EMF while Supercharging

[mongo]

No, they don’t output pack voltage until the taper portion of the charge.
The first part of the charge cycle is constant current which means that the voltage varies in order to keep the current the same. The voltage is raised to increase the current flowing into the pack. The only time that the charger voltage is the same as the pack voltage is when the charge current is zero.
While I haven’t done the math, 600v sounds completely reasonable to me for 120kW.

The voltage the pack is at, not the max pack voltage.
For bulk charge, the SC output voltage is :
(Pack voltage with x amps charge current) + X*(round trip cable resistance)
For taper (constant pack voltage):
(Pack max voltage) +Y*(round trip cable resistance)
Guessing at taper, the car tells the SC the desired current (Y) to achieve the desired pack voltage.

 

[Doug_G]

The utility transformer that supplies the Supercharger will emit a little 60 Hz EMF, inthe form of magnetic field, but it is far enough away from the cars that it won’t be significant. Magnetism drops off as the cube of the distance, so it doesn’t go very far at all. Even if you were leaning against the transformer, 60 Hz will not interact with human flesh because of the body’s low electrical conductivity.

The stack of chargers will produce a little moderate frequency EMF, but that is very easily shielded and again isn’t adjacent to the car. Shielding is required to prevent radio interference, so any field will be almost undetectable.

The power coming into the car is DC. DC does not generate electromagnetic fields at all. Basic physics.

In short, there is absolutely no reason to be even the slightest bit concerned about this. You are exposed to far more EMF in your own home, and that’s not a reason for concern, either.

 

[kingjamez]

The voltage the pack is at, not the max pack voltage.
For bulk charge, the SC output voltage is :
(Pack voltage with x amps charge current) + X*(round trip cable resistance)
For taper (constant pack voltage):
(Pack max voltage) +Y*(round trip cable resistance)
Guessing at taper, the car tells the SC the desired current (Y) to achieve the desired pack voltage.

Sorry, that's just not how it works.
You seem like you might have an engineering background so I'll just ask some questions:
In your above example, how does "(Pack voltage with x amps charge current)" happen? How does the circuit cause the "charge current" to flow into the batteries?
Hint: Ohms law. Power = V*I, and is the charger power delivered, I = the CONSTANT charge current, R= the internal resistance of the battery pack. Solve for V.

V is the required voltage that the charger must be above the pack voltage to induce current flow.

At taper, instead of the above where I is constant, V is held constant (at max pack voltage) and thus I varies. As the pack voltage gets closer and closer to the voltage supplied by the charger, ohms law again applies and the current goes down as the voltage differential gets less and less.

I agree with Doug; completely.

-Jim

 

[malcolm]

Let's compare with a hospital MRI machine:

The patient is slid into the centre of a superconducting electromagnet.

This produces a constant magnetic field which is hundreds of thousands of times stronger than any field produced by a constant current Supercharger cable.

Next, electrical current pulses in Gradient Coils in the MRI machine produce their own magnetic fields which modify the main field so that a particular strength of magnetic field only exists through one cross-sectional slice through the patient.

So instead of every part of the patient experiencing a constant 4 Teslas, one side of the patient is at (say) 3.8 and the other side is 4.2. So there is now a gradient in the main magnetic field, for the duration of the current pulses in the Gradient Coils (these repeat and are the reason why MRI machines are noisy).

Synchronized to this, an electrical current pulse in a different coil near the patent produces a radio frequency pulse at the correct Larmor frequency (typically a few megahertz).

This radio signal is absorbed and echoed back by the billions of hydrogen atoms which happen to be sitting in the cross-sectional slice through the patient defined by the correct strength of magnetic field.

It is these radio pulse echoes which are detected by the same RF coil and are processed to make the MRI image.

The point is that the magnetic field and the electromagnetic signals inside these machines are hundreds of thousands of times stronger than any you can encounter while your EV drives along or charges on AC or supercharges on DC.

Or, if you prefer, a single MRI scan is equivalent to several lifetimes-worth of EV usage.

 

[mongo]

Sorry, that's just not how it works.
You seem like you might have an engineering background so I'll just ask some questions:
In your above example, how does "(Pack voltage with x amps charge current)" happen? How does the circuit cause the "charge current" to flow into the batteries?
Hint: Ohms law. Power = V*I, and is the charger power delivered, I = the CONSTANT charge current, R= the internal resistance of the battery pack. Solve for V.

V is the required voltage that the charger must be above the pack voltage to induce current flow.

At taper, instead of the above where I is constant, V is held constant (at max pack voltage) and thus I varies. As the pack voltage gets closer and closer to the voltage supplied by the charger, ohms law again applies and the current goes down as the voltage differential gets less and less.

