Sometimes, you'll think you have the perfect generator lined up.
Powerful. Not too noisy. Easy on the wallet.
And then, out of nowhere (*cough*, Reddit) you hear about how important THD is.
The truth it, it is important...ish. Let's quickly dive in to see what the fuss is all about.
Important note: make sure you read all the way to the end for a disclaimer, and for a list of low THD generators!
What Is THD?
THD stands for Total Harmonic Distortion. This is a technical topic, but I'll keep it on the lighter side. Here are some basics:
1. An electrical signal is always made up of a fundamental frequency. Your generator produces AC (Alternating Current), and the frequency in the US is 60Hz. AC, when plotted for Voltage vs Time, will look like a 'sine' wave:
Figure 1 - sine wave of an electrical signal expressed as Voltage vs. Time.
2. However, depending on the quality of the signal, multiples of this fundamental frequency sometimes appear. These are called harmonics. Interestingly, each of these harmonics are of the same mathematical multiple. So, the 2nd harmonic of 60Hz is 120Hz. The 3rd harmonic is 180Hz, etc.
3. So, generators never really produce a perfect 60 Hz signal at all times - the frequency produces varies as time goes on. This difference is the THD.
4. The higher the THD is for that piece of equipment, the less 'clean' the power is.
In the United States, most home-based electric is around 2-3%. The worst generators? Upwards of 30%.
Why Should We Care?
Well, it depends. The thing is, if the THD of a given generator is high enough, that frequency fluctuation could seriously harm sensitive electronic devices, like phones, laptops, the wife's iPad, etc.
THD is expressed as a percentage. Generator manufacturers make the THD of any give generator public information, usually under the 'specifications' section of the product.
For example, check out the FIRMAN W03383 3300W generator. As a vendor for FIRMAN, we show the THD in the product description. The W03383 has a THD of < 3%, and is considered to produce extremely clean power.
What Is Clean Power?
According to Generac, a generator that has a THD of 6% or less is considered clean power. Anything higher than that means you may be risking damage to your sensitive devices.
Want a visual? Check it out:
Figure 2 - THD Visual. The red harmonic is distorting the black fundamental frequency.
The black curve (fundamental frequency - let's say 60 Hz) gets distorted by the red curve (the harmonic of that fundamental frequency - in this case, 120 Hz). The resulting blue curve is the distorted signal.
The blue curve dips at its peak (and raises at its lowest point) due to the impact that the harmonic has on the curve.
All this to say: the more distorted the frequency, the higher the THD. The higher the THD, the less clean the power is, and the more potential there is for the electrical signal to harm sensitive electronics.
A Disclaimer
I've done a lot of research on THD to try and provide the most helpful answer and information on this topic.
The thing is, it's not so simple. Everyone has a different opinion on THD. Some folks report that they've been using a high THD generator for years with no impact on their electronics, and that the worry of THD is overblown.
I've also interacted with others who have said that they truly believe their generator's dirty power was responsible for ruining expensive equipment.
My goal is not to necessarily settle the debate. Instead, I want you to be informed on the potential hazards out there. And at the end of the day, there's a chance that if you use a high THD generator to charge electronics, that all will go well.
But if you're like me, you want to be armed with the knowledge to make the right choice.
Here's my advice: when in doubt and if able, buy a generator with low THD.
What Are My Options?
Here are the generators that I sell that have the lowest THD and are considered extremely clean with 3% or lower THD. Whether you go with one of the below or something different, I hope this blog has given you some helpful information surrounding this complex topic.
- FIRMAN W03383 3300W
- FIRMAN W01781 1700W
- FIRMAN W01784 1700W
- FIRMAN WH03041 3000W
- FIRMAN Zero E Power Station
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Sources
*Note: I rigorously research each article to ensure completeness and accuracy. The following resources were helpful to me writing this, and if you're interested, consider reading more:
- https://www.allaboutcircuits.com/technical-articles/the-importance-of-total-harmonic-distortion/
- https://support.generac.com/s/article/What-Is-Total-Harmonic-Distortion-THD
- https://library.powermonitors.com/understanding-total-harmonic-distortion
- https://resources.hy-techroof.com/
- https://wenproducts.com/blogs/resource-center/total-harmonic-distortion-thd-in-generators-an-introduction