electroluminescent panels, lightboxes, and banding issues

[troypiggo]

Been talking to some guys about this by email, but think I'll cast it to the wider audience.

I bought one of those A4 panels from elec2go.com.au to use as a lightbox for flats. I got the 12V version.

I pretty much just mount it flat against the end of the dewshield hood on my ED80. Tried it up at Leyburn the other week running it off car battery and it worked a treat. I was really happy. Refer the first attached image.

Got back home and doing some more testing running it through a 13.8V regulated power supply off mains power. Now my flats are getting banding in them. Like the panel isn't creating even light at the same instant. Refer the second attached image.

I thought the cause might have been the shutter speed on my camera being close or syncing to the speed of the panel creating the light. Tried changing shutter speeds a bit but can't seem to prevent this banding.

Talking to another IIS member, they said it may have something to do with the reg power supply running at 50Hz causing it. Not sure of the details behind it, I had assumed the "regulated" ensured a pretty smooth output?

Could this be it? Are you aware of some way of evening out this output to stop it?

I know one solution would be to build a proper box, get the panel further away from the end of the hood and use some sort of diffusion material. But I like the way I have it because it packs nice and flat, not bulky.

[wasyoungonce]

Troy...those panels use a switchmode inverter power supply...converts 240V to 12VDC.

Most Switch modes operate at around 15-30Khz...I suspect this PSU is either radiating EMI noise or more than likely is sending unregulated noise in it's output 12V. More than likely...the latter...noise on the 12V rail.

If you move the PSU away from the EL panel (use/make a 12V extension lead)....does the interference reduce?

Or if as I suspect it's noise on the 12V rail...try a ferrite bead on the 12V PSU cord...as a RF filter..see here (http://www.jaycar.com.au/productView.asp?ID=LF1292&keywords=ferrite&form=KEYWORD)or here (http://www.jaycar.com.au/productView.asp?ID=LF1294&keywords=ferrite&form=KEYWORD)or here. (http://www.jaycar.com.au/productView.asp?ID=LF1250&keywords=ferrite&form=KEYWORD)Or even another 12VDC source.

[troypiggo]

But I bought the 12V version. A cigarette lighter type plug on the end.

The flats created from a 12V battery power supply are pretty even. But if I power it from a regulated power supply, I get the banding.

[wasyoungonce]

I looked at the PSUs from the elec2go.com.au site & assumed you had on of theirs as well as using a 12V battery source.

What type of PSU is it? Is it a switchmode?

[troypiggo]

I'll have to check tonight and post some piccies.

[Hagar]

The strobe effect must be a result of either over voltage or harminic noise from your power supply. The ferite choke for harmonics or a resister in line should drop the voltage a bit.
I always use either a sheet of white paper or white perspex in front of the sheet to allow reasonable length exposures also.
I have had my 12V A3 sized sheet for a couple of years now without a problem.

[troypiggo]

This is the regulated power supply I'm using (javascript:MM_openBrWindow('ShowLa rgephoto.asp?id=8850&PRODNAME=13.8V%2020A%20Swichmode%20 Bench%20Power%20Supply&IMAGE=','','width=460,height=470,re sizable=1,scrollbars=1,toolbar=0,st atus=1')). Does that help?

[peter_4059]

Have you tried using a 12V supply instead of 13.8V?

[wasyoungonce]

Sorry...linky broken

edit:

I edited the link & found it's the Jaycar 13.8V switchmode PSU. (http://www.jaycar.com.au/ShowLargephoto.asp?id=8850&PRODNAME=13.8V%2020A%20Swichmode%20 Bench%20Power%20Supply&IMAGE=)

I have a version of that...it's OK but not a great regulated supply. Mine squeals under loads.

I suspect that this is putting switching noise on the output line which is the cause of your trouble. You said running it straight from DC it's fine...you either need to use DC (batteries) or a better regulated PSU.

This is one of the reasons I don't particularly like switchmodes, the cheap ones can be ...very cheap in more than one way...I prefer the old stepdown transformer & discrete regulator outputs. Don't see many of them these days.


edit edit:
I meant to say..I use my small Jaycar PSU for things like DEW heater etc..not sensitive equipment.

[troypiggo]

Off 12V battery it's nice and even. See the photos in post #1 above.



Hmm, ok thanks. There's no way to put something inline after the power supply to clean the signal up?

[wasyoungonce]

You might try putting in a ferrite choke listed above...but I kinda think that the PSU is putting out harmonic switching noise which is neigh impossible to fix without re-designing it.

Anyway...it's worth a try...for a few dollars maybe try this one (http://www.jaycar.com.au/productView.asp?ID=LF1250&keywords=ferrite&form=KEYWORD).

