[Milsurplus] solid state dynamotor

[Robert Nickels]

Ray Fantini wrote:
> Anyone have a DC to DC inverter or solid state dynamotor replacement? 
>   
Ray, I posted this to another list yesterday, but since the idea is 
applicable to mil radios I figured I'd pass it along here as well.  
DC-AC inverters are getting to be really cheap, and while they all 
require  12VDC input,  voltage multipliers could be used to power higher 
current transmitters and transceivers from the higher capacity 
inverters.  For example, I saw a model rated at 100 watts with a 220VAC 
output for $12 shipped.

---

I finally had time to do a quick evaluation of what seems to be a decent 
option for generating B+ for small tube gear.   A few weeks ago I found 
the Black and Decker "Pocket Power" on the closeout shelf at a local 
hardware store for $4.99 each, so I bought a couple.   It's about the 
size of a slim paperback book, and contains a 9.6 volt rechargable 
battery and a 16 watt 120 volt AC inverter as well as a regulated power 
supply with a USB connector.  The intended purpose is for charging moble 
phones, MP3 players, etc away from a source of power, but I naturally 
saw other applications!

The first was to plus in a battery set like a Zenith Transoceanic, which 
was not successful.  Two reasons - one being the output current is 
monitored by a processor that just shuts the inverter off if it exceeds 
the design rating, which happens with tube-filament inrush on many 
sets.  Secondly, when I did get it running the RF noise was unbearable.

So I went to plan B, which was to convert the output to DC using a 
bridge rectifier and filter cap, which produces about 140 volts DC with 
a few volts of AC ripple.  A more elaborate filter could have cleaned 
that up, but this supply did a fine job of providing B+ for an ARC-5 
command set (with it's filament power coming from another source).  I 
did a quick characterization using a Clarostat 240C to load the output, 
and found that it held quite well down to about 1000 ohms,  which is  
near the rated maximum output (increased loading causes the unit to shut 
down).  Making a few assumptions about the likely battery capacity and 
efficiency, I'd guess it might provide full output for an hour or so, 
and for several hours with a more nominal load such as the 30ma draw of 
the ARC-5 receiver.  I thought I was so clever until the latest issue of 
QST magazine arrived yesterday, which included an article on ARC-5 
receiver conversions that use the very same idea!  Not a trace of RFI 
could be heard, by the way.

Inverters with internal rechargeable batteries like this have an obvious 
advantage for portable gear, but these days, using a small car-type 120 
inverter may be a smaller, lighter, and even cheaper way to build a 
small isolated B+ supply than by using a conventional transformer.  A 
quick check of eBay showed many in the $5 range with free shipping (go 
figure..)   Twelve volt power to the inverter can come from the same 
transformer or p/s used for your filaments.

Here's what the B&D unit looks like for anyone interested in trolling 
the closeout aisle: 
http://www.amazon.com/Black-Decker-CP120B-20-Watt-Battery/dp/B000H78YXQ

And having satisfied my curiosity (which involved essentially destroying 
the plastic package) - here's what's inside:  
http://smg.photobucket.com/albums/v652/ranickel/Pocket%20Power/

Too big to fit in a BC-611 battery compartment ;-(

73, Bob W9RAN