[Collins] S line power requirements Help???

[Dr.Gerald Johnson]

For sure the HP23B specs are truthful.

The limits of a power supply come from the transformer, the rectifiers, the filter 
chokes, the filter capacitors, and the primary fuse.

The primary fuse isn't particularly picky, it will generally carry 125% of the rated 
current for an unlimited time and melt at 200% of the rated current in an hour. 
Its often overrated to handle turn on transients (caused by core magnetic 
hardness and filter capacitor charging).

Doubling the load current quadruples the power dissipation in the wires of the 
transformer and the filter choke(s). That heat makes the paper insulation in the 
transformer age more rapidly. when the paper insulation turns to powder and 
the varnish gives up, wires get to vibrate and then they wear holes in the 
enamel and that leads to shorted turns that heat a great deal more.

Doubling the load current also increases the voltage drop in transformer, 
choke(s), and rectifier. In a tube rectifier going above its current rating 
significantly can increase the voltage drop faster than if it was a resistor (trying 
to get more electrons from the cathode than are available) causing a more 
rapid rise in tube temperature.

Increased current in a filter choke can cause the core to saturate and so the 
inductance to decrease drastically and that makes the ripple current to the 
filter capacitor increase drastically. If the filter capacitor can't handle that 
much ripple current, it will heat and blow its seals or expand rapidly.

Increased load current calls for more stored energy from the filter capacitor to 
supply the load between rectifier current peaks adding to the ripple voltage 
at the capacitor (and the ripple current).

Power supply design works down to battling temperature rises vs loads vs 
volume vs cost.

Transformer design can sometimes use fancier core material for a more 
compact design at higher cost and much higher magnetic retention at turn off 
and so larger turn on transients (transformers that go "Thung" when turned on). 
The more compact core generally saves on copper cost and improves 
voltage regulation from the fewer and shorter turns. But the fancy core is 
operated closer to saturation and unbalanced rectifier currents can lead 
more rapidly to core saturation. That's not a problem in the 516F-2 with full 
wave rectifiers but it might be in the HP23x with the half wave voltage 
doubler.

Saturation is a limit of chokes along with winding heating.

Bigger filter capacitors store more energy and reduce ripple voltage at the 
cost of increasing the peak rectifier current (unless limited by transformer and 
rectifier impedance and choke inductance) which increases transformer and 
rectifier heat. Silicon rectifiers take peaks better than tubes. Greater peak 
rectifier currents also make for greater ripple current in the filter capacitors 
which heats them. Bigger filter capacitors then need to have greater ripple 
current ratings which generally means a larger volume.

We have to presume (and a set of transformer and filter choke specifications 
used to buy those parts would give the design current ratings) that the known 
load of the KWM2 low voltage is the greatest of any load for the 516F-2. For 
sure the heater load of the KWM2 is going to be the greatest while the load on 
the high voltage is independent of radio in those designed to run from the 
516F-2. We then must presume that the 516F-2 has been designed and proven 
pretty well to supply those KWM-2 loads and of course the lower currents for 
the 32S. 516F-2 do fail, but not at a great rate.

Compare the PM-1 that was made as compact as possible for portable use.  I 
think it's manual would indicate that RTTY service would not be a good idea, 
nor heavy continuos duty in voice or CW operation. It seems to have a 
reputation for being fragile.

Remember that aluminum electrolytics age whether used or not, generally 
faster when not used causing greater ripple voltage for a given ripple current 
and greater heating from any ripple current. Heating can lead to destructive 
leakage that damages other power supply parts.

73, Jerry, K0CQ, Technical Advisor to the CRA

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.