Stamps Driving Transistors
Archiver
Posts: 46,084
In Al's FAQ regarding driving high power AC devices he writes:
Section 2.5:
"There you'll want to use a relay (easy and safe) or some sort of AC
switching device like an SCR. If you use a relay, you can wire the coil
like the lamp, but be sure to put a diode across the coil with the
banded end towards the power, and the non-banded end towards the
collector of the transistor. This prevents fast changes in the coil
current from generating large voltages that can fry the transistor.
Another excellent way to switch a high-current load is using a power
MOSFET. RadioShack sells the IFR-510 which is ideal for use with the
Stamp"
My Load is 4-6 (quantity) solenoids 120VAC, 12amp max each.
A DPDT switch (rated 110V at the coils, 15amp at the contacts) drives
each solenoid.
I'm still stumped how drive the high-power relay.
I've never used a MOSFET before, but I assume there is NO WAY for it to
power my high-power relay directly, but it WILL drive a low-power
intermediary relay? Is this the simplest solution? If so, what is the
max rating for a relay that a MOSFET can drive and any advice on what
rating MOSFET/Low Power relay combination I should be looking at?
Finally, in protecting the transistor with a diode across the coils,
how do I calculate the diode rating?
Thanks a bunch.
Cheers,
-Neal
Section 2.5:
"There you'll want to use a relay (easy and safe) or some sort of AC
switching device like an SCR. If you use a relay, you can wire the coil
like the lamp, but be sure to put a diode across the coil with the
banded end towards the power, and the non-banded end towards the
collector of the transistor. This prevents fast changes in the coil
current from generating large voltages that can fry the transistor.
Another excellent way to switch a high-current load is using a power
MOSFET. RadioShack sells the IFR-510 which is ideal for use with the
Stamp"
My Load is 4-6 (quantity) solenoids 120VAC, 12amp max each.
A DPDT switch (rated 110V at the coils, 15amp at the contacts) drives
each solenoid.
I'm still stumped how drive the high-power relay.
I've never used a MOSFET before, but I assume there is NO WAY for it to
power my high-power relay directly, but it WILL drive a low-power
intermediary relay? Is this the simplest solution? If so, what is the
max rating for a relay that a MOSFET can drive and any advice on what
rating MOSFET/Low Power relay combination I should be looking at?
Finally, in protecting the transistor with a diode across the coils,
how do I calculate the diode rating?
Thanks a bunch.
Cheers,
-Neal