Here's a picture of the cables to the inverter. The loose end connects to the pack inside the car in the high voltage junction box under the rear seat. i can understand a magnetic field when current is flowing but not sure what could be showing the residual magnetism by the compass when the motor is off. Can you determine if it is stronger towards the left or right side of the trunk--might provide a clue...
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I, also, just ordered a DJI Inspire 1 V2 to carry around in my P90D. So I'm going to be very interested in investigating any possible magnetic field coupling strong enough to miscalibrate the compass. I'll do some checking with my backpacking compass in various locations and report back. But I'm astonished that AllDigital reports that his compass pegs with the car completely off - makes no sense.
I said I'd report back, and here's what I got. Note that I was dubious about there being an intense magnetic field when the care was completely off... I suspected the strong fields would exist during driving or charging.
Using my handheld compass, I could not test in the bottom of the trunk or frunk while driving. So that'll need further work.
Using the handheld compass, with the car disconnected from the charger and with everything off (so far as I could tell), I found several areas that caused significant deviation of the needle. The bottom of the trunk and bottom of the frunk showed very little distortion of the magnetic field. But at the upper flat region of the trunk there was some deviation. But right at the hasp of the trunk release the field was quite strong - the compass needle tracked right around it. Also, at the front bumper on passenger side there was a similarly strong field or disturbance.
Note that the above was no different, however, from doing similar tests on my ICE SUV near various devices under the hood and at the trunk release - all the electromagnetic devices (motors and solenoids) either, because of their iron content, greatly distort the earth's field, or perhaps they acquire some residual permanent magnetism. So... typical of any vehicle with motors and solenoids.
Then I repeated all the proximity test by connecting and activating charging at 40A - and saw absolutely no effect.
Don't know what this means, but with my P90D it seems like a normal car... except that I haven't done measurements driving. I will do that.
Using my handheld compass, I could not test in the bottom of the trunk or frunk while driving. So that'll need further work.
Using the handheld compass, with the car disconnected from the charger and with everything off (so far as I could tell), I found several areas that caused significant deviation of the needle. The bottom of the trunk and bottom of the frunk showed very little distortion of the magnetic field. But at the upper flat region of the trunk there was some deviation. But right at the hasp of the trunk release the field was quite strong - the compass needle tracked right around it. Also, at the front bumper on passenger side there was a similarly strong field or disturbance.
Note that the above was no different, however, from doing similar tests on my ICE SUV near various devices under the hood and at the trunk release - all the electromagnetic devices (motors and solenoids) either, because of their iron content, greatly distort the earth's field, or perhaps they acquire some residual permanent magnetism. So... typical of any vehicle with motors and solenoids.
Then I repeated all the proximity test by connecting and activating charging at 40A - and saw absolutely no effect.
Don't know what this means, but with my P90D it seems like a normal car... except that I haven't done measurements driving. I will do that.
Here is a quick follow-up #1 -- I got smart on measuring magnetic fields. It turns out the iPhone is actually a very good device to use as a magnemometer. I downloaded "MagnetMeter" from the app store and used a few magnets in the garage to help me understand relative strength and direction. In the open, the app points down with a reading of 45-50 uT. That is exactly what you would expect from the Earth's magnetic pull. I've got a small powerful magnet in the garage that will lift 5-10 lbs. When I place that anywhere near the phone it sends the needle following and at peak it hits 3,000 uT (micro Tesla). The small magnet is so strong it also messes up the iPhone for a while and I need to reset and degauss it. That helped give me a relative sense of field strength. Earth = 50 and small super magnet = 3000.
I did a scan of the car while it was parked and off. I got no meaningful change anywhere in the Frunk. In the passenger cabin I get slight variations on the floor and around seats, but a range of 40-90. Just slightly more than the Earth's magnetic field.
In the trunk I get a lot of small variation - sometimes going to 0 (a pull of 50 in the opposite direction), but most of the trunk varies between 40-120 with the exception of two spots. I get very high readings (1200+ uT) coming from the box on the right, in the very back, behind the right tail light. It occupies the same space as the power cord storage on the left side of the car, but on the right. 1200 uT is definitely enough to mess with the DJI compass. Does anyone know what is behind the carpeted box on the right rear, about the same level as the upper deck (although pointing down)? I think this might be the 8" subwoofer (premium sound - pano roof). The other spot that showed hot was where the deck hit the rear seats, especially on the left. I got values up to 200-250 uT. Again, not enough to matter, but still interesting. I think this is near the chargers.
