Trying to understand Kill-A-Watt readings to spec freezer and then inverter

doctorZeus
doctorZeus Registered Users Posts: 24 ✭
in Solar Beginners Corner #1
I have a GE 5cu ft chest freezer I'm trying to spec for solar. I didn't have time to do much other than glance at the readouts and plug it into the kill-a-watt this morning before I left for work. (Out of an abundance of caution I waited until my gf would be home before doing this.) I cycled through the readouts and was hoping I was just missing something, but the only things I saw were watts, vamps, pf, and then the cumulative data like total time logged, total kilawats, and cost (based on adjustable kw/hr$).

I've yet to pull the trigger on an inverter, and wanted to be careful here to make sure it's spec'd out to handle the spike these freezers are notorious for when the compressor kicks on, or maybe even a more elaborate switching system between two inverters (a big one and small one, so it switches to the big one for startup and then back to the small one ones the load drops.)

Would manually clocking the watts and volt amps through a few cycles give me the information I need to do this, or do I need a new gadget? or any other suggestions? I.e., anyone have a similar sized freezer and if so, how are you setup to run it?

As always, thank you in advance!
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    you will need to know a couple things to properly run the freezer. first of all the running watts. this times about 4 should be enough headroom in most cases, but going 5 or 6x doesn't hurt. others can comment on that one if they think differently on it. another factor would be the draw while on defrost as you want to be sure that is also within, but i think it most likely would be. now i trust you are looking for a sine wave inverter and not a modsine as a modsine won't do justice to your appliance or the power consumed.

    once you know the actual power it consumes by running for a day or 2 the kwh will be shown and divide that by the hours to get the average hourly rate of kilowatts. the daily figure is more useful for solar so multiply the hourly rate x24 to get the kwh/day. this will be useful info for later calculations for your battery capacity and if applicable, your pv capacity.
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  • doctorZeus
    doctorZeus Registered Users Posts: 24 ✭
    #3
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    Thank you for the prompt feedback that was very helpful. I wanted to follow-up and post my results for a sanity check. (I've searched high and low for this info and found many similar curious forum posts and such, but none posted their measurements that I could find. Argghhh!)

    The kill-a-watt says the outlet was running at 122 volts/60hz. When the compressor first kicks on, it jumps almost instantly to 140ish watts. The highest I've seen is 146. The watts start slowly dropping down to mid-to-high 80s to low 90s. (I've never observed it below 80s before it kicked off and went down to 0.) So this means at the high point it's running ~1.2 amps, and the low point ~.66 amps. Does 1.2 amps sound right for the "starting amps" on a freezer compressor, even a small one? I expected it to be much higher than this, and maybe it's happening so quickly I miss it on the kill-a-watt? Maybe I'm confused and this is perfectly normal. (FYI - I'm not looking at the plate with volt/amp info but I believe it said it was 110v/1.29a, which is pretty consistent with my high range @ 122v.

    My first "test" is complete (29 hours of data on the kill-a-watt)..Using cold setting "5" out of 1 to 7, unit was empty and room temperature, and using Niel's guidance above, it calculated to running at .61kwhr. This is very close to what it's rated to run at according to the energy star guide (240kwhr/yr) which comes out to .66 kwhr. I suspect the .05 difference would close up or better on a lower setting and not starting with it at room temperature.

    If anyone had any comments on my starting amp question/thoughts that would be great!
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  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    #4
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    I recently added a small 3.2 cu ft G.E. refrigerator (no freezer) to my small system. When it kicks on I have noticed the kill-a-watt capture as high as 734 watts. There is no telling how high the real peak is. But it does start and run fine on my 600 watt inverter. It is located in an unconditioned space and according to the kill-a-watt was using about 1.6kw in 24hrs. That was with daytime temps where it is located reaching close to 100 deg. F. in the day and dropping only to about 85 at night. Haven't really checked, but since we have had cooler weather the last few weeks I think that figure is a bit lower now.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    sounds about right on your calcs. now multiplying by 4 will give about 600w for an inverter. if you feel that in the future you may need a bigger freezer or you wish to put other loads on it such as lights then you can get a bigger inverter to save you the trouble and extra expense of buying another one later.
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  • doctorZeus
    doctorZeus Registered Users Posts: 24 ✭
    #6
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    Niel, thanks again and your last comment leads right into another question I had.. I understand inverters have a bit of a resting power draw just for being turned on, and it can get into serious watts for a smaller system just to be turned on with no load. I didn't see any information on that in the Samlex spec sheets/manuals (granted I don't know what exactly I'm looking for), but I was looking at the Samlex 600 and 1000 watt 24V inverters. I don't mind spending a little more up front to get a better inverter with more capacity, but is there any way to spit ball what type of "vampire" draw I should expect from these two sizes? If it's not significant I'd much rather get the higher 1,000 watt model.

