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wouldn't it be logical to try to use former to wick heat away from the coil ?


aliuminum would be perfect but it would act as a braking coil


but if you make a slit in the former then it wouldn't


thats what morel has for a former - a slit aluminum one
 

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Your TC built driver most likely has an aluminum former, there are many drivers manufactured with aluminum formers. Aside from the braking you'd get from a shorted turn ,the other down side would be that thermally conductive formers are more likely to bring about adhesive failure. I had always wanted to see the cone and former laser welded and the spider clamped between support rings
 

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As Dan alluded to, a thermally conductive former can cause adhesive failures, I know years ago, Alumapro had that issue.


I have gotten my TC built drivers hot enough to smell the epoxy, and even burned a bit of the excess off, although at levels most other drivers would have long since failed.


TC LMS used TI for former, TC 1k, 2k, 3k used split AL formers. Not sure what the other models used.


Pic of 15" TC 3000 QVC coil and former that has survived a 7 hour marathon of cranking tunes. Power was QSC PLXII 3102, at levels that were lighting the clip indicators.





 

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Where are you going to conduct the heat to? Metal is not the only good thermal conductor. Carbon does quite well. But what about just using the space and mass for more turns of a self supporting coil? That is what we did with the ultra high power capstan motors back in the old 9-track days.
 

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Quote:
Originally Posted by vasyachkin /forum/post/17000944


wouldn't it be logical to try to use former to wick heat away from the coil ?


aliuminum would be perfect but it would act as a braking coil


but if you make a slit in the former then it wouldn't


thats what morel has for a former - a slit aluminum one

You have to look at the whole circuit. Take it in parts. Any design has to address all the issues. You need to get the heat away from the windings, and then out of the driver. If you have an aluminum former but no way to pull the heat from the former effectively all you are doing is slightly increasing the thermal mass and allowing a short time longer for the coil to get to failure.


An aluminum former that is solid will act as a shorted turn and effectively be a brake. It needs at least one split. Offset splits or spiral splits are better as eddy currents then act more evenly around the circumference of the coil former.


The key though is getting heat away from the coil. Many people try forced air cooling which is highly ineffective other than at high excursions. You just can't move the air far enough to get it out. Oscillating hot air back and forth in the gap doesn't do that much. Most of the hot air can never move far enough in one direction to get out of the pole vent.


The much more effective method is to sink it into the steel. The more surface area you have and the closer the coil is to the pole and or top plate, the more heat you can pull off. Kapton is a typical former material and acts as an insulator. It effectively eliminates any heatsinking ability from the coil to the pole. This was a great option back when drivers used alnico slugs in the pole. You needed to keep the heat from the alnico. Ceramic doesn't have this concern. An aluminum former allows heat to be pulled directly from the windings to the former where you then have much more surface area to sink the heat into the pole. A highly thermally conductive layer like the copper we use also increases this ability to pull heat away.


We recently had a customer drop a pair of TD12M cabinets and snapped the frames in half. They had worked perfectly until the drop incident. Upon reconing the drivers we noticed something interesting. The black anodized aluminum formers had changed color. The plating on the pole and around the Id of the top plate was discolored as well. This is something that will not happen until the driver reaches around 550F for a very long time. (this is a 2" coil driver getting 1250W of Lab Gruppen power for live sound use.) Even though the coil was this hot, the heat transfer kept moving allowing the coil to shed it's heat without ever failing. The phase plugs pulled heat from the pole and got hot enough to burn yourself to the touch, but again the driver never failed. A driver relying on forced air for cooling would have failed at only a fraction of the time period as with almost no excursion it cannot cool at all.

Quote:
Originally Posted by NEO Dan /forum/post/17002128


Aside from the braking you'd get from a shorted turn ,the other down side would be that thermally conductive formers are more likely to bring about adhesive failure. I had always wanted to see the cone and former laser welded and the spider clamped between support rings
 

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Has anyone looked at forced air cooling? For really high power drivers, I could see a fixed blower forcing air through the motor assembly coming in through the rear of the pole piect and exiting through the dustcap. Making it silent would be some fun. Yo need just enough to break the laminar flow away from the vc to over come the "pushing it back and forth" problem. Speed of the flow could be controlled be a sensor in or near the vc.


Controlling the vc tempature to extend power limits as the first goal, but a more consistent Re would be a side effect. Not sure that matters as the king of high power driver this would be needed for would never have a passive crossover, I hope!
 

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"The other common failure is where the 2 wires make their turn and run straight up the former."


To be expected until people start to use a more gradual bend. Eventually you would want the failure to be in the center of the VC. That would signify the most even heat flow. Not knowing the manufacturing process, easier said than done I suspect.


I believe one ccould form the cone and vc in one thin enough and uniform enough piece without micro welding. It is called explosive fabrication. It has been used in the aerospace industry for years.
 

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Darn, posted before I finished my sentence. ... Neither easy nor cheap. Another method is plasma sputtering on a form that can be etched away. Can be done but I could not buy one and would not even want my tax money to be spent to develop it.
 
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