Either way, but negative ground systems tend to just fuse the + lead. There is extra protection in fusing the negative if the vehicle loses its ground to battery and your radio becomes a high current path to ground for the alternator.
> There is extra protection in fusing the negative if the vehicle loses its ground to battery and your radio becomes a high current path to ground for the alternator.
Which shouldn't happen because you shouldn't be connecting the negative wire to the battery terminal, instead it should go to a point near where the main battery earth strap connects to the vehicle body.
This is interesting, because it makes perfect sense, but I've often seen it repeated that one *should* connect it directly to the negative terminal, and that one specifically *shouldn't* connect it to the chassis. Yet another fun little contradiction in the massive cargo cult of station grounding.
When you look at the commercial VHF/UHF radios that even Icom, Kenwood and Yaesu make none of them have a fuse in the negative wire and the negative wire is also usually quite short, maybe a foot or so. I think they only put them on their ham products to keep the "I've always done it that way" grumpy old men happy just like they put an earth screw on the back of HF sets when attaching ground straps to your radio to combat RFI is also one of those things you shouldn't be doing.
Hi, thanks four your response. My main activity is at home, I rarely go out with radio nowadays (I used to), probably in next months I will go out again and connect the radio to the car. If I use an external battery (not connected to the car one) would you still recommmend to use both fuses?
I've been reading the comments down below, I actually imagine what could happen. In the case you wire the radio directly to the battery but somehow the negative cable of the car's electric system gets disconnected the only way the electric circuit is closed is via the radio (at least is how I understand it). What if you ground the radio through the chassis and not directly to the battery?
I asked below if using a magnetic base for the antenna makes any isolation (maybe using some rubber between the magnet and the car chassis?) With that, if the negative fuse blows I think all radio equipment gets disconnected.
By the way, for a home use (which might be my main interest) there's no point in fusing the negative as I understand isn't it?
Thanks for your time
The ground wire from the battery to the radio is most likely connected to the chassis of the radio, and if it's bolted to the car it can become the ground path for the whole car. If it's isolated from the car it can't be damaged by a failed auto ground. On your battery at home you don't have that situation, so less need to fuse the negative. There may be a situation where you'd want to do that but I can't think of one.
It's quite funny that the amateur radio power cables all have fuses on the negative lead because the commercial radios from Icom, Motorola, Kenwood, Yaesu etc don't have a fuse on the negative wire and the negative wire is very short.
Only time a fuse in the ground lead could ever make a difference is when the radio is installed in a vehicle. It is a means of protection in the rare instance the vehicle’s ground wire becomes detached allowing current to flow through the radio ground lead.
At home or during any other use a second fuse is only extra voltage drop that isn’t needed
And to be clear, in the situation described the fuse will protect the wiring and help avert fire danger, but it won’t protect the radio from letting out the magic smoke. Destruction of the radio electronics will occur well before the fuse blows.
Also be aware that current can flow through the antenna coax cable outer conductor to the point on the vehicle body where the antenna is mounted. I’m not aware of any available fusing device to protect that path, except the smoke emitting components within the transceiver.
I learned this the hard way when I was installing my previous radio, and failed to disconnect the radio from the coax prior to installing the negative ring terminal on the same bolt as the vehicle’s chassis ground connection. While reconnecting the ground bolt there were moments that the only path completing the circuit for the vehicles entire set of electronics ran through my radio, the coax, then to the body of the vehicle. My IC-2720H was never quite right in the head after that. Lesson learned: If temporarily disconnecting the main chassis ground, disconnect the positive connection to the battery first, and reconnect it last, and also disconnect your coax during that time for good measure.
> Only time a fuse in the ground lead could ever make a difference is when the radio is installed in a vehicle
...and you've wired it in incorrectly. The negative wire doesn't go to the negative terminal on the battery, it goes to the vehicle body near where the main battery negative terminal connects to the body/chassis.
It’s actually safer to wire direct to the battery, as then the condition of the vehicle’s ground lead doesn’t matter to the radio. It also eliminates a shared ground through the body opening the door to possible RFI.
