Ferrites on Solar Gear

[svetz]

Saw a thread talking about Sol-Arc's ferrites for EMP protection and wanted to get some discussion on Ferrites for Lightning and/or EMPs. Haven't seen any EMPs hit around here, but we sure do get a lot of lightning. Ideally the goal of this thread is to get enough knowledge that someone would know enough to go to someplace like digikey and order what they needed.

Electromagnetic interference (EMI) is one of the biggest challenges faced during the production of any electronic device.

I don't know much about it, but hopefully some of the EEs on the forum can clarify and answer questions. I can at least start with the basics I picked up in a few minutes of googling.

How do Ferrites work? Ferrite beads (aka ferrite choke, ferrite clamp, ferrite collar, EMI filter bead, or even a ferrite ring filter) are passive electronic components that can suppress high-frequency signals on a power supply line. They are normally placed around a power/ground line pair that is incoming to a particular device, such as the power cord for your laptop. Many have room for the cable to be looped through for greater effectiveness.

Ferrites work according to Faraday’s Law, that is the magnetic core around a conductor induces a back EMF in the presence of a high-frequency signal, essentially attenuating the ferrite frequency response.

CFL, Lightening, EMP
Ferrites are designed to work at specific frequency ranges, so what should you get? If you're trying to filter out office noises such as those from compact fluorescent lighting, you'd pick one designed for the EMI frequency range of the source (e.g., 2 kHz to 150 kHz for CFL).

EMP
For EMP, looks like there are different types:

EMP’s frequency range, depends on the source. A nuclear weapon detonated at high-altitude produces relatively long duation EMP, thus contains low frequency components (100 MHz). Because conventional EMP devices produce explosions driven by HPMW technology, they may have a frequency in the range of 100 MHz – 100 GHz. EMP, depending on altitude and power, can generate electric field up to levels of 50 kV / m.

Frequencies
Found this chart, so lightning looks like it's low up to around 10 MHz. EMPs seem to cross the entire spectrum depending on type.

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Broadband Ferrites
I suspect the term "Broadband ferrites" is marketing upsell. But, they're advertised as have a wide range of suppression and might be the best you can do for EMPs. Could be, it's the same as any old type 61. Hopefully one of the EEs knows more.

Type 61
From this government document regarding EMPs:

Ferrite beads are widely available online and cost just a few dollars each. Normally more than one bead is required to achieve significant attenuation (~10 dB). They can be clamped on, snapped on or slipped over cables near the equipment end to attenuate unwanted high-frequency cable signals. Type 61 (HF) ferrites made of Nickel Zinc are recommended. These are designed for inductive applications to attenuate interfering pulses from 200 MHz to 2 GHz. They can be added to existing cables or purchased with ferrites pre-built in common cable types. A wholesale distributor such as Digi-Key Electronics (http://www.digikey.com/en/products/filter/cable-ferrites/840) allows for filtering any combination of sizes and specifications to fit requirements...

That same document shows national maps where likely EMP strike points are and what the power might be based on range.

Huber+Suhner
From the same document, they reference an online tool for sizing. Ideally, you want any spike to be less than 150 kV/m, but I'm not sure how the calculator can be used to figure that out....

...insert the “RF CW Power in W” (Watts), the “DC Supply Voltage” (normally zero), the maximum antenna “VSWR” (normally at least 3), and the “Impedance Z” (normally 50), and then click on the “Calculate” button. Using the H+S online calculator for three typical powers of 100, 400, and 1000 watts (with a 3:1 VSWR) results in the following required GDT voltage ratings:
100 watts has a peak voltage of 150 volts
400 watts has a peak voltage of 300 volts
1,000 watts has a peak voltage of 474 volts

That is, the 350-volt GDT may strike at only 298 volts, the 600-volt GDT may strike at only 510 volts, and the 900-volt GDT may strike at only 765 volts. Going into more detail for the last example above, a 900-volt GDT is used despite a calculated striking voltage of 712 volts (to protect an amplifier with an output power of 1,000 watts) because it might strike at a voltage as low as 765 volts with its 15% tolerance. This means that the voltage induced in the antenna lead from a lightning strike or EMP will reach at least 765 volts before the GDT fires. But the induced voltage could go up into the thousands of volts without the surge protector. Also, a VSWR of 3 may only be nominal: Many VSWRs will be higher, requiring GDTs with even higher voltage ratings. Disregarding the safety factor and the tolerance would result in selecting a GDT with a striking voltage that is too low, compounding false triggering problems.

Greek to me. Hopefully, someone knows how to size appropriately.

 

[svetz]

Let's say I want lightning protection, so 0 to 10 MHz. On the Digikey page, the key spec seems to be impedance @ Frequency.

