Car Key Transponder/RFID/Chip Key fried by Inverter Welder?

ByJohn Wuethrich

Car Key Transponder/RFID/Chip Key fried by Inverter Welder?

I’m relatively sure that I managed to fry a car key transponder (RFID tag) with a wirefeed welder.

A friend of mine was welding with his  harborfreight titanium 125 about 3ft from where my car keys sat and the next day I ended up stranded at a kwik trip station.  my ford fusion 2007 was rejecting the only key I had at the time.

This Event was 3 days ago aka imeadiately followed the construction of the  wood stove rack  project.

I drove to my empty apt from pole barn and everything was fine. I took a nap. when I woke drove to the gas station maybe 3 miles from my apt. Upon coming out of the station my car refused to start and flashed the security light.

There are tons of stories of frying out ecus/various electronic bits in cars with welders… Largely cautionary of how one grounds iirc. Yet I can’t seem to find anyone else (breif Google search) that has experienced a fried RFID /chip key.  science /physics wise i can see maybe how (I’ll get to that in a min) but it’s still freak and the main reason for attribution is lack of other cause.

The actual name for the chip is a DST tag and its made by Texas instruments. It operates at 134khz and outside the car world would be refered to as an RFID tag/chip rather than a transponder

My 2007 ford fusion’s keys were maybe 3 ft from where the welder from harbor freight was doing its thing. I drove home shortly after completion of the project (roughly a 15min drive) napped a bit and on waking drove 5min to a gas station near by. 5-10 min in the store and the car wouldn’t start after. Though I wanted it to be the battery I was pretty sure it wasn’t.

A very kind quiktrip employee offered me a jump and already having a feeling it wasn’t going to work I figured lets rule it out. The battery is probably no older than 7 months.

Why I didn’t suspect the battery:

  • light levels appeared normal
  • battery appeared new.
  • seat moved forward and back and normal speed
  • windows operated at normal speed
  • red security light on dash was a bit wonky
  • chime cadence and volume was normal
  • yet not even a click from the starter
  • negative clamp sparked decently against my car frame

My thought shortly after catching a cab back to my apt soon shifted to if it is the transponder why/how? In my mind I recalled where I had picked my keys up off of on leaving the pole bar and the welding happened right next to it.

Then I remembered that the tags operate at around 134khz and DC-DC converters  typicaly operate from 100khz up to a few mhz. Most common range I’ve seen implemented designs in or chips to get implementing… most of those are 100khz to maybe 500khz.

An inverter welder that plugs into 120 is more than likely rectifying the AC voltage and then using a DC – DC switching voltage converter to create the 10 to 25vdc for welding. I havent looked inside of found a schematic for the machine used but at the same time I know: electric archs are wide band RF/EM/EMI emissions. The earliest radio transmitters used sparkgaps and are now baned because of how much noise that would create over such a large chunk of the radio spectrum that enables modern life (cellphones, police/ems radio, air traffic control etc) so in theory any arch welder is capable of inducing a voltage on the chip key transponders internal coil.

i have to think in an inverter welder though the majority of the power is going to be centered at what ever frequency the machine is switching.

I know my ford key has a Ti DST tag transponder at 134khz I have not been able to find any documents indicating this frequency on the machine used.

it was a Harbor freight Titanium 125 flux core machine. I wasnt operating it last night but have in the past and although I prefer my klutch 140 I am truly impressed with what the little green harbor fright box can do weld wise (dont take this as a bash at harbor freights Titanium line)

but as i mentioned above the most common range ive seen for general purpose inverter/dc-dc switching circiuts is 100k to 500kish

I cant prove this but I would bet maybe 180ish khz on the machines switching frequency and because the coil of wire that acts as the transponders antea is optomized for 134khz, it isnt out of the question to consider it got a bit more power than it was intended to take.

has anyone in internet land managed to kill a keyfob? I searched and found tons of fried ecu stories related to welding but nothing about fried keys…at the same time i wonder how often it may or maynot get missdiagnosed and there is the possibility I am falsely attributing cause despite confirmed root issue.

Heres a video I took yesterday of old fob then spare.

Some info on the transponders in general

Exploiting RFIDs

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