Safety of DC fast charging for batteries and biology

BMW i3 Forum

Help Support BMW i3 Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

electronchaser

Well-known member
Joined
Nov 8, 2019
Messages
80
So for the first few weeks I was just charging the i3 through a lvl2 240/40 amp'd Juicebox40 pro. Was pretty impressive.
Last few weeks, I've been DC fast charging every time SOC is near 30ish%.
I know there are faster charge rates out there, but I think I'm happy with the i3 adding nearly 1kW of power every minute. Its really impressive putting in 3-4 miles /minute of range. Another thing I noticed is that the car accepts 100+ amps of input until the pack reaches about 93%, and then gradually begins tapering down. at 95% it was still pulling 40amps at 400v (which is where I end charge).

But it brings me to my question. How safe is it to be in the vehicle while there's 400V at 120 amps flowing into the packs? Are there EMF fields generated by the DC charging process? Seems like an insane amount of power. Just want to make sure there aren't any dangers, and if there are, how to properly mitigate them.

So far I've parked and exited the car while it charges, but that's not always possible.

Also does DC charging degrade the pack any quicker vs lvl2 charging?
 
electronchaser said:
I know there are faster charge rates out there, but I think I'm happy with the i3 adding nearly 1kW of power every minute.
It's a brave new world out there with sometimes unfamiliar units of measure. Power while DC fast charging an i3 can be as high 45 kW at certain charge levels. However, it's energy that's being added to a battery pack while charging, and energy is expressed as kWh. 45 kW x 1 min x 1 hr/60 min = 0.77 kWh of energy added per minute.

electronchaser said:
But it brings me to my question. How safe is it to be in the vehicle while there's 400V at 120 amps flowing into the packs? Are there EMF fields generated by the DC charging process?
An EMF is generated only by alternating current (AC) but not by direct current (DC), so there shouldn't be any EMF when DC fast charging.

electronchaser said:
Also does DC charging degrade the pack any quicker vs lvl2 charging?
In general, yes. Faster charging generates more heat which raises the temperature of the battery cells leading to more rapid degradation. However, the bottom of an i3's battery pack is cooled by AC refrigerant if necessary during charging, so average cell temperatures should not increase enough to accelerate degradation noticeably. That doesn't guarantee that the upper portion of each cell farthest from the refrigerant wouldn't heat enough to accelerate degradation, so it's probably best to limit DC fast charging when AC Level 2 charging is available and sufficiently fast.
 
alohart said:
electronchaser said:
I know there are faster charge rates out there, but I think I'm happy with the i3 adding nearly 1kW of power every minute.
It's a brave new world out there with sometimes unfamiliar units of measure. Power while DC fast charging an i3 can be as high 45 kW at certain charge levels. However, it's energy that's being added to a battery pack while charging, and energy is expressed as kWh. 45 kW x 1 min x 1 hr/60 min = 0.77 kWh of energy added per minute.

electronchaser said:
But it brings me to my question. How safe is it to be in the vehicle while there's 400V at 120 amps flowing into the packs? Are there EMF fields generated by the DC charging process?
An EMF is generated only by alternating current (AC) but not by direct current (DC), so there shouldn't be any EMF when DC fast charging.

electronchaser said:
Also does DC charging degrade the pack any quicker vs lvl2 charging?
In general, yes. Faster charging generates more heat which raises the temperature of the battery cells leading to more rapid degradation. However, the bottom of an i3's battery pack is cooled by AC refrigerant if necessary during charging, so average cell temperatures should not increase enough to accelerate degradation noticeably. That doesn't guarantee that the upper portion of each cell farthest from the refrigerant wouldn't heat enough to accelerate degradation, so it's probably best to limit DC fast charging when AC Level 2 charging is available and sufficiently fast.

Yeah , I was specifically referring to power. i had calc'd about 800wh of energy added per minute. But since we don't have any indicators to show real time charging rate, its a guess. It would be nice to have some graphics to show breakdown of all the parameters, temp, charge whs, etc. I would love to geek out on all the numbers that I'm sure the car is processing anyway in the background.

So just park a good deal away from the DC fast charge unit? Since its being fed a pretty insane level of A/C power.

Yeah I asked about degradation, because I've actually heard some kind of fan or pump engage usually 2-3 times throughout the DC charge session. Like every 20ish % it will whirl and then I don't hear it (not sure if its still working the background) . I've never heard this while charging at 6.6kW at home (208@32amps).
 
Personally, I wouldn't worry about the energy field. FWIW, both ac and dc will produce a magnetic field, depending on how the wires are run. Have an electric house and most things are running, sitting near the power panel could equal the amount going into your i3, but it would be an unusual situation and probably not last as long.

RF energy, OTOH, can be dangerous, but typical 50/60Hz stuff is pretty inane.
 
jadnashuanh said:
Personally, I wouldn't worry about the energy field. FWIW, both ac and dc will produce a magnetic field, depending on how the wires are run. Have an electric house and most things are running, sitting near the power panel could equal the amount going into your i3, but it would be an unusual situation and probably not last as long.

