[MRCA] MX-7777 and the mutt

[Ray Fantini]

If you pop open the MX-7777 the input to the box is from two pins off the back connector, two hot and two grounded.  Never intended it to be thought of as a regulator although it would for a short period of time but hope it trips the main first and disconnects all sensitive loads that are feed from it. The huge Zener diode, MOV or whatever it is was able to dissipate 10 or fifteen amps of current when I was abusing it with no issues and did not get hot in the process. Also I understand that it's the device that is doing the work but there is a small cylindrical circuit encased in an epoxy cylinder on top the device with a red and black small gauge wire that dose something, maybe that's the time out circuit? And the big device has a small yellow wire that attaches from the side of the device to the main circuit breaker, something like you would see on a SCR. Looked up the numbers on the mystery device but was unable to find anything.


Ray F/KA3EKH

From: mrca-bounces at mailman.qth.net [mailto:mrca-bounces at mailman.qth.net] On Behalf Of WA5CAB--- via MRCA
Sent: Monday, June 19, 2017 1:13 PM
To: mrca at mailman.qth.net
Subject: Re: [MRCA] MX-7777 and the mutt

As I wrote before, the 4-pin UW Series connector on the right or back side of the MX-7777(*) is not a signal connector.  Those have either 9 or 14 smaller pins or sockets.  The MA/FA insert has at least (I still haven't looked it up) a 50 Amp rating at 24 VDC.  Comparable to that of the MS 3102E-22-2S 3-contact connectors used on the output.

Also, the manual doesn't go into detail but it appears that the thermal switch, when it finally opens, disconnects the zener diode for about 2 minutes.  So if you hook a 45 volt supply to the system, it will only try to hold it down to 35 VDC for "a while"..  It wasn't intended for continuous operation under those circumstances.  Hopefully the supply overload would trip first.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
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