[pure-silver] Re: Enlarger Lamp Life

Many thanks for the swift reply to my questions everybody. Claudio, the problem of taking a measurment under load is the tight fit at the ceramic socket that the lamp prongs fit into. However, I will see if I can score power supply switcher or even a voltage spike protector. 
Thanks again everybody -
Eugene Barrington
On 27 Oct 2008, at 16:16, Claudio Bonavolta wrote:


The voltage at a transformer output is always higher without load.
Once you put the load, it (should) drops to its nominal value.
The voltage drop depends on the load and transformer respective impedances. 
You should measure the voltage with a new bulb fitted.

Several factors may affect the bulb life:
- input voltage, you may be close to the power plant and the voltage may be on the high side. Measure the voltage at the mains and at the transformer output (loaded of course). - the mains voltage has slightly increased these last 20 years. Here in Europe we've gone from a 220V to a 230V and maybe slightly more. So if your enlarger is old then the transformer apply to the bulb this voltage increase. Same measures to be done. - frequent switch off/on, which is the case with an enlarger, as switching on a bulb generates a current spike (a cold filament has a much lower electrical resistance than a hot one).
In my case, I stabilized the bulb voltage to the proper value (main goal was constant exposures) through a switching power supply that reduces also the current inrush which makes the bulb last longer. The protection type of the supply must be a current limitator as the common "stop-and-retry" will not work with a bulb, it will make it blink (!). 

More details on this page:
http://www.bonavolta.ch/hobby/en/photo/v35suply.htm
See "Switching Supply"

Claudio Bonavolta
www.bonavolta.ch

----- Message d'origine -----
De: Eugene Barrington <eandpbarrington@xxxxxxxxxx>
Date: Mon, 27 Oct 2008 15:31:33 +0000
Sujet: [pure-silver] Enlarger Lamp Life
À: pure-silver@xxxxxxxxxxxxx
Hello - I'm a new poster to this list but I've consulted it regularly. 

I know that this topic has been dealt with before - but the enlarger
lamp I need to  use is is rather expensive (€21,£16.96,$26.17 and so
forth) and they have a nasty habit of blowing. My enlarger is a Meopta 
with a colour head which uses  a Philips Focusline fibre optic lamp
type 6834 FO. I suspected a faulty transformer. using a multimeter I
got a maximum, but steady 13.1 volts output from the transformer. The
lamp is rated at 12volts 100w. Is it being overloaded at 13v? Could
this be the reason for the frequent blowouts or is there some
tolerance with the voltage?

Hope somone can help with this -
Eugene Barrington
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