Compact time delay on open relay needed 1

[emcto2]

I am looking for a small (~1"^3) solid state relay that will start a 120V 1/4hp AC blower when the power comes on. After 10 or 15 minutes it will open the circuit.

The application is a confined space with a blower. The blower is currently equipped with a timer set to run the blower twice a day for 15 minutes (every 12 hours).

However, if the power is interrupted to the vault, it could be more than twelve hours between blower cycles. I would like the blower to run immediately after the power comes on after an interruption (without regard as to how long the power is off).

 

[DanDel]

Just use a simple time delay-off plug-in style relay set for 10 or 15 minutes in parallel with the normal start circuit. The contact would be closed at energization and would switch off after the time delay. As long as the power stayed on, the contact would stay open, but when the power was lost, the contacts would reset to the closed position. When power returns, the motor would start.
Just make sure the proper safety requirements are satisfied.

 

[jraef]

Here is a relay that will do exactly as DanDel said.

http://www.natcon.com/timer1-8.htm

8A relay contact should handle 1/4HP 120V motor (5.8A) but check with them first. Quando Omni Flunkus Moritati

 

[jbartos]

Suggestion: Dimensions of that relay and timer will most likely be larger than specified. This is somewhat related to the cooling of switching devices.

 

[emcto2]

Thanks for the responses.

DanDel
Due to the high humidity environment, I am looking for a solid state relay.

Most plug-in relays are larger than the 1-cubic inch space requirement.

jbartos
The relay that is inked in your message will turn on after the delay. Thus, it will require a second relay to control the fan. It too is larger than 1"^3.

Any other recommendations?

 

[DanDel]

If the size must be limited to 1" square, then you may have some trouble. There is a minimum size for even 120V, 3A applications, not to mention mounting, wiring, and cooling.

 

[Shortstub]

It is do-able, but not with off-the-shelf technology.

The only suggestion I can make is to contact a firm specializing in custon-design microminiature solid-state circuits. There are others that use open, but potted circuitry.

However, unless you are talking about large quantities it will be extrordinarily expensive. If you need an example of development costs, let me know!

 

[emcto2]

Shortstub,
Who makes the potted relays? I would like to know more ablut them.

 

[Shortstub]

emcto2,

The potted "circuit", not relay, company is "Artisan Electronics" in Parsippany, NJ. This is a time-delay relay company, so you probably won't need a schematic.

The custom design house is "Aptek" in Deerfield Beach, FL. This company, at least in the past, required a schematic.

 

[emcto2]

Will the relay at:

http://www.amperite.com/st2.htm

Do what I want? I might be able to make it fit.

 

[Shortstub]

There are two problems. The first depends on what logic is to be applied. For example, how will you differentiate between a supply dip, a supply interruption, or a manual "off" command! To do that you need additional circuitry!

The second problem is interfacing the "solid-state" module with existing circuitry. I say that because Amperite uses a triac to drive the load. Thus, to interface the two, then the Amperite unit will have to drive a relay, that in turn, is used to control the motor. Ergo, more hardware.

 

[emcto2]

There are two problems. The first depends on what logic is to be applied. For example, how will you differentiate between a supply dip, a supply interruption, or a manual "off" command! To do that you need additional circuitry! Since we are venting a vault, none of the above would be a serious problem. Unless (of course) we care that the fan was running constantly or just too often due to poor quality power. One concern (thanks for bring it up) is "Manual Off". In this case the door switch should be in parallel with the relay and clock contacts. Therefore, the relay would run the blower for the time period after the door is closed. And after the clock contacts opened as well.

The second problem is interfacing the "solid-state" module with existing circuitry. I say that because Amperite uses a triac to drive the load. Thus, to interface the two, then the Amperite unit will have to drive a relay, that in turn, is used to control the motor. Ergo, more hardware.
Are you saying that the triac will not be able to run the 1/4HP blower or that it will damage the blower? (I have never tried to use a solid state relay.) Will the leakage current cause the blower motor to heat? Why is the relay necessary?

 

[Shortstub]

No, it's not a capability issue. It is how the "virtual contact" shown in the schematic is connected to the motor supply circuit. Because it is actually a "solid-state device, it can't be paralleled with the "hard wired' components associated with whatever control functions you are using. Contact Amperite again, and see if they have a unit having a dry "contact" output, instead of the triac!

Coincidently, at one time my company supplied a device such as the one you are seeking. It was called a "Motor Reacceleration Module!" It was used to reaccelerate large numbers of motors, particularly for the HPI industry, following a momentary loss of power! Unfortunately, it is no longer available. And, if it were it would have been much too large for your intent, even allowing for your concession on size.

If you are still interested contact me off-line, and I can provide you with some ideas, but, remember, it will never meet your size criterion.

 

[jbartos]

Question to emcto2 (Electrical) Feb 25, 2003 marked ///\\jbartos
The relay that is inked in your message will turn on after the delay. Thus, it will require a second relay to control the fan. It too is larger than 1"^3.
///I do not have any relay linked in my message since there is no link. Essentially, my posting expressed a concern about the physical size of the linked relay in jraef posting.\\\

 

[buzzp]

National Controls Corp makes a 2"x2" epoxy encapsulated timer that has a solid state contact. There are many others that make them in 2x2 box (SSAC is another). What you want is a delay on break timer. You may find even a smaller package from Magnecraft (we use delay on make that is mechanical contacts but is only 0.75" x ~1.25" that has to be mounted in a small socket). Not sure if any of these will handle the load you want to switch so a contactor or another relay will be required but should be in the circuit already. Good luck.

 

[emcto2]

Apologies to jbartos, I should have addressed jaref. To jabartos, thank you for the information about heating.