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Help me understand how well/poorly this portable power station might meet our needs. In a place where power outages are not uncommon, and we do not have a generator, I'm trying to decide whether to invest in something like this. Just making sure my units are correct.

It claims to have a 3840 Wh capacity, which if I understand correctly, means that it could output 3840 watts for one hour, or half that many watts for 2 hours, or something like that.

Let's say that I plugged our fridge into it. The fridge label says 690 W. And the internet estimates that fridges run for about 8 hours per day. So, one 24-hour period with 8 hours of run time would be 690 W times 8 hours, or 5520 Wh. That means that this device would be able to reliably run the fridge for significantly less than one whole day.

Have I done all that math correctly?

Relatedly, it also lists its output capacity as 100 Ah. This makes no sense, right? The unit can output both DC (at two voltage levels) and AC. But am I right that without knowing what voltage these 100 ampere-hours are at, this value is useless? So the watt-hour measure is the more useful?

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    Fridge power consumption is more like 100W average, 2kWh/day. The nameplate rating is a maximum (defrost heater running, or instantaneous compressor startup draw) - not a representative average. Plug into a Kill-a-Watt if you need to know specifically how much power your fridge uses per day. Commented 2 days ago
  • You may be able to prevent a defrost cycle (significant contributor to power usage if present) running, by unplugging it for a few hours, then plugging in to allow it to cool down. A fast chill button, if present, will prevent a defrost cycle running (and save power), but increase power consumption for a while by running the compressor flat out - which is greater depend on the model. Fats chill can of course be stopped by unplugging Commented yesterday
  • Here's a thought: how widespread are power cuts in your area? If they tend to be very localised, would you have the option to hire a small generator, just using the power pack to get you through the first night? I came close to doing this once - Christmas dinner was in the fridge & freezer and only 23 houses went out - but I spoke to the crew fixing it and was reassured it would only be a few hours Commented yesterday
  • @crip659 that sounds like a true worst case consumption - starting motors simultaneously from very cold. Either that or the peak inrush current is faster than you can measure - which isn't a problem for total capacity, but might be for the maximum instantaneous output, something @ nuggethead needs to look up in the specs (2.6kW from the linked website, so no problem). Commented yesterday
  • This isn't a direct answer to your question as most point out it would be less than one day, I wont beat a dead horse. An alternative to pulling your fridge out and plugging it directly into a power supply, I would buy a bag of ice and put it right next to the food in a bowl to catch the water. Fridges used to just be giant ice box coolers anyway. If you cant go get ice, stick the food in the freezer portion and it will last ~24hours on its own without the effort of moving the fridge and using a battery. Commented yesterday

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Your approach to this is incorrect. You cannot predict a fridge's duty cycle (the percent of time its motor runs) from its specs or from internet-derived averages.

The amount of power a fridge uses depends mostly on how full it is and how often the door is open. It depends on other things too: its efficiency, its insulation, the temperature around it. But the first two things can overwhelm the others. A big fridge, with just a few things in it, and with the door opened and closed frequently, will consume a lot of energy. How much depends on the internal and external temperatures and how long and often the door is open. On the other hand, if it's completely full of food and the door is not opened at all, it will use much less energy.

More importantly, the full fridge if undisturbed does not have to consume any energy. You can unplug it and the inside temperature may drop only a few degrees per day. Food won't begin to spoil for several days and it will consume zero power. You do have to unplug it to achieve this!

Fridges with electronics - front panels, wifi, external lights, will use more energy, and unplugging a full one will have an even better effect on your backup power, assuming you don't need the functionality during the power outage.

On the other hand, if you have a bunch of kids opening the door constantly and treating the fridge as a television, you'll run out your battery generator in 3 or 4 hours.

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  • So a simple fridge, used wisely for the duration of the power cut, could be kept cold for several days. It might do better be in a house that's getting rather cold, reducing consumption, if you're more likely to lose power (and with it heating) in winter - or of course worse in summer. Commented yesterday
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    Duty cycle is quite dependent on room temperature. This is most obvious for the one in my campervan (a 12V compressor fridge), which can have 20+°C temperature swings over a day; it barely runs at night, but gets up to about 25% on a warm day (probably much more if it gets really hot closed up in the sun, but I wouldn't be inside to notice that. Commented yesterday
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    @ChrisH Seeing a fridge is open at least once/a few times a day, I would think it would need to be powered up for an hour or two once every day or two. A chest freezer could maybe go three days if kept close. A fridge as much less temperature range before hitting danger zone, maybe 5 or 10F degrees. Commented yesterday
  • @crip659 yes; I'd go for an hour/until the compressor turns off (by ear or power meter, probably <<1 hr) 2-3 times a day. The power pack would then last several days. Personally I'd optimise, aiming to open it at most once before and once after preparing each meal, not opening separately for drinks or snacks (instead choosing things that are OK for at room temp e.g. fruit can be taken out at mealtimes for later). Then you could run for a bit after each meal to get the temp back down quickly for food safety. But I'm a person who optimises stuff, and my daughter will do as asked. Commented yesterday
  • "You cannot predict a fridge's duty cycle (the percent of time its motor runs) from its specs" Typical compressor and fan duty cycles are often listed on the technicians service sheet or service manual to provide an answer to customer concerns about excessive run time. Commented yesterday
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First of all, these 690W are probably not the number you start your calculation with. 690W looks like a small restaurant worth of refrigeration. Or, better yet, a corner case short-time power consumption for this particular fridge (e.g. a compressor inrush current, defrost cycle or something like).

