[sci.electronics] Converting a florescent hood

richard@gryphon.COM (Richard Sexton) (12/07/89)

In article <3693@convex.UUCP> tork@convex.COM (Bill Torkelson) writes:
>
>I have a couple of hoods that are very attractive and fit onto my show
>tanks.  The problem with them is that they have manual switches.  By this
>I mean that they require the switch to be held in for a certain period of
>time before the light will start.  From what I have learned from
>Richard's postings I believe that this may have something to do with the
>"balast" but I'm not sure.  What I'd really like to do is convert these
>lights to auto startup lights so I can put them on timers.  Since these
>are show tanks I would like to preserve the appearance of the hood.  How
>easy is it to convert from a manual startup to an auto startup?  Should
>I expect to make major modifications?  Is it just a matter of buying a
>shop light and taking the guts out and putting then into the existing
>hood?

Let me stick my neck out here. I know what an electron is *in theory*
and I know what a resistor does, but people have spent hours trying
to exlplain to me what a transister does, so like I'm an idiot
when it comes to this electronics stuff, ok ?

However, what I think you want to do is go to the hardware
store a buy a starter (fluorescent light starter) that is meant
for the tube you have (20 watts, 30 watts etc) and wire it 
in place where the switch used to be. I'fe just wrapped
the wire around the posts on the starter and covered it with
a bunch of electrical tape.

If this is right, good. If it's now I'm sure somebody will
point this out.

frankb@hpsad.HP.COM (Frank Ball) (12/08/89)

Subject: Re: Converting a florescent hood
Newsgroups: alt.aquaria,sci.electronics

In article <3693@convex.UUCP> tork@convex.COM (Bill Torkelson) writes:
>
>I have a couple of hoods that are very attractive and fit onto my show
>tanks.  The problem with them is that they have manual switches.  By this
>I mean that they require the switch to be held in for a certain period of
>time before the light will start.  From what I have learned from
>Richard's postings I believe that this may have something to do with the
>"ballast" but I'm not sure.  What I'd really like to do is convert these
>lights to auto startup lights so I can put them on timers.  Since these
>are show tanks I would like to preserve the appearance of the hood.  How
>easy is it to convert from a manual startup to an auto startup?  Should
>I expect to make major modifications?  Is it just a matter of buying a
>shop light and taking the guts out and putting then into the existing
>hood?

*However, what I think you want to do is go to the hardware
*store a buy a starter (fluorescent light starter) that is meant
*for the tube you have (20 watts, 30 watts etc) and wire it 
*in place where the switch used to be. I've just wrapped
*the wire around the posts on the starter and covered it with
*a bunch of electrical tape.

This is the correct procedure, but I thought a longer winded explanation
but be of some help to Bill.  The "switch" has two "switches" inside of
it.  There is a switch to turn on the power, and one to start the light.
When you push the switch it clicks on the power to the ballast, this 
power remains on after you let go, these two wires need to stay connected
as is.  The other two wires are to start the bulb, and are only connected
for as long as you push the button.  The two starting wires will go to 
pins on opposite ends of the light bulb,  you need to disconnect them
from the switch and attach a starter in place of the switch.  Starters
almost always have aluminum terminals so soldiering to them is not
possible.  Finding sockets for them is equally impossible, so I guess
you will have to make do with wrapping wire around the terminals and
taping.  There is no polarity on the starter to worry about (you can't
put it in backwards, it doesn't matter).  The wires to the switch that
you want to leave intact are the two that go to the 120 volt power cord
and to the ballast.  

Frank Ball          frankb@hpsad.HP.COM

torkil@psivax.UUCP (Torkil Hammer) (12/08/89)

[manual start of fluorescent tubes]

It is not a question of ballast but of starter.

The ballast limits the current once the tube is started.  Without ballast
the tube is likely to explode.  Be careful when you experiment.

Starting is an issue of preheating the gas by means of filaments so the
plasma can form.

The starter is usually automatic in light tubes, and usually manual in
UV tubes.  There might be a good reason for this.  There shouldn't be
since the difference between the 2 types is in the coating of the glass
but you never know.

Torkil Hammer

richard@gryphon.COM (Richard Sexton) (12/13/89)

In article <21670@adm.BRL.MIL> moss@brl.mil (Gary S. Moss (VLD/VMB) <moss>) writes:
>Recently, I learned something regarding rapid-start ballasts and flourescent
>fixtures; certain, if not all such ballasts, require that a strip of metal
>grounded to the ballast be roughly within 1 inch of the bulb along its entire
>length.  

