liamo
Active Member
I have a radio hum when I turn on the shore power or the genset. Anyone got ideas as to how to overcome this? Thanks
Radio Hum on shore power
- Thread starter liamo
- Start date
Beadle
Well-Known Member
Are the batteries on charge when on mains and generator?
Sans Bateau
Well-Known Member
Check the route of the aerial lead, I suspect it may be close to AC power cables or a battery charger.
pau1gray
Well-Known Member
Teach your radio the words and it won't have to hum any more.
(apologies I could not resist)
(apologies I could not resist)
liamo
Active Member
Batteries are on charge when genset or shore power is on. The antenna cable does not run close to any AC cabling of the battery charger/inverter (Freedom Combi 20)
lenseman
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- South East Coast - United Kingdom
Is the 'radio' your marine transciever or a broadcast radio?
If it is a broadcast radio, are you listening to FM (VHF) or as I suspect the MW or LW (Radio 4 - Shipping Forecast)?
If, when connected to shore power, you start to 'close down' the electrical demand on your boat, does the 'hum' lessen or disappear?
When you state 'hum' can you be referring to a staccato type of pulsing?
If you can move the radio around in the cabin, does the effect of the hum increase or decrease and if, when listening to MW or LW, you rotate the radio on its base, can you 'null' out the hum or weaken it down to a more manageable level?
Have you got an isolating transformer or do you have access to one to see if this will eliminate the problem?
Hum, whether mains borne or otherwise can be a devil of a problem to eliminate. Ferrite rings on both sides (Live and Neutral) of the shore power might help?
The interference you are suffering might be induced into your boat due to the fact that adding the shore power lead to your boat it is acting as an extension aerial and 'carrying' an external interference from something as mundane as a fly-killer in a nearby premises, High Frequency welding plant, burglar alarm systems, overhead electricity pylons, PWM battery chargers, arc welder etc???
Finally, is the type of interference generating the same noise (hum) whether it is shore power or genset or are they different (very important question). I suspect they are different?
Questions, questions . . . . ? /forums/images/graemlins/frown.gif
If it is a broadcast radio, are you listening to FM (VHF) or as I suspect the MW or LW (Radio 4 - Shipping Forecast)?
If, when connected to shore power, you start to 'close down' the electrical demand on your boat, does the 'hum' lessen or disappear?
When you state 'hum' can you be referring to a staccato type of pulsing?
If you can move the radio around in the cabin, does the effect of the hum increase or decrease and if, when listening to MW or LW, you rotate the radio on its base, can you 'null' out the hum or weaken it down to a more manageable level?
Have you got an isolating transformer or do you have access to one to see if this will eliminate the problem?
Hum, whether mains borne or otherwise can be a devil of a problem to eliminate. Ferrite rings on both sides (Live and Neutral) of the shore power might help?
The interference you are suffering might be induced into your boat due to the fact that adding the shore power lead to your boat it is acting as an extension aerial and 'carrying' an external interference from something as mundane as a fly-killer in a nearby premises, High Frequency welding plant, burglar alarm systems, overhead electricity pylons, PWM battery chargers, arc welder etc???
Finally, is the type of interference generating the same noise (hum) whether it is shore power or genset or are they different (very important question). I suspect they are different?
Questions, questions . . . . ? /forums/images/graemlins/frown.gif
Leighb
Well-Known Member
Interestingly I have a similar problem with a small portable radio I use to listen to Shipping Forecast.
On LW there is a lot of noise and no audible signal.
On VHF it is fine.
If I switch off the shore-power charger - but NOT the socket connection - the noise goes. So it seems to be the charger not just the connection to shore-power that causes the interference.
On LW there is a lot of noise and no audible signal.
On VHF it is fine.
If I switch off the shore-power charger - but NOT the socket connection - the noise goes. So it seems to be the charger not just the connection to shore-power that causes the interference.
