[MRCA] Re: T-195 Power Supply

[Chris Bowne]

For my 24-28 V radios, I have been using a pair of 12 V deep cycle marine batteries in series, in parallel with a high current DC supply.  This allows the supply to carry the steady state load, with the battery bank available for dyno startup surges.  This arrangement approximates the electrical system on the miltary aircraft or vehicle in which the radio was originally installed, with the power supply substituting for the original generator/alternator.

For many years I used a nominal 30A unregulated supply, fed by a Variac which I used to set the output voltage/current.  Generally I would set the voltage so I was putting a slight charge on the batteries with the load at hand in idling (not transmitting) condition.  It helps if you can put a battery current meter (zero center) in the circuit (I put it in between the two batteries) to show whether you are in a battery charge or discharge mode.

This setup was marginally OK, it really didn't hack the full load current for extended periods on transmit. Eventually the batteries would lose some voltage as part of the load was drawn from them, and transmitter output would drop off.

I recently was able to acquire a much better power supply/charger - a 24V/50A regulated unit specifically designed to float a set of batteries and a paralleled load (orignally microwave realy equipment) made by Power Conversion Products of Illinois.  They are now part of Eltek Energy Limited, and still make various versions of this type of supply. They have an excellent web site, although I imagine new units are pricey.  The PCP supply is very stiff - maintains output voltage at within 1/2 percent no load to full load! I have been running it on a fairly new set of deep cycle batteries, with the output set at 27.6V (2x13.8V). It doesnt even get warm under full load, and the radios have much more output than they did with the older lash up. Problems with output drop off over time are gone!

You might want to look for a good used marine battery charging unit using a ferro-resonant transformer (the basic design of the PCP unit), or military 24V/50A units which are out there as well.  I have been told that with some of the mil units, you need to put an isolation diode between the supply and batteies when used in a battery float mode.

Your T-195 will work much better from a supply voltage at the high end of its normal range.  At low voltage, the autotune is very sluggish, especially at low frequencies.

73, Chris Bowne, AJ1G
    Stonington, CT