How to test Fluorescent Ballast

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Hi all,

Have 2 light fixtures in a garage, with 4 fluorescent bulbs in each (4ft).
Each 2 bulbs are supported by one magnetic ballast.

The ballast is Rapid Start Magnatek 446-L-SLH-TC-P as below:

Description: Electromagnetic ballast for (2) fluorescent lamps as indicated
below:
. Line Voltage: 120 vac, + 5%, - 10%, 60Hz . Rapid Start
. Series Lamp Operation . High Power Factor

The lights got dimmer over time and now only one glows, others do not work.
The ballasts are about 10 years old.

Do the ballast "get weaker" over time?  What is the most likely failure
mode?  Is there a way to test them with VOM?

Regards,

RichK



Re: How to test Fluorescent Ballast

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The most obvious test would be to replace the bulbs.  That would
eliminate the ballast as the problem.  Sorry if you tried that already,
but you didn't mention it.  Fluorescent bulbs don't last forever :-)

--
Nelson


Re: How to test Fluorescent Ballast
Hi Nelson,


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Yes, tried new bulbs - but it did not work.  Was hoping that there is
resistance check, or voltage.

I did do the normal web search and found some info, bo in all cases it says:
replace the ballast.
In fact I already did that and lights do work now.  Ballasts are about $16
each locally to cover 2 bulbs.

Bonus question:  Several places on the web mantioned that a ground
connection to the fixture is essential for the lights to work.  These have
worked for 10 years without the ground - the original installer did not
bring good ground to the lights.

Will lack of ground reduce the life of the ballasts?

RichK



Re: How to test Fluorescent Ballast

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No.  If they start, then the ground is not needed for that.  But
there is the safety issue of any exposed metal parts that aren't
grounded.

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Re: How to test Fluorescent Ballast



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Exactly. If say, a ballast developed an internal fault, the entire housing could
become live without a ground there.

Graham


Re: How to test Fluorescent Ballast
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If you do replace it, go for an electronic high frequency ballast. You'll
get more light with no flicker, the tubes will last longer and no starting
problems.

--
*If a pig loses its voice, is it disgruntled? *

    Dave Plowman        dave@davenoise.co.uk           London SW
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Re: How to test Fluorescent Ballast

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No, but without a ground the lamps may not start, especially if the
humidity is high or the temperature in the room is low. Some
lamps/ballasts seem less prone to this than others but if a fixture
works sporadically then I usually check the ground first.

Re: How to test Fluorescent Ballast
had a dubble 20w years ago brand new
and the ballast was getting hotter than normal
thinking that ok new fitting, went out came back
home and found the 2 tubes exploded all over
the bench defuser blowen off hanging one side.
ballast shorted turn and to ground
paint black on outside of fitting.
40 watt ballast for 2x20watt.


Quoted text here. Click to load it



Re: How to test Fluorescent Ballast
had a dubble 20w years ago brand new
and the ballast was getting hotter than normal
thinking that ok new fitting, went out came back
home and found the 2 tubes exploded all over
the bench defuser blowen off hanging one side.
ballast shorted turn and to ground
paint black on outside of fitting.
40 watt ballast for 2x20watt.

Quoted text here. Click to load it



Re: How to test Fluorescent Ballast
Quoted text here. Click to load it


Ballasts can deteriorate if the winding insulation breaks down. Older
preheat twinlamp lead-lag ballasts also contain a capacitor in series
with one lamp which can fail but yours is rapid start so that isn't the
issue. Once one starts acting up you really do need to replace it
though, many fires have been caused by failed ballasts. Class P ballasts
  contain an automatic resetting thermal protector but those can and do
weld closed if they're left cycling too long.

As far as testing them, the only reliable test is to pop in a set of new
tubes, if it still doesn't work and the sockets look ok then replace the
ballast.

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