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Power relay connected to pic16f877

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New Member
Hi guys

iam having problem with the relay, there is not enough current coming off the relay going to " Ac pump", is there a way to charge the pump using other method, or maybe a way to amplify the current off the power relay.

"tell me who's your friends, i will tell you who you are."


Active Member
a little bit more info about what you're trying to do might be welcome...
What's this Ac pump ...?


New Member
re-power relay


well iam doing a greenhouse project, basically i need to send a high voltage to the power relay wich will trigger a water pump to charge and supply water to the greenhouse, the pump that i have work under 110 Ac voltage, but i can't get enough current to drive the pump.
the microcontroller is pic16f877.



Active Member
If you don't have enough current to drive the pump that hasn't got anything to do with the PIC... that's on the scondairy side of the relay...

Or is it the relay you're having trouble with switching it on ?


New Member
If microcontroller is used for mainly control input/output at low voltage level then PLC is is a device that was invented to replace the necessary sequential relay circuits for machine control(high voltage). :idea:

I dont have background about PLC so i cant say nothing but if you want to control machine i suggest you choose PLC. (You also need to learn programming languege).

Here is the introduction about PLC...

Something make fell very confuse is why you say dont have enough current??? Or, you put your post your circuit have...may be someone can help you...


New Member
How are you driving your relay? I hope you are not driving it straight from the PIC's pin right?!

Since you are involving mains I would use a optoisolator to mantain things in the safe side. Mainly because of the spikes the relay and probably the pump generates.

To think about:
-Make sure that the relay is intended for AC use and is able to handle the current load of the pump.
-Make sure that the relay coil is to be driven by a DC source, and what current it needs to switch.
-Make sure that you don't abruptly interrupt the current to a inductive load, like a motor would be. More if you are using a high current.
-Make sure that you are driving the relay coil at the right minimum voltage.
-The pic is only able to drive a relay thru a transistor

PLC are very expensive and probably an overkill for this type of project since it only needs a relay. PLC were created to emulate a whole bunch of relays, where before they had to be wired physically.

How do you know you don't have enough current to drive the pump? can you post a schematic of what you are trying to do?

Good Luck



If your pump isn't too large, i suggest you use an optocoupler with a Triac output. By using one inexpensive part you will be able to isolate the highvoltage mains from your circuit and control the pump without any external transistors or additional voltage rails (besides 5V for circuit and 120V AC for the pump). If you want to, you can also adjust the power of the pump using the same optocoupler.
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