Schematic help - contact sense

[anishkgt]

Hello All,

I am trying to sense when two electrodes makes a contact. I've put up a schematic, partially completed. How can i trigger the T1 when the electrodes the short.

Would appreciate if any one could help or suggest me a better option.

[JVR]

How about telling us what the contacts are, and where they are used. Since that schematic looks like overkill, unless some context and constraints are elaborated upon.

[anishkgt]

Oh sorry, it’s spot welder. When triggered the electrodes have 2vac at the electrodes and several amps to spot weld nickel strips to 18650 cells.


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Equipments: DSO104z, Hakko FX888D, Brymen BM869s

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[JVR]

I'd suggest a current sense method, as I assume open circuit the voltage will be higher.

[anishkgt]

2vac is actually the open circuit voltage.

Yes sounds like a better idea to sense the current.  So how many ohms resistor should I go with ? Through hole or smd ?

The resistor would go in parallel with one of the cable and two wires form both sides of the resistor the add of the muc, correct ? Would it be a good idea to sense the current during the weld also ?


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D, Brymen BM869s

Sent from my iPhone using Tapatalk

[JVR]

Here is a complete thread about the development of a spot welder: https://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/

I would sense the current using a hall effect chip, any resistance you add will sap energy away from the weld