interference from fridge

[homer]

When our fridge is running it produces bad interference on the VHF (when transmitting) and on the laptop when listening to web radio etc. As advised by the fridge suppliers, I have checked out the power connection to the fridge and I did also try fitting a capacitor across the fridge motor but to no avail. Any further advice would be appreciated.

 

[Billjratt]

What kind of fridge?
The standard (danfoss) compressor is well known for interfering with HF radios (chirp chirp chirp) but not VHF. Check voltage at battery and compressor are exactly the same and fix the difference if there is one - especially the ground return circuit.
Also worth checking the wiring to the VHF itself and the braid on the coax to the aerial.

 

[bedouin]

You need to determine whether the interference is through the wiring or through the air. Does it interfere with battery operated devices or only those running from the boat batteries?

 

[Gwylan]

Lateral solution

When our fridge is running it produces bad interference on the VHF (when transmitting) and on the laptop when listening to web radio etc. As advised by the fridge suppliers, I have checked out the power connection to the fridge and I did also try fitting a capacitor across the fridge motor but to no avail. Any further advice would be appreciated.

We had a similar problem.

Some practical solutions, based on experience

Make sure the fridge is fed by a twisted pair of leads - this will reduce radiated interference. Bummer because you need to run 2 wires from the battery to the fridge.

Put a choke on the live [+ve] lead near the actual fridge - look on Maplins site.

Install a separate battery for the fridge. Not quite as daft as it sounds, you can also run the water pump and the Eber off it as well. Tends to put all the sources of interference on the lines on one battery. Charging this then gives you a whole new field of joy and enquiry.

Also check that it is not some other device giving you grief. We spent ages, and a small fortune, blaming the fridge before we worked out that it was the Yeoman plotter that was to blame for the VHF interference.

 

[lw395]

Good advice from Gwlyan,
Also add capacitors at the input to the VHF, try feeding it from a separate battery, with no connection to the ship, that will tell you if it's radiated or conducted interference.
You could also twist the VHF supplies with its earth, likewise any data connections to the VHF.
It is a black art to some extent though.

 

[William_H]

We had a similar problem.

Some practical solutions, based on experience


Put a choke on the live [+ve] lead near the actual fridge - look on Maplins site.

A choke can be made if you are a collector of old computer junk. Many devices have a lump in the connecting cable or inside the case. The lump often is a cylinder of ferrite. This is black ceramic looking material. The main cable is often looped through this a few times. Use the ferrite to loop your power cable to fridge and or VHF through. Best if only +ve is looped through or oe ferrite for each + and -..
You can also find transformers in switch mode power supplies for computer etc. The transformer will have multiple windings which can be removed to allow your heavy power cables to be wound around the ferrite to produce inductance which inhibits the passage of the high frequency interference. Or yopu can just buy the ferrite in all sorts of shapes and sizes from RS Maplins etc. good luck olewill

 

[homer]

Thanks for all advice. I can now report the outcome which may be of interest to anyone who has similar problems.
i convinced myself that the interference was by cable rather than radio by using a handheld near the fridge (no problem) and noticing that audio interefence on the laptop stopped when the power supply was unplugged.
I put chokes on the positive and negative leads near the fridge but that made no difference. In fact the chokes actually vibrated to the extent that they made an annoying noise! I then tried putting chokes on the VHF power leads - no better.
I then ran a temporary power supply to the VHF direct from the batteries - much better.
It seems that I need to run a new power supply to the fridge direct from the batteries but that would mean by-passing the main switchboard and I would need a new circuit breaker and should really put in a relay so that it could still be switched from the main switchboard. Since the necessary parts (not even thick enough cabling) seem to be available here (in the Red Sea for the "winter") that will have to wait. Meanwhile, I ran a new, twisted pair power supply for the VHF direct from the batteries (fused, of course) so that is now ok and I will put up with the interference on the laptop (when listening to web radio).