Alarm reset timer

[KrisBlueNZ]

Not really. Just double-check and triple-check the connections up to and including the bridge rectifier. Any fault after the bridge won't cause any sparks to fly.

R1 must be connected to the Phase wire from the mains plug, and the other side of the bridge goes to Neutral. I should have made that clear on the diagram.

You could upload a photo of both sides of your circuit board for us to check.

 

[caferacer]

Assembly starts tomorrow, will post some pics prior to power up

 

[caferacer]

Hi Kris,

Okay here is my attempt at the circuit board. The relay isn't on there as yet. I need to shuffle the RHS devices over a little more to create some room.

Not powered up as yet.

A few comments/questions.

I had a slight change in my originally intended layout due to space constraints! I was intending the HV to be on the top of the board and the LV at the bottom; I didn’t realise C1 was so big!!! Therefore in my hastily revised layout, I made a bit of a boo boo, therefore had to add the small jumper next to D3 (cut C2 legs too short).

I have connected both wiper and pin 1 of the trim pot together, assume this is okay?

I have broken the copper track between the terminals of C1 and between D1/D2 and D3/D4.

I have tested all tracks for continuity/non continuity where necessary. All seem okay as far as I can tell; however, testing for continuity on the track which is across the middle of the diode bridge (either side of the break), the DVM does show a reading, which I was initially surprised at but after thinking about it, it was rising/falling, therefore I assume it’s the capacitor causing this??

On a separate issue, If there was a fault in the board operation, then there would nothing to indicate this. I have some LED’s (spec below), which I think may be worth adding one to show the circuit is okay. Would it be possible to connect at the relay to show when the circuit is operational? I know this would not show the status of the relay, only the rest of the circuit up to this point?

My intention is to mount the board in an enclosure (with mains voltage warning labels), so the LED would be connected by flying leads from the board. I'll drill a small hole to fix the LED into the enclosure lid.

Power Dissipation: 84mW
Forward Current: 25mA
Reverse Voltage: 6V
Forward Voltage: Typ, 2.4V, Max,3V

Thanks as ever.

 

[KrisBlueNZ]

Yes, connecting the wiper to one of the end pins on the trimpot is fine.

Yes, if you measure between the middle connections of the bridge rectifier, you are measuring across C2 and your multimeter will show a resistance that increases over a short time period then shows open circuit.

You can connect an LED (with a series resistor) across the relay coil to indicate when the relay has activated, or across C2 to show that the circuit has power, but you cannot run it at 25 mA; that much current is not available with this design. You can run it at 1 mA (using a 22k series resistor) and use a high-efficiency LED such as:
HLMP-K150 3 mm http://www.digikey.com/product-detail/en/HLMP-K150/516-1311-ND/637575
HLMP-D150 5 mm http://www.digikey.com/product-detail/en/HLMP-D150/516-1323-ND/637587

Yes you can mount the LED in a hole in the case. Use a plastic case.

 

[caferacer]

Hi Kris,

After a bit of fault finding, I have success!

The only issue I have is using the earth from the mains into the earthing point on the board as shown, knocks the consumer unit RCD out, which I thought may happen. So the circuit is working but only without an earth connection? is this a problem?

Thanks
Mark.

 

[KrisBlueNZ]

Great!

The circuit shouldn't have any connection to mains earth. Were you connecting mains earth through to the negative rail of the circuitry, with the downward-pointing triangle symbol? No! That's not supposed to be connected to mains earth. It's just a "0V" reference symbol for use by LTSpice, the simulation software.

 

[caferacer]

Hi Kris,

Re this circuit I built with your help. Still working great, but would like to increase the delay time.

The delay currently at the extreme of the trimpot R4 creates approx 55 sec delay. I would like to be able to push this out to over two or three minutes if possible. However, I am not sure what the limitations are on the design. I don't really want to go changing lots of components. Could a simple change of the R4 trimpot be sufficient?

Thanks

Mark.

 

[KrisBlueNZ]

Hi again Mark.

That circuit uses a simple resistor-capacitor delay. These can have problems with longer time periods because of leakage current in the capacitor. You can try increasing C3 from 22 µF to 47 µF or more but this may not be reliable. You can maximise your chances by using a good quality Japanese brand such as Nichicon, Rubycon, UCC or Panasonic. Nichicon makes a series called KL that is designed for low leakage:
http://www.digikey.com/product-sear...c01eb,fc01ee&stock=1&quantity=1&ColumnSort=13

The guaranteed worst case leakage current for the KL series is "0.002CV or 0.2 µA, whichever is greater". For the 68 µF 35V part this works out to about 5 µA. This is about five times too much, and will cause the relay to stay OFF.

That calculation is for the worst case leakage current; it's very likely the part you buy will perform a lot better than that, but since this is an alarm application, you may not want to take the risk.

Other options for longer delays are available but they are more complicated. Have a look at https://www.electronicspoint.com/resources/long-duration-timers-notes-for-beginners.4/

 

[caferacer]

Hi Kris,

Would this be okay to try?

http://www.ebay.co.uk/itm/140953388...X:IT&_trksid=p3984.m1423.l2649#ht_3936wt_1275

Thanks

Mark

 

[KrisBlueNZ]

The specifications (further down the auction page) say that the leakage current is 16.45 µA, which is three times higher than the Nichicon one that I recommended. In other words, no.

 

[caferacer]

Ah sorry I was looking further down at the DC leakage current which states 'none', but on re-reading that was for the range.

 

[caferacer]

Have looked everywhere, but can't find anything comparable to the leakage current of the Nichicon.

Because of MOQ's that narrows it to a choice of 1 for the 47µF. Assume this one is okay?

http://www.digikey.com/product-detail/en/UKL1V470MPD1TD/493-10519-1-ND/4318133

As the shipping cost is about a x1000 the cost of the caps is it worth in you opinion getting some with higher values just in case they may work?

Regards
Mark

 

[CDRIVE]

Kris, it's been a while since I revisited this thread, so I may be totally all wet here. As I understand it Q1 turns on immediately when power is applied. This in turn keeps Q2's Gate low and K1 off while C3 is charging. How about adding a second time delay cap and bleeder R between the Gate of Q2 and GND? Do you think that the lack of a fast rise time on the gate of Q2 would damage it at such a low drain current that the relay coil demands?

Chris