PeterGibbs
Well-Known Member
I too find there is interference to my portable radio on LW frequencies when the 240 v cable is ashore. This interference varies from port to port both in strength and the nature of the interference. Other frequencies are not affected.
My VHF fixed radio hums when the frig is on.
Moral - there's a lot of interference between systems on a boat. I have learned to live with this.
PWG
My VHF fixed radio hums when the frig is on.
Moral - there's a lot of interference between systems on a boat. I have learned to live with this.
PWG
rogerdog
Well-Known Member
The "batteries on charge" question is important as it sounds to me like an AC ripple being placed on your dc supply rather then other interference modes. To confirm this - try switching off the battery charger- if it goes a few possible fixes
1 Replace battery charger with another one (particularly if you have a simple "garage style" charger - these are the worst)
2 add a small capacitor across the power terminals of the radio and observe the effect - try about 5-10 microfarads - for starters (value not critical).
both easy ideas - worth a go?
1 Replace battery charger with another one (particularly if you have a simple "garage style" charger - these are the worst)
2 add a small capacitor across the power terminals of the radio and observe the effect - try about 5-10 microfarads - for starters (value not critical).
both easy ideas - worth a go?
wotayottie
Well-Known Member
The most likely cause of the 50cycle hum is pick up through the 12v feed. You can minimise this by putting ferrites on the 12v wires into the radio. They are these http://www.maplin.co.uk/Search.aspx?criteria=ferrites&source=15&SD=Y
Normally, the batteries seem to help smooth out any remaining mains hum so I wonder if you have 12v and mains cables running close together. The other issue is whether you are using other kit like fluorescents whilst on mains power ie it might not be the genny or battery charger that are the problem but some other mains equipment.
Normally, the batteries seem to help smooth out any remaining mains hum so I wonder if you have 12v and mains cables running close together. The other issue is whether you are using other kit like fluorescents whilst on mains power ie it might not be the genny or battery charger that are the problem but some other mains equipment.
Billjratt
Well-Known Member
If the charger is working hard to pull the battery voltage up, it will have more AC ripple on it. As it goes into float, it will be less, but still there. Fitting a choke and big electrolytic capacitor in the radio feed may help. Also if there's RF interference (noise other than 50cps hum), a 0.01 Uf across the 12v feed may filter it. Shops sell proper RF filters to stop interference if you're flush.
Beadle
Well-Known Member
I concur.
I would only add that a choke in the power lead may help in conjunction with the capacitor. Even go as far as a "pi" network with a choke in series with the power line and 10 microF from +ve to -ve at each side of the choke.
I think ferrites are unlikely to help much at such a low frequency as 50Hz.
It would be a really good idea to try a different charger as it may be that the output from this is the problem.
Hope this helps
I would only add that a choke in the power lead may help in conjunction with the capacitor. Even go as far as a "pi" network with a choke in series with the power line and 10 microF from +ve to -ve at each side of the choke.
I think ferrites are unlikely to help much at such a low frequency as 50Hz.
It would be a really good idea to try a different charger as it may be that the output from this is the problem.
Hope this helps
liamo
Active Member
Thank you for all the advice. I really appreciate it. It is my VHF radio and not a broadcast radio that I have. The noise is similar whether it is the genset or shore power that is turned on. I have tried the VHF with all other 240V off apart from the combi inverter/battery charger. When the batteries are being charged by the engine alternator and the 240V is off, there is no hum. I will try the small capacitor as you advise Rogerdog and I will also put a ferrite on the 12V wire as you suggest Wotayottie. The shotgun approach may work. I will try anything.
Thank you for your time.
Liamo
Thank you for your time.
Liamo
William_H
Well-Known Member
Liamo it sounds like the interference is coming via the 12v supply in that the supply is rising and falling in voltage at the rate of 50 times per second. A large value capacitor I would suggest several thousand microfarrad electrolytic rated at least at 25 volts be connected from the radio +ve input to the radio negative input. However I would suggest fitting a diode rather than choke between the +ve supply and the radio. There will be a positive and a negative lead of the capacitor. so get it right.
