Video interference problem

[Old Techo]

I have noticed that the blower can interfere with the AM radio in the van so I expect it is producing some bad RF. I may try and attach a capacitor to the blower motor when I find the time. Not sure what size capacitor to use so any suggestions, I expect the capacitors would need to go on the motor brushes to earth.

JR,

A motor with a commutator will always produce RFI. There will be direct RFI from the sparks (like the first ever radio transmitter) but also from current pulses in the power wiring to the motor. With motor rotation when the brushes change segments on the commutator there will be a very short current spike running back to the power source. A bit like your brake controller current but at a very much higher frequency. So the entire wiring acts like a long antenna.

RFI suppression needs to be applied as close to the motor as possible. Fit say 1 uF ceramic capacitors directly from each brush to the motor frame. They need to be ceramic to cope with very high frequencies. The motor frame should then be connected to earth or chassis. If not effective enough you could add ferrite beads very close to the motor. Best if the 2 power wires can pass through a single bead as a pair.

[sacredcow]

Re "When I connected the 4 pin cable at the 12pin plug I added an extra earth on the same pin so I will disconnect that to start with and see what happens. May even disconnect the video cable earth (pin 2) at the 12 pin plug as it is only going to the van camera which already has an earth."

You say that the "van camera already has an earth". The only earth it should have should be directly from the monitor which I believe you have wired through pin 2 of the 12-pin trailer plug. Whatever the earth that the van camera has should be removed. The pin 2 earth should not be used/shared with anything else. I have a similar set-up using the 12-pin trailer plug to carry the video from the van camera but I have used the MMS monitor of the 200 Series.

Perhaps you could consider pressuring your caravan with a scupper vent.

Glenn

[J.REEVES]

Well today I had another go at trying to find my interference problem with the van camera/monitor.

The monitor operating normal looking at my back garage wall the monitor looks better in the flesh than the photo

Monitor OK.JPG

The monitor with the blower running

Monitor not OK.JPG

I decided to connect my spare camera to the van plug. Yesterday I connected the spare camera to the Tojo socket without any success.
Still the same until I disconnected the coax earth (pin 9) in the plug that runs to the van camera and bang no interference.

From OT’s comment about cables acting like antennas and Glenn’s comment about only one earth from camera to monitor I started to search to see if there was only one earth for this system. Buy the way I installed it myself ten years ago.

As nothing had changed on the caravan I had in my head that the van would not be the problem but I was wrong.

When I originally wired the video coax on the van plug I added a separate earth wire to the coax earth at the plug and run it with the coax from pin 9 just in case I needed another earth one day. Pin 3 on the 12pin plug had its normal earth for normal traffic lights and the Anderson plug had a big earth for things like the fridge and all these earths come together in an electrical cubical in the van. This spare earth is connected to the van earthing system and as I said connects to the coax earth at pin 9.

Once the spare earth was disconnected all my problems disappeared.

The interference will be still happening but it’s not interfering with anything now so all is good.

OT I have taken note of your comments on suppressing electric motors so if I ever have the blower motor out I will address its RF radiation problem.

Why did I not get this interference with my old system don’t know!

How I mounted the monitor in the 200 Series.
I made a SS strap with a slotted section one end for the monitor’s SS bracket to fit in and the strap is attached to the end of the dash with double sided tape so no holes drilled in the dash. The strap follows the line of the dash and is made long so to give the tape plenty of area to hold.

Monitor mount.JPG

JR

[Old Techo]

What Glenn wisely warned about with more than one earth on a shielded cable is a 'ground loop'.

The cable shield if earthed at both ends of an installation can carry current and in doing so generate a magnetic field that is inductively coupled to the wires inside that it is supposed to be protecting from external influences.

[Browny_r33]

JR
You are not running the cable next to or close to a computer, Body control module under the seat or in the kick panel or close to a CB, these will cause interference.

[J.REEVES]

Hi Norm,
You may have missed my comment in my last post as I have solved the problem but no the cable was mainly run in a conduit along the chassis rail. It does come within 6” of my CB.

JR