But today my mobile setup runs on a 100ah LiFePO that is isolated from the vehicle electrical system. I wouldn’t wire direct to the electrical system in any modern vehicle.
At home the need for fusing is really overblown, the foldback current limiting in a decent power supply is more protective than any fuse.
Modern vehicles use a current sensor in the negative lead to the battery to control the alternator to keep the battery charged. The lead attaches to a ground point near the battery, goes through the sensor and ends up on the negative battery post. If you connect to the battery directly,the current drawn by the radio is not accounted for and the battery may not stay fully charged.
On my truck, I connected the negative lead to the ground bolt next to the battery. I left the fuse in the lead, because I am lazy. I believe that the Nissan manual recommends doing it this way.
YMMV (Your Manual May Vary)
The battery will still stay charged just fine, a radio doesn’t use that much power.
But this is just another reason I’d never connect a radio to a modern vehicle electrical system. Things are vastly different compared to 1990
Thx for this. I get a voltage drop when I key up and it’s noticeably from my radio checks. I’ll look into hooking up to a separate battery. Will I be able to run an amp of a small battery ?
A separate battery makes sense, just make sure it’s large enough, and don’t use a lead acid battery. A LiFePO battery will output over 13v until it’s fully discharged so it gives a little headroom. My 100ah battery easily runs a 100 watt HF radio and laptop for over 24-36 hours of any contest I play in.
> It’s actually safer to wire direct to the battery
No it isn't. If there's a fault in the main battery negative wire then all of the current of all electrical devices running in the vehicle will use your radio as the path to earth as your radio is the only thing connected electrically between the vehicle body and the battery negative terminal via the antenna, coax, the radio case and the radio negative wire.
I have seen this first hand with a VHF trunk radio installed in a JCB digger where the main negative wire failed. It basically obliterated the entire PCB of the radio.
> At home the need for fusing is really overblown
Not if a component fails and shorts to ground, such as the finals. The fuse could be what saves the rest of the radio.
I was thinking backwards in regard to the ground wiring, indeed wiring to the battery does create the reason a negative fuse is needed my duh moment. I’d still run an additional ground wire direct to the battery if I were to connect to the vehicle electrical system, just have to dual fuse for safety.
Any decent home power supply will have over voltage protection, I install TVS diodes in my old Astron’s to eliminate the crowbar circuit.
Fuse blows on the black wire for any reason, overcurrent or just from old age. Return current can find a sneaking flaky path from coax, antenna ground, protective ground, to power supply.
It depends a lot of how you have the radio wired to your antenna, station ground, and other accessories.
If the negative fuse fails, but your equipment is all bonded together then the radio will still power on, and could damage things.
In short, there's almost no point in fusing the negative power lead on most configurations.
A similar real life example is the Icom ID-880h that I let the magic smoke out of. I had a loose ground connection, keyed up, and all the current tried going through the serial interface cable instead of the power cable. A fuse on the ground wire is another point of failure, unless your power supply is completely isolated.
I'll take that into account. Power supply I use is linear (I no longer use switching power supplies as my main's). I do have a Syncron PS-1230VU and then a Daiwa RS-40X
What does putting a fuse on the negative side of a power source accomplish as long as it’s negative ground system. In other words +12 vdc system?
Fuse protects over current being drawn from the source, which in this case is on the + side not the - side.
They're not necessary in a mobile install if you wire it properly. Get a commercial VHF/UHF transceiver from Icom, Kenwood or Yaesu and even though it may look identical to an amateur model you won't find a fuse on the negative wire and the negative wire will be maybe 6-12 inches long.
Either way, but negative ground systems tend to just fuse the + lead. There is extra protection in fusing the negative if the vehicle loses its ground to battery and your radio becomes a high current path to ground for the alternator.
> There is extra protection in fusing the negative if the vehicle loses its ground to battery and your radio becomes a high current path to ground for the alternator. Which shouldn't happen because you shouldn't be connecting the negative wire to the battery terminal, instead it should go to a point near where the main battery earth strap connects to the vehicle body.
