CBA II Thermal Analysis -- Does the CBA run too hot?

[JohnMuchow]

Hello all,
After hearing of several CBA II's burning out their MOSFETs, often along with other components, I decided to do a thermal analysis of the CBA. I've posted it at:
http://www.camlight.com/techinfo/CamLight_Systems_CBA_II_Thermal_Analysis.pdf

For those who don't want to wade through the 37 pages :duh2:, my conclusions and recommendations are as follows:

• For reliable, long-term operation of an unmodified CBA, do not exceed 65W when discharging at under 29A.***
• To help prevent the burning out of the MOSFET (and perhaps other components) in an ummodified CBA, never exceed 86W when discharging at under 29A.***
• To help prevent the fuse and fuseholders from dropping out of the circuit board and possibly shorting out your battery pack, do not use an unmodified CBA for discharges above 25A.***
• Replacing the CBA's MOSFET and fan allows for reliable, long-term operation at up to 80W when discharging at under 29A.
• Replacing the CBA's MOSFET and fan can help prevent the short-term burning out of the MOSFET at up to 106W when discharging at under 29A.
• Replacing the CBA's MOSFET and fan can help prevent the dropping out of the fuse from the circuit board at higher discharge current levels.
• When discharging at a current level above 29A, the long-term reliability power level and absolute maximum power level mentioned above can be increased a bit. But, I recommend not exceeding the levels mentioned above to give yourself a bit of a safety margin.***

*** These recommendations are based only on temperature measurements and calculations. Any derating that might be required as the battery voltage rises cannot be determined since the CBA's MOSFET doesn't have a rating for use as a load. Even when operated well within these recommended ratings, the IRL2910 MOSFET could burn out at any time. Especially for discharges at higher battery voltages.

I'd be very interested in your thoughts on the paper and about any mods you've done to your CBA!

John

 

[Turak]

John,

Excellent work!!!

Very comprehensive study of the thermal dissipation of the unit.

Quick question for you. If someone just wanted to replace the mosfets and forego the other mods for now or just wanted a couple extras in case the existing one dies/died....

Would you be willing to supply just the Mosfets?

What would the cost be for just the Mosfets be either ea. or in a 2 pack?

 

[LuxLuthor]

John, as at RC Groups, this is an incredible amount of details and useful guidelines for using the CBA-II. Great to see revision dates, index, introduction and summary/conclusions.

Anyone using the CBA-II will find great contributions in your document. Thanks in advance of reading it all!!!

 

[JohnMuchow]

Thanks guys!

Turak, I have MOSFETs available separately but will send you a PM as I have not yet heard back from the moderators regarding my posting an announcement of the Frigi-Mod Kit. I may be selling the parts at my cost so others can benefit from the mods, but it's still selling and I want to be sure I follow the CPF rules for that.

John

 

[LuxLuthor]

John, please cc me on the PM.

 

[Turak]

John,

Thank you kindly sir. PM received and replies sent...:twothumbs

 

[JohnMuchow]

Two sets of MOSFETs on the way.

John

 

[JohnMuchow]

Update

A few people asked me about the CBA 10x Amplifier. The analysis has been updated with what little I know. This also gave me a chance to fix a few small things:

http://www.camlight.com/techinfo/CamLight_Systems_CBA_II_Thermal_Analysis.pdf

12/21/08 Release:
- Added a note to the recommended ratings for the CBA to reflect the fact that they are based only on temperature calculations. And any additional derating that might be required as the battery voltage rises cannot be determined since the CBA's MOSFET doesn't have a rating for use as a load. Even when operated well within these recommended ratings, the IRL2910 MOSFET could burn out at any time. Especially for discharges at higher battery voltages.
- Corrected a couple of spelling/grammar errors.
- Added photos of the modified CBA and Frigi-Mod Kit.
- Changed the link to the RC Groups forum discussion of the Frigi-Mod Kit.
- Added Addendum A, with info on the CBA 10x Amplifier.

John

 

[LuxLuthor]

Noted, thanks.