Power to my new CB question
JK Newbie
Joined: Jan 2011
Posts: 70
Likes: 0
From: Joliet,Il
Why fuse the negative lead? VERY good question. I'll try to explain.
Vehicles use the chassis/frame for some of their DC grounds. The negative lead of the battery is attached to the chassis and usually the engine block. The case of the starter motor is often times the ground connection so it gets its ground, back to the battery, via the block. This works fine.
What would happen if the chassis/ground connections between the negative lead of the battery and the starter became bad....or, more likely, started to get some resistance in it? The starter would have more trouble turning over the ending due to the voltage drop across that part that has a bad connection (aka., resistance).
Now...go one step further. You mount a radio in your vehicle. The power leads go directly to the battery (as they should) or to a nearby aux fuse block that was installed by you to handle your extra goodies.
The antenna is mounted on another part of your vehicle and its mount is grounded to the vehicle's body/frame (in order to work properly). The coax connects the CB radio chassis and the antenna together....and the outer coax braid is at ground also (but it is covered with an insulative coating).
OK...back to earlier in the explanation. You have a heavy current carrying device...like a starter....or maybe a light bar that is grounded to the vehicle body for the negative connection for that batch of off-road lights it is holding up. If the negative battery cable that goes to the block/chassis starts to go bad, the DC current flowing from one of these items...let's say the light bar), can find a ground through the body of the vehicle to the antenna mount and down the antenna coax and through the CB chassis/circuit board ground and through the CB negative power lead to the battery itself.
When that happens, you might very well have 30~50 amps of current flowing through the CB radio's chassis, trying to get to the negative terminal of the battery. If it were the starter motor that found its "other ground path" through here, you would have a couple hundred amps flowing.
The end result is that your CB chassis, with those tiny copper circuit board runs on it, can become a fusable link and burn open due to the excessive current flowing through the ground circuitry of your radio chassis. So...you burn out the guts of your radio.
By putting a fuse in the negative lead of your CB radio (or ANY other electronic device that is attached to the battery), it will blow open and stop the high current flow before it does any permanent damage. (just like the positive lead fuse will blow open if you shorted the hot lead to ground).
If you don't believe this, please feel free to stop by my house. If you volunteer your vehicle and radio, I shall be happy to do the "faulty ground wire" scenario on your vehicle. You can turn on the lights or crank over your engine and watch your CB radio smoke.
Vehicles use the chassis/frame for some of their DC grounds. The negative lead of the battery is attached to the chassis and usually the engine block. The case of the starter motor is often times the ground connection so it gets its ground, back to the battery, via the block. This works fine.
What would happen if the chassis/ground connections between the negative lead of the battery and the starter became bad....or, more likely, started to get some resistance in it? The starter would have more trouble turning over the ending due to the voltage drop across that part that has a bad connection (aka., resistance).
Now...go one step further. You mount a radio in your vehicle. The power leads go directly to the battery (as they should) or to a nearby aux fuse block that was installed by you to handle your extra goodies.
The antenna is mounted on another part of your vehicle and its mount is grounded to the vehicle's body/frame (in order to work properly). The coax connects the CB radio chassis and the antenna together....and the outer coax braid is at ground also (but it is covered with an insulative coating).
OK...back to earlier in the explanation. You have a heavy current carrying device...like a starter....or maybe a light bar that is grounded to the vehicle body for the negative connection for that batch of off-road lights it is holding up. If the negative battery cable that goes to the block/chassis starts to go bad, the DC current flowing from one of these items...let's say the light bar), can find a ground through the body of the vehicle to the antenna mount and down the antenna coax and through the CB chassis/circuit board ground and through the CB negative power lead to the battery itself.
When that happens, you might very well have 30~50 amps of current flowing through the CB radio's chassis, trying to get to the negative terminal of the battery. If it were the starter motor that found its "other ground path" through here, you would have a couple hundred amps flowing.
The end result is that your CB chassis, with those tiny copper circuit board runs on it, can become a fusable link and burn open due to the excessive current flowing through the ground circuitry of your radio chassis. So...you burn out the guts of your radio.
By putting a fuse in the negative lead of your CB radio (or ANY other electronic device that is attached to the battery), it will blow open and stop the high current flow before it does any permanent damage. (just like the positive lead fuse will blow open if you shorted the hot lead to ground).
If you don't believe this, please feel free to stop by my house. If you volunteer your vehicle and radio, I shall be happy to do the "faulty ground wire" scenario on your vehicle. You can turn on the lights or crank over your engine and watch your CB radio smoke.
Thank You.
JK Super Freak
Joined: Nov 2010
Posts: 1,307
Likes: 0
From: Alb., NM
billsimcox Very nice explanation. So here is a question what size fuse would one put on the neg side for the aux fuse block? does it depend on the goodies you have?
for example I have a 50A fuse on both, this would cover my HAM radio (30A on radio) and lights(20A on lights), so far that's it. CB (5A on CB I think) won't be on while the HF HAM radio is on, but could be while 2M radio is on (20A on that radio)..
for example I have a 50A fuse on both, this would cover my HAM radio (30A on radio) and lights(20A on lights), so far that's it. CB (5A on CB I think) won't be on while the HF HAM radio is on, but could be while 2M radio is on (20A on that radio)..