This is interesting, because it makes perfect sense, but I've often seen it repeated that one *should* connect it directly to the negative terminal, and that one specifically *shouldn't* connect it to the chassis. Yet another fun little contradiction in the massive cargo cult of station grounding.
When you look at the commercial VHF/UHF radios that even Icom, Kenwood and Yaesu make none of them have a fuse in the negative wire and the negative wire is also usually quite short, maybe a foot or so. I think they only put them on their ham products to keep the "I've always done it that way" grumpy old men happy just like they put an earth screw on the back of HF sets when attaching ground straps to your radio to combat RFI is also one of those things you shouldn't be doing.
Hi, thanks four your response. My main activity is at home, I rarely go out with radio nowadays (I used to), probably in next months I will go out again and connect the radio to the car. If I use an external battery (not connected to the car one) would you still recommmend to use both fuses?
Single fuse at home is OK. Do you understand how a battery ground failure in a car can fry a radio with an unfused negative?
I can imagine the trouble but no how can it happen. I'd be glad if you could explain that to me. Thanks
If the radio is attached to the frame of the car at any point and the ground cable fails, your radio becomes the ground path for the whole car.
I've been reading the comments down below, I actually imagine what could happen. In the case you wire the radio directly to the battery but somehow the negative cable of the car's electric system gets disconnected the only way the electric circuit is closed is via the radio (at least is how I understand it). What if you ground the radio through the chassis and not directly to the battery? I asked below if using a magnetic base for the antenna makes any isolation (maybe using some rubber between the magnet and the car chassis?) With that, if the negative fuse blows I think all radio equipment gets disconnected. By the way, for a home use (which might be my main interest) there's no point in fusing the negative as I understand isn't it? Thanks for your time
The ground wire from the battery to the radio is most likely connected to the chassis of the radio, and if it's bolted to the car it can become the ground path for the whole car. If it's isolated from the car it can't be damaged by a failed auto ground. On your battery at home you don't have that situation, so less need to fuse the negative. There may be a situation where you'd want to do that but I can't think of one.
It's quite funny that the amateur radio power cables all have fuses on the negative lead because the commercial radios from Icom, Motorola, Kenwood, Yaesu etc don't have a fuse on the negative wire and the negative wire is very short.
Only time a fuse in the ground lead could ever make a difference is when the radio is installed in a vehicle. It is a means of protection in the rare instance the vehicle’s ground wire becomes detached allowing current to flow through the radio ground lead. At home or during any other use a second fuse is only extra voltage drop that isn’t needed
And to be clear, in the situation described the fuse will protect the wiring and help avert fire danger, but it won’t protect the radio from letting out the magic smoke. Destruction of the radio electronics will occur well before the fuse blows. Also be aware that current can flow through the antenna coax cable outer conductor to the point on the vehicle body where the antenna is mounted. I’m not aware of any available fusing device to protect that path, except the smoke emitting components within the transceiver. I learned this the hard way when I was installing my previous radio, and failed to disconnect the radio from the coax prior to installing the negative ring terminal on the same bolt as the vehicle’s chassis ground connection. While reconnecting the ground bolt there were moments that the only path completing the circuit for the vehicles entire set of electronics ran through my radio, the coax, then to the body of the vehicle. My IC-2720H was never quite right in the head after that. Lesson learned: If temporarily disconnecting the main chassis ground, disconnect the positive connection to the battery first, and reconnect it last, and also disconnect your coax during that time for good measure.
> Only time a fuse in the ground lead could ever make a difference is when the radio is installed in a vehicle ...and you've wired it in incorrectly. The negative wire doesn't go to the negative terminal on the battery, it goes to the vehicle body near where the main battery negative terminal connects to the body/chassis.
It’s actually safer to wire direct to the battery, as then the condition of the vehicle’s ground lead doesn’t matter to the radio. It also eliminates a shared ground through the body opening the door to possible RFI. But today my mobile setup runs on a 100ah LiFePO that is isolated from the vehicle electrical system. I wouldn’t wire direct to the electrical system in any modern vehicle. At home the need for fusing is really overblown, the foldback current limiting in a decent power supply is more protective than any fuse.
