Gen 3 wall connector and EMF

[pssturges]

Hi all. My M3 arrives in a couple of weeks and I’ve had my wall connector installed in my garage on the wall right next to where the charge port will be. It will be a less than one metre stretch for the 7.3m cable.

So my understanding is that leaving the rest of the cable coiled on the hanger will create EMF while charging, which is basically a magnetic field. Best practice is that I shouldn’t do this.

So first question is why? What are the risks? What could go wrong? Is it really that significant a risk?

If I hang it in larger coils(smaller number of coils), the issue will be reduced?

I really don’t want to uncoil the 7.3m every time I connect, then recoil when I unplug, so what other solutions might there be?

Thanks

 

[cafz]

Don't sweat it. Leaving much of it loosely coiled, hanging on the wall charger while charging is fine.

It's an AC current so the net magnetic field is actually zero. The main concern with leaving the cable coiled tightly while charging at a high current for long periods is heat generation - if it's only loosely coiled the heat will be able to dissipate just fine.

 

[WoodWombat]

Just to add to what @cafz said, identical low frequency electromagnetic fields will be created no matter how the cable is coiled or not. The coil just concentrates it a bit, but it is no big deal for the typical messy and large coil that you hang on a hook.

 

[pssturges]

OK thanks. Well from the responses and my own reading elsewhere, it seems the issue is not so much EMF, but heat build up. The cable on the wall connector seems pretty well insulated. When I get my car, I’ll coil the cable very loosely and try charging at the highest rate I can and monitor for heat build up. If there is any noticeable, I’ll reassess.

Thanks

 

[Tronguy]

And, speaking as a part-time actual EMI engineer: I agree completely with the other posters. We're talking 240 VAC, 60 Hz wires running right next to each other. The currents are equal and opposite, create equal and opposite magnetic fields, which cancel. The Electric fields involved do spread out a bit, but are 98%+ between the wires.

Wavelength of 60 Hz = 3e8/60 = 5e6 meters. If one has a stub which is, say, around an eighth of a wavelength or bigger, then it's possible for radiation to carry things away (your EMF). But the length of a 3-meter cord is 3/5e6 = 0.6 e-6 wavelengths, so, no, no appreciable radiation.

Now, if one had a 60 Hz pair of wires spanning the continent, like the power companies do, then one would discover that a significant amount of the grid power gets lost to Space, no joke. Which is another reason that one sometimes runs into DC high-tension wires: They don't particularly radiate .

 

[meloccom]

I have mounted my wall connector just behind where I back my car into the garage so I don’t need to uncoil to reach the charge port. I have been charging regularly at about 7Kw for over 7 years without any issues. My car can charge at up to 22Kw and I have only done that a handful of times and the charge cable becomes slightly warm on those occasions.

 

[WoodWombat]

And, speaking as a part-time actual EMI engineer: I agree completely with the other posters. We're talking 240 VAC, 60 Hz wires running right next to each other.

That would be 50Hz here in the land down under! Otherwise very true. A nice quarter wave antenna would be about 1500km long. Nice!

 

[WoodWombat]

I have mounted my wall connector just behind where I back my car into the garage so I don’t need to uncoil to reach the charge port. I have been charging regularly at about 7Kw for over 7 years without any issues. My car can charge at up to 22Kw and I have only done that a handful of times and the charge cable becomes slightly warm on those occasions.

More likely warm from resistive losses than inductive heating though.

 

[Tronguy]

That would be 50Hz here in the land down under! Otherwise very true. A nice quarter wave antenna would be about 1500km long. Nice!

Yep, knee-jerked when I saw the post, didn't look at where it was. So, (kidding now), what's a little difference in wavelengths, 6 Megameters vs. 5 Megameters?

Most of my time spent on this kind of thing is keeping 100 GHz signals with 30 cm wavelengths bottled up inside of metals boxes that, unfortunately, have DC power feeds running in and out. It gets interesting.

 

[WoodWombat]

Yep, knee-jerked when I saw the post, didn't look at where it was. So, (kidding now), what's a little difference in wavelengths, 6 Megameters vs. 5 Megameters?

Most of my time spent on this kind of thing is keeping 100 GHz signals with 30 cm wavelengths bottled up inside of metals boxes that, unfortunately, have DC power feeds running in and out. It gets interesting.

Not to be that guy again, but you mean 3mm, right? unless you meant 100MHz, although that would then be 3m. I think that you have a bad case of the Fridays and I prescribe a trip down to the pub.

 

[Tronguy]

Not to be that guy again, but you mean 3mm, right? unless you meant 100MHz, although that would then be 3m. I think that you have a bad case of the Fridays and I prescribe a trip down to the pub.

Yep, need that pub. 3e8/100e9 = 3e-3, so 3 mm. There's reasons everything has EMI gaskets on every surface; and feed-through capacitors are a Thing.