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Old Jul 31, 2006, 09:31 PM
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Help!
West Mountain Radio CBA Owner, Help!!

It's just my luck. My first attempt to use the CBA only lasted about 10 seconds.

As I was testing a 8 cell 1900mAh NiMh SC battery pack, a loud popping noise came from the CBA unit and followed by some thick smoke and burn smell. I quickly terminated the test software and discounted the battery. After gotten past the inital shock, I procee to removing the bottom plastic cover for damage assesment. I found what appears to be a FET in TO-220 package. The device was burned and has a hole on the face its packaging. I am sure that hole wasn't there before I started the test.

So I now have two choices, send it back to WMR for repair or fix it my self. I am more inclined to fixing it my self, as the TO-220 packaging is very easy to work with. The only problem is part on the package casing was blowen away and marking on the device is no longer readable. Could any one that owns a CBA take couple minute of your time to remove the bottom cover and look at the part number for me? Once the part number is known, it will be as simple as order the replacement chip from digikey of couple of bucks.

Attach is a picture of the mishapes. By the way, I was only drawing 45 watt, which is way below the rated capacity of this CBA. Needless to say, I am little disappointed of its quality

Thanks

~ASM
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Old Jul 31, 2006, 09:39 PM
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Why did the FET blow?

- RD
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Old Jul 31, 2006, 10:05 PM
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Good question, I woudn't know.

Just bought the item from another rcgroups member. The CBA appear to be in excellent condition. The fan didn't even look dirty, which may suggested the CBA was not use much at all. It was my first test and the total current draw was only around 45 watt... Bad FET? That's my guess....

~ASM
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Old Jul 31, 2006, 11:18 PM
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I think I'd want to know the answer to that question before I tried to repair the unit. If it were mine, I'd send it back to West Mountain Radio.

I've had to do that twice with mine, and got quick turnaround and and a reasonable service charge. Just my opinion.

- RD
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Old Aug 01, 2006, 02:16 AM
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Well, I would send it back if it is something more extensive. However, after my experience of repairing many ESCs, I have found that in the high power loading semiconductor world, there are often such thing as "bad chip". Often because we modeller like to push thing to the limit. That, in result, tend to make the not so good semi chip go bad... Not all chip are created equal. Morever, the replacement chip is relatively inexpensive. Therefore, often worth the try in comparison to the OEM repair charge.

But, thanks for your suggestion.

So far, I was able to "guess" the chip marking using only part of the model number. It appear to be IRL2910 made by International Rectifier. The MOSFET cost only $3 at digikey. All I need now is for some one to confirm the part number before I procee with the repair.

Guys? Help?

~ASM
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Old Aug 01, 2006, 02:47 AM
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ASM,

Just checked mine and your P/N is correct! International Rectifier house # IRL2910. Very simple repair from the looks of it. Go and order a few!

-Mike
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Old Aug 01, 2006, 06:52 AM
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Suggest you have a look at aeroelectric site. Describes this problem with the CBA. Plus some followup.

http://www.aeroelectric.com/articles...tain_CBAII.pdf
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Old Aug 01, 2006, 10:26 AM
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Magrat Thanks for the link.That is an excellent write up on the problem and a simple fix. I have allways used my CBA on the consertive side and have never had any issues with it but I know many who have pushed thier's have found its' limit and let the magic smoke out.

Charles
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Old Aug 01, 2006, 10:55 AM
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Quote:
Originally Posted by Magrat
Suggest you have a look at aeroelectric site. Describes this problem with the CBA. Plus some followup.

http://www.aeroelectric.com/articles...tain_CBAII.pdf

That link is dead...

Can someone attach the PDF to this thread?


Thanks.
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Old Aug 01, 2006, 11:01 AM
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Link works fine for me but:



Charles
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Old Aug 01, 2006, 11:17 AM
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Quote:
Originally Posted by everydayflyer
Link works fine for me but:

Charles
Thanks...


It's very weird, as it wasn't working in Netscape! (works fine after a re-start...)

But, it's always handy to have the document as part of the thread, as who knows how long it will be maintained on that site...
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Old Aug 01, 2006, 11:23 AM
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My SOP with such is to save to HD and then print it out. There is a copy with my CBA unit just in case. I also try to keep my files backed up on a regular basis especially ones which can not be replaced.

Charles
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Old Aug 01, 2006, 11:58 AM
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Wow!! Thanks guys. I was only hoping to get a part number, but you guys came up with a complete write up and a review of CBA's thermal incapability.

So, the author of the article, Bob, mention the IRL2910 used in the device is barely capable of handling the rated 100 watt. There are planty of other semi offer by IRF that is more capable for the task, and the part he mention is IRFP2907. Has anyone try IRFP2907 as direct replacement for the IRL2910? If it work, it seems to make sense to do the modification, as even at 100 watt, CBA is consider insufficient for test most modern battery pack. Therefore, I imagin I would always be pushing to its limit quite often.

~ASM
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Old Aug 01, 2006, 12:14 PM
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I think you have to be careful to substitute the correct FET "on" voltage level.

I'm pretty sure the IRL are "logic-level", and the IRF are higher. Most likely the CBA uses some sort of PIC ot ATMel chip to control the FET, so the logic level is the one.


Just a thought...
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Old Aug 01, 2006, 01:23 PM
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thanks for the input meteor.

Let's keep those ideas coming, if IRFP2907 won't work, perhaps we can find a higher rating replacement chip. Perhaps just pairing up several IRL2910 to increase CBA's wattage rating.

~ASM
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