I agree with Doug; completely.

-Jim

Yes, I have an engineering background. This is not my first battery charging rodeo. So let's figure out where the communication barrier is.

People care about Power. The pack primarily cares about current (and max potential/ charge state/ temperature but those are more limits than control knobs).
The pack is not a constant voltage. At rest, the pack has some voltage potential based on temperature and state of charge. If you put a charge current into the pack, the voltage will go up at the pack terminals due to internal resistance and the electrochemical processes involved in the cell.

To cause this current (X for bulk case) to flow, you need to apply a higher potential at the supercharger.
The voltage at the supercharger needs to be
(Pack voltage (at pack terminals) when being charged with X amps) + (voltage drop over all cables)
Voltage drop over cable is X*(round trip cable resistance), V=I×R. Power loss in the cable is I^2×R, V^2/R, or V×I.

When the pack hits either the max voltage (either the highest cell, total pack, some other BMS factor), it can either report the current it wants or it's present and max voltage. Our systems used remote sense leads along with remote temperature sensing (and SMBus for smart batteries). Tesla uses a smart pilot signal which likely has current and voltage requests and values.

The variable current was the Y value in the fixed pack taper case (to differentiate from bulk charge (X).
Same deal (idle pack) + (rise due to variable charge current of Y) + (cable drop Y×R) = Supercharger voltage.

Edit: removed extraneous cv, if anyone cares, PM me.

 

[brucet999]

I won't have time to get to a supercharger in the next week or two, but I suggest next time you supercharge, tune the AM radio first, then start supercharging and listen to the radio after it starts. If the radio fritzes out, there is EMF at the antenna at minumum, but also probably around the cabin. If you want to see where it's strongest, take a portable AM radio with you and hold it various places around the cabin. If there is a lot of EMF, I would expect it to be strongest in the backseat area (on the S, 3rd row on the X), that's where the charging equipment is.

I do listen to AM radio and find RF interference while supercharging. I assume that it must be from the charging pedestal, since the input to the charge port is DC at less than 400V.

 

[kingjamez]

Yes, I have an engineering background. This is not my first battery charging rodeo. So let's figure out where the communication barrier is.

People care about Power. The pack primarily cares about current (and max potential/ charge state/ temperature but those are more limits than control knobs).
The pack is not a constant voltage. At rest, the pack has some voltage potential based on temperature and state of charge. If you put a charge current into the pack, the voltage will go up at the pack terminals due to internal resistance and the electrochemical processes involved in the cell.

To cause this current (X for bulk case) to flow, you need to apply a higher potential at the supercharger.
The voltage at the supercharger needs to be
(Pack voltage (at pack terminals) when being charged with X amps) + (voltage drop over all cables)
Voltage drop over cable is X*(round trip cable resistance), V=I×R. Power loss in the cable is I^2×R, V^2/R, or V×I.

When the pack hits either the max voltage (either the highest cell, total pack, some other BMS factor), it can either report the current it wants or it's present and max voltage. Our systems used remote sense leads along with remote temperature sensing (and SMBus for smart batteries). Tesla uses a smart pilot signal which likely has current and voltage requests and values.

The variable current was the Y value in the fixed pack taper case (to differentiate from bulk charge (X).
Same deal (idle pack) + (rise due to variable charge current of Y) + (cable drop Y×R) = Supercharger voltage.

Edit: removed extraneous cv, if anyone cares, PM me.

Ah.. so you are considering "pack voltage" to be the voltage that the charger is supplying to charge the pack then? When I say pack voltage, I mean the resting voltage of the pack.

I see that you do understand that whilst in constant current mode (bulk charging in some circles) the voltage of the charger must considerably exceed the resting voltage of the pack in order to charge the cells. The point that I was trying to make is that this could easily exceed 480 volts, and 600 isn't out of the question. (I don't know exactly because I don't know the IR of the entire pack).

-Jim

 

[mongo]

Ah.. so you are considering "pack voltage" to be the voltage that the charger is supplying to charge the pack then? When I say pack voltage, I mean the resting voltage of the pack.

No, I am considering pack voltage to be the voltage at the pack terminals which will increase when the pack is being charged and decrease when the pack is being discharged (instantaneous change, not change due to SOC).
This voltage plus cable loss is what the SC needs to source at its terminals to charge the pack.

I see that you do understand that whilst in constant current mode (bulk charging in some circles) the voltage of the charger must considerably exceed the resting voltage of the pack in order to charge the cells. The point that I was trying to make is that this could easily exceed 480 volts, and 600 isn't out of the question. (I don't know exactly because I don't know the IR of the entire pack).

