Which diode do I need for a pump relay?

[CheeseBall]

I have a 10amp solid state relay, ehiem 1250 (coming monday), a SPDT on-on toggle, and my trusty soldering iron. I have the basics of how to wire it up.

But I still need a diode... what am I looking for, what kind of diode do I need?

Hopefully my toggle will work, that is the right kind?... I hope.

Thaks for any help,

[TerraMex]

I used a 4007. Any similar will do the trick. You just need the diode to prevent current from flowing in the opposite direction (and burning something in the process).

http://www.fairchildsemi.com/ds/1N/1N4006.pdf

[W1zzard]

solid state relais dont need a diode becuase they build up no magnetic field

[CoolROD]

A diode anywhere in the output circuit would be a disaster...

As W1zzard said: there is no coil in a SS relay, so there is no magnetic field, and no need to clamp it's collapsing Back-EMF.

[ralf_c]

hi all

please pardon my lack of knowledge, but why is there a need for a diode in relay circuit?

[TerraMex]

Mine is mechanical.

The diode is used to stop any parastic reverse current on the circuit.

http://www.bit-tech.net/article/100/

And yes, you can discard it if you want to.

[CoolROD]

ralf_c: please pardon my lack of knowledge, but why is there a need for a diode in relay circuit?

No problem: It is not just relays, but any collapsing magnetic field.

Any current flow is accompanied by magnetic fields. The most notable is a circular field perpendicular to the current flow. When you coil a wire the magnetic fields of each winding are added together.

A change in current or direction of current flow results in a change of the accompanying magnetic field.

A change in a magnetic field will induce a voltage potential in a conductor. If the conductor has a complete circuit a current will flow.

When you drop power to a solenoid, relay coil, motor, or simple loop of wire the magnetic field that was already there collapses. As the field collapses it generates a voltage spike in the original control wires. This is similar to an automotive ignition circuit.

Big coils generate big spikes, but little coils can still damage fragile electronics. (You should see the fire in the contacts of a 500 HP electric motor starter! It is so bad that the power company gets interested )

A DC circuit is particularly bad because the power is always shut off at maximum voltage, current, and magnetic field -and the induced "back EMF" is always maximum. A diode is easy to install in a DC circuit and offers a low impedance path for the induced current to run back into the coil (which is pretty rugged) and dissipate itself.