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#162678 04/23/07 03:40 PM
Joined: Jul 2006
Posts: 272
L
Member
Been re-wiring HPS fixtures today and noticed that the new ballast kits don't come with a resistor for the capacitor. The schematic still calls for one, I bench tested one anyway to see if the lamp would fire, it did. Then after warm up I disconnected the fixture, then re-energized to ensure that it would 're-strike'. All is fine.

I am left wondering just what purpose this resistor serves. I feel like I should already know the answer to this. Never the less, I just want to figure this out, humiliation or not.

The fixtures are 400watt Holophanes, the capacitors are 56uF with typical three wire starters and 480v ballasts.






Luke Clarke
Electrical Planner for TVA.

Joined: Feb 2003
Posts: 939
F
Member
useally the restior is wired in parallel with the capaitor to bleed it down in case have to do some manatice work but if you see any cap without restior at all just keep your hand away it will hold a bit of " juice "

really it should have one on it but i dont know about other lumiaires do the same thing as well but i am sure most is pretty common the capaitor is wired in series between ballast and lamp [ this is common on " 100 volts " and higer like some 150 w hps but 200 w HPS and larger will have this set up

Merci , Marc


Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)

Joined: Mar 2007
Posts: 25
M
Member
that may be a bleed resistor. i capacitor stores a charge and even after you kill the power at the breaker you can get shocked by the capacitor (big time!). you must always discharge the capacitor before assuming it is ok to touch. the way i do it is by shorting across the terminals with a screwdriver(with the power off of coarse) usually you'll see a small spark. the recommended way of discharging a capacitor is by using a resistor across the terminals and sometimes the manufacturers install them sometimes they don't.

Joined: Jul 2006
Posts: 272
L
Member
Ok, that makes sense to me now. Thanks for clearing that up for me guys. smile I guess that should be a good rule of thumb to always be sure to bleed off/discharge a capacitor before messing with it. Considering.. that it doesn't already have a resistor wired across it.


Luke Clarke
Electrical Planner for TVA.

Joined: Jul 2002
Posts: 680
W
Member
Most are internal now, not sure if these Caps have them or not. I've seen instructions that tell you the caps have changed and the resistors are now inside the case of the cap??

Joined: Jul 2006
Posts: 272
L
Member
Hey Walrus, these new capacitors DO have a .53Megohm resistor built in to them. I had a closer look and it clearly states, (in really small print). "Internal res. 0.53 Megohm"

Thanks! laugh


Luke Clarke
Electrical Planner for TVA.


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