How Much Current Can A Receiver Connector Handle?

[ripper-911]

It seems to me that receiver board design has not changed in a very long time in terms of their ability to supply current. What has changed (i.e. increased) is the amount of current our servos now draw under various conditions.

So, my question is: how do you know when you need to use a power expander type device? For example, a 35%'er with two aileron servos on each wing and two 5855's on rudder. What should I do if I want to use just one receiver?

Help is very much appreciated.

Regards,

Robert

[Kiwi]

Robert.

The limiting factor is the JR style plug and the gage wire you use between the battery pack and your Rx.

A single JR style pin plug is rated at 3 amps continuous. It can handle 7 amps on an intermittent basis.

So the simple answer is 3 amps. Thats is good for anything up to about 6 servos, likely not digitals and definitely not Hi Torque digital servos.

If your going to use a twin battery pack setup then you can go to 6 amps continuous and 14 amps in a pinch. That will cater for most airplanes and is used by many people on 40% models with out any power issues.

However the power devices do more than just handle amps. They amplify signals, they filter, they regulate voltage to th e receiver and a host of other good things.

But its horses for courses, you use what suits you and your budget best.

[Kiwi]

Robert,

As an adjunct to your first post your very right regarding the industries sitting on hands approach to receiver design. They sell servos that can reach a maximum current drain of 4 amps and you need 12 of them in large scale applications yet they persist in selling us a receiver that is totally incapable of handling the demands of their own products.

[ripper-911]

Update! I just read the manual on the power expander and it says you can connect a servo directly to your receiver as long as the combined current draw of the receiver and the servo does not exceed one amp. One amp! Thats it!
One amp per 3 pin receiver board connection?

Do you guys agree with this?

Regards,

Robert

[Kiwi]

Robert,

The intention is actually to run NO SERVOS off the receiver if you can get away with it. All your servos should run off the Power Expander board itself. It uses power from the batteries, nothing goes through the receiver to the Power Expander. The receiver just delivers a signal to each channel on the PEX board, nothing else.

The reason there is a 1 amp limit when running directly off the receiver is the power supply for the Rx is regulated by the PEX to 5 volts. Thats so you get a perfectly constant voltage supply to the Rx which means less glitches etc. That small regulator is rated at 1 amp or there abouts. A receiver running just as the radio part and not delivering power to a servo draws about 100 MaH so that small regulator delivers ten times whats needed.

WHY??? are you trying to plug a servo into your receiver directly? Thats what I dont understand unless you have a 14 channel receiver on it.

[ripper-911]

Hi Kiwi. I was just thinking of the case where I have used all channels on the 8 channel receiver and still need one for something.

Regards,

Robert

[Kiwi]

If you need one for something then make it the throttle servo or ignition cut off servo /Choke as they don't draw enough to put the lights out on the Rx.

You can run into that problem with 9 channel Rx as well so your points very valid.

[bodywerks]

Isn't the PE pro setup for 10 channels? That is way more than any aerobatic plane and most other planes would need.
I would be careful, and reluctant, to plug anything directly into the receiver on the PE Pro, especially throttle or choke servos, as it is very possible for them to draw excessive current if they are not set up properly. I might, might consider plugging an electrinic ignition cutoff into it, but that's about it.

[thewrap]

I'm going to use a power expander on anything bigger than 33%

[GremlinX]

Wanna hear something SCAREY? A good friend of mine new to big stuff did this. He put a TBM 2 cell LiIon battery right into the RX and had 5-5955's on this 30% , plus a standard for throttle. He flew a season on that! No regs, no nothing! Poor Futaba RX took some serious abuse. I made him buy a reg and a new RX. The funny thing is that his LHS said it would be fine and he is not on the internet for all of this great info. We are quite fortunate for the info. Wild ehh?

[XJet]

	Quote: Originally Posted by GremlinX
	Wanna hear something SCAREY? A good friend of mine new to big stuff did this. He put a TBM 2 cell LiIon battery right into the RX and had 5-5955's on this 30% , plus a standard for throttle. He flew a season on that! No regs, no nothing! Poor Futaba RX took some serious abuse.

Actually it's not that scarey, at least from the perspective of the receiver.

Virtually all receivers have a built-in voltage regulator so the sensitive bits of the receiver itself would still only see the same voltge as when a regulator or regular battery pack was used.

The only real danger is that any filter cap on the battery-side of the inbuilt regulator might get stressed if its voltage rating was exceeded. I suspect most of these caps are probably 10V or 16V so running 2-cell LiIon packs wouldn't be an issue at all (although 3-cell might).

In fact, I'd go further and say that it's *not* a good thing to feed the receiver itself through a regulator -- it's just another point of failure and you gain absolutely nothing for it.

The servos however are a different story. The motors and switching bridge circuitry in the servo would have to dissipate quite a bit more power when seeing that extra voltage -- this could shorten their lives by an uncomfortable amount and increase the risk of failure.

Regulate the servo power-feed by all means but don't regulate the receiver feed.

[GremlinX]

	Quote: Originally Posted by XJet
	Actually it's not that scarey, at least from the perspective of the receiver. Virtually all receivers have a built-in voltage regulator so the sensitive bits of the receiver itself would still only see the same voltge as when a regulator or regular battery pack was used. The only real danger is that any filter cap on the battery-side of the inbuilt regulator might get stressed if its voltage rating was exceeded. I suspect most of these caps are probably 10V or 16V so running 2-cell LiIon packs wouldn't be an issue at all (although 3-cell might). In fact, I'd go further and say that it's *not* a good thing to feed the receiver itself through a regulator -- it's just another point of failure and you gain absolutely nothing for it. The servos however are a different story. The motors and switching bridge circuitry in the servo would have to dissipate quite a bit more power when seeing that extra voltage -- this could shorten their lives by an uncomfortable amount and increase the risk of failure. Regulate the servo power-feed by all means but don't regulate the receiver feed.

Xjet, I think you may have missed the point of amp draw. Think of the amp draw through that poor rx with 8.0+ volts non regulated going through it. If it is not a big deal, and the rx's have regulators, why are we all wasting time and money putting regs in?