On Fri, 3 Jan 2020, Gene Heskett wrote:
Date: Fri, 3 Jan 2020 09:41:26 -0500
From: Gene Heskett <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
<[email protected]>
To: [email protected]
Subject: Re: [Emc-users] Somewhat of a puzzler with a 7i76D
On Thursday 02 January 2020 15:59:09 Gene Heskett wrote:
Reposted with some spelling corrections, clarifying language, and a thank
you I forgot.
greetings & a happy new year to all;
I finally figured
I felt good enough to go out to the garage and see if I could resurect
the 6040. When last putzing with it I had left it with the circuit
from machine motion to lights and coolant pump, and the mist pump
disconnected from the 7i76D field output 0 & 1 and was in between
sessions in the cath-lab fixing my ticker.
One of these two was (I first thought) a dead short on the 12 volt
field supply, and when I traced the wire to the lights & motor coolant
relay, I found that I'd not installed a flywheel diode across that coil
because I was out of a suitable diode. So I ordered a bag of 100 volt
4 amp diodes.
While I'm keeping this chair warm, they came in, so I went out and cut
a 40" piece of light zip as that was more suitable wire, crimping a
diode into the hilitchi sleeves, pulled that relay loose and connected
it, throwing the other end of the wire toward the interface box. Moved
the ladder and hooked the other end up.
Cycled it on and off from linuxcnc several times, worked perfectly.
Hooked up the mister motor power again, and it worked as designed
after a couple minutes to reprime the pump as it had a good month to
bleed back.
By then my legs are telling me they are going to give me hell for
cramps in the night, I've been laying around too long.
But a tum calcium pill in each cheek headed that off.
So thats the background.
Question for Peter:
Could the lack of that diode have triggered a substrate scr in the
7i76D?, crowbaring the field power in the 7i76D, but which due to the
supply trying to cycle, never got clear to zero volts to reset that
invisible scr.
Any other failure external to the 7i76D would not have been a short.
It could only be healed with a full powerdown, which is the only
theory I can come up with that makes sense. That same 7i76D output, now
with a flywheel diode seems to be running it flawlessly now. The
supply is rated at 12 volts and 2.1 amps so doesn't (probably) have
enough cajones to burn things up. All relays on, its a tad under an
amp total.
I have seen this only 2 other times in my 70+ years of putting electrons
to work.
Thanks Peter.
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)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
I have not seen this before. usually if you switch an inductive load with too
much energy for the little MOSFETs in driver chip, they fail in shorted mode
The driver chips do have flyback protection but dissipate the energy in the
MOSFETs (if you have a flyback diode most of the energy is dissipated in the
coil)
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Peter Wallace
Mesa Electronics
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