Current sensing switch, not sure what component I am looking for?

Thread Starter

PennyRoyal AI

Joined Feb 12, 2020
5
Hello
I am attempting to fabricate a non invasive trailer lighting module in my car.
The Car uses LED tail lights that stop working if I put too much load on the circuit - this is why I need a non invasive solution.

This is the circuit i have minus the "?" component:

1581548803632.png

I have managed to find current sensors but no switches:
https://www.techbrands.co.nz/store/product/xc4610.aspx
https://www.sparkfun.com/products/11005

Specifications for the relay:
1581549191556.png

Can anyone point me in the direction of an appropriate component for this?

Thank you in advance.

Mike
 

ebeowulf17

Joined Aug 12, 2014
3,274
Hello
I am attempting to fabricate a non invasive trailer lighting module in my car.
The Car uses LED tail lights that stop working if I put too much load on the circuit - this is why I need a non invasive solution.

This is the circuit i have minus the "?" component:

View attachment 198951

I have managed to find current sensors but no switches:
https://www.techbrands.co.nz/store/product/xc4610.aspx
https://www.sparkfun.com/products/11005

Specifications for the relay:
View attachment 198952

Can anyone point me in the direction of an appropriate component for this?

Thank you in advance.

Mike
How non-invasive does it actually need to be? Are you willing to cut and splice the existing wires? Is it just ECU sensitivity you're worried about, or are there other reasons to be "non-invasive?"

I think there are a variety of solutions that would work much more easily sensing the voltage change as opposed to sensing current, but they require tapping into the wire. They wouldn't present any tangible load, and I'm 99% sure that no ECU would ever recognize the change.

However, if you don't want to cut the wires at all, things get more complicated.
 

crutschow

Joined Mar 14, 2008
24,711
Non-invasive current sensing is not trivial, especially for the low currents an LED draws.

Likely neither of the devices you posted will work.
The first has a 30A rating so will have difficulty sensing the LED current.

The second only works with AC.

Can you determine what current the LED lamps draw?

You could use a sensitive Hall-effect sensor, or perhaps a reed switch with several turns of the brake wire wrapped around it.
 

Thread Starter

PennyRoyal AI

Joined Feb 12, 2020
5
How non-invasive does it actually need to be? Are you willing to cut and splice the existing wires? Is it just ECU sensitivity you're worried about, or are there other reasons to be "non-invasive?"

I think there are a variety of solutions that would work much more easily sensing the voltage change as opposed to sensing current, but they require tapping into the wire. They wouldn't present any tangible load, and I'm 99% sure that no ECU would ever recognize the change.

However, if you don't want to cut the wires at all, things get more complicated.
Thanks for the reply

I am happy to cut the wires so long as there is no additional load placed on the cars lighting circuit.

I did try the circuit like this with the mentioned relay but i think the relay placed too much load in the circuit and the car LED's wouldn't work:
1581555228788.png
I am open to any advice on how I can get this to work
Thanks
 

crutschow

Joined Mar 14, 2008
24,711
You need to connect the relay in parallel with the LED, not in series.

And to suppress any inductive spikes from the relay coil you need a small diode (e.g 1N4148) across the coil (cathode to positive).
 

ebeowulf17

Joined Aug 12, 2014
3,274
Thanks for the reply

I am happy to cut the wires so long as there is no additional load placed on the cars lighting circuit.

I did try the circuit like this with the mentioned relay but i think the relay placed too much load in the circuit and the car LED's wouldn't work:
View attachment 198957
I am open to any advice on how I can get this to work
Thanks
I think that all you need is A MOSFET and one or two resistors. Alternately, I think if you want things you can wire up with crimp terminals and such (no soldering) that there are DC SSRs that might work here too. On phone, not computer, right now, so I can't generate schematics, but I can share circuit and/or part examples later if no one else beats me to it.
 

Thread Starter

PennyRoyal AI

Joined Feb 12, 2020
5
Non-invasive current sensing is not trivial, especially for the low currents an LED draws.

Likely neither of the devices you posted will work.
The first has a 30A rating so will have difficulty sensing the LED current.

The second only works with AC.

Can you determine what current the LED lamps draw?

You could use a sensitive Hall-effect sensor, or perhaps a reed switch with several turns of the brake wire wrapped around it.
Thank you for the advice

Can you suggest a particular hall effect sensor that would do the job?
I am having trouble locating suppliers on the net - I think because I may not be searching for the right "name" of a component?
 

crutschow

Joined Mar 14, 2008
24,711
I think the relay may work if you connect it in parallel as I suggested in post #5.

Connecting the relay in series blocks most of the current to the LED, which is why it didn't light.
 
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