By Mike Sokol
I’ve had a number of email inquiries about the boondocking power requirement while running on batteries, and one that I found interesting was the desire to run a Nespresso coffee maker without cranking up the generator. As in, “My life would be complete as long as I can make an espresso or latte or some other highly caffeinated drink in my RV from battery power.”
Now it can be told…
Well, I just so happened to have received a new Nespresso coffee maker for Christmas from my kids, so I have a good test subject for a basic demonstration. Note that this isn’t a highly calibrated test, nor did I run dozens of coffee-making cycles and average the results. But I did plug my Nespresso into a Kill A Watt® P3 meter this morning and got a few readings as I made my cappuccino. So, as they used to say, “Your mileage may vary.”
Some like it hot…
All of these pod-fueled coffee makers will make a single-serving coffee/espresso or cappuccino in less than a minute or so. But during that minute they’re drawing a lot of current to get things hot. In this case the peak amperage for the first 30 seconds or so of the cycle while it heated up the water and frothed the milk was around 10.7 amps of current.
Next, when it was only pushing pressurized hot water through the espresso pod it was still drawing around 7.13 amperes of current. No, I didn’t use a stopwatch, but the entire process took less than a minute.
How much energy did it use to make a cappuccino?
The nice thing about the Kill A Watt® meter meter is that you can not only measure amperage and voltage, it will also log the total kilowatt hours of energy consumed. In this case it was just over 20 watt-hrs, which I’ll extrapolate to 25 watt-hrs.
I can only guess the exact mount because the resolution of the meter was just 10 watt-hrs. Since the coffee maker was still running for a bit after the meter hit 0.020 kWH, I’ll make a S-W-A-G (Scientific Wild A$$ Guess) and call it 25 watt-hrs. Yes, I could meter this down to a few PPM if it was important, but I’m just looking for general numbers here. I’m not launching missiles or rocket ships, where decimals count.
How big of inverter will you need for this?
Well, this is an opportunity to do a little inverter math, so let’s have at it. If we multiply the 10.7 amperes of current at 120 volts AC, that comes out to 1,280 watts. So let’s call it 1,300 watts for grins. This suggests that you might barely get by with a 1,200-watt inverter for those 30 seconds of heating; it would be much happier running on a 2kW inverter.
What’s your battery current draw during the coffee cycle?
To get a S-W-A-G while we’re brewing our cappuccino, all we have to do is multiply the current at 120 volts by a factor of 10x, then throw in an extra 10% for basic efficiency losses in the inverter. So 10.7 amps at 120 volts times 10 comes out to 107 amps at 12 volts DC, with possibly another 10 amps of current wasted in heat.
So that’s around 117 amperes of current during the heating/frothing part of the coffee/cappuccino making. It then settles down to 7.13 amperes of current at 120-volt while its pressuring the pod, which is 72 amperes at 12 volts, plus maybe another 10% for losses, so let’s call it 80 amps or so at 12 volts DC.
What does making a cappuccino do to my battery State of Charge?
That’s the crux of the biscuit, as it were. Since the Kill A Watt meter includes a kWH function, and I extrapolated it to draw around 25 watt-hours of energy per cycle, we can simply divide the total kWH of available storage in a typical 100 amp-hr battery.
That works out to 1,200 watt-hrs of available energy if we go from 100% to 0% SOC (State of Charge) on this 100 amp-hr battery, but only 600 watt-hrs if we want to keep the SOC above 50% for best flooded-cell battery life. We could double that number if you have a 100 amp-hr Lithium battery rated to 0% SOC.
How many cups of espresso or cappuccino per battery charge?
So, if we divide 600 watt-hrs of available energy from our battery by 25 watt-hrs needed per Nespresso cycle, we come out to 24 cups of espresso with foamed milk before you’ve depleted your lead-acid battery to 50% SOC. Or 48 cups of espresso with foamed milk if you have a 100 amp-hr lithium battery.
Final analysis: And yes, your mileage may vary…
So don’t be surprised if your battery State of Charge monitor drops by 2% or more every time you make a cup ‘o joe in your Nespresso machine. That’s perfectly normal and expected.
Next time I’ll do a little ciphering to show you how fast a convection microwave or 1,500-watt hair dryer will deplete your battery. Basically, anything with a heater uses a substantial amount of power. So, yes, your beloved Instant Pot is on my list as well. Hint: It depletes the battery a lot faster than an espresso machine.
Let’s play safe (and caffeinated) out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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