[AMPS] voltage sag

[Tom Rauch (W8JI)]

Hakan Ericsson wrote:
> QROKING wrote:
> <The 4300 volts after the rectifier is 1.414 of the 3000, but that
> <is the peak of the 3000, and the peak will not offer any effectiveness
> <to the
> <"heating effect" so a voltage drop should be expected near that 3000
> vac
> <value.

I am not completely sure what that statement was intended to say. 

The "peak voltage" and "peak current" absolutely does contribute to the
power dissipated in a system, and the voltage instability of any
rectifier system.

> <Also, since SSB has become popular  nobody uses choke input
> <filters
> <any more.  Now as I recall you dont get that rise in voltage with a
> <choke
> <input filter. 

The choke supply voltage certainly will vary greatly under two common
conditions:

1.) If the supply has bleeder current that doe not always exceed a
minimum value.

2.) If the choke doesn't maintain a minimum indutance over a wide range
of currents.

The choke, if improperly designed for transcient current conditions (ie
when the supply is initially turned on, or the load current is abruptly
increased or decreased by modulation), creates very large transcient
voltage spikes in the high voltage. These spikes cause a HV surge or sag
that destroys waveshape on CW and SSB, and is *VERY* rough on other
components.

> <So maybe I should count my lucky stars I have a few
> <hundred
> <more than the effective 3000.  So what say anybody?.....73 LOU

Sometime is not correct. It is very typical to have less than 10% sag
when a properly designed and constructed capacitor input supply is
operated off a normal residential  power line.

> I have exactly the same experience as LUO, I have no succses of the
> filter Cap's holding up the 1.414. My sag is very near 1.414 becomes 1:1
> I belive the solution is to use a choke to drop the peak volt at no
> load,
> so it then will be possible to raise the secondary voltage from Xformer
> without risking to hit the anod voltage limit of the tube in question.
> Sure know Henry 4k Ultra use a choke and seems to be a smart way to go.
> Now the question: How can I use a choke if I have a voltage doubbler??
> 
> Can I put the choke in the B- side of a voltage doubbler ??

To have such poor and far from normal results, there must be very high
ESR in both supplies you fellows are using.

Choke design is critical, especially inductance recovery time, in a
conventional full wave choke supply. The potential headaches are
overwheming under transcient conditions for a voltage doubler!

It would be much simpler and less expensive to find out what is wrong
with your conventional capacitor input supplies and correct that, before
going into the unnecessary expense and design headaches of a choke
supply. A choke input supply is ONLY necessary when you have power mains
supply problems you can't correct without using a low power factor load.

If you have a varying load current, choke design is critical!! I hope
you find a VERY good choke designer for your custom choke so you don't
need to purchase three or four chokes just to find one that works.

Amateur Handbooks ignore the design headaches of a choke input supply,
because they treat the analysis under steady state current conditions of
minimum and maximum current.

73 Tom


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