    rgk1 Is your fridge a much older/less efficient model? Is it possible something got miscalculated? It is a little odd to me that you see the big spikes that I was expecting to see but haven't. I think I'm going to do some more testing to see if I can confirm high it peaks. But 1.6kwhr sounds like a lot for a mini/3.2 cu ft fridge.. 1.6 is more than a full size refrigerator with freezer (at least it's more than mine, the energy guide on my ~2 year old freezer has it at 383kwhr/yr which is just a fraction over 1kwhr. One detail I didn't confirm that you did is the location/temperature.. my freezer is inside with ambient @ 75/76 degrees f. I'd expect a measurable difference, but hmm.. I appreciate you helping with the sanity check and posting your results (especially the inverter part)!
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  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    #7
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    My G.E. is about 4 years old. I was VERY surprised to see it capture a reading that high. A while back I connected my home refrigerator, a 26 cu ft side by side, just to see if it would start. It did (compressor only), but the kill-a-watt only captured in the mid 200 watt range. It averages about 1.8kw/24hrs. Maybe the G.E. takes a little longer to start and lets the meter capture it. Not really sure.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • rgk1
    rgk1 Solar Expert Posts: 134 ✭✭✭
    #8
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    I may stand corrected. Got home today and opened the door to make the fridge come on and the Kill-a-watt captured: 183 watt, 243 watt, 114 watt, 112 watt and 111 watt in a 5 second period. For my own sanity I will have to watch it some more and see if I imagined the high reading.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #9
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    docz,
    i have to ask if this is off grid with or without the grid available as with the grid available there are options for built in charger and utility circuit feed through?
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  • doctorZeus
    doctorZeus Registered Users Posts: 24 ✭
    #10
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    Sorry about that Niel..the devil is always in the details :) The system is expected to be off-grid (though it will be sitting inside of a grid-connected house). It's main purpose is for "emergency luxury," i.e. I'd like to avoid the nearly two week straight blackout that occurred following back to back hurricanes in 2004. Under normal conditions I plan to hobby around with it for awhile by slowly taking my office/mancave off-grid (sans central air conditioning), wire the room with 12V, etc.. At the moment I have more "ideas" than I do "requirements" but the freezer is the biggest thing I'm looking to power. My load calculations have 2.2kwhr as the maximum (total) usage per day which is a little under 25% DOD for bank with a maximum (at once) draw of ~400 watts. <-- My max draw was at ~250 watts before adding and factoring in the freezer. Assuming my kill-o-watt isn't lying to me and ~150 is as high as it gets, that gets me to ~400 watts max draw at once.
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  • doctorZeus
    doctorZeus Registered Users Posts: 24 ✭
    #11
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter
    rgk1 wrote: »
    I may stand corrected. Got home today and opened the door to make the fridge come on and the Kill-a-watt captured: 183 watt, 243 watt, 114 watt, 112 watt and 111 watt in a 5 second period. For my own sanity I will have to watch it some more and see if I imagined the high reading.

