# time delay relay

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#### manz

##### New Member
hi again...

Ive built a "power-on time delay relay" from a circuit that I got somewhere on the net (cant remember where).It is to switch on something (could be anything,depends on the connection of the relay) after certain amount of time.

The problem :

1. At first the timer seems to work perfectly but after a few time using it, the timer just failed to work (but on,just not delayed)

The situation:

1. I know it could be easier if I paste the circuit here but I just dont have the schematic in the computer.It is very simple and i just draw it and didnt save the schematic.

2. I tested it by using the ac to dc adaptor (input: 240v/50Hz)rated output :12v dc /500mA/9W and it works perfectly ok even after many times using it.

3.Then I transfered the circuit to be used in the car powered by the car battery rated 12v dc / 65AH and after several time using it, the timer just fail to works.I knew the power supply is so much more different and the circuit failed due to this.(should be).

***For the info, the circuit uses 2 of 2N3904 and 1 of 2N3053, a capacitor and a resistor and a relay.( :idea: hope you can imagine hows the circuit connection :idea: )

The question:

1. Is it because of the transistor (either 3904 or 3053) input voltage I used to supply it too high?

2. Or is it because of the current supply to high for the circuit?

3. can i use a voltage regulator something like 78L05 or 78L06 or anything (i didnt know which is on the market other than 78L05,please suggest me) to reduce the feeding voltage to the circuit.because im using 6v/9v/12v relay with the circuit..

4.If there is any other way to make the circuit works with the car batt,please let me know.

Since I didnt put the shematic I know maybe it is hard to help me out but maybe some of you just can do the magic :wink:

if it is realy hard without the shematic, ill try work it out to paste it here.

#### JimB

##### Super Moderator
What load were you switching in the car?
Is it just that the relay contacts are welded together from switching to high a load current?

JimB

#### instruite

##### New Member
manz wrote:
1. Is it because of the transistor (either 3904 or 3053) input voltage I used to supply it too high?
It can not only be the transitor but other components
There are many kind of surges and spikes over the power line of the car
(normal range of battery voltage is from 9V to 16V for normal operation and it goes upto 24V for around one minute during start and then there are other spikes and surges due to operation of various solenoids and motor loads in car) and which may have damaged any component because of exceeding the specifications of particular component

2. Or is it because of the current supply to high for the circuit?
The current rating of battery specifies how much it can supply, it will supply only as required by circuit, so this rating is no reason for your circuit not working

3. can i use a voltage regulator something like 78L05 or 78L06 or anything (i didnt know which is on the market other than 78L05,please suggest me) to reduce the feeding voltage to the circuit.because im using 6v/9v/12v relay with the circuit..
Yes it is always recommended to use voltage regulators when using supply form car battery
and 7806, 7809 and 7812 are available in market

#### manz

##### New Member
hi JimB...

JimB said:
What load were you switching in the car?
Is it just that the relay contacts are welded together from switching to high a load current?

JimB
1. Ok, I use the circuit to switch the head lamp of the car. The relay is just as a switch (bypass the normally operated that is by hand).

2. I combained 2 circuits for this purpose. Firstly is the "dark activated circuit" that is to measure the light intensity and this will switch on the timer circuit so that it will only switch on the head lamp after several second of continuous darkness as i pre-set it.

3.so i think where the relay is connected doesnt matter (should be :wink: ) as it never will affect the timer circuit.The timer circuit just will selenoid the relay.

thanks..

#### manz

##### New Member
Hi instruite..

It can not only be the transitor but other components
There are many kind of surges and spikes over the power line of the car
(normal range of battery voltage is from 9V to 16V for normal operation and it goes upto 24V for around one minute during start and then there are other spikes and surges due to operation of various solenoids and motor loads in car) and which may have damaged any component because of exceeding the specifications of particular component
1. Yes im aware about that. ive measure the voltage (engine on and off) the battery voltage varries just from 9V to 14V (for my car though)

2. I dont think that any other device that is faulty because as I posted earlier the circuit just using those transistors, capacitor, resistor and lastly a relay and diode that is in parallel with it.(it should be the transistor,I think :wink: )

3. I need to know the maximum voltage that can be supply to the transistor (2N3904 and 2N 3053) so that Ill know which voltage regulator can be added to the circuit (if it is the voltage is the matter that cauused the faulty in the first place)

thanks guys...

#### instruite

##### New Member
HI manz:
1. Yes im aware about that. ive measure the voltage (engine on and off) the battery voltage varries just from 9V to 14V (for my car though)
If you measure it with multimeter you never will be able to measure spike voltage which is of 100Vs but of very short duration of nanoseconds and microseconds
Normally components can handle such voltages for such short durations (but it might not be true for all components)

2. I dont think that any other device that is faulty because as I posted earlier the circuit just using those transistors, capacitor, resistor and lastly a relay and diode that is in parallel with it.(it should be the transistor,I think )
In our designs we take care special care in resistor wattage selection because those are the components which can blow up easier during surge due to high power dissipation through them during surges

3. I need to know the maximum voltage that can be supply to the transistor (2N3904 and 2N3053) so that Ill know which voltage regulator can be added to the circuit (if it is the voltage is the matter that cauused the faulty in the first place)
2N3904 - http://www.datasheetarchive.com/search.php?search=2N3904+&sType=part
2N3053 - http://www.datasheetarchive.com/search.php?search=2N3053&sType=part

#### Sebi

##### Active Member
Possible cause: overdissipation during timing period. Without sematic i only think the circuit not a schmitt-trigger, so the transistor work in linear mode, not in switch-mode.

#### electronic spark

##### New Member
Depending on your circuit connection, the capacitor that you have is driving the base of transitor, you have to be sure that you will not oversaturate emitter-base junction, make sure you have a current limiting resistor. It would help if you show your circuit. The schmitt-trigger is not required, since the relay only pulls in at a specific treshold and then stays on.

#### ericgibbs

##### Well-Known Member
electronic spark said:
Depending on your circuit connection, the capacitor that you have is driving the base of transitor, you have to be sure that you will not oversaturate emitter-base junction, make sure you have a current limiting resistor. It would help if you show your circuit. The schmitt-trigger is not required, since the relay only pulls in at a specific treshold and then stays on.
hi ES,
Seen the date of the last thread, 2005....

#### electronic spark

##### New Member
I was looking for a circuit myself for a 5 min on delay timer for the car to use with relay that turns on O2 signal conditioning circuit for fuel economy. Since I didn't find one I designed my own, using 2 transistors 2n222, few resistors, 100u electrolytic cap and relay. I'll post the circuit later.
(I noticed the post date after I replied

#### electronic spark

##### New Member
Here is the circuit.

hmmm can't seem to insert or attach a picture of diagram? maybe..

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