Consumption comparisons

[eddie1261]

I don't know if I should find this remarkable or not. I have been living under the apparently wrong assumption that "this appliance" consumes what it consumes no matter what the power source is. I just tested that with an O2Cool fan and my Chromebook, and I found that I was wrong.

The Chromebook came with the adapter to plug it into the wall, like everything does. When I plugged that into my Goal Zero and looked at the output, with that wall wart plugged into the 110v out on the Goal Zero it used 19w and 1.5 amps. I then plugged in the 12v and saw it used 10w and .9 amps. Same device. I watched Will's current video on both so I was doing exactly the same thing in both cases.

Then I plugged in the O2Cool fan with the 110 power source. It read 18w and 1.4 amps on the lowest speed. When I switched to the 12v power supply and it was 4w and .3 amps. I DID notice on 110v that the fan , set on the same speed, ran a little bit stronger

So the question is whether appliances should consume the same amount of energy on the 110v out as they do on the 12v out, In this quick test, they seemed to be more efficient on the 12v output. That tells me to use the 12v outs in the trailer rather then the inverter. Thoughts? Comments?

 

[gnubie]

It really comes down to the device, the answer is maybe. The AC adapter itself will typically only be operating in the 80-90% efficiency range and that will vary depending on the load the device is placing on the AC adapter. A lightly loaded switchmode adapter (the most common type these days) might only reach efficiency levels in the 70% range.

When it comes to powering a laptop from a genuine AC adapter and a 3rd party DC adapter (I'm not saying this is what you are doing) the laptop itself may actually reduce its power draw if it can not sense a genuine adapter. This might include charging the battery at a lower rate and even throttling the CPU.

 

[eddie1261]

and even throttling the CPU.

That's an interesting point. After my errands I am going to hook that all back up and push the CPU, like play 6 youtube videos at once while also streaming Hulu. I can see if there is any kind of stuttering. My 12v outlet block that you saw in my video is designated for the 2 LED light bars on the ceiling, 2 USBs on a plug for the phones, the fan, and the Chromebook. Not all of that will be in use at once. Likely 1 of the light bars and the Chromebook. In warm weather the fan as well, then when I go to sleep the phones get plugged in to charge. And when they charge, they stop drawing power, right? (They will be shut off to charge. I won't miss a call. Nobody calls me NOW.....)

Worst case, I will add a 2nd Ruixu in parallel and have 200ah.

 

[svetz]

... I have been living under the apparently wrong assumption that "this appliance" consumes what it consumes no matter what the power source is....

That's correct as far as I know with a caveat. I would first suspect the gauges/meters as not being 100% accurate. But beyond that, appliances "want" a certain number of watts and if they fall below that they stop working or work out of spec.

Okay... the caveat: V=IR.

Every appliance is a set resistance, it's not going to change (some do of course, e.g. a refrigerator when the defroster kicks on or as was pointed out CPUs using varying power). So, for the same voltage the amperage should be the same.

And there's the rub... if a power source has a lower voltage (or sags) than with constant resistance the amps change. Say an appliance is 100 ohms, then at 120v its 1.2 amps; but at 110v it's 1.1 amps. In the first case the appliance consumes 144 watts, in the second case 121 watts. But at some point, there won't be enough watts for the appliance and it will stop. Also, running at voltages it wasn't designed for might shorten it's life.

An example of this is a 120V 60W incandesent lightbulb. At 110V it's a 50W bulb. Still works, just doesn't consume as much energy or shine as brightly.

 

[Ped]

A bit off topic but I just got PSW after years of using an MSW and did the same comparison but with a TRMS amp clamp. Turns out theres no difference on draw out of batteries. The PSW runs things queiter and my fridge runs slightly less as long. But thats all lost in the 3x idle current of PSW.

 

[HighTechLab]

That's correct as far as I know with a caveat. I would first suspect the gauges/meters as not being 100% accurate. But beyond that, appliances "want" a certain number of watts and if they fall below that they stop working or work out of spec.

Okay... the caveat: V=IR.

Every appliance is a set resistance, it's not going to change (some do of course, e.g. a refrigerator when the defroster kicks on or as was pointed out CPUs using varying power). So, for the same voltage the amperage should be the same.

And there's the rub... if a power source has a lower voltage (or sags) than with constant resistance the amps change. Say an appliance is 100 ohms, then at 120v its 1.2 amps; but at 110v it's 1.1 amps. In the first case the appliance consumes 144 watts, in the second case 121 watts. But at some point, there won't be enough watts for the appliance and it will stop. Also, running at voltages it wasn't designed for might shorten it's life.

An example of this is a 120V 60W incandesent lightbulb. At 110V it's a 50W bulb. Still works, just doesn't consume as much energy or shine as brightly.

This is only true for resistive loads such as space heaters, incandescent light bulbs, etc.

If you get into inductive loads such as motors, etc. then as the voltage goes down, the current increases. Think of it as the motor is driven around by the magnetic field being created and collapsing 60x/second, if you lower the voltage, then you still need the same amount of energy to create that magnetic field going around...You get into weird stuff like eddy currents and such, but at the end of the day your current goes up. There are plenty of videos on the web that can explain this much better than I can though, so the V=IR is mostly only true with DC loads and resistive loads.

Also keep in mind with alternating current, Watts = Volts x Amps x Power Factor versus a DC load where Watts = Volts x Amps

Capacitive loads such as switchmode powersupplies in computers, led lights, phone chargers, etc. only draw during the first half of the sine wave (the up slope) then current drops down to 0 on the second half of the sine wave....

MSW vs PSW screws with that power factor in the case of motors - Switchmode power supplies do not care because they are just rectifying down to DC...In fact one of my HP oscilloscopes has a matching HP square wave battery backup unit that has an inverter that outputs SQUARE WAVE ac, meaning no stepping like most of these MSW inverters are doing...The scope doesn't care because it just brings that back down to DC.