    So I just recorded it with my phone video camera to make sure I didn't miss anything and ..within the first three seconds it flashed 203, 208, 110, 109 .. for the next five seconds it flashes between 108 and 109, and then it was steady down from there for about the next minute where it made its way slowly down to 99 before I got tired of looking at it. Considering the range, that's a pretty big difference. Differences (I can think of) between my first reading and second is that it was it's first go starting up with an ambient temp freezer compartment, where the second reading it had been running for ~36 hours and turned on by itself (not me plugging it in). The take away here is (I think), there's going to be some (percentage wise) pretty big variations on these things. I bought the kill-a-watt to help me determine two things, peak draw and kwhr. I'm going to try and watch it peak a few more times just to be safe, but I'm declaring success on the load at ~.6 kwhr. For now..
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #12
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    docz,
    whoa, slow down there. you are starting to confuse me here. we haven't really gotten into battery capacity or how it is you plan on charging those batteries let alone settle on a suitable inverter. i was leading somewhere with my line of questioning as some inverters can be operated much like a computer ups. now this sounds like what you basically need, but it will be more costly than a plain inverter. the maximum ac draw at any one time will determine your wattage capacity the inverter is capable of delivering. we already figured at least 600w to handle the freezer and if you have other loads totaling 250w then add that to the 600w for 850w minimum. as you won't find an inverter rated at that as a common value then look higher much like the 1000w area. you may wish expansion in the future as i mentioned so the size you buy should take this into account now or you will risk needing to buy another one later. more on the inverter later in this post.

    now i already started discussing your wh needs briefly, but stopped to go in steps. as i mentioned, this is better figured at a per day rate. the killawatt meter can measure the actual loads over time. now i do have to say up front that it would be difficult to backup a kw with batteries for a day let alone a week or 2 for hurricane outages. this multi day situation is where the pvs or generators if gasoline is available come in to help keep things going, but let's look at 1 day for now as you would know that for each day added that the battery capacity and the charging capacity will be multiplied by that number of days.

    i will only give an example here as you need to do the actual measuring. you indicate the freezer averaging .66kwh (for hotter days and aging) and over 24hrs this will be 15.84kwh. add to that your other loads of about 250w and let's say this averages 5hrs per day for 1.25kwh. note here that the kwh is a thousand watt hours (wh) so it is easily figured. your grand total is now 17.09kwh. this is not a good wattage to have a batty at as this would totally drain the battery and we recommend at least doubling that making it 34.18kwh. now this isn't something you run out and buy a battery based on watt hours so you must divide the wh by the battery voltage you've chosen to get the amp hours battery capacity comes in. if you go with 12v the ah would be 34,180wh/12v=2,848.3ah. this will not be easily accomplished at 12v as too many batteries may need to be paralleled and we contend that going more than 2 is iffy and it gets worse with each battery paralleled. now if you find a battery with 1424ah at 12v then you could parallel them. it would be easier at 24v as the battery capacity gets divided in 2 as you would see by dividing the wh by the battery voltage. now you would need 712ah per battery and 2 in parallel. being batteries don't usually come in a 24v model then you need to put batteries in series to arrive at the desired battery voltage and we refer to batteries in series as strings. examples are, 4 x 6v = 24v and 2 x 12v = 24v. now there may still be a problem finding batteries at that ah. the best option is to have a 48v battery voltage making the current requirement on 2 strings to be 356ah. batteries are available for that ah area and if you check our host you can see some of their ah values and costs. warning-batteries are a big expense as you will see. whatever battery arrangement you go with you need the battery bank voltage to match the voltage of operation for the inverter. on a final note on batteries is that we recommend a charge range at 5%-13% with 10% fairly typical to shoot for.

    this is getting long, but the inverter type desirable would be the type with ac feed through and a built in charger. the feed through allows normal grid power to pass until you get an outage then it flips over to the batteries and inverter very quickly keeping a near seamless power transfer. if the outage stops after x number of hours then the utility power passes through again and the batteries start to charge again with the built in charger. after charged the inverter with switch to float. many inverters offer remotes for more versatility in charging and even generator auto start for some.

    for more days of autonomy you will need more battery capacity and put this in combination with other charge sources such as pv and generators. there is no guarantee you'll have enough gasoline to run the generator, pv capacity as this can get quite large in scope, or sunshine to feed the pvs their power from the sun.

    hope this helps and her's the link to our host's store for you to check stuff out on.
    http://www.solar-electric.com/
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #13
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter
    niel wrote: »
    i will only give an example here as you need to do the actual measuring. you indicate the freezer averaging .66kwh (for hotter days and aging) and over 24hrs this will be 15.84kwh.

