Monday, August 27, 2007

universal power

Today, from Sayal Electronics, I bought two RCA universal DC car adapters (model CAH55). Super cheap! CDN$7.99. Yep. I couldn't build it that inexpensively! One adapter will be used to power my palmtop computer in the field. The other will power the controller and motor for my telescope.

It had occurred to me while camping to get some adapters like these... This happened one evening as I wanted to do some writing on my palmtop. I knew if I turned on the screen backlight on the Psion, it would gobble up battery power. While I had a gaggle of rechargeable AA batteries with me as well as my solar battery chargers, I did not want to use them up. I could use my 12V lead-acid portable car battery as an external source! But that required connecting the inverter and then the Psion transformer. It seemed a little ridiculous and wasteful to step up to 120 volts and then bring it right back down again.

I had started to design my own units, using 5V and 9V voltage regulators. But then I remembered seeing an inexpensive unit (that output at 6 or 9 volts) at Active Surplus. In fact, I had bought one earlier in the year (for my in-car digital audio player project). But, ironically, I gutted it for the jack and coiled cord. The circuit board is sitting in my spare parts bin...

I quite like the design of the RCA units.
  • Outputting at 3, 6 , 9, and 12 volts, the adapter is quite versatile.
  • The amperage output varies too...
    • 3V: 300mA
    • 6V: 600mA
    • 9V: 600mA
    • 12V: 1.2A
  • Six adapter plugs are provided.
  • The adapter plugs connect to a universal plug so you can easily change the polarity.
  • The separate "block" or "brick" is substantial. The Active unit was self-contained within a larger-than-average CLA jack. But the circuit, as I hacked it, was rudimentary, and without capacitors to smooth the fluctuations. The RCA unit looks sophisticated. Admittedly, I have not opened the unit but I would not be surprised to find filtering capacitors and possibly a diode for reverse-voltage protection.
  • The block is well-ventilated. This, I know, will be important, as heat is produced by the voltage regulator and resistors in the circuit.
  • There is a red LED in the CLA jack. So you get instant feedback as you connect the jack.
  • There is another red LED on the block itself. So now I know power is being received to the main unit.
  • Oh, yes. And the CLA jack is fused!
I have tested the RCA units and they work good. Can't wait to try them in the field!


These adapters are helping me move toward being more environmentally friendly. As much as I like and want the motor drive, I did not like the idea of burning through piles (sorry!) of C batteries. First impression is that I get one evening out of a set of 6 batteries. Very wasteful.

Driving off rechargeables is better. Driving off the big chargeable, the lead-acid, is even better.


There's one small, new problem with all this...

I'm putting a tremendous load on the portable car battery! Dew heaters, motor drive, light box, palmtop, and desk light. They all can be driven now by the car battery.

If I'm near an AC outlet, I'm OK, with my special custom CLA adapter. But in a dark remote field in the middle of nowhere during a heavy dew-laden night, I'm in trouble!

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