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Power ground

Practical Harness Construction - Club Level

Discussion and questions related to the course Practical Harness Construction - Club Level


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Hello,

Small question.

Let's assume that I have a 12v sensor that is drawing 10amps.

I will connect it via relay that's ok.

But what if I need to ground it to the ECU? The ecu will have 18-20awg wire, how do I do that?

For the power, I use a relay. What do I do for the ground?

Hope I explain it right, thx (:

Hi Chen,

Could you provide more details as to what this sensor will be doing?

Hello sir,

The sensor is not the issue, I'll try to explain.

Let's say I have 1 sensor ground pin in my ECU, and I have 10 sensors that I need to connect to that sensor ground pin, they all draw 10-12 amps combined.

Usually the awg wire from the ecu will be 22-18awg.

I need to splice all the sensors ground in to my ECU,

That will be 10-12 amps to a small wire and that will cause it to heat up..

Hope you understood me, and good luck on the new job !

How did you work out you have 10-12A current draw? Most common sensors that are connected to an ecu only draw a few mA, so you can usually have at least 10 sensors connected to one 5V supply/sensor ground without even considering their current draw.

Can you list the sensors you have and their current draw?

Adam, you missed the point, I started this thread with " LET'S ASSUME"

I just want to figure out a theoretical situation.

Ok, so its hard to answer your question accurately if you are just making up an imaginary device in your head. Typically any device that draws high current would have seperate power and analog output grounds. The power ground that passes high current connects to a point capable of passing high current such as the engine block and the analog ground which passes only a few mA or uA gets connected to ECU sensor ground.

ECU sensor ground is the reference that all other sensors are measured from so you never want to pass significant current through it otherwise you will cause a voltage offset which will make all other sensors read incorrectly. All ECU manufacturers have different specifications but I would typically suggest no more than 100mA through a single sensor ground pin. Usually that will cover 10-20 common automotive sensors.

Thx Adam, that's answered my question!