Electrical issue, caused by CB - advice please

Hi Guys, wondering if anyone can help with a bit of electrical advice.
I have a PC in my car, that runs from a car power supply that is linked to a switch on the dash that when on, tells the PSU to power up, and when off sends a shutdown command to the PC.
I had an issue with when using my CB, it turns off the PC, and at the weekend I rewired everything, and fitted a second battery with a T-Max split charger.
Everything works fine; apart from I am still getting the problem with the CB turning the PC off.
The CB is on its own wire, running from the new fusebox I fitted, to the auxiliary battery.
The switches on the dash that power things like my rear work light and the PC have LED’s in them, and I notice that when I use the CB, the LED’s in the switches glow very faintly. These switches are powered from a separate feed that runs the switches that then go back to the relays that power stuff.
Could something be happening where there is some sort of feedback running back up the wires when the CB is used? I can’t think of what could be causing this kind of issue, but I am sure someone with more experience may be able to help.
Was thinking about fitting diodes to the power feeds for the CB, but not sure if that would solve the problem.

Any help or advice would be great, or if you have any more questions about the setup, please ask.

Thanks guys!

Logically Rik the CB must be drawing power from the other feed circuits that drops the voltage below the level required to stop the other kit powering off.

The LEDs dimming in the switches would support this being the case.

As to why - now there you've got me.

Would suggest disconnecting the CB, running a dedicated live feed from battery positive - if it all works as it should that confirms a wiring feed issue somewhere.

Would be tempted to put CB on a totally dedicated circuit if the above 'test' works

Station House said:

Logically Rik the CB must be drawing power from the other feed circuits that drops the voltage below the level required to stop the other kit powering off.

The LEDs dimming in the switches would support this being the case.

As to why - now there you've got me.

Would suggest disconnecting the CB, running a dedicated live feed from battery positive - if it all works as it should that confirms a wiring feed issue somewhere.

Would be tempted to put CB on a totally dedicated circuit if the above 'test' works

Click to expand...

Thanks Station House

Thats the thing, the CB is on a totally dedicated circuit. Has its own fuse, in the fuse box, with a 17amp cable running to feed the CB alone.

The LED's dont dim, they come on very faintly, even though the switches that they are on are switched off. The LED's switches are fed from a separate feed with their own fuse and cable from the fuse box also.

With the switches off, the LED's shouldn't come on, so something must be feeding back somewhere.

I have had the CB direct to the battery without going through the fuse box, but I get the same problem. I just cant see how, I guess the CB is somehow putting power backwards, or something. I cant work it out, and my A-level in Electronics hasn't helped me figure it out...

I was thinking 2 diodes, one on the live to the CB, and one on the negative to make sure the flow of current is only going one way. The CB works fine, can talk to the locals. Its just a standard midland CB radio, 1 year old.

The PC is obviously quite sensitive to changes in power changes, but I wouldnt have expected the CB to cause such issues.

:doh::doh::doh:

RikWilson said:

Thanks Station House

Thats the thing, the CB is on a totally dedicated circuit. Has its own fuse, in the fuse box, with a 17amp cable running to feed the CB alone.

The LED's dont dim, they come on very faintly, even though the switches that they are on are switched off. The LED's switches are fed from a separate feed with their own fuse and cable from the fuse box also.

With the switches off, the LED's shouldn't come on, so something must be feeding back somewhere.

I have had the CB direct to the battery without going through the fuse box, but I get the same problem. I just cant see how, I guess the CB is somehow putting power backwards, or something. I cant work it out, and my A-level in Electronics hasn't helped me figure it out...

I was thinking 2 diodes, one on the live to the CB, and one on the negative to make sure the flow of current is only going one way. The CB works fine, can talk to the locals. Its just a standard midland CB radio, 1 year old.

The PC is obviously quite sensitive to changes in power changes, but I wouldnt have expected the CB to cause such issues.

:doh::doh::doh:

Click to expand...

If it's not a short the only thing I can think of is........

How close is the aerial ??

Bromsgrove Defender said:

If it's not a short the only thing I can think of is........

How close is the aerial ??

Click to expand...

How close to what?

Its on the roof in the middle, about 3 foot from the rear of the vehicle.

Could that make the LED's glow? The cable for the aerial does run behind the switches on the dash centre console thingie.

RikWilson said:

How close to what?

Its on the roof in the middle, about 3 foot from the rear of the vehicle.

Could that make the LED's glow? The cable for the aerial does run behind the switches on the dash centre console thingie.

Click to expand...

