# Time Delay Relays

Discussion in 'General Electronics Chat' started by Jsw123, Jan 24, 2010.

1. ### Jsw123 Thread Starter Active Member

Jun 20, 2009
43
0
What is a Delay-On-Dropout-Timer relay. Is this what can be used for a glow plug timer?

2. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
DOD timers close their contacts when power is applied to the terminals, and then start their timer for disconnect once the power to the terminals is discontinued.

You can buy DOD's with many different delay-until-off times.

3. ### rjenkins AAC Fanatic!

Nov 6, 2005
1,015
69
For a glow plug timer, you probably want an 'on-delay' type then feed power through a normally closed contact on the timer (from the same controlled power as the coil).

Power turns ON, the timer starts timing and also gets fed through the NC contact to the load.

When the timer expires, the contact opens, shutting off the load after the defined time.

4. ### VoodooMojo Active Member

Nov 28, 2009
495
48
the timer relay will work for the timer part but be aware that glow plugs require
gobs of current. Most circuits used for this will include a suitable relay to handle the load of the glow plugs.
A typical glow plug will have a high initial current draw that will gradually drop, stabilizing at a constant amperage. The current draw will be dependent on the wattage rating of the glow plug. This data is available in the appropriate diesel data books.
Once the wattage has been ascertained, multiply it by the number of cylinders and then divide by the voltage to calculate the expected stabilized current. Example: -
Each glow plug = 150 watts so 4 glow plugs = 600 watts
current = watts divided by volts: 600 watts divided by 12 volts = 50 amps

Let us know how many glow plugs, their wattage, and how many seconds do you want them to be turned on.

attached here is a 0 to 10 second delay on relay. It adds a ground after the delay.
They are available in adjustable delay off also.
relatively inexpensive.

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5. ### Jsw123 Thread Starter Active Member

Jun 20, 2009
43
0

Good idea, however it would be better if the relay did not have a coil that would be constantly engaged. Is there a terminology for a relay that will be on for a set period of time when the power turns on and then shuts off until the power is turned off and back on?

My application uses a relay as was mentioned earlier. The coil amperage is .75 amps. I do not know what the inrush is though and I am not sure if itwill be necessary to consider if solid state time delay is used. The timing cycle I need is 15 seconds

6. ### retched AAC Fanatic!

Dec 5, 2009
5,197
315
A latch relay may be what you are thinking of. They change with a 20ns pulse. Like a ballpoint pen. The coil "clicks" on and off with a pulse.

The relay could latch on power on, starting a 555 for 15sec that would pulse the "un-latch" to open the glow plug circuit

7. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,765
293
20 "nanosecond" pulse!...for an electro-mechanical relay. You got a link to the spec's?

Ken

8. ### retched AAC Fanatic!

Dec 5, 2009
5,197
315
I always wondered why my latching relays didn't work!

or Why the 'm' and 'n' are so close together on the keyboard.

and whats the use of proofreading.

ok.. A 20ms pulse.