karo said:
Is'nt the the purpose of the large diode at the power input section of most cb radios>?
I have repaired several rigs that got connected back to front and some where the guy plugged the radio back in the right way and left it there .
This one guy said when he hooked his galaxy up wrong that smoke started to come out of the radio and when he hooked it back up right it really smoked.lol that's the only one I had to repair a trace on the ciruit board and replace the protection diode.
karo, the diode will be forward biased when the power leads are reversed, and since the diode is located across the power lines with no current limiting, the fuse will blow whether it is located in the positive lead or negative lead - it doesn't matter.
QRN said:
Usually when someone smokes the protection diode it is when they hooked up the wires backwards and did not use a fuse.I ALWAYS use a fuse in the B+ line and now with the newer ham gear the B- as well.The big reason for having a fuse in the neg lead is if the main ground from the battery to the vehicle's chassis fails then all the ground is flowing through your radio's neg lead and that includes the starter. :shock:
QRN, the entire vehicle electrical system has a main (single point) ground connection located on the engine block. Should the engine, battery, and vehicle body loose this single point connection, the electronics and electrical system would all be floating at different values and nothing would work as a system.
Also, since the starter is grounded to the engine block when it is bolted up, there is no way the starter current will flow through the CB's negative lead. This starter current flowing through the CB (-) connection is an internet myth...
You can fuse the negative lead if it makes you feel good, but it is not a good idea unless the positive is fused too.
The reason the positive lead is fused is to remove power from the device when there is an overload condition. If the negative lead is the only lead fused, then power will still be applied to the device when the fuse blows. This means that unless the chassis/device is floating, current will flow back to the source through whatever ground path it can find, so a fire in the wiring could still occur when over loaded.