Hey,
I am trying to work out a way to power up a receiver to an Arduino and relay system. The arduino board is powered by a 12v battery.
The receiver is a Crossfire Nano 6CH PWM and I am using an UNO R3 Board (SKU A000066). So the 5v power output is already being used by the relay, so an alternative would be to connect the receiver on a 5v BEC and to the same 12v battery that powers the Arduino board. Would this work?
If it does, do I need to establish common ground between the receiver and Arduino board or can I simply power the receiver from the same battery that will power the Arduino with a BEC and common ground is already established?
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The UNO R3 has multiple 5V pins, for instance at the SPI header, so it can be directly connected to multiple 5V devices. But I think that the power for your receiver will also be the power for the servos that you drive from that receiver, so powering it from the UNO supply is definitely not recommended. If you power it from an alternative supply then you must ensure that both power supplies, the UNO and the receiver all have a common ground. Exactly how this is wired between devices doesn’t matter, provided that the connections are solid. What matters is that all the devices use the same ground.
Whether or not you will need to add an extra ground wire to complete this common grounding depends on the components. If the device is described as ‘isolated’ then that means that the ground input is not connected to the ground output, and you could not assume that just because the battery ground is common to two of those devices their output grounds are also common. So you either need to confirm that the devices are not isolated, or just run additional ground connections regardless.
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Thank you Jeff, that’s helpful. So I will plug a pump to this system. It won’t drive power from the receiver as the pump is 12v. I’ll have an external battery powering the whole system. From what you said I believe it would be ok to power the receiver from the Arduino. I drew a diagram of the system to illustrate what I’m thinking of doing, if you can have a quick look and let me know if you think this is going to work it would be great. Sorry for the basic questions, this is the first time I am adventuring on an electronic project.
My other question is whether the relay is positioned correctly on the diagram above. In my understanding I would have to cut the positive wire and place them on the normally closed and COM ports of my relay. Is that right?
Thank you!
That would work, but I suspect it’s not what you want. It’s more likely that you would use the COM and NO terminals of the relay. That way when the relay is NOT energised the motor is OFF (connection is normally open) and when the relay IS energised the motor is ON.
You haven’t indicated what the relay is. Note that not all relays can be driven directly from the UNO pin. You should be using a relay module, with either an opto-isolator input or a FET driver circuit, to ensure that the drive current is within specification for the UNO.
If the only device that the receiver is controlling is the UNO then using UNO 5V to power the receiver will be OK - the nano will draw a maximum of about 200mA. You could consider powering the receiver direct from the 8V BEC rather than using the UNO 5V supply - that would eliminate any risk of overheating the UNO regulator, and may give better performance. However the manual is very vague about using anything other than 5V, and you would need to check that the higher voltage supply to the receiver does not create an input voltage for the UNO signal that is higher than it can handle. Again, the manual is vague on this point.
With the arrangement you have shown it wouldn’t actually matter whether the BECs are isolated or not as the two parts of the circuit are electrically separated at the relay.
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Hi Luiz,
I’ve had a look and I can’t find any specs on the Crossfire Nano 6CH PWM’s power draw, other than stating it needs 5V so it’s a bit of a guessing game to determine what kind of draw it would want from the Arduino’s built in 5V regulator. Being a receiver of that size I’d imagine it would be relatively low power, but the Arduinos 5V regulator current output is dependant on if it is connected via USB or an external supply, the limit is fairly low in both cases so an external BEC for the receiver is the safest course as Jeff has said.
Do you have a link to the exact relay module you’re using so we can check it’s specs?
