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Author
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Topic: Transformer Settings
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Paul Adsett
Film God
Posts: 5003
From: USA
Registered: Jun 2003
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posted February 29, 2008 06:12 PM
I just checked the voltage across the lamp of my Eumig S938, with the lamp running. It measured 12.7 volts, but it is supposed to be getting 15 volts (150 watt lamp). The mains input voltage to the projector measured 120 volts and the projectors transformer tap is set to the 117 volt position. So I moved the transformer tap to 110 volts and then measured 13.1 volts at the lamp, again with the lamp switched on to full power. Is it safe to run the projector this way, or do I stand the chance of blowing out the motor or sound electronics? Even now it looks like the lamp is still not getting the full 15 volts, should I drop the transformer setting down even more - to 100 volts, and is that safe to do?
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The best of all worlds- 8mm, super 8mm, 9.5mm, and HD Digital Projection,
Elmo GS1200 f1.0 2-blade
Eumig S938 Stereo f1.0 Ektar
Panasonic PT-AE4000U digital pj
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David Pannell
Phenomenal Film Handler
Posts: 1072
From: Horsham, West Sussex, UK
Registered: Nov 2004
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posted March 01, 2008 01:33 AM
Paul and Kev,
Bear in mind that if the voltage to the lamp is lower than it should be, then the voltage to all other parts of the projector will also be proportionally lower. The transformer regulation applies to all the loaded windings, and if one winding's volts are pulled down when the load is applied, this affects the regulation on the other windings, and the transformer is unable to supply the other circuits with the correct voltage.
I run all my projectors on 120 volts, as we have many American appliances in our home, so we are wired for 120 volts as well as 240 volts.
It has been my experience that all of my projectors, including the Elmos and Eumigs, have cheaply manufactured transformers, and the regulation is disgustingly poor. They are all set to the 100 volt setting, with no ill effects, and the other voltages are as they should be, according to the stickers on the transformers and circuit information.
I have found that by ensuring the volts are correct at the lamp, the volts are correct elsewhere.
You can get a rough idea as to how good or poor the regulation is, by measuring the lamp volts with the lamp off, and then on. If there is a significant variation between the 2 readings, then the regulation is bad. If there is little or no difference between the 2 readings, then the regulation is good. However, remember that the amplifier will be on for both of these sets of readings, (unless you have a switch for turning it off - in which case do so - so you won't get an exact measurement of difference), as the amplifier will be dropping the volts somewhat. The difference between no load and full load as a percentage, will be the percentage regulation of the transformer.
Therefore, if the percentage is, say 20%, then you will need to drop the voltage selector from 120 to 100 (20%) to achieve the correct output. QED
If, however, there is little or no difference between the 2 measurements, and the transformer has good regulation (which I very much doubt) then the voltage values on the tapping are arbitrary, if not incorrect, which again reflects poor and cheap design and/or poor quality control.
With regard to possible damage to the motor, this is not an issue if it is a mains synchronous induction motor, as it will be driven direct from the mains input and therefore will be unaffected by any transformer tapping. Motors of this sort are frequency conscious, rather than voltage conscious, so whilst frequency is of major concern, they can actually accept a very wide variation in voltage - (within limits, of course).
Sorry, - but there it is!
[ March 01, 2008, 03:11 AM: Message edited by: David Pannell ]
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Dave.
Valves and celluloid - a great combination!
Early technology rules OK!
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David Pannell
Phenomenal Film Handler
Posts: 1072
From: Horsham, West Sussex, UK
Registered: Nov 2004
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posted March 01, 2008 03:58 PM
Hi Paul,
Try it and see. If you still can't achieve the 15 volts, or slightly above, at the lamp with it switched on, I would suspect a fault within the transformer. Do the regulation test that I suggested, and see what the volt drop is. Measure the volts to the lamp with the lamp off and then on. Let me know what the answers are, and I will try to analyse the problem for you.
Best,
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Dave.
Valves and celluloid - a great combination!
Early technology rules OK!
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Paul Adsett
Film God
Posts: 5003
From: USA
Registered: Jun 2003
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posted March 01, 2008 08:09 PM
Thanks Kev and David,
I did some re-testing and I think the problem is non existant. Let me explain. My first set of readings, in the initial posting, were measured at the lamp pins, accomplished by withdrawing the ceramic lamp socket slightly to expose the lamp pins sufficiently to get a voltage probe to lay on the pin and get a reading. I remembered this evening that last year I had to replace the ceramic lamp holder on this 938, and I did this by cutting the lamp wires inside the machine and re-connecting up the new socket with a connector block. So I thought it might be easier to get a more reliable voltage reading by sticking the meter probes into the screws which clamp the wires inside this connector block. When I did this I got much better voltage readings with the lamp powered up:
Transformer setting 117 volts, Lamp voltage 14.4
Transformer setting 110 volts, Lamp voltage 15.2
So it looks like there was probably an oxidation layer on those lamp pins (and maybe the socket as well) which was preventing a real good contact to the pins, and giving me an incorrect low reading. This also illustrates the need to keep those lamp pins clean ( and maybe change out the socket every few years)if you want that bulb to run at maximum brilliance.
Anyway, the 938 is sitting back on the projection table with its voltage reset at 117v, and a big grin on its face! ![[Big Grin]](biggrin.gif)
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The best of all worlds- 8mm, super 8mm, 9.5mm, and HD Digital Projection,
Elmo GS1200 f1.0 2-blade
Eumig S938 Stereo f1.0 Ektar
Panasonic PT-AE4000U digital pj
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David Pannell
Phenomenal Film Handler
Posts: 1072
From: Horsham, West Sussex, UK
Registered: Nov 2004
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posted March 02, 2008 01:24 AM
Hi Chaps,
Kev; I was about to suggest the 12 volt lamp scenario, but you've beaten me to it.
Paul; I'm glad everything worked out. Sometimes discussing these things leads us to investigate areas which may not have come to mind otherwise.
Unless you're particularly fussy about lamp life, from what you say, personally I'd give the lamp the 15.2 volts on the 110 volt setting. 0.2 volts is only a 1.3% increase; whereas 14.4 volts is a 4% decrease! All my lamps are run at a fraction overvoltage and the difference in brightness is quite amazing, with little or no effect on lamp life in actual practice.
(A certain percentage increase in voltage applied to an incandescent lamp results in a far greater percentage increase in light output. It's not quite a square law, but an exponential increase. I do have figures for this, but I won't bore you any further, - suffice it to say that you're probably losing between 6 and 10% light output with a 4% decrease in voltage).
It's been an interesting thread, though.
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Dave.
Valves and celluloid - a great combination!
Early technology rules OK!
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