two 12v relays in parallel need them to engage about 1 to 2 seconds apart

Thread Starter

429eagle

Joined Jul 10, 2021
8
I build radio transmitters and sometimes the input relay is different then the output relay. this is because of the amount of power going out is much larger then the power coming in. Both relays are being triggered by an RF keying circuit which creates the ground for the two relays thru a transistor.
could use some help getting the input relay to key last so that all the power does not jump across the output relay before in makes contact. the two relay coils are in parallel. both are open frame type relays
 

sagor

Joined Mar 10, 2019
512
I would use 2 different driver transistors, one for each relay. That way you can adjust the response time of each on individually.
However, for RF switching (as in amplifiers), relays are usually "sequenced". That is on TX, Rly1 then Rly2. On Rx, it is reverse order, Rly2 is released first, then Rly1. Not trivial. See:
https://www.w8ji.com/ameritron_relay_module.htm
 

Dodgydave

Joined Jun 22, 2012
10,088
The pf capacitor is no good as an input to drive the transistor, you're better using a fet with a 1K gate drive, .

Better using two separate fets and a capacitor to delay the gate voltage.
 

Thread Starter

429eagle

Joined Jul 10, 2021
8
I would use 2 different driver transistors, one for each relay. That way you can adjust the response time of each on individually.
However, for RF switching (as in amplifiers), relays are usually "sequenced". That is on TX, Rly1 then Rly2. On Rx, it is reverse order, Rly2 is released first, then Rly1. Not trivial. See:
https://www.w8ji.com/ameritron_relay_module.htm
says that the coil currents have to be the same.. my two relays are different , one is an ice cube relay for low power input and the other is a large 30 amp open frame type for high output.
 

eetech00

Joined Jun 8, 2013
2,653
yes millisec delay is ok 30mhz 5 watts of RF output
www.eaglemade.net is my site.
You can try an RF peak Detector circuit using an RF schottky diode to rectify the input signal. See the attached PDF.
Then use the rectified output to turn on a transistor relay driver and energize the relay.
If you use a contact of the first relay to energize the second relay, there will be an inherent delay in the second relay.
#1 Contact switching time + #2 pickup time + #2 contact switching time = a few tens of milliseconds delay (depends on relays)
 

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Thread Starter

429eagle

Joined Jul 10, 2021
8
You can try an RF peak Detector circuit using an RF schottky diode to rectify the input signal. See the attached PDF.
Then use the rectified output to turn on a transistor relay driver and energize the relay.
If you use a contact of the first relay to energize the second relay, there will be an inherent delay in the second relay.
#1 Contact switching time + #2 pickup time + #2 contact switching time = a few tens of milliseconds delay (depends on relays)
i am already able to key both relays using RF , just want one to key first. All of the contacts are being used on the relays so i cant use a contact to turn the other relay on. The relay that needs to be on first has only one set of contacts.
someone mentioned using fets to trigger the relay coils. sent me an ameritron schematic. only problem with that schematic is the relay coils have to be exactly the same. Mine are not,.
 

Thread Starter

429eagle

Joined Jul 10, 2021
8
I would use 2 different driver transistors, one for each relay. That way you can adjust the response time of each on individually.
However, for RF switching (as in amplifiers), relays are usually "sequenced". That is on TX, Rly1 then Rly2. On Rx, it is reverse order, Rly2 is released first, then Rly1. Not trivial. See:
https://www.w8ji.com/ameritron_relay_module.htm
you think this circuit would work if i have to completely different relay coils.
 

vanergr

Joined Nov 23, 2020
10
I didn't see anyone mention it so my suggestion is use a 555 timer circuit that charges the appropriate cap when the first trigger occurs and when the 1 or 2 sec past triggers the second relay.
 

eetech00

Joined Jun 8, 2013
2,653
i am already able to key both relays using RF , just want one to key first. All of the contacts are being used on the relays so i cant use a contact to turn the other relay on. The relay that needs to be on first has only one set of contacts
can you connect another relay in parallel to gain more contacts?
 

sagor

Joined Mar 10, 2019
512
you think this circuit would work if i have to completely different relay coils.
The circuit should work with different relays as long as their total coil current is around the design limit of 70mA. As designed, one relay could be 40mA, the other 30mA. The first relay gets a 70mA jolt from the higher voltage for a short time, then both relays share the current limiter 70mA (as drawn in that link).
You could adjust the constant current to a different value, and use different relays, but odds are that the coil voltages should be identical and current ratings of both coils combined match the constant current setting.
 

eetech00

Joined Jun 8, 2013
2,653
i am already able to key both relays using RF , just want one to key first. All of the contacts are being used on the relays so i cant use a contact to turn the other relay on. The relay that needs to be on first has only one set of contacts.
someone mentioned using fets to trigger the relay coils. sent me an ameritron schematic. only problem with that schematic is the relay coils have to be exactly the same. Mine are not,.
You can try something like this (I haven't tested this).
I'm assuming your RF key circuit works and holds Q1 "on" when keyed.
In the simulation below, Q1 is your existing transistor. Since I have no idea what the relay coil voltage/current/resistance spec is for the relays your using, I've used standard 12v, 75mA relays. The delay is set by adjusting R3/C1. (BTW-most(or all) of these BJT's can be replaced with mosfets)

1626200543210.png
 

sagor

Joined Mar 10, 2019
512
What is unknown so far, does this user require the reverse order at end of engagement? Or, is it irrelevant?
Keying on with a delay can work as shown by eetech (I think), but what happens (what is required) when the SIM "key" is released? In almost all transmitter circuits with sequenced relays, the order has to be reversed in the "off" state to prevent RF contact burns (hot switching).
In most RF amplifiers, the output relay is switched first, then the input RF is engaged after a short delay. When TX stops, the RF input must be released first, then the output stage relay. Basically, engage the amplifier before feeding it RF on TX cycle, and disengage RF feed first before turning off the amplifier output.
 

sagor

Joined Mar 10, 2019
512
This relay keying could also be done with a simple 8 pin PIC or ATTiny processor, where one can program in the delays and the sequence in which it happens. Feed the micro output pins to a standard logic level N-MOSFET (5V gate voltage for full on) to drive the relays.
 
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