Power wiring for dual band mobile

#1
After our recent thread about the value of dual band ham transceivers, I now have one on the way. I'm thinking about the power connections. I know I can run the time delay shut-off on the radio and wire straight to the battery (with a fuse of course) but I don't do anything the easy way. I'd like to have the option of running the radio for extended periods without the truck on (monitoring or as a crossband repeater for my HT for instance) but in my daily short trips to work and around town I want it to power automatically with the ignition. This assumes the radio retains programming when voltage is suddenly cut, but it should. I find turning the HT off and on all the time annoying.

My thought on this is to run main power through an appropriate fuse and relay to the battery. I'll run an ACC hot wire to the signal terminal of the relay, thereby turning it on when the car starts. In addition, I'll run a (fused) hot wire through a dash-mounted SPST switch from an always-hot source to the same signal terminal. This should allow me to flip a switch and have the radio on when the truck is off.

What tiger traps have I missed in that plan?
 

dreadlocks

Active member
#2
Have you bothered checking your radio's power specs? for example one of my kenwood mobile radios I looked up and its:
Receive: 420 mA (max vol, max lights, no signal), 203 mA (standby, no lights)..

If put in a vehicle that is driven like once a week or more frequently, you can just leave it on all the time... mebe put a LVD just incase you store it and forget to turn it off, depending on your TX power you might be able to use a cheap one for a dashcam
 
#3
Verkstad: I wondered about this too. Adding a diode in the line between the ACC source and the other hot line should avoid the problem. I think.

Dread: It lists 500 mA, squelched. Doesn't mention details beyond that. So yeah, I could leave it on, but I just don't like the idea of having something powered up just sitting there, especially tied directly to a battery. I know, fuses, etc, but.... I've seen more than one car burn down due to failed electrical components. I know if I'm running it as a repeater and away from the truck I still run that risk, but at least then the possible benefits outweigh it. Just sitting in the driveway.... I also dislike the hardwired timers because of the repeater use thing. If I'm out hiking and have a problem I don't want the thing to turn off if it takes longer than I think to get back.
 
#4
Wire up a double pole double throw switch, where one direction would allow a switched power source to trigger a relay, and the other direction would connect an always on power source to trigger a different relay.
You could use an on-on switch so it's either one or the other or an on-off-on switch to you have a dead spot in the middle where the radio wouldn't get power from either source.
 

dreadlocks

Active member
#5
if you seen a car burn down it was likely due to failed fuel components, not electrical.. just sayin, my house has had electrons running amok in the walls for over 60 years and its still standing.. If you wire it up correctly there is practically zero risk.. and if your a HAM, the only electricity you should be loosing sleep over is that which comes directly from the hand of Zeus.. lightning is our mortal enemy.

You can always train your self to turn the radio on/off your self as you need it, but if your planning for the exceptions here how about you wake up at 2am, look out window.. see some jackass in your Jeep, so you pick up your handheld and say "Freeze Police, get on the ground" and watch the guy in your car **** him self when that comes over the radio..
 
#6
Actually, a friend lost a nice 1972 Skylark convertible to a faulty headlight switch about 10 years ago. The old push-pull switches ran some serious amperage through them. Fire started behind the dash, burned the interior and ragtop completely out. Car was a total loss but the engine (a nice crate 350) wasn't even singed and the fuel tank never went up.
 
#7
Wire up a double pole double throw switch, where one direction would allow a switched power source to trigger a relay, and the other direction would connect an always on power source to trigger a different relay.
You could use an on-on switch so it's either one or the other or an on-off-on switch to you have a dead spot in the middle where the radio wouldn't get power from either source.
ahhh...okay, taking that idea and running with it... what about a SPDT switch that uses the 2 throw terminals as my source (ACC or ALWAYS) and runs the single output to my relay? now THAT sounds like an idea!
 

dreadlocks

Active member
#8
ok, take a mental note that in 26 years you should check the wiring of your Radio.. :p

yeah I believe that, my 1975 Westfallia Bus runs all the starter amps through the ignition switch.. the battery and starter are 2ft apart, and ignition is on the other end of the vehicle..

this was back in cave man days tho whadda ya expect.. its just amazing the electronic fuel injection ECU still works over 40 years later..
 
#9
ahhh...okay, taking that idea and running with it... what about a SPDT switch that uses the 2 throw terminals as my source (ACC or ALWAYS) and runs the single output to my relay? now THAT sounds like an idea!
I thought about that, but I don't like having all the power running through the switch to the radio.
 
#11
ok, take a mental note that in 26 years you should check the wiring of your Radio.. :p

yeah I believe that, my 1975 Westfallia Bus runs all the starter amps through the ignition switch.. the battery and starter are 2ft apart, and ignition is on the other end of the vehicle..

this was back in cave man days tho whadda ya expect.. its just amazing the electronic fuel injection ECU still works over 40 years later..
Yeah...but I'm in a Jeep designed by Chrysler in the early 90s and wired by Lucas...the wiring is uh...entertaining.

I've always thought the old westies are cool but never felt the need to own one.
 
#13
What kind of radio do you have? I have a TM-V71A and it has a setting where it will automatically turn off after 30, 60, 90, 120, or 180 minutes and it also IDs while in cross-band mode. With my specific gear, I would just set the auto-off to 30 minutes and be done with it, the ID for the repeater mode will reset the clock. Check your manual to see if that will work.
 
Top