Best circiut to power CB radio

I've never even seen a 2000 Disco up close, so I can't help you in terms of the layout of the electrics, however from the radio's perspective, it's best if you run wires all the way to the battery. You need to make sure you switch off the radio when not in use, but even if you don't, it shouldn't be a problem as most radios don't drain much current when receiving anyway.

Connecting it directly to the battery will provide higher voltage to the radio, which in turn should maximise your power output.

Direct from the battery.

Steve. Suffolk. remove 'knujon' to e-mail

Don't forget to put an in line fuse in to both the +ve and the -ve if connecting directly on to the battery posts, as close to the battery as possible. Alternatively connect the -ve to chassis and just an inline fuse in the +ve line.

What purpose does a fuse in the -ve feed serve, other than one more potential cause of a dodgy connection?

The idea is that if the main earth to the vehicle's engine fails, when you go to crank the engine, it doesn't draw a massive amount of current through the radio and damage it but instead it blows the fuse. This is the guideline laid down under MPT1362 for installation of radio equipment in to land based vehicles. If you connect the -ve down to the vehicles chassis it is then not necessary to incorporate a fuse in to the -ve line. I hope this answers your question my friend.

Thanks - it makes sense.

On or around Fri, 15 Oct 2004 08:08:45 +1300, EMB enlightened us thusly:

bugger all, I expect.

I'd be inclined to hunt a permanent live from the fusebox. You might even find a spare fuse, or feed it from the interior light circuit or something. Most CB installations have their own fuse anyway, inline.

"Austin Shackles" wrote in message news: snipped-for-privacy@4ax.com...

It's permissible to find an alternative feed for a transceiver radio but you have to be careful and sensible about it! It's ok to connect to a main cable, i.e., a main feed to or from the ignition switch as there is plenty of current at this point and hardly any voltage drop. Depending on whether you want the radio to be powered up permanently or whether you want the radio to be ignition switched is another question. you have to weigh up the prose and cons, for instants, if you connect the radio so that it isn't ignition switched and you accidentally leave the radio switched on all weekend you may well have a flat battery on monday morning especially if the battery is getting a little old and tired. On the other hand, if you connect the radio so that it is not ignition switched you may well be tempted to leave the keys in the ignition to keep the radio alive especially if you are not to far away from the vehicle and are waiting for a call over the radio from somebody In the latter case you may be distracted for a moment and the next thing you know is your pride and joy is off down the road, leaving you without a vehicle and void insurance. I have known the latter happen and in my opinion it's far better to suffer a flat battery than a lost motor vehicle. Connecting to an interior light and other such circuits is a no no. Why? PMR devises such as CB radios etc are capable of drawing up to 15 amps, and more, when in transmit mode, depending on what the power output level has been set at. I have seen many burned out wiring looms and horrendously expensive damage over the years because people have connected these devises to inadequate power supply sources on vehicles. On more modern vehicles problems can arise when electrical devises are connected in to wiring loom as serial data is transmitted along these cables and this can cause corruption and damage to the vehicle's ECU's. So either connect on to a heavy cable around the ignition switch or better still go straight to the vehicle's battery, Use good quality water proof fuse holders and you wont have a problem.

Thanks much for the info. My Jeep had a switched accessory circuit so it was very nice. I was hoping for an option like that on the Rover that I was overlooking. I believe I just piggy backed on the stereo circuit for my truck.

It seems clear my best option is to wire direct to the battery and mind my power switch. I have a ham radio that has been tweaked for extra power output even in the CB bands, so concerns about too much amperage being drawn are warranted.

Could something be done with a relay?

Have an "auxiliary power" switch in parallel with the ignition switch, controlling a relay which switches the power to the radio.

You are very welcome.

It certainly could, no problem at all. It would get round the possible flat battery scenario.

You would need a diode between the ignition switch and the relay, so that current wouldn't go through the auxiliary switch to bypass the ignition. Not a problem -- the relay coil is low current.

You wouldn't really need a diode as all you need to do is connect one side of the voltage coil to the switched side of the ignition switch and the over side down to earth/chassis.

I think it's been lost in quoting, though you can see a trace of it, but the idea was partly to have an auxiliary-power switch so that the radio could be powered without the key needing to be in the ignition.

It's possible to use a three relays so that the auxiliary switch is a momentary contact, and the ignition circuit switches the auxiliary input off when it goes live.

Relay A -- coil powered through auxiliary switch. When contacts close, output also feeds coil through Relay B, so the output remains live as long as Relay B contacts are closed.

Relay B -- coil powered from ignition switch. Uses n\c contacts for latching circuit for Relay A.

Relay C -- coil powered by both Relay A output and ignition switch, the latter through a diode. Switches power to radio.

With this system, or a solid-state equivalent, the power to the radio circuit can be switched on by pressing the auxiliary button, if the ignition is off. You might want some sort of warning light.

Next week: How to build a computer in the back of yout 101 from the LR Spares Catalogue.

-- David G. Bell -- SF Fan, Filker, and Punslinger.

"History shows that the Singularity started when Sir Tim Berners-Lee was bitten by a radioactive spider."

I guess you could do it that way but you would need a heavy rated diode because of the amount of current drawn when transmitting.

did'nt know you could still get the valves for it :-))