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[DonTom]

It is a mystery to me what they do and how they work. 

They work by what is called "skin effect".

What they do is reduce the high frequency radiation. In the case of a Zero, I expect its reason for being there is part 15 of the FCC rules.

To put it in laymen terms, it means so it does not cause interference to nearby radio receivers.  Switched-mode power supplies (your Zero charger) has a lot of stray oscillations that can radiate quite a distance. Since radio frequencies travel over the "skin" of wires and not down the wires themselves, the ferrite core over the wire blocks the radio signal right there. That way that wire cannot be used as an "antenna"  to radiate the signal for a greater distance.

Other than that, it has NO effect on your power supply and can be removed.

-Don-  Reno, NV

[DonTom]

Your burnt up PC board seems to indicate that you had the typical chain reaction of when one part shorts out in a switching power supply, it causes many other components to short out and burns up the board.

I have wondered if they could design a switched mode power supply with about 30 fuses to prevent that. Or some type of current limiting that won't reduce efficiently and won't increase cost and size. It's such a common issue, I would think by now somebody could design a safer way than letting the PC boards burn up.

-Don-  Reno, NV

[Richard230]

It is a mystery to me what they do and how they work. 

They work by what is called "skin effect".

What they do is reduce the high frequency radiation. In the case of a Zero, I expect its reason for being there is part 15 of the FCC rules.

To put it in laymen terms, it means so it does not cause interference to nearby radio receivers.  Switched-mode power supplies (your Zero charger) has a lot of stray oscillations that can radiate quite a distance. Since radio frequencies travel over the "skin" of wires and not down the wires themselves, the ferrite core over the wire blocks the radio signal right there. That way that wire cannot be used as an "antenna"  to radiate the signal for a greater distance.

Other than that, it has NO effect on your power supply and can be removed.

-Don-  Reno, NV

Thanks for the reply regarding Zero's choke, Don. That makes sense and I can now understand why it is just attached to the outside of the power cord. Still, it seems like such a simple device to actually work like that. That is probably the simplest, and likely least expensive, electronic device on the whole bike. 

[DonTom]

Thanks for the reply regarding Zero's choke, Don. That makes sense and I can now understand why it is just attached to the outside of the power cord. Still, it seems like such a simple device to actually work like that. That is probably the simplest, and likely least expensive, electronic device on the whole bike. 

FWIW, you can buy ferrite cores here.

But most of the parts in the charger are a lot cheaper. Diodes usually cost less than a dime when purchased in qualities. Same for resistors and even transistors and most ICs are cheap these days. In fact, there isn't anything expensive in your rather expensive charger. But to design it for just a few motorcycles makes it cost quite a bit. Most of the money is spent on the design, not what's in them.

I am very familiar with ferrite  cores for many reasons. I was in radio professionally as a technician  for most of my life. Also, ferrite cores are handy to stop TVI (TeleVision Interference) from near by ham radio operators. I  have also been a HF ham for most of my life. A clean ham radio signal can wipe out a TV that is on TV cable from overload just  by being close, like a next door neighbor in the bay area where most of the  houses are very close to each other.

The very strong ham radio signal travels down the TV cable. Right before the cable enters the TV coil a few turns around a ferrite core. Like magic, the interference is totally gone! In most cases, not even a trace of the interference if done correctly.

On the source of the noise, such as your charger, the ferrite should be right where the wire comes out of the case. On the TV, it's the opposite, right before it goes into the TV, to  reduce the RF coming down the shield. It has negligible effect on the center conductor that carries the TV signal because it is protected by the shield of the TV cable.

-Don-  Reno, NV

[Crissa]

Of course, cable tv isn't just used for low-band television anymore.

-Crissa

[MrBlc]

I don´t want to be "that guy", but the whole purpose of a ferrite core is to be a common mode EMI filter.. As such, when clamped on a cable it only has one turn trough the transformer setup it creates and therefore the filtering effect is only about 3%..
(this varies depending on the frequency and misalignment of the interfering signal.)

More info here: https://en.wikipedia.org/wiki/Common_mode_choke

As such.. the so-called "skin effect" doesn´t exist.. Current doesn´t travel on the outside of a cable´s sheath unless it´s made of metal. Electromagnetic fields however does.

[Crissa]

I'm not sure why DonTom linked to the 'Skin Effect' but all cables are made of metal.  The nonconductive sheathing of a cable is not bound to the cable in any way that would change this (semiconductors aside).

-Crissa

[DonTom]

I'm not sure why DonTom linked to the 'Skin Effect' but all cables are made of metal.

Which part did you not understand? Higher frequency RF travels via skin effect on the top of metal cables, easy to block with a ferrite core, even if the wire is insulated.

In transmitters, in the output stages , coils are often made with hollow wire in the tuners because the RF travels better that way because then there is "skin" on both sides, so it's more efficient than solid wire for RF.

But on a solid wire, a ferrite core works great because it blocks the RF on the "skin". Solid wire is great to carry normal current, but not so great  for RF and extremely  poor when it is blocked by a ferrite core.

So why would I not link to "skin effect" when that is exactly how  ferrite cores work?

-Don-  Reno, NV

[Crissa]

The skin effect is how high frequency travels faster and overloads the surface and doesn't use the core of a wire.  I thought you were linking to it to explain that high frequency develops more pronounced EM fields around wires.

All variable current (including base signal AC) has the skin effect?

The ferrite absorbs the signals emanating from a wire and sends them back, creating destructive patterns at a frequency range according to the wraps.  It doesn't touch the skin of a wire.  It's a little echo box.

-Crissa

[Fran K]

Is this what a ferrite core looks like?  This is inside my Husqvarna pole saw or pole pruner.

Sorry for the derail if it is such.

[DonTom]

I thought you were linking to it to explain that high frequency develops more pronounced EM fields around wires.

Switching power supplies  radiate unwanted garbage, such as harmonics and  parasitics  along with the wanted switching frequencies from their "chopper" stage.  It radiates much like an oscillator, which is what produces RF for transmitters.   This unwanted garbage can cause interference to radio receivers and part 15 of the FCC rules limits how far it can radiate.  Since this garbage is HF, it travels down the "skin" of wires and becomes much like an antenna. The ferrite prevents that from happening by blocking what comes down the "skin".

-Don-  Reno, NV

[DonTom]

Is this what a ferrite core looks like?  This is inside my Husqvarna pole saw or pole pruner.

In the upper right hand corner, it sure looks like such, with a coil of the wire around it. Perhaps that is the AC cord?

Motors also put out a lot of HF garbage.

-Don-  Reno, NV

[Fran K]

It is a 36 nominal volt lithium ion battery device.  The 3 wires that go around the metal cylinder go to the motor on the end of the pole that drive the chainsaw chain.  I would guess it is some sort of pulsed dc, similar to 3 wires that go to battery powered  motorcycle motors.

[MrBlc]

@Fran K
This is a classical Common Mode filter setup. In this case it has 2 windings,which means it´s twice as good as a single passthrough. (so about 6 %)
Basically, what it does is to create more resistance as frequency of EMI increase, which in turn makes it dissipate in the metal ring rather than travel along the unscreened cables making them become antennas. This is a heavy oversimplification, but the essence of the function.

[Richard230]

Is this what a ferrite core looks like?  This is inside my Husqvarna pole saw or pole pruner.

Sorry for the derail if it is such.

This is what Zero's charger ferrite device looks like.