I need to fabricate a Time Delay Relay Circuit and need some help doing it.

Thread Starter

Howard Walker

Joined Jul 26, 2022
8
I need a Time Delay Relay circuit, which will keep a 120VAC fan, working for approximately 3 minutes, after the 230VAC is turned off. The 230 VAC input is controlled by a front panel DPST rocker switch, which has two unused input solder terminals, which will still have 230 VAC present, when the DPST rocker switch is turned OFF.

1. I don't want to change the fan, which is 120 VAC, that is powered by a 120VAC tap on the High Voltage Transformer. However the fan could be wired to be permanently connected to the output of the Time Delay Relay. Some one once suggested that.
2. I don't want to use a momentary switch to trigger the Time Delay Relay.

So what I need is a schematic, and a parts list, so I can breadboard the circuit, and connect it to the 120 VAC fan.

Howard Walker
[Email was deleted, please don't post Email address on forum, it may bring Spambot to forum and your Email address.]
 

Ya’akov

Joined Jan 27, 2019
6,265
Welcome to AAC.

Your description is a bit fuzzy, as @crutschow ’s question points out. But I think you would be much better off with something like this commercial DIN-mount time delay relay than trying to cobble together your own.

Working with 230V is not a trivial matter and being a neophyte it is particularly not a safe activity. I think the linked relay will do the job for you but it is hard to tell from your description.

Does the 230V on the unused switch terminals appear only when the switch is turned “off”? If so, this relay is a solution. If not, it would need something more, or something different.
 

MisterBill2

Joined Jan 23, 2018
12,697
Big questions that need answers before any really good solutions are given. Next question: does that DPST switch cut off the line power before it gets to anything else, including the transformer? If so, powering the fan will not be a small challenge. You will need either another transformer or some sort of voltage control device, possibly a resistor or a capacitor. I have seen both used for fans.
OR, and here is another question: Does the (whatever it is) also have a neutral connection? That would allow the fan and timer to have a 120 volt supply with as much capacity as you could need. And not require a transformer.Then a simple 120 volt delayed off timer would be easy. So let us know if a neutral connection is available. You might be able to get away with using the green wire safety connection, if one is present. Some folks will freak out at that suggestion, I am quite aware.
 

crutschow

Joined Mar 14, 2008
30,438
As MB2 noted, a series film capacitor is one way to reduce the 230Vac to 120Vac with high efficiency for the fan.
The problem to watch for is that the capacitor could develop a resonance with the motor inductance, which would lead to high operating currents.
 

ebeowulf17

Joined Aug 12, 2014
3,306
I need a Time Delay Relay circuit, which will keep a 120VAC fan, working for approximately 3 minutes, after the 230VAC is turned off. The 230 VAC input is controlled by a front panel DPST rocker switch, which has two unused input solder terminals, which will still have 230 VAC present, when the DPST rocker switch is turned OFF.

1. I don't want to change the fan, which is 120 VAC, that is powered by a 120VAC tap on the High Voltage Transformer. However the fan could be wired to be permanently connected to the output of the Time Delay Relay. Some one once suggested that.
2. I don't want to use a momentary switch to trigger the Time Delay Relay.

So what I need is a schematic, and a parts list, so I can breadboard the circuit, and connect it to the 120 VAC fan.

Howard Walker
[Email was deleted, please don't post Email address on forum, it may bring Spambot to forum and your Email address.]
I'm a little confused on what you have available to work with here, and based on responses above, I think others are too.

If I've read your post correctly, you have the following:
  1. 120VAC available at all times (not lost when your main switch is turned off)
  2. 230VAC available at all times.
  3. Switched 230VAC controlled by the switch at the heart of this project (this power will turn off at the beginning of your three minute timing window.)
  4. A 120VAC fan that needs to keep running for three minutes after the 230VAC switch is turned off.
Is that all correct? If not, please clarify with as much detail as possible.

If I've got the idea right, then I think there's a fairly simple solution involving a 230V delayed off timer, which might require a separate relay to switch the 120VAC circuit (if I'm remembering this correctly, which I'll double check once the project specs are confirmed/clarified.)
 

Thread Starter

Howard Walker

Joined Jul 26, 2022
8
Welcome to AAC.

Your description is a bit fuzzy, as @crutschow ’s question points out. But I think you would be much better off with something like this commercial DIN-mount time delay relay than trying to cobble together your own.

Working with 230V is not a trivial matter and being a neophyte it is particularly not a safe activity. I think the linked relay will do the job for you but it is hard to tell from your description.

Does the 230V on the unused switch terminals appear only when the switch is turned “off”? If so, this relay is a solution. If not, it would need something more, or something different.
The 230VAC is on the two unused pins all the time. It is only removed from the input of the HV transformer when the Rocker switch is turned to the OFF postirion. There is a 120VAC tap on the HV transformer to supply the fan. When the 230VAC is off, there is no voltage to the HV transformer, and no 120 VAC to the fan. This is a Heathkit SB-1000 HF Amplifier.
 

Thread Starter

Howard Walker

Joined Jul 26, 2022
8
I'm a little confused on what you have available to work with here, and based on responses above, I think others are too.

