[TenTec] Cautionary Tale: Orion 13.8 V connector (long)

[Dr. Gerald N. Johnson]

On Tue, 2007-05-29 at 17:38 -0400, Paul Christensen wrote:
> > My current Omni 6, I pulled out the dc cable connector and installed 
> a pig tail with a much stouter dc connector...30 amp power poles.

I was taught at Collins Radio in 1963 that one NEVER depends on the
pressure of a plastic for an electrical connection, whether hard or soft
plastic. That makes the power pole unacceptable since its connection
pressure depends on the plastic case. Remember the definition of the
word "plastic." Deforms under pressure to relieve that pressure.

Since then I've fixed many a radio locally or remotely that depended on
a screw squeezing a PC board to the chassis to make a ground. Tightening
those screws fixes those radios again and again, all neglecting that
basic rule at Collins, never depend on a plastic for the pressure to
hold a connection.
> 
> As a pig-tail, this is probably fine.  However, I have measured as much as ~
> 0.3 VDC dropped across properly crimped, standard-sized Anderson PP
> connectors under 12VDC/20A loads.  In some instances, the very act of
> crimping will bend the contact surface such that it is no longer in-line
> with the barrel.  The result is that the contacts may not mate evenly.
> After each crimp, I check for barrel-to-contact alignment.  It's really a
> shame that such extraordinary measures are required to properly seat the APP
> and keep them mated.  
> 
> I cannot imagine the APP connector being used directly on the rear panel of
> a transceiver, although one manufacturer is about to release a 100W rig in
> July with APP panel connectors.  Since heavy gauge wire is generally used
> for powering, the slightest movement of the radio may be enough to slightly
> unseat the connector and that's something you don't want to see at 20A while
> transmitting.  Since the APP is a non-locking device, I've seen them weld
> together while they are inadvertently flexed under high-current conditions.
> 
> 
> A APP connector that appears to behave fine, may be on the ragged-edge of
> acceptable conductivity.  The way to know for sure is to measure the voltage
> drop across the connector under full load.
>   
> While at Dayton, I noticed that the folks at DCPwr.com had a nice power
> distribution panel with 80-amp APP connectors.  While we do not need 80-amp
> connectors for the 100W class of radios, I find that the high capacity APP
> connectors offer much better mechanical rigidity than the junior sizes.  
> 
> http://www.dcpwr.com/products/product.php?id=134
> 
> Personally, I would be perfectly happy with insulated, quarter-inch brass
> bolts placed on the back of the transceiver, allowing the owner to connect
> directly from the bolts to the power supply, or as you have done to your
> Omni Six, add the connector of your choice as an in-line pig-tail.

Better if one is much larger than the other so that they can't be easily
interchanged, like lead acid battery posts, since the modern solid state
radio tends to not survive reversed polarity (though a diode and a relay
in its internal power switch circuit could prevent that relay closing
with reversed polarity, but too often the PA circuit is not switched).

Unfortunately the average among us finds which polarity works by
experiment and fries the radio half the time and the best of us makes
that mistake on semi-rare occasions.

I think it boils down that the DC power connector should have machined
contacts that are well supported and that may mean a metal cased
connector, some Mil spec item perhaps, that would be large, ugly, and
raise the cost of the radio $37.
> 
> Paul, W9AC
> 

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer