How-to Test Fluorescent Ballast

[Brian [B.] Collins @2M53 [BNR]]

I have checked the FAQ and have searched the WEB, but I have not found
any information on how to test if a fluorescent light ballast is any good.
I will be helping to re-lamp my daughter's gymnastics club in the near
future and I would like to test the ballasts that seem questionable.
These are standard four-foot, two lamp fixtures that are row mounted.
I have installed new fluorescents many times, but I am not familiar with
the internal operation of a ballast. Any help that you can provide
regarding ballast operation and test would be appreciative. I have a
multi-meter, but is there any (low cost) specialised test unit or methods that
might be necessary.

Thanks,

Brian Collins
--
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[Sam Goldwasser]

I bet you haven't checked this FAQ:

http://www.misty.com/~don/f-lamp.html

In any case, the best way is to simply install new tubes. There isn't much
else in a fixture besides ballast, tubes, wiring, sockets. The wiring rarely
goes bad. The socket could but it usually would be obvious. This leaves
the ballasts. Since ballasts for 4 foot dual lamp fixtures are not simple
inductors (there are circuit diagrams in the FAQ but not all are the same),
testing is a pain.

--- sam : Sci.Electronics.Repair FAQ: http://www.paranoia.com/~filipg/REPAIR/
Coming soon to a computer screen near you: http://www.repairfaq.org/
Preview of V3.00 (ASCII): http://www.pacwest.net/byron13/sammenu.htm

[Dan Kuechle]

Another question is how do you test a single fluorescent bulb? I'm
thinking
about the 4' bulbs that ALWAYS seem to travel in pairs. I'm never sure
which bulb is bad (it almost seems that a bad bulb can work fine in one
slot
and not work at all in the other slot). I usually swap bulbs and fixtures
for
as long as my patience lasts, then replacing them all.

Dan

Brian [B.] Collins @2M53 [BNR] <bcol...@bnr.ca> wrote in article
<60bs7j$o...@bcrkh13.bnr.ca>...

[Sam Goldwasser]

In article <01bcc9e7$0be33800$1f38...@dan.i-tech.com> "Dan Kuechle" <dan_kuechle@SPAM_NOTi-tech.com> writes:

> Another question is how do you test a single fluorescent bulb? I'm
> thinking
> about the 4' bulbs that ALWAYS seem to travel in pairs. I'm never sure
> which bulb is bad (it almost seems that a bad bulb can work fine in one
> slot
> and not work at all in the other slot). I usually swap bulbs and fixtures
> for
> as long as my patience lasts, then replacing them all.

As long as the filaments are good - check continuity between the pair of
pins at each end - your only real test is to try in a known working fixture
with another known owrking bulb.

[Asimov]

bcol...@bnr.ca said the following to All on the subject of
How-to Test Fluorescent Ballast (24 Sep 97 17:12:35)

bc> I have checked the FAQ and have searched the WEB, but I have not found
bc> any information on how to test if a fluorescent light ballast is any
bc> good. I will be helping to re-lamp my daughter's gymnastics club in the
bc> near future and I would like to test the ballasts that seem
bc> questionable. These are standard four-foot, two lamp fixtures that are
bc> row mounted. I have installed new fluorescents many times, but I am not
bc> familiar with the internal operation of a ballast. Any help that you
bc> can provide regarding ballast operation and test would be appreciative.
bc> I have a multi-meter, but is there any (low cost) specialised test unit
bc> or methods that might be necessary.

A ballast is a simple transformer with a very high impedance secondary
winding which makes its current self-limiting. It also has windings for
each lamp filaments. At startup the filaments get most of the power and
heat up to facilitate ionization.

Meanwhile the secondary builds up a very high EMF which finally fully
ionizes the plasma between both filaments. At this point the effective
resistance of the conducting plasma is quite low and the current flow is
limited by the secondary's impedance. This also partially saturates the
core and as consequence reduces power to the filaments.

The usual failure in ballasts is that the secondary's insulation
deteriorates and it starts leaking to ground. Often because the proper
wiring polarity was not observed. The secondary can thus no longer
generate the high EMF required to start the plasma conducting.

The KISS test method is to use a known good lamp. If it lights, the
ballast is good too. The ballast can also be tested with the power off by
checking for continuity in the filament windings and a very high
resistance to ground for each filament. Don't try this with power on!
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