Current Limiting

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Current Limiting
From: Tesla List <tesla-at-stic-dot-net>
Date: Sat, 31 Jan 1998 14:39:49 -0600
Approved: tesla-at-stic-dot-net

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From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent:  Saturday, January 31, 1998 10:44 AM
To:  Tesla List
Subject:  Re: Current Limiting

> 
> 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 
> series]. 

You bet it will work. Of course, lightbulbs don't have constant resistance,
which actually helps in this application. As the current increases, the
resistance increases, which reduces the current, etc.  This is a standard
technique for stabilizing the amplitude of audio oscillators (cf.
Hewlett-Packard designs from day one) and emitter ballast on bipolar
amplifiers.

Lightbulbs and their sockets ARE more expensive than surplus power
resistors or stove elements though. And, they give off all that light, as
well.

Inductive ballasting (e.g. NST shunts) is nice because it limits the
current without loss.