Optical Build a ballast for an Osram Hg-Cd/10 spectral lamp

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The discussion centers on designing a ballast for the Osram Hg-Cd/10 spectral lamp, highlighting the need for a specific starting voltage and operating conditions. Participants clarify that while a simple resistor could serve as a ballast, a more sophisticated design is necessary due to the lamp's high cost and operational requirements. Safety concerns are emphasized, particularly regarding handling high voltages and the importance of understanding the lamp's I-V characteristics. Suggestions include using chokes for current regulation and the potential benefits of purchasing a pre-made ballast instead of building one from scratch. Ultimately, the conversation stresses the complexity of the task and the need for careful experimentation and safety precautions.
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Could you clarify a bit? The word "ballast" in an electronics context to me implies the need to step up AC Mains voltage to a higher voltage, for example to start fluorescent lights. But this device looks to need 30Vdc at 1A, so if anything you will be stepping down AC Mains voltage to drive it?

Sorry if I'm missing the obvious.
 
DrDu said:
Sorry, the german word is "drossel" which for me is simply an impedance.
Here is what I mean:
https://www.lighting-gallery.net/gallery/displayimage.php?album=5387&pos=2&pid=161485
You're english was correct. Glow discharge lamps often require a ballast. In the simplest case this is just a big series resistor. In more sophisticated designs it is a power supply, or a transformer, with intentionally high output impedance. The point is that the glow discharge region of the paschen curve has a negative resistance that makes the circuit unstable without compensation.
 
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The lamps are very expensive, so I would like to use some rather professional ballast.
 
DrDu said:
The lamps are very expensive, so I would like to use some rather professional ballast.
But you want to design and build it yourself? You may be better buying it, IMO.

Magnetic ballasts aren't the easiest to figure out (or build). You will probably be better off with a high voltage (like 100 - 200VAC or so) and a big series resistor for ballast. You can't buy or sell it because it's an unpleasant thing to have in your lab. The resistor will be big and hot, very inefficient. But the design is simple.

If you don't have experience designing and building stuff with dangerous voltages, then get help from someone who does (fuses, insulation, isolation etc.).

The correct way to do any ballast design is to understand the I-V curve of the lamp, like a Paschen curve. They have only given you the nominal operating point, you really want to know about the small signal resistance (slope, dV/dI).
 
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I guess I am saying that the designer of a "professional ballast" would get more data or would be willing to do some experiments that might destroy a lamp or two, they would also have the equipment and background knowledge to collect the information they need. Sorry, I just don't do this sort of design by guessing; perhaps my standards are too high. Have you tried to ask anyone at Osram about these lamps? Have you looked on the web to investigate spectroscopy lamps?

When you buy a product that is well designed, some of what you are paying for is the result of product development.

OTOH, sure try it, why not; I don't have anything to lose. Those numbers sound ok for a first attempt. How will you know if you have the design you want though?

Please try your very best not to hurt yourself in the process.
 
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This lamp needs an actual ballast that can supply a very specific starting voltage and then drop down to its operating specs. It is a mercury vapor discharge lamp and just supplying 30v @ 1A will not work. here is a link to a spec sheet for the ballast that runs this lamp. Https//www.lej.de/ebs-60-ac.html (I don't know how to post a clickable link -sorry). I suggest you find a manufactured solution to run this lamp, as there are safety concerns.
 
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Thank you, yes, I too found some more detailed information in the meantime. Finally, I decided to buy a used balast at ebay.
 
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I asked the OP question of my friendly Light Globe Collector. After it languished in my spam for a while I found and so present his reply.
I have those lamps and they aren't that difficult to get up and running. They have hot cathodes at each end of the arc tube. These need two floating 4v A.C. supplies with a low enough source impedance the deliver about 1A but they can be started without pre-heating.

The arc current for those lamps is 2A, so you only need a choke in series which will limit the arc current to about 2A. If you can't find the exact value choke, you can get one...or a parallel/series combination of other chokes and adjust the supply voltage with a Variac to fine tweak the arc current. The characteristic arc voltage is pretty low as these are low pressure lamps...I don't think it exceeds 30v...so the chokes will drop about the full mains...(Choke voltage, lamp arc voltage and mains voltage are the three sides of a right angle triangle...I.E. vector addition).

I'd start by using two 40w fluoro chokes in parallel and just wire it up bringing the active off the Variac wiper, through the chokes to any pin on the base of the lamp. Touch the neutral to the other pins until you find a pin where the lamp either starts or there is no spark, (i.e. a pin that connects to the one end of the other electrode, not the other end of the same pre-heat electrode which will be almost a dead short.) So you only need to use one end of each pre-heat electrode...any/either end. Once the pair of pins is found where no current flows (or the arc starts by itself) short out the pins with a screwdriver then remove it suddenly...the back E.M.F. of the chokes should start the arc...if it doesn't start first try, repeat until it does. Run it off a Variac and adjust the Variac whilst monitoring the arc current with an ammeter...adjust until arc current is 2A. Continue to tweak as lamp runs up to keep it near 2A. If you can't get the arc current down to 2A without the arc extinguishing, increase the inductance of the combo of chokes. If you can't get the arc current up to 2A but the arc is running...decrease the inductance of the choke combo a bit and try again.

James Hooker's data on these lamps...sorry, no electrical data...and I haven't got round to measuring mine yet.
http://www.lamptech.co.uk/Spec Sheets/D SP GEC MLD.htm
http://www.lamptech.co.uk/Spec Sheets/D SP GEC CLD.htm
http://www.lamptech.co.uk/Spec Sheets/D SP GEC CMLD.htm

The original gear would have been a clumsy power resistor which was inefficient and provided no back E.M.F. to re-strike the arc after zero crossing. A choke, or combination of chokes will be far more efficient and provide back E.M.F. to maintain the arc without need for heating the electrodes.
 
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