Our (European, fairly typical, ~300 liter each, ~10 years old) fridge and freezer both use ~500-600W inrush power (for 1/2 second, when the compressors kick in) and 60-80W when the compressor runs. Each of them daily uses 0.3-0.5kWh.

I am not sure what their labels say, these numbers are from the smart plugs they are plugged in and the data pretty much aligns with what I know about the refrigeration in general.

One thing to consider is that the fridge energy consumption varies a lot with the climate and the use pattern.

This is why you have to use an energy-measurement tool (kill-a-watt or similar) to estimate the fridge power need in your particular use case.

My bet is that the device in question will give you 2-3 days of backup. If this is not the case, replacing the fridge with modern, energy efficient one could be the cheaper option in the long run.

Edit: I found the worst case datapoint - the kids left the freezer halfway open for a weekend and the compressor did not stop until I found out. The full 24-hour consumption was 1650Watt-hours. As I said above, it is usually 1/4 of this.

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  • i'm kind of fascinated in the end you came up with a 2-3 days value, which is what bluetti published on that webpage for a fridge based on 1kwh/day usage. but a common residential full size fridge in Merica the compressor running on 120V pulls around 6 amps = around 690w. I would like to know your make/model of fridge that can run at 60-80 watt. Commented 9 hours ago
  • @ron: The source needs to be able to supply 6 amps, but that is the peak current, not the long-term average. You won't find a normal-sized fridge that doesn't exceed 80 W during any part of its cycle, but that might well be the average. Commented 9 hours ago
  • @BenVoigt I am not moving neither the fridge nor the freezer out of their places before my wife tells me so more than once. I found the freezer model: Snaige 3v44fsnbb, it happens to be 230L instead of 300, the label lists 210kWh/year. The average power drain is well below 80W - ok, ok, sometimes the kids leave it slightly open and the average becomes 80W. If left alone its duty cycle is 20-30%. Its startup current is ~3 ampere and this corresponds to ~6 ampere in the US, but it is what it says - a startup current. After less than a second it goes down to half ampere or thereabouts. Commented 8 hours ago
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Your math is correct: as you state, a 3,840 W-h capacity supply might operate it for ~5 hours total, or ~15 hours, running 1/3 of the time. The fraction of the time the compressor runs depends on room temperature, how often the fridge is opened, etc., but that seems a reasonable estimate.

As for the "100 A-h" rating, that implies the supply is ~39 volts. I.E., 100 A-h * 39 V = 3,900 W-h. Using dimensional analysis: V*A = W, and multiplying by hours give W-h. Or, it could be a typo, and max instantaneous current rating might be 100 A (not A-h).

In any event, it seems like a that (likely costly) supply would not give one whole day of refrigeration. For longer operation, consider a generator (alternator, actually) powered by petrol (gasoline), propane or natural gas.

Also, electric vehicles with bidirectional charging are the equivalent of a huge battery pack and inverter. Depending on the size of the battery, one might power the whole house for three days or more. While it's not economical to buy a car just for that purpose, if you're considering purchasing an electric vehicle, consider one that can feed into the electric system. Of course, you'll need to have this safely wired with a transfer switch, and that adds some cost.

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    Doesn’t even have to feed into the house if you just care about the fridge: an V2L adaptor and a long extension cable will be enough. Commented yesterday
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In addition to the other answers, I would recommend buying a power meter (kill-a-watt is one I'm familiar with, but there are many to choose from). With this device, you can track your actual power usage, and then size a battery solution appropriately.

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  • This is the aporoach taken in this YouTube video by TheSolarLab. They measured a consumption of about 1.4 kWh per day, on 3 different fridges. So signifcantly less than most answers here. youtu.be/OfR53ZZ2gSc?si=Dp8sCUo7NYpoJcAZ Commented yesterday
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I can hardly do better then recommend you check out videos from the Solar Lab Youtube channel: https://www.youtube.com/@TheSolarLab

In a recent video - https://www.youtube.com/watch?v=ishoyff15QY - they estimate a relatively modern fridge would use ~1300 watt hours per day.

