please can someone help ... when high pressure discharge lamp luminaries ar starting they... use less current ...or have higher than normal running currents ... or light as soon as their switch is turned on ... or loose all voltage when switched off. im suck on this in my on line electrical course many thanks steve

Capacitor will sort that

Cap will help correct the power factor, only thing that will help the inrush current is a HF ballast.

Quote:

A capacitor will not reduce the start up current, only imporve the power factor.



There is two types of 'startup current' to consider.

You will get an inherent inrush of current due to switching on an inductor (the balast).  This presents a near short circuit to the supply for a fraction of a second until it sets its magnetic field up where it then 'chokes' back the current.  This startup current lasts for a second or so.

While the lamp starts and comes up to full brightness there will be more current flow as the lamp heats up and vaporises the gases and metals and gets the electrons and stuff excited and moving.  While this is happening more current will be drawn.

Once the lamp is upto full operating output, the current will have reduced and steadied.  This can take several minutes depending on the type of discharge lamp and the wattage.

Lectrician wrote on Mar 31^st, 2009, 7:00am:


Thanx for that in depth description lec, very informative. Don't these lights use more current when the caps cease to work, I was told this in college. When we did a test we measured how much current was used with the cap and without, the results were that the current was more when the cap was out of the equation. This is where my original answer came from, I must have misunderstood the test in college and the question. They are both different.