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I hope you need to on/off 230V AC pump;
Option;
1. Use a motor-contactor to on/off the AC motor;
Use a triac (eg. BT139) to switch contactor;
Use a opto-isolater triac-driver (eg. MOC3022) to switch the triac;
PIC can on/off the triac driver opto-isolarot
2. Use a motor-contactor to on/off the AC motor;
Use a DC relay (5V) that can switch AC (1A load capacity is enough) to on/off the motor contactor;
Use a transistor to on/off the DC relay;
PIC can bias the transistor;
yes there are many electromagnetic relays having the coil built for 5 Vdc and contacts suporting higher voltages and a few amps .
Not all relays are used for the same task and different relays can have different clamp voltages .
Usually they are built with coils for 5 , 12, 24 V in dc and 220, 380 V in ac . Rallays have several normally closed and/or normally open contacts
You can use electromagnetic relays to command power circuits, to multiply contacts or to detect treshold voltages.
Advantages : the command circuit (as your PIC mcu) is electrically separated from the power circuit (as your pump).
Disadvantages : they take a little power from the command circuit (you feel that when you are runing from baterys), contacts get used after a time
About using them as contact multiplyers: Suppose you have a number of consumers powered from diferent electrical circuits (ac power line, battery's, ....) , and want to start and stop them with a single button, you can use an electromagnetic relay that has sufficient contacts for each of your consumer.
Using electromagnetic rellay's for detecting treshold voltages: for exemple if you put a 12 V rellay in a circuit, when the voltage in the circuit is below ~7V the rellay will not clamp. Abowe ~7v the rellay will clamp and it's normally closed contacts will open and it's normally open contacts will close
Use decent relay dont use small relays if you want all to be safe, and long life of circuit. There is relays on 5V, 6V, 12V, 24V,... Thise on 5V are often smaller, and for weaker currents.
You need to make sure that the high voltage side of the relay can handle the load of the water pump as the current will pass to the water pump through the relay.
You need to make sure the low voltage side of the relay - the coil - draws an amount of current that does not damage the driver. Remember to use a freewheeling diode across the coil. The voltage rating has been talked of above.
Since the output current of the PIC is limited (and output voltage decreases with increasing current), you should consider using a separate driver for the relay. A simple NPN transistor can do the job. Make sure the NPN transistor has a higher current rating than the maximum current the relay coil will draw.
An alternative to the relay: a phototriac. Since it's a phototriac, its de facto optoisolated.
One example: sharp's S2 16S02 (16 amperes). 2 pins are for led A and K, and the other pins
are for AC switch.
MOC3041 is an opto-triac, not an optocoupler (with an NPN transistor).
Plus, if you're using common ground for both the input LED and the transistor, you don't need to use opto-coupler, since you're just not making use of isolation - what it was meant to be used for.
Plus, the opto-coupler might not be able to handle the current.
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