    This completely lost me. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    why's that? it is what he said it is rated at in post #3. he measured .61kwh.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter
    niel wrote: »
    why's that? it is what he said it is rated at in post #3. he measured .61kwh.

    Because of the use of kilowatt hours for both figures.
    660 Watts * 24 hours = 15.84 kilowatt hours.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #16
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter
    niel wrote: »
    why's that? it is what he said it is rated at in post #3. he measured .61kwh.

    He measured those kwh over more than a day (29 hours). You then multiplied that by 24 and concluded that the freezer uses 15.84 kwh per day.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #17
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    oops my bad. disregard my math, but i think he gets the idea.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #18
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    And for those who like math ...

    0.66 kilowatt hours measured over 29 hours is 22.75 Watts average per hour or 546 Watt hours per day.

    :D
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  • doctorZeus
    doctorZeus Registered Users Posts: 24 ✭
    #19
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    My apologies for any confusion, riding the bottom of the learning curve still I should have been more detailed and showed my calculations. But to clarify, the kill-a-watt showed I used a TOTAL of .6high-something kwhr over 29 hours, which when I calculated with Niel's instructions told me I was using .61kwhr over 24 hours.

    NOTHING is connected at this point, but here is a much more detailed post of my system/specs:

    Batteries
    Eight 6V 215aH golf car batteries connecting two 24V series strings to a parallel string giving me 24V / 430aH (~10,300 watts total, 2580 watts 25% DOD).

    PV / Charge Controller
    Three grape solar 250Watt panels (w/ two more on the way) connected to a Midnite Solar 200 classic lite in a single series string. To account for loss and conditions I'm doing total panels (5) * 250 (listed watts) to give me TOTAL PV input power as = 1250 watts for the array (per sun hour). I'm taking 60% of that, .6 * 1250 = 750 watts to account for system/efficiency loss (this is an unscientific "get me in the ball park" number), then I'm using four sun hours per day, so 750 * 5 = 3750 watts per day on average. (Any thoughts on this being a reasonable expectation of daily PV input power to the system with five 250watt panels?) EDITED- I calculated it out as 5 sun hours instead of 4 which I understand is a bit high of conservative, so just to be clear I meant to do it at 4 which would gets me to 3000 watts per day of PV.)

    Daily Power Requirements
    My current estimated load is mostly low draw equipment (fans, phones/tables, laptop, battery chargers, cable modem), but I've since added the freezer. Assuming I'm not missing any major "spikes" because I've only measured the freezer, I'm looking at my maximum-at-one-time draw to be ~450 watts. (When I'm spec'ing the inverter, should I be doing the 4x,5x,or 6x calculations for the lower draw stuff I mentioned above?)

    Some earlier helpful responses has me targetting 25% DOD for daily usage, with PV input targetting double that to account for inclement weather, over usage, etc. Since my daily input is ~3750 and my 25% DOD is 2580, I understand I need to get my PV input up to ~5,100 in order to accomplish that goal but for now, I plan to move forward with the current setup and add PV later.

    With all of that said, I'm now shopping for an inverter. Obviously I would like for it to be as efficient as possible in the conversion and have minimal power draw without pushing things so close to its capacity that it's running hot and increasing wear and tear. Eventually I'd like to be able to use my generators and a battery charger (I have a 2000 and 3500 watt continuous generators) to supplement charging to the batteries on an as needed/manual basis, but I don't plan on addressing that until after I get the system off the ground.

    I haven't started that actual install process. Note that I don't have ANY other equipment like junction boxes or monitoring equipment (I will be using my computer to log data from the charge controller though). I planned on building wooden ground frames for the panels, and a wooden frame for the batteries, charge controller and inverter (going to make sure I can get to the batteries/caps easy enough for maintenance and minimize cable lengths here). I planned to do all of the hookups in a very laymen and simple manner - 12 awg mc4 cables from the panels to the charge controller, 4 awg from charger controller to the battery bank, and 2 awg battery bank to the inverter. At present I don't have any plans for fancy junction boxes or monitoring tools for the initial setup. I will likely get some as I get off the ground, but mainly looking for anything major that I could be overlooking. Thank you very very much everyone!
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #20
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    It is pretty well established that 'little' refrig's doesn't mean little power. Size proportions do not correlate to power consumption proportions. Generally you will be lucky if the little refrig draws less then 75% of full sized refrig, even though it is less then a quarter the cu. ft. size in volume.

