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Old Apr 03, 2009, 11:27 PM
Registered User
Gary, IN, USA
Joined Jul 1999
940 Posts
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Matching brushless ESC and A123 battery

How critical is the match-up of a battery voltage for a brushless ESC? I am switching to A123 cells from lipos. The motor powered with 3 lipos will now have a 4 cell A123 battery. This summer, I plan to have a EDF jet that will have the 4 cell lipo replaced with a 5 or 6 cell A123 battery. My first converted 4 cell A123 powered plane has not released the magic smoke from the ESC. Am I getting close to exceeding an ESC limit? With 5 or 6 cells?
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Old Apr 04, 2009, 02:39 AM
Registered User
Letchworth, Great Britain (UK)
Joined Jul 2004
11,424 Posts
Your ESC must be rated for the volts you plan to use. 3S LiPo is nominally 11.1v, and 4S A123 is nominally 13.2v. Even if your model is designed for 4S LiPo it could well have an ESC that is rated for more than 11.1v. Whether or not your particular ESC can handle a voltage overload will depend largely on what make it is and how close to its amps limit you plan to run it.

Post the make and model of your ESC(s), and what volts and amps you intend to draw, if you want real-life experience from others.
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Old Apr 04, 2009, 07:21 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,648 Posts
The 2.1V higher starting voltage also has an effect on the load on and heat generated by the ESC's linear BEC.

The ESC has to drop the battery voltage to the 4.8-6.0V needed by the receiver and the linear BEC circuits do that by converting the excess voltage into heat.

And if you are using three or four servos that further increases the load on the ESC because the BEC is drawing more current.

You can reduce the load/heat generation in the ESC by changing to an external switching mode BEC (most commonly called a Universal BEC or UBEC). A switching mode BEC generates very little heat.

You can see effect of using a UBEC by running the the motor for 10 seconds of so at a typical flying throttle setting and touching your finger to the surface of the ESC. Don't be surprised if you can't keep your finger on it, that would be hotter than 130F and that is not unusual or abnormal. If you can barely stand to touch it, it is a lot hotter than 130F. Try the same thing with a UBEC replacing the ESC's BEC circuit and you'll find the ESC is running cooler. Sometimes a lot cooler.

Many ESC makers rate their ESC's as OK with 3-4 cell LiPo and OK with x number of servos. But they don't mention that if you use both the max voltage and the maximum number of servos, you are threatening the ESC quite a bit more.

Read some of the FAQ here at Castle Creations for an ESC similar in size to the one you are using, it will help explain some of the overheating and overloading considerations:

http://www.castlecreations.com/support/faq/index.html

The considerations would be the same for the imported ESC's.

I've been using a couple of the inexpensive (less than $10) imported UBEC and have have good luck with them so far, no failiures and the ESCs (Phoenix and Thunderbird models) were much cooler to the touch.

Jack
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Old Apr 04, 2009, 11:32 AM
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Gary, IN, USA
Joined Jul 1999
940 Posts
Bingo! I knew there was something I saw but didn't see.....the ESC heat difference between the 2 types of batteries. Extremedeals sold me a nice UBEC ($10) for my optic ESCs and there wasn't any shipping cost. I hope others switching to A123 cells upgrade to UBEC and ALSO remove the red wire from the receiver plug to kill the BEC from the ESC.
The instructions from the UBEC were not nearly as good as the unit......typical Chinese faulty translation into the worlds most bastardized lanquage...English.
Thanks guys.
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Old Apr 04, 2009, 04:08 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,648 Posts
"..and ALSO remove the red wire from the receiver plug to kill the BEC..."

Right, good warning. I make up a sort (1-1/2" long) servo cable extender with the center (red) lead left out of it and use that on the BEC lead from the ESC.

That way if I want to program or reprogram the ESC I don't have to mess around with putting the red wire back in to the housing and then and taking it out again, I can just pop the extension off.

And if you are running out of channels to plug things in to, the UBEC can be plugged into a "Y" cable on any of the channels and it will provide power to the receiver.

Jack
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Old Apr 04, 2009, 08:37 PM
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Gary, IN, USA
Joined Jul 1999
940 Posts
Good reminder about the Y.....my F9 Panther EDF project may use up the receiver plug-ins for the multi-functions.
Thanks
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