120V Bed Outlet waveform/etc.

I took some time today to investigate the waveform and other characteristics of the OEM 120 VAC inverter on my '09 DCSB--here's what I found:

Tacoma OEM Inverter w/ no load -- waveform is a so-called "modified sine wave" (i..e. squint real hard and it will look sort of like a sine wave) at 310 V pk-pk, 60.48 Hz, 121.0 V RMS, 50.9% duty cycle:




Tacoma OEM Inverter w/ 60 W resistive load -- just a modest output drop to 301 V pk-pk, 60.36 Hz, 120.0 V RMS, 51.0% duty cycle:



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For comparison here's the output of a cheap, real cheap, Endurance 400 W inverter I picked up new, for $18, at the flea market in Daytona. Note that with "el cheapo" it doesn't matter how hard you squint there is no way it looks like a sine wave.

Endurance 400 W Inverter w/ no load -- 256.6 V pk-pk, 61.02 Hz, 116.9 V RMS, 50.0% duty cycle:




Endurance 400 W Inverter w/ 60 W resistive load -- output drops considerably to 232.5 V pk-pk, 61.03 Hz, 108.1 V RMS, 49.9% duty cycle:



I need to find something with a 350 W or so reactive load and see how the Taco inverter handles it...

 

Cool. I think? Can you interpret what this means for those of us without an electrical background?

 

None of them look anythink like a sine wave. Look more like a square wave or a gated pulse. Some electronic equipment will not work with that type of an output.

 

some kind of Voodoo!

 

I'll add a better interpretation of the above later tonight when my insomnia kicks in--however as non-true sine wave inverters go it's not too bad. The "Endurance" el-cheapo is a real bottom-of-the-barrel unit but I've used it to power my pirate FM station with acceptable (barely) noise levels

 

What witchcraft is this?

 

If Jer doesn't get it.. it doesn't bode well for any of us.

 

This is 110% in the "You asked for it." class of stuff--I will start with the waveform considerations and then briefly touch on the output voltage.

Waveform:

Normal what-we-expect from a wall outlet 120 VAC power has a sinusoidal waveform--i.e. its voltage vs. time represents the natural output of a voltage created in a coil of wire by a rotating magnetic field. The waveform repeats at 60 cycles/second (Hertz, Hz); in its purest form it "looks" like this.

Kikusui ORC-11 Low Distortion Oscillator -- 60 Hz Sine (0.002% total harmonic distortion):


Note the symmetry of the top and bottom curves, and the connecting slopes--this is the essence of what all of our AC powered stuff expects to "see" in its power source.

However in real life such perfection does not exist. Here is the waveform of what Florida Power & Light sends me.

FPL 120 VAC 2017-06-19 -- Note minor 3rd harmonic distortion at + and - excursions:


The power from FPL contains some 3rd and 5th (etc.) "odd" harmonic (180 Hz, 300 Hz, ...) frequency components that when combined with the base 60 Hz wave create the distorted "sine" wave shown above. These are perfectly normal in commercial power systems and cause no problems for all but the most sensitive (i.e. nothing anyone would have in their home) electronic equipment.

Here is the "normal" household AC power from FPL waveform overlayed on the output waveform of the Tacoma OEM 120 VAC inverter--this illustrates where the so-called "modified sine wave" crap comes from.

FPL "real sine wave" compared to Tacoma AC Inverter "modified sine wave":


You can see that the output waveform of the onboard inverter is not all that far "off" from the FPL supply--although it does contains a bunch of high frequency "noise" as it is fundamentally a square wave¹. However many, perhaps even most, modern consumer electronic equipment will run acceptably from this sort of source as their internal power supplies are designed to accept less than perfect AC input power, filter it, and supply the device with clean DC power.

Some audio and video devices may exhibit a small to unacceptable level of background "static" related to the odd harmonic components of the "modified sine wave"²; but often with newer stuff it is not even noticeable. The output frequency of the Taco inverter at 60.4 Hz is a bit fast, but in any practical short term use it is close enough to the 60 Hz standard.

Voltage:

Referring to the FPL waveform above note that the peak-to-peak voltage is 343.0 V, and the RMS (Root Mean Square) voltage is 123.0 V. The RMS voltage is the square root of the average of the squares of all instantaneous values--it is a practical way of defining the useful average voltage of AC waveforms. In the US standard household electrical power is expected to be 120 VAC RMS.

Note that the Tacoma inverter "modified sine wave" output has an RMS voltage of 120 VAC even when loaded to 60 W--this is good.

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¹ - An ideal square wave is the sum of all odd harmonics (3rd, 5th, 7th, etc.) of the fundamental frequency.

² - It is not really a "modified sine wave" as one would have to start out with a sine wave in order to create a "modified" version of same. What it is is a square wave, generated so as to somewhat resemble a sine wave--but that would not make especially good ad copy.

 

Those are some pretty gnarly waveforms...I used to work on inverter circuits back 20 years ago or so. I would've thought the technology would've gotten better since then but it appears not...unless Toyota is using a very basic inverter. It would be interesting to see that waveform running an AC motor.

 

ROFL.

 

They have gotten better but way more expensive. Toyota uses the bare minimum and cheapest one to stay with the rest of the industry. I have one that I wanted to use to charge my laptop while camping. Would not charge a single one that I tried.

 

A 400 W true sine wave inverter can be purchased (retail) for a bit over $100. I'd bet Toyota could have got them for $30 or so (the unit they used probably cost $10 to $12), which certainly would not have "broken the bank"--however most buyers would not know the difference so WTF.

Having owned my '09 for 8 months and having yet to use it for anything; and in fact having survived driving for 60+ years without a vehicle with an on-board 120 VAC power source; I cannot envision my ever needing to use it for anything.

I do find it odd that it was setup to provide 400 W with the engine idling/vehicle stationary; and 100 W with the vehicle in motion--must have been some sort of big brother "safety" concern, or maybe some perceived liability issue. There is no electrical or other design based reason for it that I can come up with.

Also I have seen it mentioned that it works with the engine off; on my '09 it does not, the engine must be running as is stated in the OM...

 

@cliffyk , bad ass post. I always knew the stock inverter was pretty much garbage from an output perspective but I never thought to check with an oscilloscope to see the actual waveform. I'd love to have a true 15A in the back of the bed for cooking purposes but that would require a GIANT inverter. I searched pretty hard for a solution but never found one and kinda gave up. The stock alternator is rated at 130A but I'm sure doesn't put out close to that at idle. So I'm down on power to begin with. Couple that with the size of a 2000W inverter that I'd need kinda was a buzz kill.

 

What kind of equipment are you referring to?

 

Precision electronic and other laboratory test equipment--stuff like this, I have a very old Sola 3 kW power conditioner/isolator I use with much of this:

 

Is there any way to take "dirty" power and make it clean enough to use with more sensitive equipment?

 

Power line conditioners--"google" it and decide how much you want to spend, but like most things keep in mind that "If you buy the cheapest there is, there is a real good chance you will get the cheapest there is..."

 

I have no need for one, but this intrigues me a bit, so I thought I'd ask the pro.

 

Figures. Toyota cheaped out. I have heard of people plugging in usb chargers and the like but a laptop charger? Maybe.
has anyone tried the Ford version of the truck outlet?