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Pics and relays

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New Member
i would like to control a 12V 30 Amp Relay with PIC16F84 and i dont know how.

plz help



Active Member
I assume you mean 12V 30mA, cause 30A would be quite a coil :)
To switch it, use a transistor, like this (FIG A or B)

The signal from the pic will turn the transistor 'on', drawing only little current from the PIC.

fig C and D are only needed if you want to drive really big loads, using such big transistors that the pic can't drive them directly and needs an extra buffer

The diode acts as protection for the transistor. When a coil is deactivated, it returns a charge in the opposite direction, which could kill your transistor. The diode will neutralize this charge


Well-Known Member
Does the relay coil draw 30 amps, or are you trying to drive a relay that can switch a 12 volt, 30 amp load?


New Member
it cannot be 30A for the coil. if it was a 30A coil, probably it is as big as your monitor and switches on what? a nuclear power station???
i am sure it is about the contacts that he talks about
for this relay i think that 100mA rating for the transistor is preety enough. so use something like BC547,-8, -9, or BC171, or whatever transistor you feel like using.


Active Member
vxr said:
no 12V 30Amps relay i know the PIC cannot but there should be a way..
Like the others said. If it says 30A it is probabely the contact that can switch 30A, the pic drives the coil that makes the contact move, and that coil will only draw a little bit current (mA's).

a 30A 12V coil would be 0.4 ohm... Doesn't sound realistic to me
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