Hi all,
I'm new to this board and I'm a novice when it comes to electronics. I know enough to know when I'm in over my head and it's time to ask. I've been working on this project for a few months on and off and I'm interested in finally getting it finished. Hopefully someone here can help me out and i'll be able to complete this. What i'm trying to build is a controller for a set of lights that I use in my Saltwater tank. I've used the basic controller shown at http://chaokhun.kmitl.ac.th/~kswichit/f84rtc/f84rtc.htm to get me started. I've then added to it OZ-SH-105LM1 relays (as shown in my photo below). The lights i'm trying to control are shown at http://www.catalinaaquarium.com/prod...eb70426df6f0f8 The problem that i'm running into is that when I try to turn off a relay that has a light on it, it somehow resets my controller chip. I.e. the chip no longer knows what time it is and I have to press the momentary switch again to get it to start working. I was pretty sure the problem was just the inductive load and it feeding back when the relay opened up, so i tried an MOC3041 optical relay inbetween the L74S07 and the relay that controlled the lights and found that the optical relay got very hot and stopped working. So I'm sort of at a loss now as to what to do. I'm looking for an easy way to control 4 of these lights without having 4 large mechanical timers that do not stay in sync with each other, and without spending $150+ on parts. Any help/suggestions would be welcomed.

 

No wonder because you have not followed the general rule of supressing the inductive kick when the relay turns OFF.

You can do that simply by placing a diode across the coil of the relay. Two of the diodes is shown but you'll need a total of six if you have six relays. The direction(polarity) of the diodes must be pointing towards the +V side. The common diode 1N4001 or even the 1N4148 willl work.

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__________________
L.Chung

 

I think that i've tried that already but I'll take out the failed optical triac and rewire this time including the diode as you've shown. I'll post my results shortly. Thanks for the quick response..

 

In that case then also use a bigger capacitor like 100uF instead of 10uF across PIC pin 14 and 5 and also a 0.1uF ceramic capacitor as close as possible to the PIC pin 14 & 5.

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L.Chung

 

OK I've got it set up as specified above and with one relay controlling one light it seems to work great. This unit is going to be controlling 6 lights total. I guess my question at this point is can an 74LS07 handle 638.4mA? Each of the relays has a nominal coil current of 106.4mA I've read the data sheet on this component and I see that it says "the maximum sink current is 30mA for the SN74S07" which is what i'm using. I'm not sure if i'm just reading things wrong or what. Later in the data sheet it says that max limits are 40mA for the SN74S07 which would mean that the relay that I'm currently useing by it'self should not be working since it's a 106.4mA coil. Or am i just totally lost? FYI i'm using a relay made by OEG it's OZ-SH0105LM1

 

That's correct. TI recommends a max output current of 40mA for their 74LS07.
Didn't your 106mA relays cause it to smoke?
Didn't the supply pin burn off?
I am surprised that it worked.
I don't think it would be reliable.

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Uncle $crooge

 

1. Use additional voltage regulator for high-current relays (7805) the L05 output current max. only 100mA.
2. Use transistors for relay driving, the common emitters must be wired directly to PWR input GND.
3. Use snubber RC component in AC side, this protect the relay contacts and reduce the spark when the contact opened (the capacitor value depend from load and must be X2 type, this designed for continous AC use).
3. Never don't leave the 100nF ceramic capacitor from regulator output and nearby the PIC (and any other IC) supply pin.
4. I think, the PIC cannot work perfectly with 2,3V. Use schottky diode in D2 position and/or apply 3*1,5V battery.

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The original circuit designer has already stated clearly that each 74LS07 output can only handle 30mA maximum. You should use a NPN transistor if you want to use relay with higher coil current.

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L.Chung