Any real difference between 5' and 6' ballasts?

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SuperSix
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Any real difference between 5' and 6' ballasts?

Postby SuperSix » Mon Apr 11, 2011 9:08 pm

This is something that's puzzled me a bit, I've noticed on some older chokes and ballasts for 6' 85W tubes it says they're also suitable for 5' 80W. James Hooker told me once that the 6' 85W was designed to run on existing 80W gear too.

I've seen the same thing printed on some 6' 75W or 5' 65W ballasts, the two are dual rated for either tube so is there really any difference in the ones specifically labeled for either a 5' or 6' tube?

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Kev
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Re: Any real difference between 5' and 6' ballasts?

Postby Kev » Mon Apr 11, 2011 10:54 pm

I have also noticed that some Thorn fitting have the same ballasts in for the 5' anf 6'! When ordering them though i order 5 and 6 foot Tridonic ballasts seperate!

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Re: Any real difference between 5' and 6' ballasts?

Postby sailormoon01uk » Tue Apr 12, 2011 6:32 am

Both the 5ft 65w and 6ft 75w Fluorescent tubesare the same current 0.67 amps, the only difference is the arc Voltage the 5ft 65w being 110 volts, and the 6ft 75w being 130 volts, as there is only 20 volt difference they can be safely used on both 'ballasts, however a old 5ft 80w Tube is slightly under run by current as they are 0.8 to 0,85 amps and over voltage as they are 100 volts again as you raise the lamp voltage the lower the current becomes so the old 5ft 80w Tube will happally run on a modern 5ft 65w or 6ft 75w Ballast

Out of interest there used to be Universal Tubes on the market, they were 5ft 65/80 watts for use on Both Older 80w Fittings (with Bi-pin to BC adaptors) as well as the later 65w Dittings, and the 6ft 75/85w ahgain for use on older 85w fittings as well as the modern 75w fittings, as we know Fluorescent lights have again being re rated with the introduction of the T8 (1in) Dia Tubes i.e. 5fts are 58w and 6fts are 70 watts, again the Tubes are interchanable on Conventional Control Gear.

All the Best

Colin

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Re: Any real difference between 5' and 6' ballasts?

Postby Kev » Tue Apr 12, 2011 4:31 pm

Hi colin

All new SLI T12 5' and 6' lamps still have the old wattages on. These are new on my van last week. I still keep a fair amount of T12 lamps on my van as i use use as many T12s as i do T8s. I also keep a few 8 foots in different wattages and colours on my can too! Enjoy!
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Tom
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Re: Any real difference between 5' and 6' ballasts?

Postby Tom » Tue Apr 12, 2011 6:07 pm

I've seen Thorn 65-75w SRS ballasts. For ballast and starter switch. Upon switch-on, the starter closes and preheats the tube's cathode filaments. Upon opening, the magnetic field within the ballast collapses, causing a voltage pulse which strikes the tube. This is often repeated twice or more, causing the distinctive blinking at startup.">switchstart, Thorn used to make a dual rated ballast for both 5' 65w and 6' 75w that was fitted to the old Pop Packs of the late 70s. For 65w it was wired for lagging power factor (HPF) with the cap across the mains. For 75w it would be wired as a leading PF circuit with a 440v cap in series with the live feed. I've also seen an Atlas 80/125w ballast in an old 5' Superslim which suited both the old 5 and 8 footers wired as per before.

Out of interest the 6' T12 Pop packs were offered with both leading and lagging PF circuits with a separate 75w ballast also.
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SuperSix
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Re: Any real difference between 5' and 6' ballasts?

Postby SuperSix » Tue Apr 12, 2011 6:24 pm

Well thanks for clearing everything up, the two ballasts are deffinately suitable for both tubes then.

Colin, I thought it worked the other way round with over/under driving tubes? I thought it was current dependant so if you stuffed more current through a tube the arc voltage will fall? I'm not really making sense now but I thought you couldn't over volt a tube, only over current it. I might be wrong though!

Tom, was the 80/125W ballast you saw black? I've seen a black Atlas ballast in an old 5' Superslim too that had in smaller print something about it also being suitable for 8' 125W. I take it you just use a series cap with it for 125 watters then?

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sailormoon01uk
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Re: Any real difference between 5' and 6' ballasts?

Postby sailormoon01uk » Tue Apr 12, 2011 7:02 pm

Actually if the current is the same match the Lamp voltage will correct itself, as long it's in the 20% Region

Example a 80w MBF/U runs at 115 volts 0.8 amps utthe arc voltage can vary between 110 and 130 volts on a 220/250v supply even on a 200/220v supply the Lamp voltage drops down as far as 100 volts, any low the arc will become unstable and any fluctuation wil extinguish the lamp

All the Best

Colin

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Re: Any real difference between 5' and 6' ballasts?

Postby Tom » Tue Apr 12, 2011 7:09 pm

@ Eliot I think it was that classic bronzy-gold colour but it was many moons ago LOL. I think the series cap increases the wattage. I remember it being the usual 7.2uF 440v rating. Incidentally, the 5' 50w Arrowslim had a series cap! Well, the original Atlas Blackender I saw did anyway. Something like 2.8uF 440v!
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Re: Any real difference between 5' and 6' ballasts?

Postby Kev » Tue Apr 12, 2011 9:51 pm

That was a problem with the 6' fluorescents and the 8 foots is that the 7.2 Mf caps always pack up. In one of the fire stations almost every single bloody cap has failed. I have just linked them out lol


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