company would not necessarily be up on building codes for regular household electrical circuits.

An example of a GFCI outlet:
https://www.amazon.com/Tamper-Resistant-Weather-Resistant-Receptacle-Indicator/dp/B08159L787

 

[trailer-t]

Ticklebelly, Thanks. For your excellent post above! Can you describe what kind of fridge you refer to?
Mainly the size, and whether it is 12 volt vs 120, and does it include a freezer? Mine is a 120 volt- 3.3 cubic feet- with no freezer (energy star efficient or whatever). Just looking for a ballpark amp draw over a day to estimate sizing some potential solar panels. (thinking maybe 300-400 watts mono). t