[h0ughy]

http://www.iceinspace.com.au/forum/showthread.php?t=48335&highlight=flats+box using th A3 sized panel from that shop

[avandonk]

Switch mode power supplies are really good for interference with just about anything. Just get a regulated standard power supply. If the power supply is light it is switch mode.

I had a laboratory type variable regulated power supply which died due to being rained on.

Tried a switch mode in it's place and both of my GstarEX's had banding on the images. Guiding was compromised and I suspect even image quality in the Canon as well due to interference with it's well regulated 240V power supply.

You cannot beat a stand alone battery as an ideal source of quality DC.

Bert

[netwolf]

Would using a Jump start battery while its also connected to the 240 mains power for chairing provide a regulated supply?
As your taking the power from the battery side while charging the battery at the same time, would not the battery act as a kind of Regulator?

[avandonk]

Any ripple due to the charger would be superimposed on the dead flat DC signal. The battery would attenuate the amplitude depending on it's internal resistance. In the case of a charger it is either 50Hz or 100 Hz or both. Switch mode run at a few kHz with all the associated harmonics and very high voltages so they are far worse. A square wave as generated by a switch mode power supply contains all possible frequencies and are radiated everywhere.



Bert

[rally]

Dont the EL panels operate at 100-200v internally ?

If that is the case then maybe the ripples are coming from the stepup supply rather than the 12v supply.

Just a thought.

[avandonk]

It is all to do with the super position of waves. Unlike quantum states that ignore each other these nasty EM waves interfere with your careful attempts at noise free data aquisition.

Bert

[mithrandir]

I have a

http://www.jaycar.com.au/productView.asp?ID=MP3098&keywords=lab+supply&form=KEYWORD

Have not noticed it annoying anything with interfecence.

[troypiggo]

Sorry guys. The power supply has "DC Regulated Power Supply" on it. Doesn't that mean it's a regulated power supply?



Bert - what do you mean "light" - you mean the almost white coloured box on the power supply like the one Mithrandir quoted? Isn't the black one I have regulated? I must be missing something.



Thanks mate. I have made a lightbox to hold the panel in place. Difference with mine is it is flat, so doesn't have the diffusion that yours does, so the banding is noticeable. Yours may well be gettingi the banding, but it doesn't matter because of the diffusion. I wanted something flat for easier packing. I'm thinking I might make a foldable one.



I was tossing up between the one I got and that one.

[troypiggo]

How many of those do you use? Just one enough? Does it matter where? Close to the power supply, or at the EL panel end?

[h0ughy]

well the box it is in is only 4cm high - so if that isnt flat enough for you you are hard to please? yes i had the banding - thats why i put it in the box with the drafting film - its the only way you will remove it

[wasyoungonce]

Well yes it's regulated in that it regulates an output voltage but it's/they are not good at producing an output with low "Hum" or "Noise" levels.

Even Step down transformer PSUs can have hum & noise but switch-modes are more susceptible to creating noise on their outputs. It's due to the they way they "switch" a high DC voltage (at high frequencies...15- 30Khz) to produce pseudo AC...which is in turn rectified, regulated & filtered to produce an output voltage.

Switchmodes are used because they are more efficient, size is smaller & use less copper.

Good or well designed switchmodes are very good & efficient bad ones or badly produced ones are Ok for general work..but not for sensitive equipment.

As I said I have a version of that PSU my self...and it creates noise. So I adapted a computer PSU as a 12VDC supply (for my mount supply). Sure it's a switchmode as well but in general these are very well designed & create less output noise. It's ok for my equipment ATM.

Soon...in the future I'll be building my own step-down transformer DC regulated supply for the mount & other equipment. I prefer them as it's much easier to produce a nice "clean" output.

Not many step-down transformers PSUs are available now days...pity!

[troypiggo]

Have you been talking to my wife? :)



Thanks for putting up with all my questions. What about those ferrite rings - how many, where?

[wasyoungonce]

no problems...easiest thing to try is to just put one ferrite bead (http://www.jaycar.com.au/productView.asp?ID=LF1250&keywords=ferrite&form=KEYWORD) on the cord running to the device (either the +ve or -ve lead). Loop the cord thru the ring once...and out to the device (if you can).

Or try one of the other Jaycar ferrite chokes.

Problem is your trying to fix a design that may be uneconomic to do so.

[netwolf]

The refrence to "light" earlier is to the Weight of the power supply. The switchmodes are usually very light weight.

I would also be interesting in getting a non-switchmode regulated 12V unit with enough amps to power a scopes and accesories. If someone knows one please link to it.

Regards
Fahim

[mswhin63]

Mains hum is on many occasions a bit of a problem and requires significant filtering to reduce or eliminate the problem. Ferrite bead and inductive filter is more designed for High Freq filter where as large capacitors are design primarily for low freq filtering. Combination provide bandpass or bandstop filtering.

Batteres are one very big capacitors. It is possible that the regulated PSU has not got enough filtering for EL lighting cct's.