Film-Tech Forum ARCHIVE: Solar Cell Testing

This is topic Solar Cell Testing in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jim Somich (Member # 3597) on 08-27-2006, 11:17 AM:

Does anyone have a good way to test solar cells? I have one that puts out about 1/2 volt in normal daylight with no load, but it seems to have low output in the projector. Is there any reference voltage that would put me in the ballpark? Is there anything that will work as a substitute from Radio Shack etc? At least for testing. Thanks.

Posted by Marin Zorica (Member # 1716) on 08-27-2006, 04:07 PM:

1/2 volts....hm that sounds good to me!

But best way is to put and set dolby level (or other kind of level concidering you're processor-preamp)

YOu can use some photodiodes that fits in you're cell housing, but if You have stereo cell, than is bit dificult to find something other for stereo, but is possible depending are you want to have fun with that, concidering you can get new stereo solar cell for about $30.

Posted by Jim Somich (Member # 3597) on 08-27-2006, 06:46 PM:

Can you tell me your source for cheap solar cells? Thanks.

Posted by Dave Macaulay (Member # 813) on 08-27-2006, 11:38 PM:

Open circuit voltage on a silicon photovoltaic cell is about 0.5VDC so that sounds OK.
The cell needs a load resistor or the sound is distorted; the cell is actually a current source and the load resistor is what gives you a reasonably linear voltage response to varying light input.
Maybe you have some unwanted resistance, if it's been like this since installation. Or the cell is bad and can't provide its rated current; this doesn't necessarily show in an open circuit test. This is quite common when the cell is physically damaged - ie cracked from someone whacking it with a metal tool when working on the prjector. A stereo cell chip should be perfectly rectangular with sharp edges, mono cells are either square or round and may have a collector lens.
Most likely is that your slit lens optics are dirty on the outside or inside. Exciter lamps get mighty hot, several projector brands and models are known to drip oil - the lens breathes in and out as it heats and cools sucking in a bit of oil vapour (or liquid oil if things are really drippy!) eventually coating and darkening the lens elements inside the barrel... hard to clean.

Posted by Marin Zorica (Member # 1716) on 11-13-2006, 03:12 PM:

Today I went to cinema running changeover with MEOPTA MEO5XB....so i set up A-chain on projector 1, when I start to set PROJECTOR 2 i didn't have Left channel.....I inspected all including changing projector inputs...but solar cell was bed, l channel is dead, even i pull it out and connected to ohm-meter, one channel showing something, and other nothing, i even think that cell cable is bad, but I checked it direct on cell...nothing.

I newer had problem like this!

Posted by Paul Stevens (Member # 4016) on 03-11-2007, 01:57 PM:

After replacing a lot of sound drum bearings lately and going over "A" chain setup procedures, I noticed a peculiar trend among the three tested thus far. Although not exactly the same among those tested, the Dolby level test comes up short of the specified targets. This plant is about 9.5 years old with 16 projectors all with the same gear.

What kind of service life can be expected from these LED/Photo cell systems? Must one routinely expect to refurbish these devices in the normal course of component aging? Does anyone rebuild these sound heads on an exchange basis.

All the usual suspects of course were checked to optimize the amount of energy supplied to the input preamplifier of the CP-500. To use an old broadcast engineer phrase, "these things just don't put out enough smoke."

Any suggestions would be appreciated.

[ 03-12-2007, 10:31 AM: Message edited by: Paul Stevens ]

Posted by Sam D. Chavez (Member # 1841) on 03-11-2007, 10:54 PM:

Paul,

I assume you are talking about Red LEDs and not exciters here.

The LEDs do wear out faster than anticipated so three to five years before they will no longer put out enough smoke as you say.

You did not mention the projector or the brand of the reader so I can't make any specific comments but all the LEDS are Dolby 32075. Some brands are easy to change, others are not so easy, but you certainly don't need to refubish the whole sound head for a dimming LED.

Posted by Paul Stevens (Member # 4016) on 03-12-2007, 10:40 AM:

The machines were from Strong. The LED's appear normal but of course that is not any accurate measurement. I am more suspicious that the readers may be going a little flat over time, but I could be wrong.

Does this help?

Posted by Dave Macaulay (Member # 813) on 03-12-2007, 03:16 PM:

Strong factory installs Component Engineering basement readers in the SImplex 5-star, they may be another make if they were retrofitted. The reader part is unlikely to drop in performance - excepting dirty optics - while the LEDs are guaranteed to, so I would look to the LEDs as your problem. The LED array is a Dolby 32075 like Sam says, it is relatively easy to change on the CE design if you're good at working with tiny things and have a temperature controlled soldering iron with a small tip. You can get the LED array from many sources, you want the plain unmounted component with full leads: buying another brand of reader's specific replacement LED may get you something you can't use because of mounting or modifications. Just cut the leads to match the removed array.
Once replaced, the best practice IMO is to set the processor input gain just below full and then lower the LED current to set the Dolby level. Setting a high (ie factory specification) LED current and then attenuating the signal at your processor just shortens the LED life.

Posted by Pete Naples (Member # 761) on 03-12-2007, 05:00 PM:

Dave, all the 5 Stars I've seen over here come with Kelmar readers on, come to think of it the last load of Century heads I worked (a couple of years old now) were fitted with Kelmar too. However I'm more used to seeing CE on the Century machines.

How different is changing the LED pip on the Kelmar to the CE? Never had to do one on a Kelmar as yet.

Posted by Richard Fowler (Member # 893) on 03-12-2007, 05:57 PM:

Te CE is solder to a flexible circuit ribbon. The Kelmar "plugs" in to receptacle. There is usually miniture teflon insluting sleeves in the holes.

Posted by Steve Guttag (Member # 268) on 03-13-2007, 06:20 AM:

The CE is socketed! Kelmar's socket floats so they are a little more tricky.

Posted by Pete Naples (Member # 761) on 03-13-2007, 07:39 AM:

Aye, teh CE is a doddle, two wee screws, clean it up, chop the legs down a bit, smear of heat sink paste, put it back together and re-align. Done.