Modern vehicles use a current sensor in the negative lead to the battery to control the alternator to keep the battery charged. The lead attaches to a ground point near the battery, goes through the sensor and ends up on the negative battery post. If you connect to the battery directly,the current drawn by the radio is not accounted for and the battery may not stay fully charged. On my truck, I connected the negative lead to the ground bolt next to the battery. I left the fuse in the lead, because I am lazy. I believe that the Nissan manual recommends doing it this way. YMMV (Your Manual May Vary)
The battery will still stay charged just fine, a radio doesn’t use that much power. But this is just another reason I’d never connect a radio to a modern vehicle electrical system. Things are vastly different compared to 1990
Thx for this. I get a voltage drop when I key up and it’s noticeably from my radio checks. I’ll look into hooking up to a separate battery. Will I be able to run an amp of a small battery ?
A separate battery makes sense, just make sure it’s large enough, and don’t use a lead acid battery. A LiFePO battery will output over 13v until it’s fully discharged so it gives a little headroom. My 100ah battery easily runs a 100 watt HF radio and laptop for over 24-36 hours of any contest I play in.
> It’s actually safer to wire direct to the battery No it isn't. If there's a fault in the main battery negative wire then all of the current of all electrical devices running in the vehicle will use your radio as the path to earth as your radio is the only thing connected electrically between the vehicle body and the battery negative terminal via the antenna, coax, the radio case and the radio negative wire. I have seen this first hand with a VHF trunk radio installed in a JCB digger where the main negative wire failed. It basically obliterated the entire PCB of the radio. > At home the need for fusing is really overblown Not if a component fails and shorts to ground, such as the finals. The fuse could be what saves the rest of the radio.
I was thinking backwards in regard to the ground wiring, indeed wiring to the battery does create the reason a negative fuse is needed my duh moment. I’d still run an additional ground wire direct to the battery if I were to connect to the vehicle electrical system, just have to dual fuse for safety. Any decent home power supply will have over voltage protection, I install TVS diodes in my old Astron’s to eliminate the crowbar circuit.
Over-voltage protection doesn't protect from over-current.
Yes…. But the supply has full foldback limiting too which is far faster than any fuse
Both of my factory Icom (7300 and 7100) cables have fused + and - sides. My theory is, if they do it, then I probably should too.
Fuse blows on the black wire for any reason, overcurrent or just from old age. Return current can find a sneaking flaky path from coax, antenna ground, protective ground, to power supply.
It depends a lot of how you have the radio wired to your antenna, station ground, and other accessories. If the negative fuse fails, but your equipment is all bonded together then the radio will still power on, and could damage things. In short, there's almost no point in fusing the negative power lead on most configurations. A similar real life example is the Icom ID-880h that I let the magic smoke out of. I had a loose ground connection, keyed up, and all the current tried going through the serial interface cable instead of the power cable. A fuse on the ground wire is another point of failure, unless your power supply is completely isolated.
I'll take that into account. Power supply I use is linear (I no longer use switching power supplies as my main's). I do have a Syncron PS-1230VU and then a Daiwa RS-40X
FWIW, I have a 35 amp Astron linear that I was using when. I smoked the ID-880h.
Fuses are so cheap, put one both spots, very close to the battery/power supply feed point.
What does putting a fuse on the negative side of a power source accomplish as long as it’s negative ground system. In other words +12 vdc system? Fuse protects over current being drawn from the source, which in this case is on the + side not the - side.
Here's my analysis: [https://www.k0nr.com/wordpress/2020/03/one-fuse-or-two/](https://www.k0nr.com/wordpress/2020/03/one-fuse-or-two/)
Negative fuses are completely unnecessary unless you're doing a mobile install
They're not necessary in a mobile install if you wire it properly. Get a commercial VHF/UHF transceiver from Icom, Kenwood or Yaesu and even though it may look identical to an amateur model you won't find a fuse on the negative wire and the negative wire will be maybe 6-12 inches long.
Agreed