Kindly review this material before proceeding.
The case against synthetic voltage
Bypassing the BEC
As the manufacturer of ProModeler servos we advise using a 2S LiIon or LiFePO4 dedicated pack or a BEC. And we offer them all (to include a very good quality 20A BEC, which is American made). So technically, we don't really care which you use - but - our advice is . . . rely on a pack, instead.
BEC failure types
Have you ever heard (or seen) when someone mentions their ESC went up in flames? What happens to the BEC, when this happens? Think it keeps working? Maybe, maybe not! Usually not.
Anyway, one thing about a battery pack is they can NEVER exceed the chemical voltage, e.g. 8.4V with a LiIon. Unfortunately, a BEC circuit can fail in several voltage-related ways. Three of them include;
- V-low (0-volts)
- V-high - for a 6S propulsion pack, this means more than 22V . . . or poof!
- V-intermittent - this is really the most aggravating failure
Then there's the issue of reliability; a dedicate-pack has two cells plus two leads - total four. However with an BEC, there its components, plus the same two leads, plus all the ESC components (and they all have to function perfectly). Thing is we're talking many, many more components! Ever heard about the KISS principle? This is the acronym of Keep It Simple Silly and the reason it's a thing amongst engineers is statistic. Statistics are a branch of math that informs the savvy that you're better off with fewer components. In short, keep things simple as simple as you can to reduce the potential for failure. Yet with a BEC, we've gone out of our way tom complicate things. Duh! Anyway, this is probably the main reason experienced modelers don't usually rely on a BEC.
Who never uses a BEC
Ever noticed where you never see a BEC being used? Examples include pilots of expensive aircraft. Just eyeball the equipment list for pricey aircraft equipped with 12S power system; like 78", 89", and 105" models . . . these are always powered by a dedicated battery (or almost always).
And in the truck world, the top drivers know they can't rely on a BEC to deliver sufficient current. Not for a big hairy steering servo, so they use a dedicated 2S LiIon or LiFePO4, instead. Yup, dedicated to just the steering servo, nothing else.
Anyway, depending how long you've been around, maybe you don't realize how BECs were develop/created. They came about for one reason and one reason only . . . to save money.
Initially by RC-truck manufacturers (so they could hit target prices using a 60¢ BEC-circuit versus a $15 dedicated control pack). However, they were soon adopted by the small toy-like model aircraft manufacturers for the same reason, plus they reduced weight, which is good.
However, soon thereafter thse BEC circuits were being added to the ESCs (as these manufacturers sought another competitive selling feature). Heck, even our own line of ProModeler ESCs have a BEC - but - while it's there so we don't lose out amongst those who use a feature-checklist when buying, we don't recommend using this one, either!
Bottom line? BECs are not offered because they perform better, but because they're cheaper. BECs are all about saving money. They're present as a cost saving measure. Sure, some view the weight savings of eliminating a pack as important - but - highly experienced pilots and drivers accept the weight of the dedicated pack because of higher performance and reliability. So there's a good reason experienced modelers rely on a dedicated pack instead of a BEC. Unfortunately, it takes a while to gain experience. And you know why they say experience is a bitch, right? It's because she administers the test, and then applies the lesson.
Think about what this really means. You crashed your model because the ESC failed, which took out the BEC also. With a dedicated pack you'd just glide to a landing. If you're smart, you learned a lesson about relying on BECs for control power but along the way it costs you maybe $1000, $2000, or more! Point being, gaining that experience meant paying the price of one very expensive lesson, agreed?
Our official position
Our official position at ProModeler is this; the servo doesn't care as long as the source can deliver sufficient current at the stated voltage. However our advice is this; use chemically-derived current, e.g. a dedicated battery pack instead of electronically-synthesized current, meaning a BEC.
Final point; I've recently noticed other top manufacturers similarly advising against BEC-use; Futaba USA recommendation against BEC use . . . so this is not just John advising you to use a dedicated battery pack.