Fused Ground?

[Extreme]

New Kenwood mobile power harness has inline glass fuse holders (old school) on both positive and negative wires (red/black).  Gotta be something to do with RF?   But I'm not finding the answer in searches or in the Manual.  Please explain.

[marcspaz]

It's very common in expensive and/or high power Ham radio gear (100w+) to protect the vehicle.  Most radio manufacturers fuse the B+ side at the battery so if the B+ power lead gets shorted to ground, your vehicle doesn't burn down. Some also fuse the ground wire to prevent fires.

 

This is mostly a risk for vehicles with a separate frame and body.  In a vehicle, the body is typically the ground for most electronics in the vehicle. If the body has a poor ground or the chassis ground is broken all together and the radio ground lead gets shorted to the body somewhere, all of the electronics grounded to the body will then try to use that ground wire as the primary ground. 

 

Obviously the positive fuses for all the other circuits won't blow because the current on the B+ side is whats expected.  The ground wire is sized for the radio and not all of your onboard electronics.  So, to stop the negative lead from burning the car down, it gets fused at the battery side for the same reason as the positive lead.

[Extreme]

Thank you sir!   Interesting tidbit to stash away.

[coryb27]

If the vehicles (factory) ground strap from the battery to the engine block fails, the radio acts as the negative side for the whole vehicle. The radio might not like seeing all the current of the starter motor. I have seen equipment fail this way, the end result is the junk pile or needs repair table at the next ham fest....

 

Yea I'm am back from my forum break

[Extreme]

Welcome back Corey.  I filled everyone's time with endless questions, like this one.  

 

15a fuse in both ok?

[marcspaz]

If the vehicles (factory) ground strap from the battery to the engine block fails, the radio acts as the negative side for the whole vehicle. The radio might not like seeing all the current of the starter motor. I have seen equipment fail this way, the end result is the junk pile or needs repair table at the next ham fest....

 

Yea I'm am back from my forum break

 

 

Where you been man?  Haven't even seen you much on FB.  Hope all is well.

 

 

Welcome back Corey.  I filled everyone's time with endless questions, like this one.  

 

15a fuse in both ok?

 

 

Depends on the wire gauge.  What size it is?

[Extreme]

Looks like 12ga.

Looked it up and they say 18a max if for that gauge if I remember.

[Jones]

I'm of the school of professional installers (MECP) who never fuse the negative side of electronics in a modern negative-ground vehicle, but then I also NEVER hook anything directly to the battery of any vehicle made after 1995 or so.  That really old-school thought from the 60s and 70s needs to be re-educated.

 

If you think you absolutely MUST hook the radio "straight to the battery", then I guess you should fuse both leads.  If you want to do it right, the negative lead should be hooked directly to the body electronics common, or "Star" ground point of the vehicle, (the primary ground for body accessories, isolated from starter) and the positive should be hooked to the vehicle manufacturer's designated accessory power takeoff point with the proper sized fuse as close the the power takeoff point as possible.  (Power takeoff point is usually located within 2 feet of the battery, fed with a LARGE red wire, and is normally a plastic-capped block with a large bolt that has everything else hooked to it.)

 

If you install the accessories like the car manufacturer intends you to do, and you never hook anything straight to the battery, then you won't need to worry about the starter back-feeding through your antenna and blowing up your radio.

 

Hooking a radio straight to the battery in any modern car is foolish, and can cause noise pickup from the car's other electronics.

[Extreme]

Appreciate the enlightenment.  I'm installing a Kenwood TK-880 into my new Yamaha Wolverine (side-by-side) tomorrow.  Got it mounted tonight and will wire tomorrow, fish the antenna cable, etc.  I expect to have it up and running by Sunday latest.  Ford pickup is next for the same radio.

[marcspaz]

I'm of the school of professional installers (MECP) who never fuse the negative side of electronics in a modern negative-ground vehicle, but then I also NEVER hook anything directly to the battery of any vehicle made after 1995 or so.  That really old-school thought from the 60s and 70s needs to be re-educated.