For spike protection, wouldn't I want a lot of ohms at my target frequency with 0 ohms at the normal frequency? Having no real clue what I'm doing I pick one at random and find a chart in it:

​

Ah! So, the first thing to look at must be the "material type".

"LF" is obviously what I want, as I recall that's one of the "material types". So, back to the selection page, select LF, and narrow my picks. But none of them clip together. Hmmm. So what are these types? Googling a bit, I find some general recommendations:

• Material 33 - 0 to 3 MHz​
• Material 43 - 20 to 250 MHz​
• Material 61 - 25 to 200 MHz​
• Material 67 - high frequency for the design of broadband transformers, antennas and HF, high Q inductor applications up to 50 MHz​
• Material 68 - high frequency for the design of broadband transformers, antennas and HF, high Q inductor applications up to 100 MHz​
• Material 73 - < 30 MHz​
• Material 77 - < 100 MHz​
• Material 78 - < 200 MHz​

It looks like different manufacturers have different names for material types, so no confusion there. But... for lightning (0 to 10 MHz), probably material 73? No snap ons <sigh>. No Material 33 listed in digikey. Well let's just pick a couple and see what happens.

So, they're rated by that Impedance @ Frequency column and the most are listed at 1 MHz. Ah, I get it... the actual impedance is dependent on the frequency, e.g., this 60Ω @ 1 MHz is 20Ω at 100 kHz and 60Ω at 1 MHz. The first number is telling you the impedance and the second number is giving you the range it's used in (probably easier than materials).

How much impedance do I need? That must be Ohm's law... so if there was 1,000V spike what happens? Let's say the normal resistance is 5Ω, from V=IR that means I=200 amps in the spike. If it was 1 MHz, then at 65Ω the current drops to 15 amps.

What if there were two turns? From that datasheet it would go from 60 to 115Ω, or reducing the current in the hypothetical spike to 8.3 amps:

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Okay, so back to the top and first select all the clamp types. There's a few at the 10 MHz range. Let's look at the largest 65Ω @ 10 MHz, it's 20Ω at 1 MHz and 5Ω at 300 kHz. How's that compare to a 525 @ 100 MHz? 108Ω at 10 MHz & 28 Ω at 1 MHz (80Ω with two turns). So, it seems like the latter is better, but there's no data listed below 1 MHz so it might drop off faster leaving less protection at lower frequencies. The 1000Ω @ 100 kHz isn't as good at 10 MHz though. Hopefully, no EEs hurt themselves laughing while reading this.

 

[MurphyGuy]

Ferrites are mostly used for noise attenuation. I've used them on servo drives when hooked up in the same control panel as something like a Variable AC motor speed controller. When dealing with millivolt signals from things like optical encoders, a three phase AC drive can saturate a line and cause position problems.

Ferrite coils work well, but their application is limited. For example, they're not going to save you from a lightening strike. They might help if the pulse is just above the damage threshold, but that would kind of be an edge case. For lightening, you want a whole house surge protector like the Siemens FS140 that I installed on my home.

As for EMP protection.. hmm. it would depend on the strength of the incoming pulse, how it arrives, and how sensitive the components are that you're trying to protect.

Solar EMP isn't a concern as Ferrites would be useless, but a Nuclear EMP will arrive with two flavors.. one is conductive, which is a nanosecond spike being transmitted through the power lines feeding your house. Once again, for this type of problem, you want the Siemens FS140 to shunt it to ground. The other flavor of Nuclear EMP arrives as an inductive pulse and comes through the air like a radio signal. A whole-house surge device won't help much here. Ferrite cores can certainly help with the inductive component, but they would need to be placed right next to the item you're trying to protect and their effective protection would depend on the signal being just above the damage threshold. In other words, filling your breaker box with them isn't going to provide very much help because the inductive component will just couple into the power wire that is used to plug your device in.

It really all comes down to a cost-benefit analysis. While the coils are relatively cheap, you'd need an entire box of them to protect most stuff, and that protection factor, while it all counts and adds up, will still be minimal.

You're far better off spending a few hundred on good whole-house surge protector that will provide protection across the entire range and for the entire house.
Also, in the case of a Nuclear EMP, protecting your television or other household gizmos, will be the least of your worries.

In a nuclear emp, any solar components that are working will most likely be toast. Some panels might only be slightly damaged, but everything else is going to be a paper weight.

 

[svetz]

...Ferrite coils work well, but their application is limited. For example, they're not going to save you from a lightening strike. They might help if the pulse is just above the damage threshold, but that would kind of be an edge case. ...As for EMP protection.. hmm. it would depend on the strength of the incoming pulse, how it arrives, and how sensitive the components are that you're trying to protect.

Sol-Ark uses them as a part of their EMP solution. Based on my math above (assuming the math isn't all utter hogwash), I can see why they'd be good to have.

