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From: Mike Mocha <mocha@mailexcite.com>
Subject: Re: Philips TL-S bulbs
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On Wed, 10 Apr 2024 17:16:42 +0100, Liz Tuddenham wrote:

> Mike Mocha <mocha@mailexcite.com> wrote:
> 
>> On Wed, 10 Apr 2024 08:44:52 +0100, Liz Tuddenham wrote:
>> 
>> > Mike Mocha <mocha@mailexcite.com> wrote:
>> > 
>> >> Hey all,
>> >> 
>> >> I have an old rail car design that used ballast-free florescent
>> >> tubes in a 600 VDC circuit; bulbs used in series with power
>> >> resistors, the circuit basically put 100 VDC or 60 VDC over each
>> >> bulb.  There's no AC source on the car.
>> > 
>> > I think those tubes needed special switches to reverse the polarity
>> > each time they were switched on.  This was to prevent darkening of
>> > one end of the tube after a few hours, caused by migration of the
>> > mercury.  You may have to replace the switchgear if you fit
>> > inverter-powered lamps.
>> > 
>> > If you contact a tramcar manufacturer, they should be able to put you
>> > in touch with some companies that supply modern lighting equipment
>> > for 600 VDC.
>> 
>> You might be correct about this in terms of a good practice, but in the
>> design I'm dealing with this is not the case, and thus possibly the
>> reason so many of the tubes burned out.
> 
> Are you sure they have, in fact, burnt out?  If they have gone black at
> one end, that is most likely because of the mercury migration problem.
> Reversing the polarity should restore them for a short while until the
> mercury migrates the other way.
> 
> There is a lot of information about this in the Philips Technical
> Review, I remember reading it but can't remember the date (it might have
> been in the 1930s).

That's actually a good point.  I don't think the maintenance people tried 
that.  I'll go and check if they still have the bad bulbs.  Thanks.