I am building a large twin-engined model for electric power. The two escs each have 5 amp becs. I would like to have the two throttle channels mixed and so use both becs to power the Rx from different Rx sockets.
Each motor has its own separate 6S Lipo. The two escs are identical, but the output voltage from each cannot be exactly the same. I know that many folk use two Rx batteries, without diodes, plugged into opposite ends of the Rx and have had no problems. Does anyone out there have a definitive, fact-based answer?
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Use of twin becs on a twin
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Peter Balcombe
- Posts: 1399
- Joined: 18 Mar 2015, 10:13
- Location: Clevedon, North Somerset, U.K.
Re: Use of twin becs on a twin
All receivers use common busbars on their internal circuit boards (PCBs) for 0v and +ve. All Rx channel ports then connect directly to these busbars.
The reason that connecting 2 ESC outputs to a receiver via diodes works is that the diodes isolate the ESC supplies from each other. However, it is also almost certain that as the ESC output voltage/diode forward drops will not be identical (and will vary anyway with supply current) only one diode will be conducting at any instant, thus you are unlikely to share the current between each ESC as you might expect.
What you do have though, is a method of maintaining power to the receiver in the event that one ESC BEC supply fails.
The old advice for larger electric models, particularly those with more than 3S propulsion power packs, was to use a separate radio system battery so that if the ESC BEC failed then you always had control. This was particularly the case when the BECs were simple linear regulators as they would get much hotter as the number of cells increased, as they had more voltage to drop (at the BEC supply current so volts x amps = watts of heat to dissipate).
Nowadays, ESCs tend to use switching BEC regulators (SBECs) which are more efficient at producing the output voltage whilst producing less heat.
However, if you are using an ESC BEC at all, then the ESC is going to get hotter than it would if it had no BEC, or you were not using the BEC output.
Using a separate BEC device takes that heat away from the ESC which should improve its reliability due to the lower operating temperature.
Alternatively, you could use a separate radio system battery which may also overcome the need to use any regulator and you isolate the radio control equipment from the power train altogether.
Hope this helps.
The reason that connecting 2 ESC outputs to a receiver via diodes works is that the diodes isolate the ESC supplies from each other. However, it is also almost certain that as the ESC output voltage/diode forward drops will not be identical (and will vary anyway with supply current) only one diode will be conducting at any instant, thus you are unlikely to share the current between each ESC as you might expect.
What you do have though, is a method of maintaining power to the receiver in the event that one ESC BEC supply fails.
The old advice for larger electric models, particularly those with more than 3S propulsion power packs, was to use a separate radio system battery so that if the ESC BEC failed then you always had control. This was particularly the case when the BECs were simple linear regulators as they would get much hotter as the number of cells increased, as they had more voltage to drop (at the BEC supply current so volts x amps = watts of heat to dissipate).
Nowadays, ESCs tend to use switching BEC regulators (SBECs) which are more efficient at producing the output voltage whilst producing less heat.
However, if you are using an ESC BEC at all, then the ESC is going to get hotter than it would if it had no BEC, or you were not using the BEC output.
Using a separate BEC device takes that heat away from the ESC which should improve its reliability due to the lower operating temperature.
Alternatively, you could use a separate radio system battery which may also overcome the need to use any regulator and you isolate the radio control equipment from the power train altogether.
Hope this helps.
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GordonT
Re: Use of twin becs on a twin
I'd pretty much go with what Peter said - use a separate BEC and isolate the ESC BEC's, then use a smaller receiver battery as backup via the device of your choice.
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flihijohn
Re: Use of twin becs on a twin
Thanks for the replies, folks. Your viewpoints are very much what I thought myself. I'll use a separate power system for the radio side of things and let the escs get on with what they do best!
All my large, 12S electrics use 15 amp BEC/Lipo power for the radio and are trouble free. With the twin I just saw the opportunity to save a bit of weight.
Thanks again,
John H
All my large, 12S electrics use 15 amp BEC/Lipo power for the radio and are trouble free. With the twin I just saw the opportunity to save a bit of weight.
Thanks again,
John H