 

[MurphyGuy]

Sol-Ark uses them as a part of their EMP solution. Based on my math above (assuming it isn't all utter hogwash), I can see why they'd be good to have.

The problem is that Sol-Ark doesn't publish their EMP protection specs (not that I'm aware of), so the term "EMP Protection" could mean almost anything. For example, to protect against a solar EMP, all you'd need is a voltage sensing switch that opens when grid voltage goes over a set point. And lightening arrestors are commonplace and cheap...
Nuclear EMP is a special animal and without published specs for their claim of protection, the term "EMP protection" or "EMP Hardened" is pretty meaningless. Actually, its less than meaningless, it could be and probably is deceptive.

Also, the use of ferrite cores is common and found on almost everything these days. Take a look at your computer monitor's HDMI cable or a printer's serial cable, and you will find an odd looking cylinder thing molded into the cord... that is a ferrite core to attenuate noise.

My personal opinion, and this is just my opinion based on reading between the lines, is that Sol-Ark is a gimmick company that markets products and depends on the ignorance of their customers. The whole "Made in USA" thing got blown out when people figured out that the major components are made in China and run Chinese software.. Their advertised power ratings are advertising a spec that is not what most people think (assume) it is.. For example, their 12k inverter is not going to "inverter 12kW of power".. Power inverters label their output specs, not their input.. so when you purchase a 2000 watt inverter, you expect it to be able to power 2000 watts of loads, but not with sol-ark.

So with that said, while I have zero actual experience with them, I would be suspicious about anything they claim without some detailed specifications to back it up.
Nothing wrong with ferrites, they will help attenuate any spikes.. just don't expect them to save anything from an EMP delivering an E1 pulse.. They should be treated as "helpers", not your primary defense.
When it comes to Nuclear EMP, your primary defense against the conductive pulse should be a whole house surge protector with a nanosecond response time.. If you're lucky enough to be partially shielded from the accompanying radio wave, the surge protector might save you. When it comes to the inductive (radiative) pulse, there is no defense as the radiative component will couple directly into your semi-conductors at the board level.

The only real defense is having spares in a Faraday cage, and if you're talking about computer processors, a really good Faraday cage.

 

[svetz]

...My personal opinion, and this is just my opinion ...

I disagree with most of those opinions regarding Sol-Ark, but I'd hate to see this thread become a Sol-Ark thread.

 

[MurphyGuy]

I disagree with most of those opinions regarding Sol-Ark, but I'd hate to see this thread become a Sol-Ark thread.

Get yourself one of these

 

[svetz]

While it's fine to opinionate that they won't do diddly for lightning or EMP and are just gimmicks, obviously others have different opinions and some even sell products with them.

The math in post #2 seems to indicate the one looked at could drop the current on a 1000V spike by 185 amps at 10 MHz, so I can see why it might be useful (although the math could be complete crap since I just applied basic principles to something where it might not apply). I do know those tiny spikes day in and out take a toll on electronics. Considering many are very low cost (e.g., less than a $1), it might be really cheap insurance even with a whole-house protector (I'm sure my AC creates spikes on my side).

As the OP says, that's the real topic of this thread: understanding ferrites. Knowledge of a thing will help us to understand if/when/where they'll be useful, how to go about picking the best fit, and if they bring actual value.

Get yourself one of these

As it happens, I've had a whole-house surge protector for years and there are other threads about them where they can be discussed ;-)

 

[svetz]

For EMI spikes created in the home, it might make more sense to put ferrites on the noisy item rather than the delicate electronics. Let's say you measured an air conditioner to be 600V @1 MHz when it starts up and shuts down. The $5 65Ω @ 10 MHz ferrite has 90Ω with two turns at 1 MHz. Assuming the math in post #2 is right, then if the base circuit had 5Ω resistance, the spike's current reduction would be 600/5 - 600/(90+5) ~= 114 amps or a 95% reduction. Assuming it's not just a gimmick, it might be something professional installers like @Supervstech might be interested in as it might distinguish them from competitors (at least for preppers, HAM enthusiasts, and RFI sensitives).

Not sure how you'd find the actual frequency or voltage without an oscilloscope. I've read in the home noise is generally 7000 Hz to 50 MHz, but who knows. Always the $50 oscilloscope game.

... Let's look at the largest 65Ω @ 10 MHz, it's 20Ω at 1 MHz and 5Ω at 300 kHz. How's that compare to a 525 @ 100 MHz? 108Ω at 10 MHz & 28 Ω at 1 MHz (80Ω with two turns). So, it seems like the latter is better, but there's no data listed below 1 MHz so it might drop off faster leaving less protection at lower frequencies. The 1000Ω @ 100 kHz isn't as good at 10 MHz though.

Was thinking about this, there's no rule that you couldn't use one of each AFAIK, to protect at both the lower and upper frequencies.