Overspec ESC

[Matt Carlton]

Hello chaps

Quick question.

Is there any reason, other than money/weight/space not to use an ESC with a greater limit than needed?

An Overlander 50A XP2 is £24

The 30A version is £19

Is it worth the extra £5 for a 20A buffer? Let's say if the motor/prop combo is drawing 24A. Would a 50A ESC stay cooler on the basis that is was handling less current as a percentage of its limit?

[Geoff S]

All other things being equal/irrelevant (ie weight and space) then always go for the highest spec ESC and prop to suit the motor current specification. It will keep cooler, too. For the sake of £5 I'd go for bigger ESC and did so myself when I opted for an 80 amp Neuron ESC even though I needed no more then 60 amps tops for my Sopwith Pup.

Geoff

[Nigel R]

Treat ESC ratings a bit like Lipo 'C' ratings, i.e. keep some headroom above your max; say 30%.

Drawing 24A, I would go to a 40A ESC.

As Geoff eludes to, cable size will get larger with a bigger ESC, which might be important on a small model, as packing in the wiring can become awkward.

Last, more cells means less amps means a lighter gauge wiring and smaller ESC.

[kc]

A somewhat larger ESC is fine but I think that there is some reason not to go to extremes - read it somewhere.

It is important that the BEC side of the ESC is sufficient and can give sufficient amps for the number of servos used. That would be the deciding factor.

[john davidson 1]

It seems to be perceived wisdom that becs are ok up to 3s and separate receiver battery beyond that,, however on advice from George at 4Max I have used 5cell BECwith no untoward effects, and on a recently bought spec sheet for a Robotbird basic 80A UBEC the out put is 5v 5Amp, and giving capability - 3s 8servos. - 4s 6 servos and 6s 6servos. Who to believe?

[Dickw]

A linear BEC reduces the voltage via resistance (i.e. heat) and the higher the voltage input the more heat, so a linear BEC is not a good idea over 3s.

A switch mode BEC, often referred to as a UBEC, use a diferent method to reduce the voltage and is no problem over 3s.

Dick

[Simon Chaddock]

Matt

"stay cooler on the basis that is was handling less current as a percentage of its limit?"

Not exactly but it would run a bit cooler simply because it is physically bigger so would dissipate the same heat over a bigger area.

The 50 A version is 15 g heavier, probably not significant, but with planes 'every little helps'.

[Matt Carlton]

Thanks everyone, that helps.

[Nigel R]

"run a bit cooler simply because it is physically bigger"

There is that, but also, FETs run at their current limit tend to be slightly less efficient. So running an ESC right on the button would generate proportionally more heat than using a slightly larger one at lower capacity. There's no mileage in going overboard though.

[Geoff S]

Posted by Simon Chaddock on 03/11/2020 18:58:52:

Matt

"stay cooler on the basis that is was handling less current as a percentage of its limit?"

Not exactly but it would run a bit cooler simply because it is physically bigger so would dissipate the same heat over a bigger area.

The 50 A version is 15 g heavier, probably not significant, but with planes 'every little helps'.

Well, not only that but the bigger FETs are capable of passing more current because they have a lower resistance so the I^R will be lower, hence so will be the temperature. Let's not forget that any heat in an ESC is because of inefficiencies and ideally should be zero (fat chance!)

As for the extra weight - well it might even be desirable in some models (even Depron ones in your case ). My bigger esc in the Pup is as far forward as possible yet there's still a lot lead in there.

I'd always go for the biggest practicable ESC based on size and cost as I would for other components in the power train. I like under powering motors, too.

Geoff

[Nigel R]

Motors are more efficient if under-driven too. And again, more mass means better thermal handling.