On Mon, 11 Mar 2019, Gene Heskett wrote:

Date: Mon, 11 Mar 2019 21:55:59 -0400
From: Gene Heskett <ghesk...@shentel.net>
Reply-To: "Enhanced Machine Controller (EMC)"
To: emc-users@lists.sourceforge.net
Subject: [Emc-users] until I get chips for C1G, moving everything to the 7i76

For PCW.

I have 100's of 1N914's. And I'm going use some 12 volt coil 4pdt relays
in din rail sockets, that when on will draw around 180 ma from a 12 volt
supply. Thats well within the on ratings of a 7i76 output. Are the
1N914's enough to protect the 7i76 from the off edge back emf, or do I
need to src some heavier current ratings than the 200 mills they are
rated at? I'm bearing in mind the speed of these 1N914's compared to the
many times slower common 1N4000 power diodes. Speed is likely the
important item, but whats Peter got to say?

I am also thinking of using one of those same relays to start and stop
the spindle coolant pump by driving it with spinena, since the pump is
heating the water 20F or more if left on overnight.  Anybody see
anything wrong with that?

Thanks a bunch.

Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

The 7I76s driver chips have built in flyback protection (basically a zener diode that keeps the output MOSFET on if the source --> drain voltage exceeds about 40V) This dissipates the stored inductive energy in the output MOSFET. At higher currents its possible to exceed the energy absorption capabilities of the MOSFETS so its neccesary to use a flyback diode (with a flyback diode the bulk of the stored energy is dissipated in the relay coil) Either a 1N914 or a 1N400x diode are fine (speed is not important)

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