RF energy, OTOH, can be dangerous, but typical 50/60Hz stuff is pretty inane.

Would you mind elaborating further if you know more about this stuff. I'd love to know.

And by RF you mean RF coming from the on board stuff ? or just RF in general?

I kinda trust the germans have done proper shielding to protect occupants during use, but charging always kinda concerned me (since its mostly unoccupied during charging).

Would you know where the a/c- d/c inverter is located, and if that produces any EMF when being fed with a/c power.
 
IMHO, people get too bent out of shape about things like high voltage power lines. Lots of studies, indeterminate results.

The thing that gets dangerous is ionizing radiation. 50/60Hz isn't anywhere close to being ionizing radiation. RF has the potential to be dangerous once it gets up into the megahertz range, and can be more dangerous up in the gigahertz range. FWIW, WiFi isn't ionizing, but at high levels, might give some concerns. If you want to be really careful, you'd never put your cellphone up to your head - wired headphones are better for you. Short term exposure doesn't seem to be an issue. RF up into the x-ray frequency range is ionizing. It has enough energy to damage cells. But, some people will not go to the doctor's office to get a needed x-ray, but will fly cross-country which will get you the same exposure as a typical chest x-ray. Pilots and flight attendants do that day after day. Flying say to Australia and back would exceed the maximum yearly x-ray exposure (the atmosphere blocks a lot of that ionizing energy, but you're above the thickest part when flying long distance) recommended. You don't see pilots or flight attendants dying off from the effects.

So, you can worry about it, or just live life. I'm not going to promote fear, as I don't see any in charging your car, whether you're sitting in it using an EVSE or CCS unit.
 
jadnashuanh said:
IMHO, people get too bent out of shape about things like high voltage power lines. Lots of studies, indeterminate results.

The thing that gets dangerous is ionizing radiation. 50/60Hz isn't anywhere close to being ionizing radiation. RF has the potential to be dangerous once it gets up into the megahertz range, and can be more dangerous up in the gigahertz range. FWIW, WiFi isn't ionizing, but at high levels, might give some concerns. If you want to be really careful, you'd never put your cellphone up to your head - wired headphones are better for you. Short term exposure doesn't seem to be an issue. RF up into the x-ray frequency range is ionizing. It has enough energy to damage cells. But, some people will not go to the doctor's office to get a needed x-ray, but will fly cross-country which will get you the same exposure as a typical chest x-ray. Pilots and flight attendants do that day after day. Flying say to Australia and back would exceed the maximum yearly x-ray exposure (the atmosphere blocks a lot of that ionizing energy, but you're above the thickest part when flying long distance) recommended. You don't see pilots or flight attendants dying off from the effects.

So, you can worry about it, or just live life. I'm not going to promote fear, as I don't see any in charging your car, whether you're sitting in it using an EVSE or CCS unit.

Good stuff ! Ya I might have spent less than 20 min in car while dc fast charging, but always good to ask in case other have stumbled across data that I had missed.

On another note, last night, I got the flashing red indicator around the charge port and dc charger terminated session. I waited a few minutes, tried it twice more, it ramped up to 100ish amps, held for another minute then shut down again, both times.

I'll deplete charge again and try it at another fast charger. Weirdly the one last night only gave me 36kW (102amps x 356V) power at peak. Battery temp was ideal. plugged in at 26%, was at 76% in 30 min. Kept the 100amps until about 85% and that was the first time it error'd and shut down.

Nothing on dash, msg wise.

Any one experienced the red flashy thing? is it car or evse related issue?
 
alohart said:
An EMF is generated only by alternating current (AC) but not by direct current (DC), so there shouldn't be any EMF when DC fast charging.
I was incorrect when I wrote this. All electrical current creates an EMF around the conductor. However, the DC used for DC fast charging creates a constant EMF; i.e., the EMF isn't oscillating as it is with an EMF created by AC. Any danger to life created by an EMF is limited to AC EMF because all of us are continuously exposed to the significant DC EMF created by the Earth. So you shouldn't worry about sitting in your i3 during DC fast charging.

When AC charging, the maximum power is 7.4 kW. That's a tiny fraction of the power conducted by the electrical distribution network that creates an AC EMF that some worry about. The EMF strength dissipates rapidly with distance from the conductor. The i3's chargers are in the rear on top of the electric motor. The chargers boost and rectify the AC input current to a DC output current at over 400 V which is necessary to charge the battery pack. So the AC EMF should be strongest at the rear of the car.

However, while driving, the AC propulsion motor operates at as high as 125 kW and produces a much stronger AC EMF than charging would. There is almost certainly EMF shielding that protects occupants. However, the radio antenna picks up AC EMF in the AM radio frequency range, so shielding isn't 100%.

The bottom line is that no one should worry about EMF dangers inherent in the charging and operation of EV's. Regulatory agencies in the U.S. and E.U. have required sufficient shielding to protect those in and near EV's.
 
For what it’s worth, Tesla encourages staying in the car now that you can watch movies and play video games on the screen !
 
Back
Top