# 12v not enough?

#### lastone

Joined Oct 29, 2019
10
I have a deep cycle battery in my camper.

Powering my TV from it. is no problem however there is no sound.

When I switch on the engine the oscillator churns more voltage into the battery and then the TV speakers work.

After turning off the ignition there is sound for a short amount of time until the voltage drops back down.

Why then does the TV function completely fine but for the sound?

#### crutschow

Joined Mar 14, 2008
24,709
What TV?
Is the TV designed to operate from 12Vdc?

Can you measure the voltage of the battery when the TV quits?

#### lastone

Joined Oct 29, 2019
10
It's a Voxson and originally had a transformer to be used on 240v input but yes it is a 12v TV. I have attached an image for further info.

You mean the voltage when the sound goes? Because the picture and operational function of TV is completely fine just the lack of power to the sound.

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#### lastone

Joined Oct 29, 2019
10
The sound starts to lessen around 12.46v

#### crutschow

Joined Mar 14, 2008
24,709
The sound starts to lessen around 12.46v
Yes, I meant when the sound quits.

12.46V is a normal voltage for a 12V lead-acid battery, so the problem apparently is that the TV was not designed to operate on a 12V battery.

How much current does it take?
Measure the battery voltage and compare to the voltage at the TV when it is operating.
You might may able to gain a few tenths of a volt by using larger wires directly to the battery (with appropriate fuse in series, of course).

Otherwise you could use a buck-boost switching converter to output 13V or so, independent of the battery voltage.
Again, need to know the current the TV requires.

#### Papabravo

Joined Feb 24, 2006
13,459
Yes, I meant when the sound quits.

12.46V is a normal voltage for a 12V lead-acid battery, so the problem apparently is that the TV was not designed to operate on a 12V battery.

How much current does it take?
Measure the battery voltage and compare to the voltage at the TV when it is operating.
You might may able to gain a few tenths of a volt by using larger wires directly to the battery (with appropriate fuse in series, of course).

Otherwise you could use a buck-boost switching converter to output 13V or so, independent of the battery voltage.
Again, need to know the current the TV requires.
The label on the TV says 6A. Hard to know if that is average or peak demand

#### lastone

Joined Oct 29, 2019
10
Can you explain to me how everything works bar the sound. Surely it would be possible to fix this?

#### crutschow

Joined Mar 14, 2008
24,709
Can you explain to me how everything works bar the sound.
The sound circuitry apparently is designed to stop operating at a higher voltage than the video circuits.
No particular reason, just sloppy design limits.
Surely it would be possible to fix this?
Possibly, if you have a schematic of the audio section.
Otherwise, not likely.

#### lastone

Joined Oct 29, 2019
10
Otherwise you could use a buck-boost switching converter to output 13V or so
Could you point me in the direction of a suitable one please?

#### AlbertHall

Joined Jun 4, 2014
9,622
It might simply be that the TV has a fault which shuts off the sound at lower supply voltages.

#### LesJones

Joined Jan 8, 2017
2,598
Where are you measuring the voltage ? At the battery or directly at the power connector to the TV when it is switched on ? I am thinking that the problem could be voltage drop between the point where you take the voltage reading and the 12 volt input connector to the TV.

Les.

#### lastone

Joined Oct 29, 2019
10
Where are you measuring the voltage ? At the battery or directly at the power connector to the TV when it is switched on ? I am thinking that the problem could be voltage drop between the point where you take the voltage reading and the 12 volt input connector to the TV.

Les.
I measured both at the battery terminals and at the wired sockets a and the voltage was the same.

When I measured the current to the TV the voltage was below 12v and so the TV would not power on with the multimeter attached.

#### lastone

Joined Oct 29, 2019
10
It might simply be that the TV has a fault which shuts off the sound at lower supply voltages.
How would this we rectified? How could I pin point where this is happening?

#### AlbertHall

Joined Jun 4, 2014
9,622
How would this we rectified? How could I pin point where this is happening?
At least we would need a schematic to be able to suggest anything.

#### Alec_t

Joined Sep 17, 2013
11,119
How old is the battery? Maybe it can't provide the 6A required for sound plus vision (but in that case you would expect the voltage to sag).

#### BobTPH

Joined Jun 5, 2013
2,345
This sounds very odd to me. Circuits do not generally,unless specifically designed that way, cut off sharply at any particular voltage.

I wonder if a mute pin on the amplifier chip might be pulled up slightly too much resistance?

Do you still have the AC adapter that it runs on? Have you measured its outpit when running the TV?

Bob

#### lastone

Joined Oct 29, 2019
10
I found this very suspicious too, Bob.

So what would I be looking for exactly?

I don't have the AC adaptor but could try and find one.

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#### lastone

Joined Oct 29, 2019
10
How old is the battery? Maybe it can't provide the 6A required for sound plus vision (but in that case you would expect the voltage to sag).
How could I test for this?

#### AlbertHall

Joined Jun 4, 2014
9,622
This sounds very odd to me. Circuits do not generally,unless specifically designed that way, cut off sharply at any particular voltage.
I set off a long car journey and turned on the radio all was well as long as the engine RPM was lowish. At higher RPM the radio cut out. I knew that I had a repair job to do on the radio - at 12V it was fine but at 14V it wasn't.

When I arrived at my destination I discovered that the battery would no longer turn over the engine. It turned out that the alternator regulator had died and the charging voltage was around 19V so both alternator and battery needed replacing.

So actually radio worked at 12-14V but cut out at 19V. I doubt it was designed like that.

#### bwilliams60

Joined Nov 18, 2012
1,282
Is this running off of the chassis battery or do you have a deep cycle stand alone battery (house) to run this off of? Is it the only thing running when you are doing these tests on this battery?