Gord, some assistance required

I am trying to make a 12VDC to 6VDC converter so I can free up my cigarette lighter again. I suppose quitting smoking is the thing to do, but that's for another topic.

Of course, I can't get my hands on a 7806 6V regulator, only 7805's.

Here is a schematic for a 14V input converter. I want to replace the rheostat/pot with a fixed resistor for 6VDC.

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What value do I need to use to replace the pot?

Thanks...

Reply to
Hachiroku
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Actually, I may have found a circuit that will work. It is here in NS's LM317 Data Sheet:

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Take a look at the 6v Current Limited Battery Charger.

It is regulated at 6VDC with a current limit of 600mA which is just about where I wanted to be, At this current, I shouldn't even have to heatsink the LM317.

There are simpler circuits using a 7806 reg and two caps, but I can't find a 7806 regulator :(

Reply to
Hachiroku

Damned near missed this one Hashi...was sick for a day over the wkend and this ng gathers a lotta stuff if you're off of it for that long...there was a BUNCH and I just marked the whole group 'read' then noticed my name on this one...

Aaaanway...it's hard to tell because of variances in different voltage regulators etc so the best way is the KISS method (keep it simple stupid - or maybe more politely, keep it stupidly simple)

Turn the voltage down low, connect your equipment and plug it into the car, then put a VOM onto the leads, bring the voltage up to 6 Volts, try the transmitter and notice whether the voltage goes below 6, adjust it so that it doesn't get very much below 6 or much above 6 from full load (transmit on -OR- set turned off).

Now just measure the pot between the center tap and the end going to the negative lead. The 317 is a good regulator...this should save you a lot of those damned AAA batteries...a little hint, don't start your car with this plugged in...there's sometimes large transient voltage spikes from the starter or relays that can trash the regulator and/or the radio...

Reply to
Gord Beaman

KISS, and be done sooner to boot. Install an accessory "lighter" socket hidden up under the dashboard, tap off a fused switched circuit (to turn it off with the key) and plug your radar detector power adapter into it. Thread the cord around to the detector, Done.

Or buy a built-in kit from the radar detector people if the unit is still under warranty - because if your power supply design doesn't work and the radar detector blows up, so does the warranty.

Most factory adapters have a crowbar over-voltage circuit inside to pop the fuse if the regulator shorts, and they usually have a "only use a factory authorized power adapter" clause in the warranty.

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Reply to
Bruce L. Bergman

Ah...I was just going to hard-wire it into the same circuit as the radio.

Also, I found this:

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Doesn't get much simpler than this! The whole kit, with the PCB is ceaper than I can buy the parts for, and I don't have to think too hard about trying to wire it up.

Funny thing is, if you look at Fairchild's 'poop sheet' for the regulator, this almost exact same ckt, less the diodes, is listed as a 'test curcuit'. I would add some kind of micrfuse just to keep things safe.

BUT: I went to the local Radio Shack Sunday, located all the parts I needed, and the box, ckt board, etc, and then planned an hour or two for building and testing, put all the stuff back and...

bought two 12V power outlets and have already installed one in the Supra...

Reply to
Hachiroku

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