The diode needs to be rated at least 15 amps the voltage rating is not significant. Again there is correct way to fit the diode. It will have symbol on it like an arrow into a bar. The tail of the arrow goes to +ve supply the bar goes to the radio. I assume it is a transmitter as well as reciver hence the high current rating of the diode.
If you have a large value capacitor and a diode you will find that on turning the batteries off the radio will continue to operate for some seconds. This is because the capacitor acts like a battery to supply the radio until it is discharged. The diode is like a one way valve that stops the capacitor's charge going to power the rest of the ship.
So the combination means the capacitor charges to the highest peak of the 12v hum via the diode but this peak is only discharged via the radio and does not fall with the 12v supply on vthe trough of the hum cycle. The voltage will remain high in the capacitor until the next peak. A capacitor without the diode (a choke of sufficient inductance will do the same thing) will be discharged immediately on each hum trough back into the rest of the ships electrics. Only the inductance and resistance of the wiring between the capacitor and the rest of the ship can limit this discharge.
The diode will lose .7 volt of supply to the radio which should make little difference.
The diode and capacitor can be bought from any electronics store or TV repair man. quite cheap.
If you want to use an inductance it needs to be an iron cored many turns of at least 1 Henry and rated for the transmitter current. A ferrite ring will not help much.
This arrangement of diode and capacitor is also good for supplying a GPS to ensure it does not power down when starting engines which causes (12V) voltage to fall. good luck olewill
The diode needs to be rated at least 15 amps the voltage rating is not significant. Again there is correct way to fit the diode. It will have symbol on it like an arrow into a bar. The tail of the arrow goes to +ve supply the bar goes to the radio. I assume it is a transmitter as well as reciver hence the high current rating of the diode.
If you have a large value capacitor and a diode you will find that on turning the batteries off the radio will continue to operate for some seconds. This is because the capacitor acts like a battery to supply the radio until it is discharged. The diode is like a one way valve that stops the capacitor's charge going to power the rest of the ship.
So the combination means the capacitor charges to the highest peak of the 12v hum via the diode but this peak is only discharged via the radio and does not fall with the 12v supply on vthe trough of the hum cycle. The voltage will remain high in the capacitor until the next peak. A capacitor without the diode (a choke of sufficient inductance will do the same thing) will be discharged immediately on each hum trough back into the rest of the ships electrics. Only the inductance and resistance of the wiring between the capacitor and the rest of the ship can limit this discharge.
The diode will lose .7 volt of supply to the radio which should make little difference.
The diode and capacitor can be bought from any electronics store or TV repair man. quite cheap.
If you want to use an inductance it needs to be an iron cored many turns of at least 1 Henry and rated for the transmitter current. A ferrite ring will not help much.
This arrangement of diode and capacitor is also good for supplying a GPS to ensure it does not power down when starting engines which causes (12V) voltage to fall. good luck olewill
lenseman
Well-Known Member
- Joined
- 3 Jun 2006
- Messages
- 7,077
- Location
- South East Coast - United Kingdom
Before you try the 'shotgun approach', when the hum is apparent, try just disconnecting your antenna from the radio and you will then be able to tell if the 'hum' is being introduced into your transceiver via the antenna socket or up the DC supply leads.
It would be very doubtful that the hum is getting into your set via the case so if you eliminate one means by which it might be entering, you are half way to getting a result.
<span style="color:red"> DO NOT transmit whilst antenna is disconnected as you might do damage to the output stage of the transmitter!! </span>
It would be very doubtful that the hum is getting into your set via the case so if you eliminate one means by which it might be entering, you are half way to getting a result.
<span style="color:red"> DO NOT transmit whilst antenna is disconnected as you might do damage to the output stage of the transmitter!! </span>
