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F.S.U's and Wattage Ramblings.

An F.S.U. is a little canister unit that helps start a fluorescent tube in an old magnetic ballasted fluorescent fitting. It is a Fluorescent Starter Unit, thus F.S.U. We don't use them now in modern electronically ballasted fluorescent fittings or with L.E.D. tubes.


In the days when unicorns roamed the Serengeti, we had two popular tubes of F.S.U., one was rated at 4 to 65 Watts, the other up to 125 Watts. This referred to the rating of the tubes. 4 to 65 Watts covers a single tube up to 5 feet long, and the other F.S.U. (up to 125 Watts) covers up to 8 foot long tubes.


I had to change some tubes and starters in an old animal sanctuary yesterday. When I came to buy some new F.S.U.s they were rated 4 to 65 Watts or 70 Watts. The 70 Watt version covers the modern 70 Watt 6 foot tubes. 


Now, a Watt is a very small unit of power. Old tungsten car side lights were just 5 Watts. Dashboard indicator lights might have been just 1.2 Watts. Bright headlights 55 Watts.


So why make two F.S.U.s these days just 5 Watts apart? Why not make just one rated 4 to 70 Watts?


Z.


  • The crucial difference was not in fact the lamp wattage but the lamp VOLTAGE. The nearly universal starter was for tubes with a lamp voltage of up to about 120 volts, which in practice meant all common types of lamp up to and including 5 feet in length.

    The six foot and eight foot lamps had a running voltage in excess of 120 volts and required the higher voltage starter. These starters were more costly to manufacture, and would in fact start the smaller lamps also, but such use was rather a waste as the starters were more expensive than needed.

    Older stocks of the more common lamp starter were marked 4w/80watts, this was misleading as  they would not reliably start a 6 foot 75 watt lamp. The marking was historical from when 6 foot lamps were rated at 85 watts.

    It would have been more accurate to mark the cheaper and very common starters "for all standard types of tube up to five feet in length" and to mark the higher voltage starters "for six foot and eight foot lamps"


    There were also a third type of fluorescent lamp starter for lamps with a much lower operating voltage of up to about 75 volts. These were intended for operation of a 4 watt up to a 22 watt  lamp on a 110/120 volt supply, or for operation of two such lamps in series from a 220/240 volt supply.

    The use of these lower voltage starters was also recommended, but not required, for a single small lamp on a 220/240 volt circuit.


    Many suppliers of fluorescent lamp starters followed the same colour code for markings on fluorescent lamp starters.

    The nearly universal type=blue.

    The 6 foot and 8 foot starters=red.

    The 110/120 volt starters =green.


    Various special types of starter existed in addition, including thermal starters (large 4 pin), glow starters in a 4 pin can intended to replace thermal starters, double glow starters with two starters in a 4 pin can, others for lamps of unusually high rating. None were popular.

  • broadgage:

    The crucial difference was not in fact the lamp wattage but the lamp VOLTAGE. The nearly universal starter was for tubes with a lamp voltage of up to about 120 volts, which in practice meant all common types of lamp up to and including 5 feet in length.

    The six foot and eight foot lamps had a running voltage in excess of 120 volts and required the higher voltage starter. These starters were more costly to manufacture, and would in fact start the smaller lamps also, but such use was rather a waste as the starters were more expensive than needed.

    Older stocks of the more common lamp starter were marked 4w/80watts, this was misleading as  they would not reliably start a 6 foot 75 watt lamp. The marking was historical from when 6 foot lamps were rated at 85 watts.

    It would have been more accurate to mark the cheaper and very common starters "for all standard types of tube up to five feet in length" and to mark the higher voltage starters "for six foot and eight foot lamps"


    There were also a third type of fluorescent lamp starter for lamps with a much lower operating voltage of up to about 75 volts. These were intended for operation of a 4 watt up to a 22 watt  lamp on a 110/120 volt supply, or for operation of two such lamps in series from a 220/240 volt supply.

    The use of these lower voltage starters was also recommended, but not required, for a single small lamp on a 220/240 volt circuit.


    Many suppliers of fluorescent lamp starters followed the same colour code for markings on fluorescent lamp starters.

    The nearly universal type=blue.

    The 6 foot and 8 foot starters=red.

    The 110/120 volt starters =green.


    Various special types of starter existed in addition, including thermal starters (large 4 pin), glow starters in a 4 pin can intended to replace thermal starters, double glow starters with two starters in a 4 pin can, others for lamps of unusually high rating. None were popular.




    Thanks Broadgage,

                                      are you referring to the F.S.U's Voltage rating? I thought that the striking Voltage was connected to the type of ballast (or choke) design. I remember using F.S.U.s rated at up to 22W for Minipack  under unit fluorsesent fittings made by Thorn. The tubes were 12 inch 8 Watt or 21 inch 13 Watt I seem to remember. The 21 inch tubes were also used in street bollards and signs.


    Z.


     

  • I refer here to the voltage across the lamp under steady state operating conditions. This voltage varies from about 25/30 volts for a 6 inch 4 watt lamp, up to about 160 volts for an 8 foot 125 watt lamp.

    The striking voltage of the starter must be greater than the lamp operating voltage, but less than the mains voltage, and by a generous margin in both cases to allow for manufacturing tolerances and supply voltage variations.


    The starters for 6 foot and 8 foot lamps have to reliably strike from a 240 volt nominal supply mains that is down to 220 volts actual, but also to reliably NOT strike from the normal lamp voltage which might be about 175 volts under adverse conditions.


    The nearly universal starters have a much wider voltage tolerance and are therefore cheaper to make.


    Because 6 foot and 8 foot lamps operate at a higher lamp voltage than other types, they need a nominal 240 volt supply for reliable operation. Such lamps on standard switch start control gear do not work well or reliably from 220 volt circuits, which may in practice be below 200 volts at the point of use.

    6 foot and 8 foot lamps can of course be used from 220 volt circuits if the fitting incorporates a step up transformer, but the extra costs, losses and complications tends to drive the choice to five foot or shorter lamps in 220 volt countries.

    An electronic ballast can of course be designed to work any lamp from any supply voltage, including say an 8 foot lamp from a 220 volt supply.


    Longer lamps a UK thing, and also popular in the USA from 277 volt circuits.

  • Thanks Broadgage,


    here is a present for you, longer than an 8 foot tube......

    https://www.youtube.com/watch?v=1kQYCqGGCqU


    Z.
  • I came across this video about the operation of a fluorescent lighting circuit using an old style fluorescent starter unit and magnetic ballast. It refers to 60 Hz frequency,  but the U.K. 50 Hz mains' frequency is still valid and the principle is the same.

    https://www.youtube.com/watch?v=z55566ep0Hg


    Z.