DC voltage change

[surekandoo]

I'd like to run 1 x DAB radio which requires 9v dc on my boat from the boat's 12v DC supply.

How do I reduce the voltage? I seem to remember from school (many years ago!) that I need some sort of resistance in the circuit.

Can anyone help?

 

[Anthony]

get a 12v voltage adapter from maplins or ebay etc, easy cheap solution.

Anthony

 

[Gumpy]

I found a 12v-6v coverter on ebay for mine
something like this
http://cgi.ebay.co.uk/12V-DC-DC-Converte...93%3A1|294%3A50

 

[lenseman]

Get obtain or purchase 5 diodes (1N4001) and solder them in series and then use them in series in the positive supply lead. Don't forget to also include a fuse.

Each diode will drop 0.7 volts and five of them in series will drop 5 x 0.7 = 3.5 volts.

As the on board DC supply is 12.8 volts you will then have:

<span style="color:white"> xxxxxxxxxxxxxxxxxxx </span>12.8volts - 3.5volts = 9.3 volts /forums/images/graemlins/grin.gif

 

[William_H]

Much depends on how fussy your radio is regarding input voltage. It may but is unlikely to cope with 14volts as your battery will be when on charge.
The diode idea is OK but will still see the voltage to the radio varying between 9volts and 11volts if on charge.
The ideal is a voltage regulator. As said these can be bought commercially all fitted with a cigar lighter plug. Or you can buy a microchip 7809 is the generic number ( less than a squid) which has a transistor internally which acts like a resistor whose resistance is automatically varied to ensure the output voltage is precisely 9volts regardless of current drawn or voltage within limits at the input. A small capacitor is connected from the output to ground. Put it in a box .... da da.
As a matter of interest a 7805 gives 5volts 7812 gives 12v etc. etc. There is also an LM317 which is designed to have a variable rsistor at it s output to give any chosen voltage. (less than input) All of these will give 1 amp providing voltage difference i/p to o/p is not too great that power dissipation gets too much.
These simple regulators are not to be confused with the type which will give a range of voltages above what you put in. Much more complicated
good luck olewill

 

[christo2024]

I once had a baby alarm intercom on my boat (dont ask!) which used a 9v battery. I used the boats 12V supply and soldered a 3v torch bulb in series with the live supply which I was told would sort it.
It certainly worked OK for years but not sure if the theory was correct!!

 

[st599]

But the current at start will be higher than that and you could blow the DAB. Get a DC-DC Voltage regulator.