Portable radio running off 12v..

[majdrew]

Hi Everyone!

I have a nice little portable radio that I would like to use on my boat, however, there is only a connection for a 240vAC, it runs on batteries otherwise.. 9v
There is no seperate external 9v input socket though..

Is there a way to run it directly off my 12v onboard system?

I know I could get an inverter for my 12v and then plug this into the ac socket.. but it can't be efficient, since the radio must again convert back to 9v DC.

Just wondered if anyone had done anything like this..

All the best!

 

[leomagill]

You can get a linear voltage regulator that could be attached straight to the battery terminals and hooked to 12v dc, I think it's a LM7809 you need for 9v, probably not even need a heatsink for the current required to run a radio.
I've done it before with LM7805's to power a gps mouse for serial output.

 

[Zephyr362]

If there is no other input then you will have to drop the 12v down to 9v. If you have a friendly electronics technician it's an easy job or buy such a device from someone such as Maplin http://www.maplin.co.uk/Module.aspx?ModuleNo=48574
Neil

 

[Mandarin331]

You can get adaptors which will convert 12 v downwards (or upwards - designed mainly for cars & caravans.

See http://www.amazon.co.uk/Bandridge-12v-dc...458&sr=8-15

We've got one on board and it works fine. If the radio does not have a 9v inlet, make up some doweling the same length as the battery space, attach the wires to each end with a screw & washer insert and off you go! (just make sure the polarity is correct)

Good luck
(another) Neil

 

[Twister_Ken]

OTOH batteries are cheap and last a long time, so why complicate?

 

[majdrew]

Excellent! Some good ideas there thanks.. I'll try the dowelling idea I think, I have a step down converter.. just wasn't sure how to attach.. and batts as a backup..

All the best!

 

[lw395]

Another approach is to get a nicad charger which can run off the boat's 12V, then only buy torches, radios, GPS, cameras which use AA batteries.
Keep some Alkaline batteries in reserve!

 

[Guest]

A 7809 would be favourite, or simply connect 5 silicon diodes in series - such a chain will drop 3 volts.

 

[lw395]

The diodes in series approach does not take into account the charging voltage or noise/spikes present on the '12V'. A portable radio may have quite poor conducted immunity if it's not intended to run from noisy mains. Likewise some of the DC-dc downconverters may affect the sensitivity of the radio, radio LW being often badly affected.
For a low current device like a radio, the linear regulator is probably best.

 

[LadyInBed]

Rechargable Cells and a Charger that works off 12v
Needles to say, Maplins sell them