[pure-silver] Re: Enlarger Lamp Life
----- Original Message ----- From: "Eugene Barrington" <eandpbarrington@xxxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, October 27, 2008 1:44 PM
Subject: [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:
A better way to stop spikes is to use a Sola constant voltage transformer. They are somewhat expensive new but older ones show up fairly frequently. The main failure of a CSV is the capacitor since they are rely on a resonance effect. One virtue of a CSV is that the output shuts down completely if its shorted. They are much more effective in removing spikes and other power line noise than the usual spike protector which is usually no more than a couple of diodes. The voltage at the lamp socket depends on what is supplying the power. If the enlarger has an internal regulator it may need to have some minimum load for the voltage to be correct. If its just a transformer then I disagree that the open circuit voltage will be much greater than the load voltage. Your measured voltage is about 9% high which is enough to shorten the lamp life. I don't have a chart of tungsten lamp life vs: operating voltage handy but know that lowering voltage even 5% below the rated voltage will substantially increase life and raising voltage will materially shorten it. I would also examine the socket. Sockets with corroded or dirty contacts can cause localized heating which shortens lamp life. Its hard to know the design life for a lamp but lamp manufacturers often have data sheets which specify it. BTW, check the line voltage. This is important because it may be quite high. "Normal" voltage in the US has gone from 115V to 117V and is now 120V. Local voltage is sometimes up to 122V (as measured by a Tektronix true RMS voltmeter). This is another reason for using a Sola transformer. The elevated line voltages are the result of the power company trying to deliver more power through the same wires, that is the resistance losses are less and is the reason distribution lines run at very high voltages. If you are a power company it doesn't take much to to save some money. 

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx


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