Boat (car) radio switches off

[kingfisher]

I just installed a new radio/CD player in the boat. It's a dead standard car radio. However, once the volume goes over 40, the radio switches itself off.

2 remarks:
The radio is rated at 4 ohms, the speakers at 8 ohms. Speakers are connected to L- and R-front, with all the negatives (radio and speakers) going to a common -

The heat sink at the back of the radio gets quite hot.

 

[tobble]

sounds like maybe you haven't connected up all four speakers, if that is the case then the unused transistors will be dumping lots of heat, which is tripping some sort of thermal cut out. either connect up another pair of speakers, or wire the stereo out puts into series in two pairs, giving you two 8 Ohm outputs instead of four four ohm outputs.

 

[savageseadog]

You might find a bad connection in the 12 volt supply cables or inadequate cable size. Try connecting a meter as near to the radio as possible, turn u the volume. If it drops below 11.5volts or so the radio might be "protecting" the battery by shutting down.
Solution is better cables and a large capacitor up by the radio.

 

[kingfisher]

Radio was running with charger on the batteries, receiving 13.8V, so low voltage is not the case.

Indeed the rear speakers are not connected. I'll wire the 2 speakers to the F+R connectors. Makes sense.

So LF+(out) and LR+(out) go to L speaker+(in)
RF+(out) and RR+(out) go to R speaker +(in)
all negatives go to common -

 

[savageseadog]

Yes, but what is the voltage at the radio?

 

[Ruffles]

[ QUOTE ]
ISpeakers are connected to L- and R-front, with all the negatives (radio and speakers) going to a common -


[/ QUOTE ]
Car radios use bridge amplifiers. You cannot connect the -ve speaker wires to common cos you're shorting the amplifier!

To explain - a bridge amp has signal on the -ve output which is the inverse of the +ve output. This is done so that the radio can put 24v peak to peak across the speaker. i.e. it can deliver (24v/2) * sqrt(2) RMS.

 

[Guest]

I vote with Ruffles. Assuming it is a good amplifier design it is probably shutting down on thermal ground as the current limiters are in operation.

The only reason speakers have -ve and +ve is so that you connect stereo pairs in phase. If one is connected the opposite way around you get a terrible effect. That is why they are marked at all.

It has nothing to do with 0v or what we call -ve on batteries.

 

[Ruffles]

Says something for the design that it works at all.

Mind you they have to cope with being installed at Halfords ....

 

[kds]

"once the volume goes over 40, the radio switches itself off."

This has to be a major breakthrough ! Once you have found out how it is done - I want the circuit details. There are a lot of cars round here that I would love to fit it to !!!

/forums/images/graemlins/laugh.gif
Ken

 

[freebird1]

I have to say that I had the same problem with a car cd player that I fitted on my boat. I contribute this to voltage drop - most car radios are fitted out to prevent the battery from being run flat.
I felt that the power cable i used was too small (it was the feed to a chart table light) so i put a much larger diameter cable in instead. Result - radio does not cut out any more. I think in my case, this was the problem - If i turned anything else on - the radio cut out.

 

[William_H]

I vote with Ruffles and Solar neil the negative speaker leads should not be connected to -ve power or earth
It is highly unlkikely the ampliffier will be troubled by no connection to the rear speaker outputs. Modern amps are happy with no load.
olewill

 

[kingfisher]

And the winner is.... Ruffles.

I went down to the boat today and rewired the radio. The negatives are now no longer combined, the -out from the radio speaker now goes to the relevant -In from the speaker. It goes at full blast now, without stop.

Is there no problem this forum cannot solve?