You can change a new transistor on board.Can use part number MJE2955 or TIP42.

Nice Mod Putsa. since  your are extending the power Transistors leads, put ferrite sleeves close transistor legs cl:
http://uk.rs-online.com/web/2606773.html.

Though it may work for surface vehicles like Boat/Cars, one should put an ESC with 1.5x the max current rating of the BL motors to keep things cool. The TO-220 Tx and the heat sinks would at least add 50-60g  to the AUW.

555

Quote from: ujjwaana on April 25, 2011, 01:21:17 PM
one should put an ESC with 1.5x the max current rating of the BL motors to keep things cool.

Do let me know if I am overlooking something but what would the current rating of the motor have to do with the BEC?

Quote from: sushil_anand on April 25, 2011, 06:09:01 PM

Quote from: ujjwaana on April 25, 2011, 01:21:17 PM
one should put an ESC with 1.5x the max current rating of the BL motors to keep things cool.

Do let me know if I am overlooking something but what would the current rating of the motor have to do with the BEC?

Opps!! My Bad.. I read this ESC... and that was my take.... Well anyway my other calculations - The BEC should be 1.5 times the max current consumption to be on the safer side , and putting ferrite filter on I/O lines.

The heat sinks are generally connected to collector. In BEC, (Electronic Speed Controller of DC Motors), you can use a common Heat Sink, but in case of Brushless motors, the 6 Transistors, you cannot use a common heatsink without Electrical Insulation.

Moreover, the power tracks thickness is to be checked so that the track foils not burn due to increase in current. You may scratch off the green paint and use copper and solder to thicken the track.

The battery lines to ESC and from ESC to motor are also needs same attention. The reverse freewheeling diodes connected to the transistors are need to check the current capacity as that has too withstand. The di/dt protection capacitors need to recalculate to avoid noise feeding back to receiver circuit and thus ferrite beads/Chokes.

Again, for the increase current, the feed back resistor in over current protection will need to be modified otherwise, over-current shutdown will occur at same current. It will be compensated automatically if the circuit senses across the transistors voltage instead of voltage across a very low value resistance. Please keep in mind that reverse engineering skill is valueless in this case as all the things are now controlled by micro-controllers instead of discrete circuit. The under-voltage circuit will work as usual and need no attention.

Above all, all this experiments will increase the weight than a ready-made (In fact Optimized) ESC with increased current carrying capacity and
Cost of (Low current ESC + Modification) > Cost of Higher value ESC

and of course RISK.

However, DIY deserve a charm. A link may help you.
http://www.stefanv.com/electronics/escboth.html

Kalyan

The modifications suggested are for a BEC and NOT ESC. Your inputs, though valid, do not apply.

I don't know much about electronics, but a BEC overheating is a very very serious issue in an airplane. may not be as serious an issue in a car or boat.
The BEC powers the reciever & servos and it has absolutely no business heating up. And you have a model with a resonable amount of power- if you as using an opto ESC for a electric set up or a glow model- the BEC is bound to burn/ short circuit leading to a model flying out of radio control.
If your lipo does not catch fire/ explode before that.
I would not use that BEC- I would show it to an expert. the BEC costs 5-600Rs. A run-away model is bound to cost several times more-even if it hits something inexpensive.
Please check that you are not using a 3 or 4 cell lipo with a BEC rated for 2 cells.
regards,
Avijit

Quote from: sushil_anand on April 26, 2011, 11:55:37 AM
The modifications suggested are for a BEC and NOT ESC. Your inputs, though valid, do not apply.

The rule of power electronics design and subsequent pitfalls for ESC hold as true for BECs as well. I would second the opinion by Kalyan and Avijit. Its better to do though testing for any power related DIY as it may cost dearly on mishaps.

One silent member from Bangalore , mr Raghavendra may put more light as he is Power electronics design professional.

I don't think there are any issues with "power electronics and general pitfalls". The suggestions made seemed quite SPECIFIC about ESCs on a thread that pertained to improving current handling of a BEC.

And that is all I was trying to bring out.

Quote from: avijit17basu on April 26, 2011, 01:39:13 PM
I don't know much about electronics, but a BEC overheating is a very very serious issue in an airplane. The BEC powers the reciever & servos and it has absolutely no business heating up.

I had experienced a BEC getting hot today.
What had happenned is that the on the output wires, there was 5-8mm of wire exposed without insulation beyond the PCBand they had got twisted together short circuiting the BEC. fortunately the heat shrink was transparent i i could see the problem.
When I untwisted the wires it worked fine.
So i cut out the wires, cut off the bare parts and re soldered them back with no exposed bits of wire.
Ishould have taken a pix of the twisted wires, A picture is worth a 1000 words and so on.

does this shed light to your problem?
regards,
Avijit

I dont have a very good knowledge about this stuff, but from whatever I know, I think inplace of changing the Transistors, changing the heatsink itself will be a better idea. Most of the BECs in the market lack a good heat sink and only have metal sheet. A good heatsink with a large surface area should be used... Please correct me if I am wrong...

Related... I once got around the problem with just ensuring airflow around the ESC.

http://rcqatar.com/helicopters/scorpion-commander-45a-esc-heat-problem-solved/