Driving a GigaVAC with MOSFETs

[MaxG]

The GigaVAC is a big (350 A) DC latching relay, which I will use to disconnect a 400 Ah battery in case of a cell voltage going over/under their thresholds.
gxl14.pdf (935.3 KB)

This is what I came up with; the question being, while this looks like it would work, is there a need for extra caps or other components?

The relay has a set and reset wire, hence, the two identical circuits; with the relay being connected to 1 and 3 with 2 being common ground.
R3 and R4 are for the Arduino UNO to connect to.
5V and 24 V will be provided by the 52.1 V battery, via DC/DC converters.

I am happy to learn if have covered the basics. Thanks.

[edit]Just to clarify: I do not have the optional contacts mentioned in the datasheet.
I have another system that drives the same GigaVAC with MOSFETs; hence, we can disregard any internal of the relay, and can focus on the circuit for driving (assumed 150 mH) coils at 24 V.

Relay connected to blue, red, black.
[/edit]

[DrDiettrich]

@MaxG

coils at 24 V.

You'll need logic level MOSFETs or NPN Darlington transistors for 24V and 2A (1.7+).

[TomGeorge]

Hi,
So everybody knows what we are looking at;

Tom....

[DrDiettrich]

I wonder which FETs will require 1.7A set/reset current.

[MaxG]

@TomGeorge

So everybody knows what we are looking at;

Nope... I have the GXL14 C1C which does not have the aux (optional) contacts.

If all fails, I can look into the box where I shared the circuit board, and read what the component is they used to drive it.

[TomGeorge]

@MaxG

Nope... I have the GXL14 C1C which does not have the aux (optional) contacts.

Thanks.

Tom....

[MaxG]

I updated the O.P. with the missing schematic. Thanks Paul.
Apologies to all for buggering this one up.

[jim-p]

@MaxG

and can focus on the circuit for driving (assumed 150 mH) coils at 24 V.

How did you come up with 150mH?

The Vgs of the IRF9540N is only 20V. So your circuit need some changes.

[MaxG]

@jim-p

How did you come up with 150mH?

Guesswork.

[PaulRB]

@MaxG

is there a need for extra caps or other components?

What is the purpose of R2 and R6. I'm not sure they are needed.

@DrDiettrich

You'll need logic level MOSFETs

Now that @MaxG has updated post #1 with a schematic, we can see that logic-level MOSFETs won't be needed. But you will need P-channel MOSFETs rated for more than 24V, as @jim-p said.

[jim-p]

I'm confused about the set/reset voltage specification.
If the coil voltage is 24V, why is the max set/reset voltage only 15V.

Don't forget about the MOSFET Vgs!

[PaulRB]

@jim-p

why is the max set/reset voltage only 15V.

Maybe it's an error and was supposed to read min, not max ...

[MaxG]

@jim-p

If the coil voltage is 24V, why is the max set/reset voltage only 15V.

It had me puzzled too...

@PaulRB

What is the purpose of R2 and R6. I'm not sure they are needed.

R3 (220 Ω): Gate resistor between NPN collector and MOSFET gate; Limits transient current between NPN and MOSFET gate during switching.

[PaulRB]

@MaxG

is there a need for extra caps or other components?

I guess my other comment would be about safety, given the amount of power that battery could put out if things went wrong. Does your circuit fail in a safe way? If the signals from the Arduino are not behaving as wanted because of some fault in your code, or the Arduino gets disconnected, is it ok to leave the GigaVAC in the set position?

[PaulRB]

@MaxG

Limits transient current between NPN and MOSFET gate during switching.

Ah, because of the capacitance of the MOSFET gate, got it. (But it's not R3!)

[MaxG]

@PaulRB

Does your circuit fail in a safe way? If the signals from the Arduino are not behaving as wanted because of some fault in your code, or the Arduino gets disconnected, is it ok to leave the GigaVAC in the set position?

Hmm, valid point... safety is paramount.
I wonder what is safe in this case? I would leave the GigaVAC in the position it is in, in case the UNO dies. The battery is connected to an inverter/charger with safety functions (over/under voltage, or current draw), so I am not too worried. The main function for me is to switch this battery on and off, without having to pull the DC fuse, or disconnecting a cable.

@PaulRB

(But it's not R3!)

Correct, and apologies... I think I should go to bed, it has been a long day.
To be clear: it is R2 and R6 (220Ω) we are referring to.

[MaxG]

@PaulRB

Maybe it's an error and was supposed to read min, not max ...

This data sheet has a lot to be desired!
I am happy to run it on 24V.

@jim-p

The Vgs of the IRF9540N is only 20V. So your circuit need some changes.

Agree; this V divider leaves the us with a 23.8 Vgs.
Well, let's add a 15V Zener diode... which seems to be the case in the photo too.

[PaulRB]

@MaxG

let's add a 15V Zener diode

Would that work? Don't Zeners work by conducting some current? Where is that current gonna go?

Wouldn't it be better to choose a MOSFET with a higher Vgs?

[jim-p]

I don't think that circuit will work at all and may actually damage the relay.
You need to provide a pulse to the relay, something that goes LOW and HIGH. LOW being 0V and high being 24V.
Your circuit goes High Impedance and HIGH.