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Voltage dropper

Hi Folks I'm trying to run a tiny 6 volt radio for as long as possible off a 12 volt car battery. I came across a 7806 but was disappointed to find that it is nominally only 50% efficient. The heat dissipation (voltage drop times load current) being much the same as the load (out-voltage times load current)

I read some primer on dc-dc converters that claimed that synchronous rectification could get to 95% efficiency. Is there some way to achieve a reasonable efficiency here? I even thought about centre tapping the 12 volt battery and using the two 6V halves in parallel. I suspect I might need a diode in this circuit and that would not bode well for the hopefully intermittent charging from a small solar panel in Winter. I will also be running a 12V, 1 Watt LED from this battery at night when the Sun definitely don't shine.

I'm worried that if there is a weeklong rain period with no charging, I may flatten the battery too far.

Perhaps two or three car batteries in parallel might be a better bet, but the ones I have are all different brands, sizes and ages, and would definitely self-destruct by trying to charge the weaker ones without diodes, but how do you rig up diodes to allow charging and draining?

Thanks for any ideas or suggestions, jack

Reply to
spamfree
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you can use one of those DC-DC converters how ever, i think you might find it more interesting if you were to make one of your own. using a Cmos version of the 555 timer which i think is the 7555 ? , these use power, and then you can use this as a PWM (pulse width modulator) at high freq driving transistor into saturation mode into an small inductive coil that has a cap on the end to filter all of this. Then build your self a little regular to alter the charging cycle of the 555 timer.. I know this all sounds like a lot how ever, you can actually get good efficiency doing this. I've do this before when looking around for a high efficient regulator just for the same reason you are..

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Reply to
Jamie

A radio will draw more current the louder you play it, so looking for the lowest drain radio is a non-starter. It needs to be lowest drain at the volume you have in mind.

A battery lightly loaded will have more total capacity than a battery heavily loaded. Your 30 Ah battery into an 83 mA load will last longer than your figures. That

30 Ah rating is figured at a higher load.

A 12 volt radio will produce as much volume as a 6 volt radio at ~1/2 the current, all other conditions being equal.

Last, but not least, you should have an automatic shut off circuit to prevent your battery from being over discharged.

Ed

Reply to
ehsjr

You could try an old 12 volt car radio. I have a 1980s Ford AM radio that only draws 80mA with the dial light disconnected. It's very sensitive with good fidelity from a 4 inch speaker, and the push buttons are handy for changing stations in the dark. But you will need an external antenna and ground.

Don't use any switching power converters if you want to listen to AM radio. They generate too much noise on weak stations.

-Bill

Reply to
Bill Bowden

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