So that Bluetti you linked could be just a hair less than 3 days of backup. Of course - if you can use solar panels - you could just get a smaller unit and keep charging it.

They also make the important point that battery systems have idle power consumption of their own. They included their estimate for standby consumption in their calculations - I think about 37W continuous with the AC outlets active. That means a fridge might technically use only ~600Wh a day - but including the standby power bumps it up to ~1300Wh/day.

So - if you can manage to manually turn the battery unit on and off during an outage you could avoid a lot of standby consumption. Let's say you keep it off for 3 hours - then back on to let the fridge cool for while - then off again. You might be able to stretch it out for another day or two.

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I would say basically your math is pretty close. What will really impact your run time will be the number of times your fridge cycles on and off because the starting current will be at least three times the running watts. Your defrost cycle kicking in will impact the run time too. My advise, try it out ahead of time so you know for sure. I've done this before many hurricanes down here in Florida.

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    The 100Ah is probably based on the voltage of the internal cell voltage. LiON cells at around 3.8 volts works out about right. Commented 2 days ago
  • As @DoxyLover states, 100 A-h * 38,.4 V [10 LiIon cells in series) = 3,840 W-h Commented 2 days ago
  • Not only the defrost heater, but the starting current of the compressor. Commented yesterday
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    @MikeWaters I think I mentioned that. Commented yesterday
  • i disagree. the bluetti rating is in kw, the fridge is in kw. Not VA. the power factor is already accounted for in the kw rating by the fridge, for which is apparent power is not real and is not lost as power draw from the bluetti. not to mention power factor is caused by the load not the supply. Commented 9 hours ago
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Your fridge probably lists the KWh/year (or kWh/a where a stands for annus) it consumes, at least in the marketing material for it. This is a estimate that the fridge in a typical household will consume and how it impacts the yearly energy bill. That's why it has a time unit in both the denominator and the numerator, it gets you to the number that requires the least amount of math to use.

If you divide that number by 365 you will get a (very) rough estimate of how much it consumes per day. You can get a better estimate by using a kill-a-watt or similar to measure how much your fridge actually consumes).

The product page you linked has a "scenarios" tab which lists a fridge with 1kW/day power usage which would run for over 3 days (in the most optimistic of circumstances of course).

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Even the watt-hour figure may be misleading. It will be the capacity of the DC battery inside the box. Unless your fridge can run on 12V DC, you will need to turn on the 120V inverter on the power station to run the fridge.

If you leave that inverter running all the time, it will consume battery power even if the fridge's compressor is off. As a result, you may get a significantly shorter run time that you calculated.

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In addition to the other excellent answers I would like to suggest preparation.

Most important, keep your refrigerator condenser coils clean. Dirty coils have to run hotter, which means decreased efficiency and decreased equipment lifetime. You should clean your coils (brush/vacuum) every six months. More often if you have a pet that sheds hair or live in a dusty area. Clean coils mean your refrigerator will run longer on your back-up.

If you have a fridge/freezer, keep a bunch of ice packs in your freezer. You can move them to the refrigerator section in case of power outage. This provides additional thermal storage - less drain on your back-up.

During power outages keep the door openings and door opening times to a minimum. Every time you open the fridge door warm air enters. This is a major heat load for your refrigerator, so take a couple of seconds before you open the door to plan exactly what you want to take out.

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Real life example: Samsung RB38C705CB1 connected to APC 3500Wh worked for almost 7 days. In house, average temperature 25'C . In datasheet yearly consuption is 169 kWh.

If Yours is around 700kWh per year then Your 3840Wh supply will work for 2 days.

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bro

that webpage you linked says refrigerator at 1 kWh/day = 78.8 hours (3.2 days) runtime from their "BLUETTI Elite 400 Portable Power Station | 3,840Wh, 2,600W"

a fridge and/or freezer doesn't run continuously and how much it does is highly dependent on how often its accessed and warm food is put into it, if your label says 690 watt then 690w / 120v = 5.75A which seems in the ballpark.

If the fridge ran continuously for 1 hour then that would be 5.75 amp-hours of draw, for which the unit you said is good for 100 Ah, so if the fridge ran continuously never shut off then it would use 5.75 ams x 24 hours = 138 Ah, which would also be 690w x 24 hours = 16.5 kwH per day if it ran continuously if u left the door to it open living in the southwest. But bluetti estimates a 1 kwh per day use as a reasonable estimation, which could be more if you're family is crazy or less down around 500 wh per day if stuff in it is already cold and the environment it's in isn't hot; using a kw meter to actually know your usage is how you would know. so maybe a little less than 3 days, or up to 6 days if you minimally remove from it and don't add warm food to it which it then has to cool. As well delta-t, if it's winter so the inside of the house is 55°f then fridge will use less energy vs if you're in arizona and it's 100°f in the house with no ac.

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