Relay
Archiver
Posts: 46,084
Mark,
I wasn't quite "with it" yesterday, and didn't think your question through
completely.
A "clamping" or "wheel" diode across a relay's coil works great *IF* the
voltage applied to the coil is DC. However, this won't do for AC, as the
clamping/wheel diode would present a dead short to ground for 1/2 off the
cycle (when the AC voltage went negative).
For this reason, in AC circuits only, you must use a shunt resistor across
the relay's coil (or other inductive load).
Original Message
From: Mark Adams [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=jNml1vPC8RzxpvtlP7shn3juOMzve6XvkwRTcdK3hhKA40t5mV6IaLEPHoSNNHXbb_Ygn_Pf8lsE-ZiG]madams@a...[/url
We were looking at some BOSCH relays and they listed an option that
included a 'shunt resistor' and the ones we currently purchase with an
included diode. Now, the question is why is the shunt resistor there?
<snip>
I wasn't quite "with it" yesterday, and didn't think your question through
completely.
A "clamping" or "wheel" diode across a relay's coil works great *IF* the
voltage applied to the coil is DC. However, this won't do for AC, as the
clamping/wheel diode would present a dead short to ground for 1/2 off the
cycle (when the AC voltage went negative).
For this reason, in AC circuits only, you must use a shunt resistor across
the relay's coil (or other inductive load).
Original Message
From: Mark Adams [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=jNml1vPC8RzxpvtlP7shn3juOMzve6XvkwRTcdK3hhKA40t5mV6IaLEPHoSNNHXbb_Ygn_Pf8lsE-ZiG]madams@a...[/url
We were looking at some BOSCH relays and they listed an option that
included a 'shunt resistor' and the ones we currently purchase with an
included diode. Now, the question is why is the shunt resistor there?
<snip>