[ARC5] Re: [Milsurplus] question re filter caps

[Mike Hanz]

David Ross wrote:

>The dynaverter's main filter cap appears to be a single 3uF wet-slug
>tantalum.  What sort of cap should I replace it with?  The dynaverter
>puts out 270VDC @ ~70mA, switches at ~2KCs, and space is somewhat
>limited.  
>
Depends on whether the noise is propagating from the input or output 
side, Dave.  Like John, I think I'd see what was actually causing the 
problem - it might not be the tantalum, which IIRC is a low voltage 
(60uf/50v) on the primary side anyway, not an output cap, which is a 
small can type with a ceramic top.  Some probing with a scope should 
tell you pretty quickly from which side the majority of the noise is 
originating.  Tacking a temporary substitute will confirm the solution.  
I'm assuming you're talking about the PP-2792 series, which actually 
only has four caps total, counting the two commutating caps.

>Would it be useful to build in a pi-filter setup with a pair of caps
>and a small choke?
>
I guess it depends on whether the receiver is noisy with the inverter 
operating up to spec.  The filter cap on the output that seems to do a 
fairly decent job on mine, and the built-in audio frequency rolloff in 
the military sets makes it almost inaudible - certainly less that the 
400~ whine in the countermeasures sets.  In addition, on the later ARC 
receivers using this inverter I have sometimes seen a nickel plated 
copper strap (or two) between the snap slide post on the shock mount and 
ground - that works a good deal better than a high inductance wire at 
completing the ground shield for these units.  This inverter does a nice 
job in a number of receivers, including the BC-348.  Nice sub if you 
don't like the maintenance aspect of rotary devices.

73,
Mike