you are currently using
Turn on relay to open contacts:
normally open contacts using active on with passive off.
You could change your logic and use
Turn off relay to open contacts.
Normally Closed contacts using passive off with active on.
Not saying this is a option for you, just to get you thinking.
The passive above is the reverse diode.
As you have stated,
you see a lot of fast on times but slow off, WHY?
Relays are not really voltage based devices. Think more of a relay as a current based device.
It is an inductor and resists current change. It takes time for the current to increase or decrease.
One common thing to do if current increase is to slow is to use more voltage to make it increase faster.
An example may help
The holding Voltage/current to keep a relay on is normally lower then the voltage needed to turn it on. Keeping the higher voltage/current across the relay just heats the relay.
I think your using
Voltage -> Switch -> Relay -> Voltage
an example of above for DC would be
(More?)Voltage -> Resistor -> Cap -> Switch -> Relay -> Voltage)
Note: in steady on state the relay voltage would be between the dropout voltage and the turn on voltage, the remaining voltage is across the resistor.
The cap must not be so large that the active voltage across the relay goes above it's max voltage rating when changing.
two more options.
passive on, passive off
it's a switch not a relay
and
Active On, Active Off
you reverse the power to the relay for a bit of time to turn off.
Be sure to think of other things that happens. Normal turn on for a relay may be like closing a door gently. When you make it faster you start slamming the door closed. To much, you break the door or door frame and it will not last as long.
To much active open and you have broke the door or broke the door stop.
I actually saw a design once where they had no other options. They used over voltage to start relay turning on. A set of on contacts to sense when the contacts closed and when reversed the voltage on the coil for a time to prevent slamming in to the relays stops. Still would not last long, contacts were hammered and the faster close made the contacts bounce longer.
Guess I am missing something here,
a very quick look a SFA says very low capacitance on the Output so that the output can respond fast. Why idle at high power level, why not switch from a low power, low current state to a high power, high current state when needed?
C