Does anyone know why ?

frankb@hpsad.HP.COM (Frank Ball) (12/13/89)

*From: richard@gryphon.COM (Richard Sexton)
*Subject: Re: Re: Converting a florescent hood
*Newsgroups: alt.aquaria,sci.electronics,misc.consumers
*In article <21670@adm.BRL.MIL> moss@brl.mil (Gary S. Moss (VLD/VMB) <moss>) writes:
*>Recently, I learned something regarding rapid-start ballasts and flourescent
*>fixtures; certain, if not all such ballasts, require that a strip of metal
*>grounded to the ballast be roughly within 1 inch of the bulb along its entire
*>length.  
*
*Does anyone know why ?

I would suspect it is for the starting circuit.  They use a high voltage 
spike to ionize the gas inside, the spike is applied between the pins
on the end of the tube and the ground strip.  This sounds very similair to 
the triggering of a xenon flash tube, which have a trigger electrode that
is connected to the outside of the glass tube.

Frank Ball          frankb@hpsad.HP.COM

swine@softway.oz (Peter Swain) (12/20/89)

richard@gryphon.COM (Richard Sexton) writes:

>In article <21670@adm.BRL.MIL> moss@brl.mil (Gary S. Moss (VLD/VMB) <moss>) writes:
>>Recently, I learned something regarding rapid-start ballasts and flourescent
>>fixtures; certain, if not all such ballasts, require that a strip of metal
>>grounded to the ballast be roughly within 1 inch of the bulb along its entire
>>length.  

>Does anyone know why ?


Eureka! That's why half my fluoros don't start reliably!

This metalwork would affect the shape of the field when the starting-kick
is applied. The field strength (volts/inch) would be heightened by the ground
plane.

An isolated tube refuses to fire:

	[--------------------------------------]
	[                                      ]
	[--------------------------------------]
	|<-- voltage developed across here --->|

But a tube with metal near whole length can break down in stages:

	[--------------------------------------]
      __[.....                                 ]
      ^ [--------------------------------------]
      |      .
      | _____.__________________________________
                                               
      V ---->|                                
                                             

with a short arc sneaking out internally, sustained by the capacitance of
the air gap (low dielectric const, but a little higher than the rarefied
nothing inside, no?).

This arc would creep along until it met the other end, with the field 
strength essentially constant, as the resistance of the arc is exceedingly low
once struck.

	[--------------------------------------]
      __[****************                      ]
      ^ [--------------------------------------]
      V                 .
      v_________________._______________________
                                               


I'll wind a bit of wire around my flakey fluoro, that should fix it.

Does this make any sense??
-- 
Peter Swain - Softway Pty Ltd		(swine@softway.oz)
    79 Myrtle St, Chippendale, NSW, Australia
PHONE:	+61-2-698-2322		UUCP:		uunet!softway.oz!swine
FAX:	+61-2-699-9174		INTERNET:	swine@softway.oz.au

michael@xanadu.com (Michael McClary) (01/17/90)

In article <2485@softway.oz> swine@softway.oz (Peter Swain) writes:
>richard@gryphon.COM (Richard Sexton) writes:
>
>>In article <21670@adm.BRL.MIL> moss@brl.mil (Gary S. Moss (VLD/VMB) <moss>) writes:
>>>Recently, I learned something regarding rapid-start ballasts and flourescent
>>>fixtures; certain, if not all such ballasts, require that a strip of metal
>>>grounded to the ballast be roughly within 1 inch of the bulb along its entire
>>>length.  
>
>>Does anyone know why ?
>
>
>Eureka! That's why half my fluoros don't start reliably!
>
>This metalwork would affect the shape of the field when the starting-kick
>is applied. The field strength (volts/inch) would be heightened by the ground
>plane.

Bingo.

(I recall an analysis of a powerline insulator design which flashed
 over at an unexpectedly low voltage, by exactly this mechanism.
 The dilectric constant of the insulator, combined with its shape,
 concentrated the field at the bottom of the insulator, and arcs
 would strike at the skirt and climb up the outside.  The cure was
 to conductive-coat about the bottom third of the INSIDE of the
 insulator, which evened out the field on the outside surface.)