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Multi-lamp fluorescent sign ballast mystery

C

Chuck

Jan 1, 1970
0
I am helping a friend who owns a restaurant to repair a large marquee sign
in his front parking lot. The sign was working fine for the last 3 years
until recently. The sign uses two separate horizontal banks of 5 linear 72"
(F72T12/D/HO) lamps per sign ballast. The pin style is recessed double
contact. The input voltage is 120VAC. The label on the sign ballast has
aged but looks like its a Rapid Start - Magnetic, Valmont 6G3959WF. I
think this is a 4 lamp ballast (not a 5 lamp). There are a total of two
ballasts, one for each bank of five lamps, for a total of ten lamps. One
bank of five lamps works just fine. However, on the other set of five, only
one lamp, the one at the bottom physically closest to the ballast lights up.
All of the lamps have been confirmed to work by removing them one at a time
and testing them in the working lowest socket. I now need to troubleshoot
this bank of lamps while standing on top of a 12ft step ladder in the middle
of a parking lot.

Troubleshooting Questions:
- Since one lamp still works, can the ballast be considered 100% good?

Chuck
 
J

JohnR66

Jan 1, 1970
0
Chuck said:
I am helping a friend who owns a restaurant to repair a large marquee sign
in his front parking lot. The sign was working fine for the last 3 years
until recently. The sign uses two separate horizontal banks of 5 linear
72" (F72T12/D/HO) lamps per sign ballast. The pin style is recessed double
contact. The input voltage is 120VAC. The label on the sign ballast has
aged but looks like its a Rapid Start - Magnetic, Valmont 6G3959WF. I
think this is a 4 lamp ballast (not a 5 lamp). There are a total of two
ballasts, one for each bank of five lamps, for a total of ten lamps. One
bank of five lamps works just fine. However, on the other set of five,
only one lamp, the one at the bottom physically closest to the ballast
lights up. All of the lamps have been confirmed to work by removing them
one at a time and testing them in the working lowest socket. I now need to
troubleshoot this bank of lamps while standing on top of a 12ft step ladder
in the middle of a parking lot.

Troubleshooting Questions:
- Since one lamp still works, can the ballast be considered 100% good?

Chuck
5 Lamps on 4 lamp ballast? Something screwy here. Need to see the wiring.
 
C

Chuck

Jan 1, 1970
0
Victor Roberts said:
No. I can't find your ballast, or any other 4-lamp ballast,
but 2-lamp and 3-lamp magnetic rapid start ballasts usually
have the lamps wired in series and use what is known as
"series sequence start." For two lamps that means that
one of the lamp has a small capacitor wired in parallel with
it so that all the open circuit voltage is applied to the
other lamp. Once the first lamp starts, the impedance of
the operating lamp is lower than the capacitor across the
other lamp, so all of the remaining voltage is now placed
across the second lamp. You can extend this idea to 3 or
even 4 lamps. If the small starting capacitor shorts out,
then the second lamp will never start.

But, you also know that the ballast is not OK because you
said that all the lamps are OK.

As has been said, operating 5 lamps on a 4-lamp ballast is
not possible, so the original ballast may be 5-lamp. Why do
you think it is a 4-lamp ballast? How may pairs of
different color wires does it have going to the lamps? If it
has 5 pairs it is a 4-lamp ballast. If it has 6 pairs it is
a 5-lamp ballast.

Vic,
I will be taking my second look at the lamps and ballast tomorrow weather
permitting. I will open up the wire channel hats and will count the
wires/colors pairs then for a positive identification. I think it is a 4
lamp ballast only because of the ballast label that reads 6G3959WF which
happens to be a 4 lamp sign ballast per (
http://www.advancetransformer.com/uploads/resources/CR_SignBallast.pdf ).
Will get back to this thread shortly thereafter. Thanks.

Chuck
 
C

Chuck

Jan 1, 1970
0
Victor Roberts said:
No. I can't find your ballast, or any other 4-lamp ballast,
but 2-lamp and 3-lamp magnetic rapid start ballasts usually
have the lamps wired in series and use what is known as
"series sequence start." For two lamps that means that
one of the lamp has a small capacitor wired in parallel with
it so that all the open circuit voltage is applied to the
other lamp. Once the first lamp starts, the impedance of
the operating lamp is lower than the capacitor across the
other lamp, so all of the remaining voltage is now placed
across the second lamp. You can extend this idea to 3 or
even 4 lamps. If the small starting capacitor shorts out,
then the second lamp will never start.

But, you also know that the ballast is not OK because you
said that all the lamps are OK.

As has been said, operating 5 lamps on a 4-lamp ballast is
not possible, so the original ballast may be 5-lamp. Why do
you think it is a 4-lamp ballast? How may pairs of
different color wires does it have going to the lamps? If it
has 5 pairs it is a 4-lamp ballast. If it has 6 pairs it is
a 5-lamp ballast.
I replaced the single known-bad bulb in the unlit bank of four and..... they
all lit up. The single lamp on the bottom that was always lit was wired to
another ballast (I overlooked) from the lamp bank on the other side. In
conclusion, there were a total of three ballasts, two four lamp sign
ballasts and one two lamp sign ballast. Problem solved. Thanks for helping
me think this through.
 
J

Jeff Waymouth

Jan 1, 1970
0
I don't have any references I can look up (I've been out of town for
some time), but I woudl venture to guess that this is a speial class of
ballasts called sign ballasts. Often they will be rated in terms of
total length of lamps, rather than number of lamps. The facttthhat the
lamps involved are HO types is also at least suggestive of this.

Jeff Waymouth
 
C

Chuck

Jan 1, 1970
0
Jeff Waymouth said:
I don't have any references I can look up (I've been out of town for some
time), but I woudl venture to guess that this is a speial class of ballasts
called sign ballasts. Often they will be rated in terms of total length of
lamps, rather than number of lamps. The facttthhat the lamps involved are
HO types is also at least suggestive of this.

Jeff Waymouth
I replaced the single known-bad bulb in the unlit bank of four and..... they
all lit up. The single lamp on the bottom that was always lit was wired to
another ballast (I overlooked) from the lamp bank on the other side. In
conclusion, there were a total of three ballasts, two four lamp sign
ballasts and one two lamp sign ballast. Problem solved. Thanks for helping
me think this through.
 
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