Tomorrow I'll try and do a drive test for follow-up #2. I need to stuff my son in the trunk and drive around the block. With the car off, I do not see anything strong enough to mess with the DJI compass, unless it was directly against the back right side.
I did a scan of the car while it was parked and off. I got no meaningful change anywhere in the Frunk. In the passenger cabin I get slight variations on the floor and around seats, but a range of 40-90. Just slightly more than the Earth's magnetic field.
In the trunk I get a lot of small variation - sometimes going to 0 (a pull of 50 in the opposite direction), but most of the trunk varies between 40-120 with the exception of two spots. I get very high readings (1200+ uT) coming from the box on the right, in the very back, behind the right tail light. It occupies the same space as the power cord storage on the left side of the car, but on the right. 1200 uT is definitely enough to mess with the DJI compass. Does anyone know what is behind the carpeted box on the right rear, about the same level as the upper deck (although pointing down)? I think this might be the 8" subwoofer (premium sound - pano roof). The other spot that showed hot was where the deck hit the rear seats, especially on the left. I got values up to 200-250 uT. Again, not enough to matter, but still interesting. I think this is near the chargers.
Tomorrow I'll try and do a drive test for follow-up #2. I need to stuff my son in the trunk and drive around the block. With the car off, I do not see anything strong enough to mess with the DJI compass, unless it was directly against the back right side.
ken830
Model S 85, Model 3 Performance, Model X LongRange
Yeah. Subwoofer definitely has a strong permanent magnet. When the vehicle is off, there will be no magnetic field within/around the motor -- it is named after Tesla for a reason.
steph280
Member
I've carried all sorts of drones (DJI, Align, Mikrokopter) in my 70D without issues. But now you got me worried and I will pay closer attention.
AllDigital, 'offered' that to my daughter but no joy, so still no driving readings.
I admire your even more analytic approach. But surprised you found no deflection near the trunk hasp (the passive part of my motorized latch) or at the lower passenger side front bumper. My readings were very strong there.
Follow-up #2: Ok, I stuffed my son in the trunk with the iPhone and the MagnetMeter app. It is rainy and wet here, so we couldn't peak out acceleration, but here is what we found. With regular cruising around the neighborhood, the uT are in the 100-200 range, but when I accelerate from a stop the values go way up and seem to be strongest in the center (3 inches off center to drivers side) and about 6 inches from the backseats - measured on the trunk deck. Accelerating 0-40 with about 75% pedal we hit 1600 uT. About half the strength of my very strong small magnet. 0-20mph with half the power was about 1000 uT, so it felt proportional. We didn't venture out to bigger roads, since he was already bouncing off the walls of the trunk testing acceleration and it was raining. It would be interesting to see the values with full throttle up a hill. I suspect they might almost double. Again, these are short bursts -- not sustained, but I suspect they are enough to occassionally mess with a sensitive compass like the DJI on longer trips.
Going down hill with full regen didn't generate much. Also, other places in the trunk were all substantially less. Strib, I did retest and I found high values with the car off in the same places you did. The lower passenger front bumper and lower driver front bumper each gave me about 300-400 uT, although the reading was from outside the car and not strong enough to do much. The trunk motorized latch (in the hatchback) gave a reading of about 300. Stronger than other "off readings", but not enough strength to matter much.
So, using a very crude back-of-the-napkin approach, it appears there is a meaningful amount of magnetic force generated while driving (above the coil in the trunk) that could interfere with a sensitive compass, like on the DJI, but in relative terms the EMF is very small. Too small to erase a credit card or hard disk, but I wouldn't put a pack of 5.25" floppy disks in the trunk.
Going down hill with full regen didn't generate much. Also, other places in the trunk were all substantially less. Strib, I did retest and I found high values with the car off in the same places you did. The lower passenger front bumper and lower driver front bumper each gave me about 300-400 uT, although the reading was from outside the car and not strong enough to do much. The trunk motorized latch (in the hatchback) gave a reading of about 300. Stronger than other "off readings", but not enough strength to matter much.
So, using a very crude back-of-the-napkin approach, it appears there is a meaningful amount of magnetic force generated while driving (above the coil in the trunk) that could interfere with a sensitive compass, like on the DJI, but in relative terms the EMF is very small. Too small to erase a credit card or hard disk, but I wouldn't put a pack of 5.25" floppy disks in the trunk.
whitecotton
Member
I have a phantom 3 pro and I noticed the compass needed calibration as well. 2013 P85 by the way.
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