In theory, but not likely unless your running a burner

I think it's more likely a short somewhere that you have overlooked

Bad ground and/or short. Could be anywhere in your electrical circuit though.

Im not running a burner, so thats out.

What is strange is it did it before and after the rewire.

Before the CB was connected to the cigarette lighter feed, as where the switches.

When I rewired, I put everything on its own circuit, the CB goes directly from the new fuse box, negative is connected to a bus bar on the fuse box that goes through a 110amp cable direct to battery negative on the aux battery, and the live is connected to the fused bus bar that is also fed from a 110amp cable direct to aux battery live.

Compared to my 4 55watt spot lamps, I wouldnt have thought the CB would draw so much power. Do CB's feed back somehow?

RikWilson said:

What is strange is it did it before and after the rewire.

Click to expand...

Not strange at all. You need to look at all your wiring you have something shorting out.

Are you sure the aerial co-ax isn't shorting?

Sorry Rik - should have read some of your post more carefully

Anything change if you run a dedicated earth from CB to battery?

Weird one

Station House said:

Sorry Rik - should have read some of your post more carefully

Anything change if you run a dedicated earth from CB to battery?

Weird one

Click to expand...

There is a dedicated earth to the battery, before the rewire it didnt have a dedicated earth.

I have basically rewired all the accessories to a new fuse box.

The antenna isnt shorting, I have checked all the wire to rule that out.

Had a look on the net and apparantly there can be problems with CB's interfering.

Was thinking of somthing along the lines of this:
20 amp inline noise filter - Stops electrical interference/noise on auto power source fed to CB Radio, Power Amplifier, Ham Rigs, etc.

And some ferrite clamps to go over all the cables. Not sure if this will solve anything however.

Some of the radio ham's use capacitors and stuff, but not sure why.

think I've misunderstood - interpretded that the earth went to a bus bar which had other things attached to it as well.

Was wanting to completely isolate the CB from all other kit to prove or disprove any power feedback

Out of ideas - sorry Pal

Ferrite shields and in line capacitors can't do any harm, but no idea if would cure.

Worth checking no short from aerial coax to bodywork as well

Will keep an eye on this thread for when you find the solution!

If possible, fit a ferrite ring to the power feed for your PC, as you might be picking up spurrious RF signals from your CB, which may be causing your problems.

Failing that, it might be the screening on your CB coax which is leaking. In the olden days I had a problem between the CB and the wireless, and cured that by running the coax in galv trunking rather than on the surface. It worked then, but there again we were using AM CB's.

OSD

Oldseadog said:

If possible, fit a ferrite ring to the power feed for your PC, as you might be picking up spurrious RF signals from your CB, which may be causing your problems.

Failing that, it might be the screening on your CB coax which is leaking. In the olden days I had a problem between the CB and the wireless, and cured that by running the coax in galv trunking rather than on the surface. It worked then, but there again we were using AM CB's.

OSD

Click to expand...

Thanks. Will try that. Ill put ferrite rings everywhere if neccessary...

Will give it a try and see if that works, and report back.

Any ideas what would cause the LED's on the switches that are turned off, to glow dimly when the CB transmits.

RikWilson said:

Any ideas what would cause the LED's on the switches that are turned off, to glow dimly when the CB transmits.

Click to expand...

That could theoretically be signal radiation from the aerial coax cable - I think i read that it runs behind the switches

Station House said:

That could theoretically be signal radiation from the aerial coax cable - I think i read that it runs behind the switches

Click to expand...

See post 6

You beat me to it BD!

Thought I'd read somewhere it was possible

Bromsgrove Defender said:

See post 6

Click to expand...

Cheers guys. Will try the ferrite rings and report back. Could I put ferrite rings around the coax cable, or would that not have any effect, or a negative effect?

It wont be until after the LandyWatch Autumn Adventure.

Did I mention the LandyWatch Autumn Adventure - this weekend - Welcome to Landy Watch. Keeping an eye on your Land Rover

Don't put the coax round the rings, as RF travels in straight lines wherever possible and your SWR would go through the roof!!

However, if you had any ferrite rods taped to the straight sections of the coax, it might be an expensive way of finding out that it doesn't work!

OSD

Oldseadog said:

Don't put the coax round the rings, as RF travels in straight lines wherever possible and your SWR would go through the roof!!

However, if you had any ferrite rods taped to the straight sections of the coax, it might be an expensive way of finding out that it doesn't work!

OSD

Click to expand...

Ha, thanks...

I will put them on the power lines for the PC and try that. Hopefully that will solve my problems!