Kind of a big difference, even though there is no direct comparison between the sources (10%Cu vs 10%Cu content).
You can see here a whopping 78W/m.K for the SnAg 96.5/3.5 alloy from a study (seems too high in my opinion), while 2 manufactures rate it much lower at 55W/m.K and 33W/m.K. https://budgetlightforum.com/t/-/24901
Sure would suck to use a coin and then find out that it might have been worth thousands as a rare strike.
I have wondered what silver rod might cost, as compared to copper.
But hey, onlinemetals.com has started using USPS flat rate as a shipping option! I just ordered a 1” long 1.375” dia copper bar and a 2” long .75” copper bar with $6.xx shipping for a total of $24.37 shipped. Easy enough now to get the copper you need, why deface old coins?
The 1.375” piece will be going into a D MagLight, the little one cut up for AA MiniMags. 
why bother?? it does not do much good anyway.
i do think good HTR of sinkpads and noctigons, are more result of soldering led directly, than because it is made from copper. old stars had delectric layer that had single digits HTR, direct path has same rate that of solder that is used to reflow led, which is about half of auminium. so why bother with stars\pills that can do 400+ when heat does not transfer any faster than 50?
the way i see it, no matter how many windows in your house you open, a person with a plastic bag over his head will still not breathe any better.
It's NOT illegal to melt US coins. It IS illegal to remove part of a coin or make a fake coin and pass it off as a real unmodified coin. Go ahead and do whatever you want to your coins. It's legal as long as it doesn't go back into circulation.
“Under the new rules, it is illegal to melt pennies and nickels. It is also illegal to export the coins for melting. Travelers may legally carry up to $5 in 1- and 5-cent coins out of the USA or ship $100 of the coins abroad ”for legitimate coinage and numismatic purposes.”
Violators could spend up to five years in prison and pay as much as $10,000 in fines. Plus, the government will confiscate any coins or metal used in melting schemes.”
There is also that age old “Give unto Caesar that which is Caesar’s” , the currency actually belongs to the US Government, we use it in a sort of barter system. Our tax base supports the minting of coinage and as such, the government (we the people) owns the coinage. Debatable all around of course.
And directly from USMint.gov (April 17, 2007)
“WASHINGTON - The United States Mint today announced a final rule to limit the exportation, melting, or treatment of one-cent (penny) and 5-cent (nickel) United States coins, to safeguard against a potential shortage of these coins in circulation.
United States Mint Director Edmund C. Moy had approved an interim rule on December 12, 2006, to be in effect for 120 days. Enactment of the final rule was pending public comment, solicited during a 30-day period from the date of the interim rule’s publication in the Federal Register on December 20, 2006.
“The new rule safeguards the integrity of U.S. coinage and protects taxpayers from bearing the costs to replace coins withdrawn from circulation,” said Director Moy.”
Cool news about online metals. Finally!
Okay, sure, if you're doing it for business you might face problems. Doing it for a hobby is no big deal. Melt and press coins for all your lights and no one will care about the miniscule amount of coins you're taking out of circulation.
This is where specific heat capacity needs to be considered. Aluminum is 0.897 and copper is 0.385. That means it takes more than twice as much energy to heat aluminum than copper.
A star would have to get pretty hot to transfer a given amount of energy to an aluminum pill. With a copper pill, the star won’t need to get as hot before the copper takes that same amount away. A cooler star means a cooler emitter. Even with an insulating layer under the emitter, it still works the same as long as there’s a temperature gradient.
You could also think of aluminum as being a better thermal insulator than copper.
I believe brass is worse than aluminum too
The good thing is, you can put a copper base UNDER the emitter, even sitting in an aluminum or brass pill, the surface area of the copper helps move the heat away from the emitter more efficiently, just not as efficient if the entire pill were copper
The reason copper sinkpads and noctigons are so popular is that they are direct copper with the only insulation between them and the emitter being to solder used to keep them on the star. Under that star is another layer of insulation being your thermal paste or epoxy. As stated above that is next in line of importance after the copper sinkpad.
