dual coil relay coil polarity

[VEGETA]

I however checked its table and showed Vgs th to be max of 3v so I said it could work

Max Vgs th is defined by output current (typically very small, here 1mA).
Practically you need max Vgs th about 1V below voltage you will be using to drive it.

so you mean i need 2.3v if i use 3.3v to drive the gate? my understanding is the datasheet puts min and max Vgs_th, more like best and worst case, meaning the worst case it will need 3v to be fully activated which means my 3.3v should be totally fine.

is this correct? what do you suggest instead?

[Psi]

You maybe able to turn the fet on, but the Vgs also effects Rds which affects current.
So if you are too close to the Vgs your fet will be on but the Rds will be too high to flow much current.
Does that make more sense?

[VEGETA]

You maybe able to turn the fet on, but the Vgs also effects Rds which affects current.
So if you are too close to the Vgs your fet will be on but the Rds will be too high to flow much current.
Does that make more sense?

well, that is known but as you mentioned it does not clearly show the behavior in the graphs. 7000 shows like 4.5v Vgs having something like 2.8 ohms of Rdson, thus for 3.3v maybe i can say 4 ohms it will be the resistance.

the coils are 100 ohms of resistance for the relay mentioned, which means a maximum of say 5 ohms from the mosfet won't do much effect. what do you think of this on this application?

still, it would be nice to have a better performance, so maybe reverting back to npn with some resistor at the gate is better. 2n2222 is cheap and with 220 ohms at its gate it will be fine. esp32 can deliver such very low current as well.

do you recommend going with this npn solution or mosfet?

the only concern with npn is 0.7v drop which makes coil voltage 4.3 instead of 5v. PRL6-5V-DC-1A datasheet says minimum voltage is 4v, which i think is good margin.

[Peabody]

I am just a hobbyist, but it seems to me that what matters here is the current the mosfet can pass at the voltages involved.  The datasheet will have a diagram of Vg/s versus drain current.  However, that curve is probably "typical", not worst case.

It seems that EEs often use the lowest voltage at which behavior is characterized as the lowest voltage for which the part can be used (4.5V in this case).  It's not clear that manufacturers intend for that to be the case.  But I guess experience suggests that's a good rule of thumb since behavior at lower voltages is not specifically defined.  Maybe one of the experts here can clarify that.

But for a hobby project, if I found a convenient (TO-92) mosfet like the 2N7000 or BS170 that convincingly switches the relay, I would use it.

[PGPG]

my understanding is the datasheet puts min and max Vgs_th, more like best and worst case, meaning the worst case it will need 3v to be fully activated

Where from have you taken 'fully activated'? This term is even hardly possible to define. I think fully activated = have minimum Rds is when Vgs is the highest that is allowed (so 20V in this case).

See bottom of page 2 in:
https://www.onsemi.com/pdf/datasheet/nds7002a-d.pdf
It is hardly to believe that you see 3V but don't see Id=1mA in the same line.

In worst case it will need 3V to drive 1mA what is certainly not enough for your relay.