 

If you think you absolutely MUST hook the radio "straight to the battery", then I guess you should fuse both leads.  If you want to do it right, the negative lead should be hooked directly to the body electronics common, or "Star" ground point of the vehicle, (the primary ground for body accessories, isolated from starter) and the positive should be hooked to the vehicle manufacturer's designated accessory power takeoff point with the proper sized fuse as close the the power takeoff point as possible.  (Power takeoff point is usually located within 2 feet of the battery, fed with a LARGE red wire, and is normally a plastic-capped block with a large bolt that has everything else hooked to it.)

 

If you install the accessories like the car manufacturer intends you to do, and you never hook anything straight to the battery, then you won't need to worry about the starter back-feeding through your antenna and blowing up your radio.

 

Hooking a radio straight to the battery in any modern car is foolish, and can cause noise pickup from the car's other electronics.

 

 

I go straight to the battery because I have an insane amount of voltage drop on transmit when I use the factory common ground and B+ bus bar.  Like... 14.6v in standby dropping to 12.4v (sometimes less) on transmit.  Going direct to the battery, even with my 200w amp, I never see more than a 0.3v drop.

[coryb27]

Where you been man?  Haven't even seen you much on FB.  Hope all is well.

 

 

 

 

Depends on the wire gauge.  What size it is?

 

Hey Spaz!

 

I been around just took a break to play radio, holiday, vacation. Time to get back in the swing of things, all is well!!

[Jones]

I go straight to the battery because I have an insane amount of voltage drop on transmit when I use the factory common ground and B+ bus bar.  Like... 14.6v in standby dropping to 12.4v (sometimes less) on transmit.  Going direct to the battery, even with my 200w amp, I never see more than a 0.3v drop.

The only few times I have had that kind of a voltage loss, the problem was solved by replacing, or in one case, upgrading the stock battery cables.

 

If you are grounding an amplifier system in the trunk of a vehicle, it is sometimes necessary to bond the rear ground bus to the front of vehicle ground bus with a copper strap or #8 wire.  Some cars are not as conductive as others - too much aluminum and plastic these days.

 

There have also been a few instances where I have had to run an additional ground strap from the body ground to the case of the alternator to get rid of "whine" because the factory engine block ground isn't low-impedance enough. ...again, particularly when there is a lot of aluminum and plastic involved on the engine.

 

I guess every install is different, but just hooking accessories straight to the battery, while solving some problems, will create other potential problems....corrosion being #1.

[Extreme]

A bit surprised when I installed the 880 in my Yamaha SxS today.  Last thing I did of course is put fuse in.  Connecting positive first as always.   Ground had not been connected yet.  Radio powered up as soon as I installed a fuse in the B+, red, hot. 

 

Is this an issue?  Floating ground?  Hmm..

[BoxCar]

Probably used the coax shield as its ground path. Shows the antenna has a good ground plane.

[Extreme]

Probably used the coax shield as its ground path. Shows the antenna has a good ground plane.

 

Wow.  Would never have thought of that.  Yes, I tried hard to get a decent ground plane, otherwise, why bother..

[Jones]

Yes, it grounded through the antenna, and/or the mounting bracket of the radio. (Kenwood 880s are not floating case. the metal case and bracket IS negative ground.)  That's another reason NOT to fuse the negative power lead of a mobile radio. If that negative fuse blows, you might not ever know until you burn up the shield on your coaxial cable by pulling 20 Amps of DC across it.  Also, I don't know where you learned the bit about "Connecting positive first as always" ...but that only applies to replacing the battery.  It is totally backwards with regard to hooking up accessories in a negative ground automotive situation.  After everything is mounted and grounded, then and only then should you hook up the positive "Hot" wire,, and install its fuse LAST.

[Extreme]

Got it.  More good stuff.  Thanks.

 

In effect, even if by mistake or dumb luck, the positive was hooked up last since the radio is grounded through the coax before installing the fuse.

 

Had I done it properly, the radio would not have powered up w/o ground connected to the battery, I would have thought nothing of it, I wouldn't have asked the simple question about negative fusing, or learned all I have in this thread.  I could have assumed that Kenwood knows what they're doing by having both sides fused, and by having instructions to wire to positive and negative battery terminals.. and with my luck could have burned down my brand new UTV or pickup.  That's why we ask questions..