I think this is the issue, the voltage at the pack terminals is higher than the resting voltage during charge due to the pack resistance and the electrochemical activity going on (around 0.1 Ohm or so combined during discharge). But that voltage is not considerably higher.

The BMS will not allow cell voltages over 4.2V, with a 100kWh pack 86p96s that is a 402V pack max. If the remote SC terminals were at 480V the cable would be dropping 78V (480-402) at 299A (120kW/402). That would be 23.3kW of waste heat.
Industry standard minimum gauge for a 300A load (75C column) is 350 kcmil for copper. If the pedestal were 100 feet from the SC (200 foot round trip) the resistance would be .0308 (mOhm/ft)×200ft=6.16 mOhm. Voltage drop is 6.16 mOhm × 300A = 1.85V. Total cable loss of 300^2×6.16mOhm=554 Watts.

Call it 2 volts on top of 402V max for pack add 1 V/ 300W for connection losses/ wire heating, SC output should normally not exceed 405V.

 

[wdolson]

I do listen to AM radio and find RF interference while supercharging. I assume that it must be from the charging pedestal, since the input to the charge port is DC at less than 400V.

AC signals can be induced onto any wire, including the cables running to the car.

 

[kingjamez]

No, I am considering pack voltage to be the voltage at the pack terminals which will increase when the pack is being charged and decrease when the pack is being discharged (instantaneous change, not change due to SOC).
This voltage plus cable loss is what the SC needs to source at its terminals to charge the pack.


I think this is the issue, the voltage at the pack terminals is higher than the resting voltage during charge due to the pack resistance and the electrochemical activity going on (around 0.1 Ohm or so combined during discharge). But that voltage is not considerably higher.

The BMS will not allow cell voltages over 4.2V, with a 100kWh pack 86p96s that is a 402V pack max. If the remote SC terminals were at 480V the cable would be dropping 78V (480-402) at 299A (120kW/402). That would be 23.3kW of waste heat.
Industry standard minimum gauge for a 300A load (75C column) is 350 kcmil for copper. If the pedestal were 100 feet from the SC (200 foot round trip) the resistance would be .0308 (mOhm/ft)×200ft=6.16 mOhm. Voltage drop is 6.16 mOhm × 300A = 1.85V. Total cable loss of 300^2×6.16mOhm=554 Watts.

Call it 2 volts on top of 402V max for pack add 1 V/ 300W for connection losses/ wire heating, SC output should normally not exceed 405V.

You are right. After using your 0.1ohm IR, it appears that the maximum difference between the charger voltage and the pack voltage is roughly 30 volts (assuming 300 amp charge rate), but that would only occur at max charge rate which in turn only happens at low SOC (and thus low voltage), so a maximum voltage that is very close to 402V+cable loss makes sense.

-Jim

 

[mongo]

You are right. After using your 0.1ohm IR, it appears that the maximum difference between the charger voltage and the pack voltage is roughly 30 volts (assuming 300 amp charge rate), but that would only occur at max charge rate which in turn only happens at low SOC (and thus low voltage), so a maximum voltage that is very close to 402V+cable loss makes sense.

-Jim

As an addendum, it's not a pure R for the 0.1 ohm, that is my estimate of pack droop under heavy load so it also includes cell chemical reaction effects.

A large portion of that effect takes place inside the cell so the 4.2V max cell voltage already bakes most of that in. Confounding a module resistive estimation that is that the BMS measure voltage at the bus bars, so the module resistance is largely included in the 4.2V. The pure R items that aren't in the BMS measurements are the 15 internal module jumpers, pyro fuse, 2 contactors and assorted fuse, contactor, and output wiring.

So additional voltage on top of the 4.2V cells would be <<5V (guess) at 300A. There may also be a maximum pack voltage limit which would limit charging at a lower total pack value.

Good discussion!Been a few years since I built a charger.

 

[gregd]

Oh. My. Lord. I'm not sure if I should laugh or cry. If there was ever a click-bait source for Seeking Alpha, this thread is it. OMG, Photon Exposure! Tin Foil Hats for everyone!

All we're missing is a link to the risks of suffocation through Di-Hydrogen Oxide poisoning. Seriously, folks. It's a real thing.

To the OP, and anyone else who has been fear-mongered into thinking there's a problem here, the simple answer is no.

 

[wdolson]

Oh. My. Lord. I'm not sure if I should laugh or cry. If there was ever a click-bait source for Seeking Alpha, this thread is it. OMG, Photon Exposure! Tin Foil Hats for everyone!

All we're missing is a link to the risks of suffocation through Di-Hydrogen Oxide poisoning. Seriously, folks. It's a real thing.

To the OP, and anyone else who has been fear-mongered into thinking there's a problem here, the simple answer is no.

