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6 watt laser build, host tail cap can't handle the current

kuhny1

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So I recently built the strongest laser I have ever made, and have ran into a problem.

Everything went together fine, and after a 5 second "on" to test, I took out the batteries to test current draw to gauge the life time of one charge.

Right when I took off the tail cap I smelled the all to familiar burning electronic smell. I tested the driver and LD through the meter and it lased just fine, drawing 3 amps. The laser itself wasn't starting to fry so that's good. Then I smelled the tail cap because it felt a tad warm. Sure enough, that was where the smell came from. I put the cap back on and kept the laser on for about 10 seconds, turned it off and brought the top part of my lip near the spring. I could feel the heat coming off of the spring, and it actually oxidized a little turning slightly black.

So I guess the tail cap isn't rated for 3 amps, but I think it's more the spring being how thin it is. :(

I did some searching and couldn't find any high rated tail caps. And even if I did they would most likely not thread correctly.

The host is survival lasers s4 host and the diode is DTRs NUBM44-81 6 watt with driver. Now, I was going to put it in the s4x host for the extra heat sinking but they didn't have an adapter yet for the 20mm modules. Both my 1 watt green, and my 3 watt 445nm are in those host and I can run them almost forever.

If anyone has an idea as to where I can get a higher rated cap that fits the s4 host or maybe how to mod the spring, please let me know.

Thanks!
 

BobMc

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Any chance you can take the tail cap apart and make/solder wires over the existing contacts whereby increasing their current capacity?
 

kuhny1

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Yes, there are 2 dimples on the metal ring that I can take off, but I'm not sure if I can get inside the switch itself. If I can, I'll try that. But I will still need to fix the problem with the spring nearly melting. I just measured it with a thermal couple and its hitting about 200F after a 15 second on.
 

BobMc

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Yes, there are 2 dimples on the metal ring that I can take off, but I'm not sure if I can get inside the switch itself. If I can, I'll try that. But I will still need to fix the problem with the spring nearly melting. I just measured it with a thermal couple and its hitting about 200F after a 15 second on.
Can you leave that spring on and add another one also?

Edit; or find a heavy spring?
 
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kuhny1

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Ok, I have found another spring and threaded it into the other one and it seemed to have lower temps by about 15 degrees. I can use this for now and just limit my on times. Luckily it cools down faster than it heats up.

I'll still be searching for a higher rated tail cap with a beefier spring. Just so its more permanant.

Thank you for your quick help!
 

Alaskan

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If you could somehow take some braided wire, like copper shield from some RG-58 coax, you could try to somehow jam it into the tail cap and wrap it at the tip of the spring as a low resistance shunt to ground.
 

RedCowboy

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The switches seem to keep getting cheaper and flimsier in a line of flashlights as production goes along and this is a problem for diodes like the 44

( If it's a survival lasers host then talk to Gary ) I just saw that, this is how I fix flashlight hosts.

I often retrofit a much larger general purpose switch and a heavier battery spring, you can find both on ebay.

I just cut out rectangle edges in the round hole and hand fit the parts.









 

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BobMc

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Your welcome

If you can, the more surface area, the more current can pass. Try anything that is flexible that conducts current. Best wishes :)
 
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Encap

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DId you contact Gary at Survival Lasers and ask him about the problem and tail cap current capacity--maybe has a solution or heavier duty switch and spring?
 
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kuhny1

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Thanks all for the replys. Sorry for my late response

Redcowboy: Very, very nice mod their. I will definitely be trying that. And yes it's the cap of the SL S4 host.

For those who recommended beefing up the spring, that seemed to have worked. I "threaded" another spring from another aixiz module into the existing tail cap spring. It doesn't seem to heat up nearly as much now.

However I think I'm risking having the laser flick on randomly if the spring slides just right. I would definitely not want to have a laser of that power turn on by itself, catching something on fire, or blinding someone. I'll leave the tail cap off while not in use or if its in my pocket.
 
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paul1598419

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There are several contact springs available on eBay that can be switched out. I'd do that before jury rigging the spring that's in there. A heavy duty switch is also a great idea in this case.
 

Benm

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Is it the actual spring that is too flimsy, or the switch?

The problem with spring contacts is that they are generally not very good for high currents: they are made of steel which is rather bad inductor and surface contact resistance with the battery can also be a problem. A simple mod could be to solder a piece of braided copper wire from the contact end of the spring to where it goes into the switch. Copper is a hugely better conductor, the resistance of a copper wire of equal diameter to one made from steel is a factor 10 or so better.

Then again there is the actual switches though, which are an abomination on some hosts. The may work sort of okay when used with a led but are already hugely overdriven at that point (i've seen 3 watt flashlights with the switch rated for only 50 mA, 1/20th of what would be required for the original application). If you pull even more current through them you could either melt them open, or weld them closed.

Maybe the best way in general is to bypass the back switch and use something on the electronic side, like a hall sensor which you activate by placing a small Nd magnet somewhere specific on the laser. This would also add a bit of security since a random person would probably not know how this works nor where to place the magnet.
 

kuhny1

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Very cool idea benm, however I don't think I could cram a hall effect, an amplifier, and a mosfet into that tiny tail cap. I probably try it anyways because it would be pretty cool. Powering the amp off the batteries could be problem. But magnet switched laser would be a whole new thread on its own.

Ill be getting a copper spring, my only worry is that I won't get that soldered back in.
 

Cyparagon

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Copper is easier to solder than steel. However, copper has a lower plastic region. In other words, it is more likely to permanently deform instead of spring back.
 

WizardG

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I'll second Ben's suggestion of soldering a length of copper braid (heavy solderwick should work great) from the top of the spring to the bottom bypassing all the high resistance steel spring.
 




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