If I've read your post correctly, you have the following:
  1. 120VAC available at all times (not lost when your main switch is turned off)
  2. 230VAC available at all times.
  3. Switched 230VAC controlled by the switch at the heart of this project (this power will turn off at the beginning of your three minute timing window.)
  4. A 120VAC fan that needs to keep running for three minutes after the 230VAC switch is turned off.
Is that all correct? If not, please clarify with as much detail as possible.

If I've got the idea right, then I think there's a fairly simple solution involving a 230V delayed off timer, which might require a separate relay to switch the 120VAC circuit (if I'm remembering this correctly, which I'll double check once the project specs are confirmed/clarified.)
The 120 VAC is only available when the HV transformer has 230 VAC being supplied to its input.
The 230 VAC is available at all times on the two unused pins on the rocker switch.
The 120VAC fan needs to keep running for three minutes after the 230VAC switch is turned off. YES
 

Thread Starter

Howard Walker

Joined Jul 26, 2022
8
Big questions that need answers before any really good solutions are given. Next question: does that DPST switch cut off the line power before it gets to anything else, including the transformer? If so, powering the fan will not be a small challenge. You will need either another transformer or some sort of voltage control device, possibly a resistor or a capacitor. I have seen both used for fans.
OR, and here is another question: Does the (whatever it is) also have a neutral connection? That would allow the fan and timer to have a 120 volt supply with as much capacity as you could need. And not require a transformer.Then a simple 120 volt delayed off timer would be easy. So let us know if a neutral connection is available. You might be able to get away with using the green wire safety connection, if one is present. Some folks will freak out at that suggestion, I am quite aware.
Their is a Neutral connection to the chassis.
 

ebeowulf17

Joined Aug 12, 2014
3,306
Can we move the 230V to 120V transformer from the switched 230V to the un-switched 230V so that we have 120V still available even when the switch is off? If so, I think this is pretty manageable. If not, things get more complicated.
 

MisterBill2

Joined Jan 23, 2018
12,697
In post #19 the TS states that there is a neutral connection. And given that the Heathkit amplifier only has one transformer there is no way to leave it powered.
But now, knowing that it is for cooling down purposes, an alternative scheme appears.
Power the cooling fan between one unswitched line side and the neutral connection. Use a snap action thermostat to control fan power, the thermostat sensing the discharge air temperature. Add a small relay in parallel with the thermostat to run the fan whenever the amplifier is on. OR use a second pole on the standby/operate switch, instead of the relay, to also run the fan,
 

ebeowulf17

Joined Aug 12, 2014
3,306
How could that be done?
I apologize, I missed the comment about this being within a Heathkit SB-1000 HF Amplifier. Now that I've seen the schematic (thanks to @MrSalts for posting that - having a schematic is a huge help!) I realize that I was misunderstanding how the available 120V related to the rest of the circuit. What I was thinking before is no help. I'll give it some more thought and see if I come up with anything useful to add, but for now, you can safely ignore my previous comments.
 

vu2nan

Joined Sep 11, 2014
262
Hi Howard,

Here's the modified schematic of the Heathkit SB-1000 HF Amplifier, to keep the fan running for three more minutes after the 'mains on' rocker switch is turned off.

1.png

In the absence of the neutral, the addition of a small 240V / 120V transformer is a must.

Also required is a 240 V ~ operated, 'true off-delay' timer that is to be set for a 3' delay.

With the rocker switch turned on and the timer energised, its contact closure is immediate and the fan motor starts.

With the rocker switch turned off and the timer de-energised, the delay in its contact opening keeps the fan running for 3 more minutes.

Nandu.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
12,697
I asked about a NEUTRAL connection without having a schematic to look at. And still, my comment applies to a NEUTRAL wire.
It may be simple for the TS to add a neutral wire to the power connections. Certainly for the other equipment in the station there must be 120 volt circuits where a neutral can be tied into.
My suggestion to use the NEUTRAL is totally safe, it is others who jumped on concluding that I meant the ground wire, WHICH I DID NOT MEAN THE GROUND WIRE.
In some localities the code requires that if the 220 (or 240) volt pair is used, that a neutral be included, in addition to the green wire frame ground.

for that matter, if the safety ground is actually connected correctly, that would work as well and be quite as safe. Not to the code, but safe.
 

crutschow

Joined Mar 14, 2008
30,438
A question not asked:
Why do you need the fan to run after the power is turned off?
Normally the hot elements will just cool off to the ambient air since there is no power to keep them hot, and there is no need to rapidly cool them.
 

MisterBill2

Joined Jan 23, 2018
12,697
A question not asked:
Why do you need the fan to run after the power is turned off?
Normally the hot elements will just cool off to the ambient air since there is no power to keep them hot, and there is no need to rapidly cool them.
OK, understand that this device is a tube-type high power RF amplifier. The power tubes are forced air cooled, but the internal temperature is much hotter than the exterior where the cooling air flows by. So just like the engine compartment of a car, the temperature will rise quite a bit as heat flows out from where it s generated, after the flow of cooling air stops. Thus it is a benefit to keep the cooling air flowing for a while. That is why I suggested a thermostat, besides that it needs no external power. The extreme heat is not beneficial to the rest of the components, especially the power supply filter capacitors.
 
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