Stop subduction!

 

[Shock-On-T]

good luck.


From what I've heard (from someone who takes all this very seriously, owns an EMF reader and a Tesla), the car does not emit anything harmful while driving, however there is enough to be concerned during supercharging. He has advised that I not sit in the car while supercharging.

Unless you have a pacemaker there is almost no amount of EMF that will harm you at all.
Even high power industrial EMF such as right next to an electrical aluminium smelter has zero effect on people.
Additionally, I’ve tested pacemakers right next to supercharging at 100kW with no noise detected.

 

[Shock-On-T]

Hi All
I know this is not how the internet works but:

I know what I’m talking about and you don’t have to worry about EMF.

Goodnight all!

 

[TechOps]

So if I can summarize this in terms of field strength, there would be three events where the magnetic field changes. One, when the car is first plugged in, the magnetic field goes from near-zero, to ramping up to a higher field strength as the charge voltage builds. Second, if you're sitting in the car while charging, the field will gradually taper down as the current flowing through the cable lowers when the battery is closer to charged. And third, it goes from that lower field back down to zero when you unplug, correct? But while you are sitting in the car, because it is a DC current, there is not magnetic field oscillation as would be the case with AC charging, which means a safer environment for the human body.

(NB: I don't find the comparisons to MRIs to be particularly useful, since the strength of those magnetic fields is generally not good for the human body and we don't all go out and get MRIs on a regular basis.)

 

[gregd]

So if I can summarize this in terms of field strength, there would be three events where the magnetic field changes. One, when the car is first plugged in, the magnetic field goes from near-zero, to ramping up to a higher field strength as the charge voltage builds. Second, if you're sitting in the car while charging, the field will gradually taper down as the current flowing through the cable lowers when the battery is closer to charged. And third, it goes from that lower field back down to zero when you unplug, correct? But while you are sitting in the car, because it is a DC current, there is not magnetic field oscillation as would be the case with AC charging, which means a safer environment for the human body.

Almost, but not quite. It's better than that.

If you put a current through a single wire, you get a magnetic field. If you put the reverse current through the wire, you get the reverse of the field. There are always two wires to create a circuit (in and out). Since the current going into the car is the same as the current going out of the car, and the wires for the most part are close together (e.g. in the charging cable), those magnetic fields cancel each other out and you get nothing, whether the current is changing or not. Note that this applies to both AC charging too, since the AC currents are confined to the charging cable. Only where the wires separate will there be a net field, and as you point out, it is a static field unless those currents are charging.

The strength of a magnetic field is related to both the current and the number of turns that the wires make in a loop. Recall your science class where you wind a wire around a nail a bunch of times to make an electromagnet. The current here is large, but instead of a bunch of turns, the path the current goes is for the most part, in, around, and out. One turn, since current paths that turn back on themselves cancel each other out. That makes the field strength all that much lower.

The frequency of that magnetic field, what there is of it, is directly related to the rate of change in the current. We're talking about changes on the order of many minutes to hours per cycle. Hazardous field frequencies are in the range of hundreds of millions to billions of cycles per second. We're so so so far away from that with the charging circuit that it is totally inconsequential.

If there was really a significant magnetic field being generated by an EV, wouldn't it be a hazard to every manhole cover on the roadway? Think about it.

 

[Ande]

I am just watching this thread to see how much more NUTS it can be, I wait for some of the more EMF concerned users will start to preach flat-earth soon

 

[wdolson]

Resurrecting this thread...

I did some testing on my own. I got a fairly good EM meter with different bands. Last night I did some testing in the car while it was charging on AC. On the RF band the EM in the car was lower than it was in the house unless I got the meter right next to the center screen, then there was a small spike in EM.

The meter also has two low bands, one 50Hz-1KHz and the other 50Hz-10KHz. The low bands were OK in the front seat, but massively high in the back seat. I would not want anyone in the backseat while the car is charging. The cable was also putting out some intense fields while the car was charging.

This morning with the car plugged in, but not charging, there wasn't anything remarkable in the backseat or the cable. I didn't test anything while we were on the road.

We had an opportunity to supercharge and I plugged in for about 15 minutes to do some testing (we had enough juice to get home, but free energy and a chance to test). There was nothing remarkable on any band while supercharging. The only reading we got above background was holding the meter up to the center screen and my SO's iPhone when she was sending a text. The meter really lit up when she clicked send. I did neglect to test the input cable, but since there was nothing in the car, I suspect the cable was fine too.

I don't know what the reading was the earlier poster in this thread had, but I found no notable EMF while supercharging.

 

[ricebucket]

DC current has no changing flux, so should not irradiate any EM radiation. This is probably what you're seeing.