5A BEC Problems

[Will16 45]

Hi guys,

I brought a scaler a few weeks back. It was fitted with a 5A BEC. Now I'm not sure what a BEC's job is butt I'm sure it is getting extremely hot when the battery is plugged in, and then heating the ESC. the ESC is this one - http://www.lrp.cc/en/products/electronic-speed-controls/brushed-forwardbrakereverse/produkt/ai-runner-reverse/details/

I think it has a BEC already fitted! Should I just cut it out?

Many Thanks,

Will

[B.M.T. 127]

If you have two BECs working together you are at risk of blowing both of them up because they get some kind of frequency harmonics going on... all bad news.

I take it that you simply plugged the output into the battery port on your receiver? If so, easy fix. Take the middle wire(normally red, but can be orange on JR)from the ESC's receiver plug out by releasing the tab in the plug and bind it up with insulation tape of a little piece of heat shrink.

This will let you control the speed via the signal wire and the negative from the ESC, and all your radio power is going appear via the BEC. Simples.

[fastfordrc 22]

The BEC (Battery Eliminator Circuit) was originally introduced to power the receiver and servos from the main battery pack, removing the need to use a separate 6V receiver pack on electric models. The packs were either 7.2 or 8.4V which was too high for the receivers and servos, so the BEC is a voltage regulator circuit that takes the input voltage from the battery pack and outputs a regulated 5 or 6V (though now they are available up to 12V to power high-torque servos).

BECs originally started off as separate module you plugged into the receiver battery socket (The Hotshot came with one in the kit, as it had no space for a receiver pack), then started being built into receivers and ESCs. Nowadays with LiPo packs available in higher voltages, servos being available that can take more than 6V or need a high-current supply and micro receivers with no onboard BEC, external BEC modules have made a comeback.

Electrically, there should be no reason why you couldn't use 2 BECs together in parallel - for instance, say the ESC's BEC could deliver 3A at 5V, and you plugged in an external BEC that had the same rating then theoretically you would have the ability to supply 6A at 5V. However, in real life this would only work if both the BEC circuits were of the same design and the same type.

There are 2 methods to deliver a regulated voltage - a linear regulator circuit (mostly found in receivers) and a switched-mode regulator circuit (which is used in most ESCs). External BECs can be of either type. You can only use linear regulators in parallel, and then only if they have the same output voltage. Trying to use a linear and switched-mode or 2 switched-mode regulators in parallel is not a good idea at all, and it what BMT is referring to when he says about harmonics interfering with each other (which is what you get with 2 switched-mode regulators). They interfere with each other's load-detection circuitry which can cause them to go into overload, get hot and either be damaged or go into thermal shutdown (if they have been designed properly)

BMT's advice about isolating the positive supply pin in the ESC's lead to the receiver is correct, and usually appears in ESC manuals to cover installs where they will be used with an external BEC.

[B.M.T. 127]

^ It's the switching frequencies of the units that cause conflicts. Transistorised BEC's operate with high frequency switching action, and if you have two the same but out of sync or two totally different frequencies all together, they can either cancel each other out, or the electrical feedback harmonics can destroy both units. Both scenarios will result in severe damage to your onboard electronics.

The same red wire removal has to be done to one ESC if there are two or more attached to the same receiver too. Some companies, who realise their product is being used in twin motor applications (like Pro class crawling) are now designing ESCs with buffers to prevent this, but still, pulling one little wire is cheap insurance.