> Just for grins, why are you turning it off so slowly?
>
> So not intentionally turning it off slowing, it is just a side effect of
the requirement to use absolute minimal parts and space and  wanting a
delay of approx 1.5min after the existing coil power feed drops off.

The space is limited by the area between the spade terminals on a standard
12v relay.  I would most likely use a 555 if more space was available.

This is a retrofit, so limited to designing something that goes between the
relay and the existing female spade terminals it plugs into.

End user removes relay, inserts this device in its place then inserts relay
into this device.

As mentioned previously, it is very unlikely that the contacts will
actually interrupt current flow.  But may happen from time to time.

So ...

Advantages:

1. Only 4 parts.
2. Small foot print
3. Soft off ... testing indicates no snubber required
4. Simple
5. Cheap

Disadvantages

1. During turn off while not turned hard on, FET dissipates power which may
cause FET damage.  But this is brief and unable to detect temperature rise.

2. As suggested, contacts more vulnerable during brief end period as FET is
turning off.  But highly unlikely current is flowing at this time..

At this stage I am happy to lock in the design that does not include the
snubber diode.  Additional  automated bench test have continuously cycled
the device off and on giving a rough indication that the device should be
able to handle at least 2 years of service.  Testing continues.
--=20
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