Then you have your pill. The Pill can do one of two things, They can act as a heat sink or a heat trasfer unit. (both actually) To get the heat to the pill it must transfer there from the star. If the pill is not perfectly flat, you will have insulation in the form of air or extra thermal paste/solder/whatever. So if you use a coin you will lose a bunch of it the sanding and lapping process. I have done this with old copper pennies. It’s a PITA but it works. Silver isn’t going to be a lot better than older copper pennies if any better depending on the purity.
Now if you want to create a heat sink, you need something large that can absorb a lot of heat. A big chunck of copper will do that really well. A small piece of silver, not so much. If you want to use the pill to transfer heat out of the flashlight then again you run into the insulation factor between the pill and the flashlight body. Just how do you get this dime with insulation all around it that is now paper thin after sanding and lapping to make enough contact with the flashlight to be of any more value than a penny? It won’t be and it certainly won’t be worth the time, effort and money. Take your silver coins and save them for a rainy day.
Not that it was a bad thought, just that when you work out the math it’s just not going to fly.
I suppose if money was really no option you could buy 99.9% silver and machine pills out of that and you would see an improvement. Maybe that is what surefire does? LOL That would finally explain their cost. Maybe some of the CPF guys are really hording all the silver???
Brass is 0.377 so it ain’t bad. Now I see why brass appears to work better than expected. Surface area is important and it should directly relate to the heat capacity of the material. To match copper, the surface area of aluminum would need to be more than double. Brass would need less.
Silver is .233.
Get ready for head ’splody time!
Fourier’s Law express conductive heat transfer as
(wow…copy/paste doesn’t work!)
These are the factors to calculate the thermodynamics of the materials involved
That one is actually fairly simple, Thanks WH
For me…my brain goes boom
My wife on the other hand that does calculus for fun…she just laughs at me
My wife can’t stand math but corrects my Ensligh all the time. :bigsmile:
Besides the fact that most numbers posted above are probably not correct because we dont know the exact alloy of Sinkpad/Noctigon/generic brass pills etc., we are talking about a difference in the ballpark of 5%. Less than the tolerance of Cree binning..
People have tested the same LED on copper screwed down to a copper, aluminium and brass heatsink of the same size and the difference was negligible.
If it was easy to solder to aluminium, we would see aluminium stars with direct heat path.
Has anyone tested an aluminum Sinkpad yet? Not too long ago someone said they had a couple they'd donate for testing.
Anyone know calculus well enough to figure out the best height:diameter of cylinder based on the heat conductivity and emission of...pick your choice of alloy?
The copper used for Noctigon boards is C1100, pure copper.
And all of this has come about as being common knowledge in the last 2 years.
My first custom made light was by a known guy over at CPF, supposed to be one of the best. He bragged about a 1D “Stubby” MagLight making a whopping 1000 lumens with his mod. I got one. Love the 1D chop, at the time I thought the output was pretty impressive. But of course, it wasn’t making 1000 OTF. It had a 2.8A driver in it, with an XM-L on Al, mounted on an Al heat sink that had a riser post machined in it to be able to focus the emitter in the stock Mag reflector.
I decided the other day to modify this old expensive mod (cost me $165 a couple of years ago)
I popped the reduced diameter Al star off the post and guess what I found? He’d bored out the middle of the post quite large, 3 or 4 times larger than needed for the 2 26ga wires! Yeah, the Al star was essentially sitting on a hollow pill! Nothing more than the Al star itself directly under the emitter!
I now have a 1” thick plug of copper at 1.375” diameter on the way. Will be utilizing an XM-L2 on a Noctigon re-flowed to the heat sink and output through a 45mm TIR. Probably with an FET driver. With the 26650 Powerizer I usually use in this light, I should see something in the 6A range and it will definitely be making in excess of the original claimed 1000 lumens.
The only pennies harmed in this little venture are the multitudes exchanged in it’s creation…