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I have a Coachman Mirage 350/2 1994

With EHU I get interferance to radio/dvd player plus freeview unit all working off 12 volt battery (buzzing + poor picture) when battary charger is switch on.If I switch it off all works fine.

Can anybody help? ADGE11

Thanks mked

with only the radio on and battary charger on I get the buzzing.

Turn the charger off the buzzing stops  Going to car spares shop to-morrow for suppressors

My first guess is the charger is out of control and pumping out over 15 volts! this certainly interferes with radio reception but is also wrecking your battery!!

Voltage reading should be no more than 13.8v, if you have a coloured volt meter in the van, then this should read 1/3 up the green.

If it's hard over to the right then it's 15v+

HI Gary

tested voltage output 13.6v 

battary output is 12.8v

Hi Pete

the charger is the one fitted as new with the van Coachman Mirage 350/2 1994. Power Management System (PMS 1 HS)

I find the same if we are abroad. I like to listen to radio 5 live on med wave but can't get it if the charger is switched on. Too much interference. Turn it off and reception is fine. We don't keep the charger permanently on. Just switch it on for an hour or so each day.

The PMS1, infact all PMS units, are very stable 'switch mode power supplies,' not simple 'transformers' as Pete described. 

So the source of the humming, given it's not over volting, might be the battery on it's way out and overloading it, in general they are silent

Switch the 'car/van' switch to the middle position, this disconnects the battery and leaves the charger to supply the van on it's own, see if the noise stops then?

Not sure other than that, could be a lot of things?

Thanks Charly008

Went to Maplin got one, but it did not work thay told me to fix it on the battary wires beteen battary and charger

Hi Gary

I did what you said,caravan switch in the middle it worked no buzzing etc.

This I will do next time we have EHU

May I say a LARGE thank you to all how helped with my problem