Last edited by JK-jeepit; Apr 13, 2011 at 06:11 PM.
JK Jedi
Joined: Aug 2007
Posts: 5,813
Likes: 0
From: Kenai Peninsula, Alaska
Why fuse the negative lead? VERY good question. I'll try to explain.
Vehicles use the chassis/frame for some of their DC grounds. The negative lead of the battery is attached to the chassis and usually the engine block. The case of the starter motor is often times the ground connection so it gets its ground, back to the battery, via the block. This works fine.
What would happen if the chassis/ground connections between the negative lead of the battery and the starter became bad....or, more likely, started to get some resistance in it? The starter would have more trouble turning over the ending due to the voltage drop across that part that has a bad connection (aka., resistance).
Now...go one step further. You mount a radio in your vehicle. The power leads go directly to the battery (as they should) or to a nearby aux fuse block that was installed by you to handle your extra goodies.
The antenna is mounted on another part of your vehicle and its mount is grounded to the vehicle's body/frame (in order to work properly). The coax connects the CB radio chassis and the antenna together....and the outer coax braid is at ground also (but it is covered with an insulative coating).
OK...back to earlier in the explanation. You have a heavy current carrying device...like a starter....or maybe a light bar that is grounded to the vehicle body for the negative connection for that batch of off-road lights it is holding up. If the negative battery cable that goes to the block/chassis starts to go bad, the DC current flowing from one of these items...let's say the light bar), can find a ground through the body of the vehicle to the antenna mount and down the antenna coax and through the CB chassis/circuit board ground and through the CB negative power lead to the battery itself.
When that happens, you might very well have 30~50 amps of current flowing through the CB radio's chassis, trying to get to the negative terminal of the battery. If it were the starter motor that found its "other ground path" through here, you would have a couple hundred amps flowing.
The end result is that your CB chassis, with those tiny copper circuit board runs on it, can become a fusable link and burn open due to the excessive current flowing through the ground circuitry of your radio chassis. So...you burn out the guts of your radio.
By putting a fuse in the negative lead of your CB radio (or ANY other electronic device that is attached to the battery), it will blow open and stop the high current flow before it does any permanent damage. (just like the positive lead fuse will blow open if you shorted the hot lead to ground).
If you don't believe this, please feel free to stop by my house. If you volunteer your vehicle and radio, I shall be happy to do the "faulty ground wire" scenario on your vehicle. You can turn on the lights or crank over your engine and watch your CB radio smoke.
Vehicles use the chassis/frame for some of their DC grounds. The negative lead of the battery is attached to the chassis and usually the engine block. The case of the starter motor is often times the ground connection so it gets its ground, back to the battery, via the block. This works fine.
What would happen if the chassis/ground connections between the negative lead of the battery and the starter became bad....or, more likely, started to get some resistance in it? The starter would have more trouble turning over the ending due to the voltage drop across that part that has a bad connection (aka., resistance).
Now...go one step further. You mount a radio in your vehicle. The power leads go directly to the battery (as they should) or to a nearby aux fuse block that was installed by you to handle your extra goodies.
The antenna is mounted on another part of your vehicle and its mount is grounded to the vehicle's body/frame (in order to work properly). The coax connects the CB radio chassis and the antenna together....and the outer coax braid is at ground also (but it is covered with an insulative coating).
OK...back to earlier in the explanation. You have a heavy current carrying device...like a starter....or maybe a light bar that is grounded to the vehicle body for the negative connection for that batch of off-road lights it is holding up. If the negative battery cable that goes to the block/chassis starts to go bad, the DC current flowing from one of these items...let's say the light bar), can find a ground through the body of the vehicle to the antenna mount and down the antenna coax and through the CB chassis/circuit board ground and through the CB negative power lead to the battery itself.
When that happens, you might very well have 30~50 amps of current flowing through the CB radio's chassis, trying to get to the negative terminal of the battery. If it were the starter motor that found its "other ground path" through here, you would have a couple hundred amps flowing.
The end result is that your CB chassis, with those tiny copper circuit board runs on it, can become a fusable link and burn open due to the excessive current flowing through the ground circuitry of your radio chassis. So...you burn out the guts of your radio.
By putting a fuse in the negative lead of your CB radio (or ANY other electronic device that is attached to the battery), it will blow open and stop the high current flow before it does any permanent damage. (just like the positive lead fuse will blow open if you shorted the hot lead to ground).
If you don't believe this, please feel free to stop by my house. If you volunteer your vehicle and radio, I shall be happy to do the "faulty ground wire" scenario on your vehicle. You can turn on the lights or crank over your engine and watch your CB radio smoke.
Every 12v HAM radio I've seen has fuses on each leg. They're too spendy to take the chance...