    Unless you really need it to be physically small (like, say an RV application) you might as well go for a 14-16 cu ft. full sized refrig which will draw 600-800 WH's per day.

    My 27 cu ft side by side draws about 1 kWH per day on average. Numbers depend on how many times and for how long the doors are open.
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  • doctorZeus
    doctorZeus Registered Users Posts: 24 ✭
    #21
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    RCinFLA, that's perspective setting for me - it hadn't occurred to me that you're not (even close to) saving proportionally as you get smaller, but you're absolutely right. Looking at the energy guides on homedepot.com, comparing the GE models of 5cu ft and 14.8 cu ft, kwhr usage goes up only 33% while size goes up a whopping 300% .. wow!!

    A couple of other things to consider though..if size isn't an issue, costs can be (the initial cost more than doubles going from 5ft to 14.8ft)..I've budgeted pretty carefully for this. At this stage of the project and funding I am being careful to "stick with the plan." But if I'm going to oversatisfy a requirement it's NOT going to be on the freezer. :) It's just my g/f and me, and 5 cu ft is actually bigger than I expected to start with! (We could easily fit 6 months of our "freezer" food in here, probably double that if I excluded frozen dinners. And perhaps most important thing is to ensure we aren't overlooking the scale from which the usage is being measured. "Condition green" on grid power, I don't think there's any arguing that the difference is negligible. But on a battery powered off grid system calculated to a minimalist load, the ~31% power increase between the 5ft (240kwhr/yr) and the 14.8 ft (357kwhr/yr) can get very relevant very fast.

    I lucked out here a bit when I bought the 5 cu ft ignorant to this because even looking through the hindsight goggles I would still go for the 5 cu ft.. Thanks for the feedback !
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  • Skippy
    Skippy Solar Expert Posts: 310 ✭✭
    #22
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    A couple of things jump out at me on this one.

    1. When I was testing my frost free fridge with the k.o.w meter, I found that when you pulled the plug, and then plugged it back in, the fridge thought it had to defrost and restart EVERY time . . so I cannot get an inverter that has a sleep mode. You may want to redo your test with your freezer . . plug in the meter, wait till it reads 0 . . nothing happening . . everthing is cool (litterally), then pull the plug (from the meter, do not pull the plug on the meter it will reset) let it sit for a minute, and then plug it back in. If it defrosts and restarts again, then you might not want to get an inverter with a built in "sleep" mode . . I did that little test with my fridge - 3 times in a row, and every time, it restarted and cooled down - in about 15 minutes. Not good. A regular inverter takes a bit more power, but it won't have any false starts or stops either. Just my thoughts

    2. I found that for the amount of extra power needed for a seperate freezer, I did not use the chest freezer enough to warrant it, so I gave away my little chest freezer and picked up a fridge/freezer combo. Since I don't need all that freezer space. Again, just a thought.. .
    2 - 255W + 4 - 285W PV - Tristar 60 amp MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
    1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
    3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
    9 -220W PV - net meter - Enphase inverters and internet reporting system.
    420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
    Current project is drawing up plans for a below grade Hobbit / underground home.
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  • westend
    westend Solar Expert Posts: 46 ✭
    #23
    Re: Trying to understand Kill-A-Watt readings to spec freezer and then inverter

    If you can, contact the Mfg. and ask for the locked rotor draw of the freezer. This may save you some grief if you decide to power it with a smallish inverter. I was unable to power a small 1.8 cu.ft. dorm fridge with a Samlex 600w inverter. The startup draw exceeded the inverter's capacity. I have, since, bought a Xantrex SW1000w inverter and that handles the fridge and my other devices. I don't have a data logging meter that will exactly measure the draw of the small dorm fridge but I would estimate it is in excess of 4 amps. Your freezer will probably be more than that.
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