From: Esondrmn-at-aol-dot-com [SMTP:Esondrmn-at-aol-dot-com]
Sent: Friday, January 30, 1998 1:08 PM
Subject: Re: Current Limiting
In a message dated 98-01-30 00:59:54 EST, you write:
I was thinking this morning about current limiting.. [I still dream of
the day I can get that Pig... and want to be ready] I thought of
something that is a) very simple, and b) probably does not work.
So someone tell me why please :)
Since I am mostly a software kinda guy, with a smattering of digital
design, dealing with this high-power AC stuff always confuses me.
If I understand it correctly - the idea behind reactive or resistive
loads is to place an IR drop in series with the pig, such that when
the current reaches a certain point, the IR loss prevents it from
rising further [I know, the wording sucks, but the idea is
clear, I hope]
So.. based on this idea.. and the fact that lightbulbs don't exactly
short things out, why not use lightbulbs as resistive ballast?
I am not exactly sure what the VA rating for a bulb is.. but for
grins sake, assume a 100W bulb is 100VA, paralleling 2 bulbs gives
you total power flow of 200VA, 3.. etc. [ for 220, use 2 110V bulbs in
Power control is two fold: Voltage via variac, and current by switching
in more or less bulbs in series.
- snip -
Your approach will certainly work as well as using heater cores, oven elements
and other resistive elements. However, it is not an ideal solution. Resitive
ballast will drop quite a bit of voltage across it and lower the voltage
available to the primary of the HV transformer. Using reactive ballast such
as a variable inductor will also drop some voltage across it because if its
internal resistance but not nearly as much as a resistive ballast.