CamLight
Joined: 19 Dec 2008
Posts: 11
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 Posted: Sun Dec 28, 2008 12:18 am Post subject: CBA II Thermal Analysis - Does the CBA run too hot? |
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Hello all,
After hearing of several of them burning out, I did an analysis of two West Mountain Radio CBA II's and have written it up:
http://www.camlight.com/techinfo/CamLight_Systems_CBA_II_Thermal_Analysis.pdf
Bob wrote up a really great analysis back in 2005 (which is still being passed around) but a couple of my conclusions differ from those Bob made so I wanted to post here to discuss them. Those conclusions are:
- The MOSFETs in the CBA and the 10x Amplifier are not rated for use as a load and are subject to failure at levels significantly below the CBA's 100W rating. This includes the IRFP2907.
- Paralleling switching MOSFETs is very, very problematic and each should be driven by its own local control loop.
- Due to overheating, the CBA should not be used at a level above 65W for long term reliability. Never exceed 86W to prevent failure of the MOSFET.
- Discharging packs at above 20V (and perhaps even lower) significantly increases the risk of the CBA burning out, at almost any power level.
A fun note...
After reading Bob's analysis a couple of times, I suddenly noticed that he uses the exact same graphics to represent/model the thermal resistances of a MOSFET that I've always used. Important? No. But it was fun to realize why it was such easy reading for me. 
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John M.
Owner
CamLight Systems |
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