[MRCA] MX-7777 and the mutt

[Ray Fantini]

After much thought I was able to incorporate the MX-7777 transient and surge protector into the mutt DC distribution project. After installing the two ten foot power cables and tray from the driver's side of the mutt to the battery compartment did not want to go back and install the MX-7777 at the radio using the three foot jumpers that I had for direct connection to the MX and have to say that I am leery of passing all that current thru the signal four pin connector on the back of the MX to begin with. So I modified the MX and installed it in the accessory compartment next to the battery compartment. The modification consisted of removing all the plugs from the MX on both sides and the back and hardwiring two 8 AWG cables for the input and output along with a third for grounding the suppressor. By using the accessory compartment on the mutt I am able to connect the ground side of the suppressor directly to the same point that the negative side of the battery grounds to the chassis. The two #8 power cables travel into the battery compartment thru the same hole as all the radio cables with one end going to the power distribution stud and the other directly to the battery terminal. Only issue so far is now have two #0 cables for slave and mutt power system and this new #8 all connecting to the battery terminal and it's a bit of a octopus.  One of the other advantages now with the suppressor in the accessory compartment is it's a good place to have the radio master disconnect switch that's not out in the open so by turning off the suppressor that removes  power to all the radios. Two concerns are that the MX-7777 has an internal circuit breaker rated at 50 Amps and that one breaker is powering the GRC-106, VRC-12 and URC-110 so think it's right around capacity, I did run all the radios last night and transmitted with all at once and did not blow the breaker so going to assume its ok. The MX has a bypass switch (Battel Override) that will bypass the device but that switch is rated at 50 amps so it looks like 50 amps is the limit for that device. It's also interesting that if you switch in Battel Override and keep the main switch on the transient suppressor will still be in the circuit. The other concern is the issue of shock mounting. To make it fit in the accessory compartment I had to remove the rubber shock mounts. Have no idea why it needs shock mounts anyway being the case of the device is grounded. So I am planning on just bolting the suppressor directly to the bottom of the accessory compartment. Going to assume that the shock mount was to deal with vibrations that were encountered in mobile service?
Doing some work on the bench found that the MX-7777 not only removes short duration spikes and transients but also serves as a brute force regulator keeping the DC bus below thirty five volts. It had no issues loading down my bench supply beyond ten amps or so in keeping it below that voltage so will assume that in a weird case where if you louse regulation the suppressor will just keep loading down the circuit till it blows its internal circuit breaker and will protect the radios that way.
I attached the new drawing and will send out pictures of the completed installation soon.

Ray F/KA3EKH

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