[Milsurplus] 800-1 800 cycle rotary inverter

[Richard Brunner]

Dennis wrote:

> Interesting....  I don't recall that my TBW book says anything at all 
> about line voltage variation, only filament voltage.  The TBW didn't 
> originally run off of an aircraft type inverter but likely that it's 
> cousin the GO-9 did.  Using primary keying as the TBW and GO-9 do would 
> present the input power source with an abruptly switched on/off 200W+ 
> load that probably includes a nontrivial reactive component.  Wouldn't 
> be surprised to see the power source "reacting" under these conditions.  
> Would be interested in more detail on the (strange) line voltage 
> variations referred to in your e-mail.

As presently adjusted the line voltage goes up, key-down, from 115-120 
volts to about 135-145 volts.  From experience it seems that the 
key-down voltage will go either up or down, depending on the dc input 
voltage.  This may reflect lack of optimum adjustment at another 
voltage, but I thought the carbon pile regulator is supposed to 
accomodate all voltage and load changes.  I also made a solid-state 
replacement for the carbon pile, but it didn't work any better.  I used 
a small transformer to isolate the ac output from the dc feedback, and I 
think reactance crept in again.

The plate and filament transformers are fed in parallel, (with series 
resistance to the filament transformer) and the line voltage is measured 
between the series capacitor and the generator, so the line voltage is 
not so significant to the transmitter. (that reactance again)

There are three adjustments available.  The carbon pile has a screw at 
the carbon pile end, and a screw at the solenoid end.  The carbon pile 
is fed off the ac output through a dropping rheostat to a full-wave 
rectifier.  I think the proper adjustment is to adjust the carbon pile 
at light load, and the rheostat at heavy load.  The carbon pile shunts a 
15 Ohm resistor in series with the feedback winding, passing more 
current to keep the voltage up.

The series capacitor in the transmitter is supposed to neutralize 
reactance in the generator, so theoretically the line voltage should be 
pretty constant.  The Airborne Electrical Maintenance Notes say that you 
can load the generator up to only 500 Watts without a series capacitor, 
   and they recomment at least 1.5 microfarads of series capacitance for 
each ampere of load.  The also tested and rated it at 1350 Watts for one 
hour and 1200 Watts continuous at 90% pf.  An ac generator can be 
modeled as a perfect generator in series with resistance and reactance, 
so if the resistance and reactance drop exceeds the maximum internal 
generator voltage capability, you aren't going to get full voltage 
output at heavy load - and need capacitors.

Richard Brunner, AA1P