With the recent surge in interest in the use of high-power bulbs in the MagCharger, there will also likely be more reports of thermal damage from the increased power. The most popular drop-in upgrade is the WelchAllyn WA01160. This is a spec rated 5V, 3.45A, 17.25W unit that when pushed by the appropriate MC pack, reaches 6.05V, 3.5(?)A and 21.18W. This is a 2.5X increase over the stock bulb, which is an 8.4W unit.
The damage is most likely to occur at the pin socket. This is a plastic slug with the two pin receivers embedded in it. The two pin receivers are connected to two metal contact tabs which make contact with mechanisms inside the metal lamp pedestal to complete the electrical circuit. I've 95% disassembled the MC switch/charger core and this plastic cylinder appears to be the most glaring weakpoint in the MC powertrain. It is unfortunate that it is at the one point in the entire light that will certainly be exposed to the most punishing conditions.
Since this area of highest stress is also readily accessible to the general user, I decided to see if an easy, drop-in solution could be developed to protect the stock part. This is desirable to the more robust, engineered solution of a purpose-built high temperature replacement part as disassembly of the MC is involved and difficult.
To that end, I ordered and received a sample of clear mica in 0.29mm or 0.0115" thickness. This is the pure mineral as I have found that even 750F rated fiberglass insulation and mica composites were unable to withstand the temperatures that the bulb capsule reached. My contact thermocouple registered temperatures of over 560F, the point at which I stopped the test due to smoking of the TC lead insulation.
I machined circular disks from the mica slab and drilled three holes in it. Two for the bulb pins and one for the bulb "tail." Here are photos of the shield slipped over the bulb pins and the bulb and shield in place in my MC. You can see the it's some fine work as the two pin holes are just over 1mm in diameter and 4mm apart. The central hole is about 2.5mm in diameter. Don't mind the jaggedness of the outer edge. These were prototypes and the jaggedness does not detract from the thermal performance.
So how did it work? Well, not too bad at all and certainly far better than nothing at all. In this next pair of pictures, you'll see the pristine pin socket on the left and the same socket after a full-out 61.5 minute run with the WA01160 driven by a UMP nimh battery pack. How hot does it get? Well, hot enough that you can't hold your hand 3" in front of the bezel for more than 7 seconds. Hot enough that the beam will soften a plastic milk jug enough so that you can dent the softened wall with a finger. Hot enough so the the head is too hot to hold against the back of your neck.
The damage is very slight and is seen as a shallow melting in the area between the pin holes and the central tail hole. This is far less severe than the broader, deeper melting that has occured in my other MC.
While these results are promising, the single-thickness mica shield does not offer 100% protection. I can, however, recommend it as a sensible precaution for those who are running high-power bulbs in their MC, especially if they tend to run for more than 10 minutes at a pop. Keep in mind that I would consider this test exceptionally severe as I used a new bulb and a freshly charged high current, high capacity battery pack.
I will continue the experimentation tomorrow with a double or triple thickness shield. The objective would be to prevent the glass tail from dropping into the socket hole and thus further insulating the bulb glass from the vulnerable socket. I believe that the range of the MC focusing cam would still allow one to achieve maximal beam tightness even if the bulb is lifted 2mm from the stock position.
Wilkey
The damage is most likely to occur at the pin socket. This is a plastic slug with the two pin receivers embedded in it. The two pin receivers are connected to two metal contact tabs which make contact with mechanisms inside the metal lamp pedestal to complete the electrical circuit. I've 95% disassembled the MC switch/charger core and this plastic cylinder appears to be the most glaring weakpoint in the MC powertrain. It is unfortunate that it is at the one point in the entire light that will certainly be exposed to the most punishing conditions.
Since this area of highest stress is also readily accessible to the general user, I decided to see if an easy, drop-in solution could be developed to protect the stock part. This is desirable to the more robust, engineered solution of a purpose-built high temperature replacement part as disassembly of the MC is involved and difficult.
To that end, I ordered and received a sample of clear mica in 0.29mm or 0.0115" thickness. This is the pure mineral as I have found that even 750F rated fiberglass insulation and mica composites were unable to withstand the temperatures that the bulb capsule reached. My contact thermocouple registered temperatures of over 560F, the point at which I stopped the test due to smoking of the TC lead insulation.
I machined circular disks from the mica slab and drilled three holes in it. Two for the bulb pins and one for the bulb "tail." Here are photos of the shield slipped over the bulb pins and the bulb and shield in place in my MC. You can see the it's some fine work as the two pin holes are just over 1mm in diameter and 4mm apart. The central hole is about 2.5mm in diameter. Don't mind the jaggedness of the outer edge. These were prototypes and the jaggedness does not detract from the thermal performance.
So how did it work? Well, not too bad at all and certainly far better than nothing at all. In this next pair of pictures, you'll see the pristine pin socket on the left and the same socket after a full-out 61.5 minute run with the WA01160 driven by a UMP nimh battery pack. How hot does it get? Well, hot enough that you can't hold your hand 3" in front of the bezel for more than 7 seconds. Hot enough that the beam will soften a plastic milk jug enough so that you can dent the softened wall with a finger. Hot enough so the the head is too hot to hold against the back of your neck.
The damage is very slight and is seen as a shallow melting in the area between the pin holes and the central tail hole. This is far less severe than the broader, deeper melting that has occured in my other MC.
While these results are promising, the single-thickness mica shield does not offer 100% protection. I can, however, recommend it as a sensible precaution for those who are running high-power bulbs in their MC, especially if they tend to run for more than 10 minutes at a pop. Keep in mind that I would consider this test exceptionally severe as I used a new bulb and a freshly charged high current, high capacity battery pack.
I will continue the experimentation tomorrow with a double or triple thickness shield. The objective would be to prevent the glass tail from dropping into the socket hole and thus further insulating the bulb glass from the vulnerable socket. I believe that the range of the MC focusing cam would still allow one to achieve maximal beam tightness even if the bulb is lifted 2mm from the stock position.
Wilkey
