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jbourd

Jeff's 2005 Dalek

58 posts in this topic

Just found this handy little tool for adding a current limiting resistor to a single LED, an array of LED's connected in parallel or serial (though it correctly states that for parallel usage that it should be one per resistor & simply outlines the reasons why).

 

You can now play with the variables to your hearts (singular or binary vascular system depending on your species & do they work in series or parallel, ideal speculation for a Saturday morning that can be covered elsewhere :D) content.

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I purchased a few of these LED clusters, one for Dalek Luce and one to maybe upgrade Dalek Cas.  Cas' 1W LED is almost bright enough, so this might be an improvement.  The 11V spec for this doesn't seem very accurate.  I think they list the same spec for all colors, but not all color LEDs have the same voltage.  I measured the power vs. voltage curve with no limiting resistor.

 

58b87f64e03fb_4x4BlueLEDAssemblyPvsV.thumb.jpg.031dd30fa36ccc521ded2289eae9b7f7.jpg

 

It is almost exponential, so that confirms there is no built in current limit resistor.  It would have hit it's 7W max rating at about 13.6V.  I didn't actually go that high, because it was getting quite hot.  I measured the aluminum back plate to be 140°F out on the bench.  It would get hotter inside an enclosed eye, which might cause issues with the 3D printed iris.  I'm thinking of running it at 2W instead of 7W, as that is twice as bright as the one I'm using now.  That would be 8.8Ohm (10 is close enough) with a 13.5V ("12V") freshly charged SLA battery.  or 12.0V exactly with no limiting resistor, assuming your cluster is matched to mine.  You can try your regulated 12V supply without a resistor if it can supply 170mA or more current or you can wait for the SLA battery to arrive, and use it with the 10 Ohm resistor.

 

Mike

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My test power supply puts out 12v @ 700ma is what it says on the transformer that plugs in...

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The 700mA will be the maximum that the transformer can provide.  The current that actually gets used will depend on the demands of the item that is being powered.

 

Vince.

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Well, you have had all the theory, and a bunch of helpful comments. I suspect we are now confusing you. On a practical level, grab yourself 10 x 1 ohm resistors and string them all in a chain. Connect the chain in between the battery and the LED. Power it up and see how it is. Remove one resistor and it should be a little brighter. Remove one more and it should be brighter again. Check the led's are not running too hot at each step and continue until you get the brightness you want, or they are running too hot. Once you have the right value, either just tidy it up and use as is, or buy a single resistor of that value. If you have a 12 volt battery (car battery, motor bike battery etc.) I'd use that just to remove the complication of your smallish test power supply.

 

Simples.. :)

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The light is bright!

IMG_7992.JPG.958e08db8b31f5507e065793dec9704b.thumb.JPG.0bc999fb0ca0994e2c7cdc71ef1a6304.JPG

The plate and LEDs warm up a bit (,ax out at 97 degrees) which doesn't seem to hot as I can handle them and not get burned. Should they be cooler?

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That looks like a 10 ohm resistor. Elembivos strikes again... ;) They should be warm to the touch, but not hot I suspect. If they are hot, their life may be limited. Will they be on permanently, or part time? Part time they should be fine. If you are running them all day, then I'd probably add a little resistance to drop the power a little.

 

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Part time for sure!

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Got my tube of aluminum yesterday for the eye stalk, not very shiny. I googled how to polish it and got about a thousand different ways that are all the (best).

Since I trust the forum anyone or everyone want to chime in on best way to get it polished?

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Any not-too-abrasive metal polish. Something made for copper or brass, or even silver. Products for polishing car paint or chrome are fairly gentle and will also work. Work end-to-end, not in all directions.

 

Don't keep switching to a clean bit of cloth/rag. Fold a thin pad and keep using the same bit. Not only will it darken as you polish, it will also start to look metallic. You're effectively using the metal to polish itself.

 

(I've done a lot of this kind of thing!) :) 

 

If there is pitting or noticeable scratching, there are easy solutions for that as well.

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It is a little dinged up from shipping a few pits and scratches some a little deep, I'll try to snag a picture tonight and post

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The best polish I found  is "Solvol Autosol"  I achieved  some good results on pretty rough aluminium and bought it up to a mirror finish, lots of elbow grease but worth the effort.

 

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Did you do it by hand or with a buffer? 

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