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Posted: Mon Feb 10, 2014 8:10pm

Post Subject: 12 Volt equipment

Hi Tony I want to run a DAB / FM radio / docking station from 12v rather than 240v to avoid running the inverter when moored. How stable should the 12v be, is it affected by spikes? 12v TV's seem to be in plentiful supply (and run off the boat 12v)quality radios other than car radios seem to be thin on the ground. I thought if the device was running a 12v supply from a 240v transformer then I could just cut the transformer off and put the necessary plug on the lead. Can you offer any help please?


Posted: Tue Feb 11, 2014 8:43am

Post Subject: 12 Volt equipment

The 12V system is subject to large transitory spikes cause by any motor or relay turning on and more importantly off. These might be in excess of 100 volts. It is also a "close to 15v" system when the alternator is charging and could go higher with a battery charger. The battery and the wiring runs will tend to damp the surges BUT it very much depends upon how the boat is wired. The upshot is that bets practice is NOT to simply cut the mains transformer off things like TVs and radios that are designed to be powered from the mains but run at 12V. Having said all that I know many people do as you suggest without problem so it is down to you to make a decision, I simply can not say it is OK to cut the transformers off (actually some supply low voltage AC, not DC so take care). I use a stabiliser for my TV and I am sure one would be fine for a radio. I got mine from a supplier of boat TVs and it cost £40. It may also be worth looking at the specifications for 12V power supplies for computers, some of those have a 12V setting and should damp the surges. Two other things that you may not have picked up on. The DAB signal is of a higher frequency than FM so it can be hard to use the built in internal aerial inside a steel narrowboat. In poor signal areas you may need a specific DAB or wide band (AM, FM, DAB) amplified external aerial. There is also sufficient indications that some LED lights cause interference, particularly on DAB radios. This seems to be caused by the LED driver circuit that is limiting the current and damping spikes so another make of bulb can cure it. Tony BRooks

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