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using the car radio, - power consumption. Can it be powered from Leisure batteriy


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Iain Strachan's thread (https://www.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Sound-from-TV/33163/) raised the issue of using the car radio as a means of amplifying/ improving TV sound.


I've now bought a baby FM transmitter, which I feed from satellite receiver or computer and use the vehicle radio to listen.


But after a full evening (dusk st 1800 till midnight) off EHU the starter battery is well down (*see below), so I thought about feeding the radio from the leisure batteries.


My plan was to replace the permanent 12v live that feeds the radio (from the vehicle system) with one from the TV circuit on the schaudt electroblok.


Here's the snag: - The vehicle system has a common return via the vehicle chassis. The living area has a two wire system , so all circuits are separately earthed back to the electroblok. Using any circuit it appears that I'd need 2 wires + & - from the electroblok to the radio. But it's in contact with the chassis so there's a potential for harm or electrical noise there.


Just to complicate matters further, there's a switched live from the ignition to take into account. It would need the chassis earth to complete its loop.


This is a real techie headache. The starter & leisure batteries are never at the same potential and I don't even know if the earths are common.


Clearly I have to be very careful before proceeding, or it may not be possible... Has anyone overcome these obstacles? is a diode the solution?


(*) One for the mathematicians. If a car radio can deliver 4 x 40 watt channels, - is it really consuming 160 watts or more all the time, - or just when the volume's up high?

160 watts at 12 volts is 13.5 amps. After 5 hours that's >65Ah, - if it's really consuming that much, - no wonder my battery looks a bit sick.


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Car stereos use class B amplifiers which that only use a small quesant current when there is no input as the output level increases the current drawn increases, so it will only draw max power when running at max volume.


Wiring the power to the leisure battery is straight forward and is standard in many Motorhomes such as Hymer's. Easiest way is to run two wires + & - to the radio directly from the Elektroblock from an output that is permanently live, for the neg connection there is normally a screw terminal on the back of the stereo. For the memory back up connect to the live feed via a small say 1 amp fuse.

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So here is what I did with mine:


Ignore the Electroblock.


Disconnect the radio from both the switched power (Ignition) and the permanent cables.


Take a pair (Pos and neg) from the Leisure batteries via a fuse to an illuminated switch which I fitted on the dash.


Wire from the switch to both the Ignition and permanent side of the radio and a neg to the neg side of the radio. nb you will probably require a cable from the switch to ground so the light will work.


(note 1 - the permanent live is only a lightweight cable to keep the memory alive - note 2 there is often a second switched live from the lighting circuit so that the radio illuminates when the lights are turned on)


There should be no problem with the chassis neg as the EBL is wired to the neg side of the starter battery (chassis) as well.


Depending on the radio type there is an alternative to an FM transmitter. If the radio has bluetooth you can buy a bluetooth transmitter which plugs into the earphone out of your tv. http://www.ebay.co.uk/itm/251365260524?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 . The advantage is that you don't have to retune every time you move and find there is a local station broadcasting on the same frequency. It also is broadcasting to an antenna which is inside your 'van - some of the FM transmitters are not powerful enough to give a good signal to an external radio antenna.


The wattage quoted for amplifier power output has nothing to do with the consumption of the radio on 12 volt - your radio will consume about 5 amps depending on if it is running a CD player etc.


When the radio is not in use I turn the illuminated switch off - modern radios are like mini computers with bluetooth etc and can use a fair amount of power even when they are switched off so turning the illuminated switch off saves that power too.


Sorry Lenny - crossed post.

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The leisure battery negtive is connected to the chassis of the motorhome so you only really need to connect a fused feed from the leisure bttery to the permanent live feed to the radio INSTEAD of the original one from the starter battery. On pre X250 Fiat?Citroen/Peugeot vans you could also connect a manually switched feed into the ign switched (with a couple of diodes to prevent reverse feeding) so as to maintain the auto switch on/off with the ignition switch and also have the facility to switch it on/off when stationary. I've donethis on numerous motorhomes including several of my own.





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Agreed Dave. I should have asked Hughmer if he had a Fiat radio.


I actually ran a pair because I powered both the Radio and a 3 way plus USB socket mounted on the dash. That way both the radio and the sat nav were kept away from the Fiat wiring. I can plot the route on the sat nav without having the ignition on and when I start up the sat nav doesn't reload.


Rather than have the Fiat radio I have a cheapy from Aldi - Great piece of kit with bluetooth and audio in. I can play audio from the TV or laptop or tablet to the 4 speakers - tidy!


Recently treated myself to this http://www.bose.co.uk/GB/en/home-and-personal-audio/bluetooth-ipod-speakers/bluetooth-speakers/soundlink-mini-bluetooth-speaker/ - Now I can have great sounding music and with the bluetooth kit I mentioned above can have the tv sound close to us on a table rather than booming in the cabinets which in turn booms outside disturbing the local wildlife (caravanners) :-D

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Barrie i don't agree with ignoring the Elektroblock as using the Elektroblock makes the connections a lot easier, there is nearly always spare positions on the unit just need to crimp a couple of AMP pins on your cables and push them into the plug (only one if you use chassis earth). The output will also be fused.


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I have a Vanbitz batterymaster on mine, IF ! you have one fitted and havn't mentioned it you can cut the switched live at the back of the head unit and connect to the permanent live, any power usage is then topped up by the batterymaster! I realise you may not have a BM in which case ignore this, ! Dave
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