I am not sure if this is the right place to post this question, and any help is appreciated.
I am testing a controller based on Nano clone, it is powered by a car battery.
Battery -> DC charger -> Computer -> USB cable -> Nano -> 12V power -> Battery
I measure the total current draw of entire system.
If computer is idle and screen is off, total current draw is ~0.2A if USB cable is NOT connected
If computer is idle and screen is off, total current draw is ~0.6A if USB cable is connected, regardless whether or not 12V to Nano is connected. This is not expected (it is ~0.4A on 12V, or 1A on 5V).
I also tried disconnecting 12V to Vin of Nano, but it dd not make any difference.
Another issue I have is that it seems that USB cable may back power 12V, because even I turn off 12V power, the LED on my battery pack is still lit once USB cable is connected. I am not sure this is related to power drain over USB.
I am not sure this is due to Nano board design issue, or my setup.
Confusing story.
e.g. car battery changes into battery pack with LED.
The Nano has a schottky diode between USB supply and onboard regulator 5volt supply.
If USB voltage is ~0.2volt higher than the onboard regulator output, USB supply is used.
No current can flow from Nano to USB.
If the Nano would draw 0.4Amp, you would know.
0.4A is 2watt on 5volt, and 4.8watt on 12volt.
Someting will get hot.
I will have to go back home for the drawing.
Just to clarify: I use one 12v battery to power both Nano based unipolar stepper motor controller and laptop, which are connected together using usb.
Everything works fine.
One thing I don't know is that if I turn off 12v battery switch, and connect usb, led on battery pack is lit, looks like the current flow from usb to battery through Vin pin.
This is the simplified drawing.
Battery pack (12v) power both Arduino/stepper and laptop (dc to dc converter).
If I power Arduino with 12v, without connecting usb, everything looks fine.
If I connect usb, with or without 12v, current draw goes up.
If I connect usb and switch off 12v, led is lit, which means than current flow from usb to vin. The only thing there seems 5v regulator on nano board. If I disconnect vin from 12v then led won't lit
If you power the Nano via USB, the internal reverse protection diode of the onboard regulator will conduct.
There will be ~4.3volt on Vin.
Loading Vin (LED, stepper) is an unhealthy situation for the onboard regulator.
Use a 1N4004 diode in the Vin line, cathode to the Nano.
An Uno/Mega has that standard buildin.
Leo..
Wawa:
If you power the Nano via USB, the internal reverse protection diode of the onboard regulator will conduct.
There will be ~4.3volt on Vin.
Loading Vin (LED, stepper) is an unhealthy situation for the onboard regulator.
Use a 1N4004 diode in the Vin line, cathode to the Nano.
An Uno/Mega has that standard buildin.
Leo..
Leo,
Thanks for the reply, it is really helpful.
I dont usb to power nano, but at times 12V might be switched off, and I think I will add a diode as you suggested because it is confusing when LED is lit.
But this does not explained the current draw over USB, as I tried disconnecting VIN from 12V, it does not help. What else could be the reason?
I meant to say is that I dont need power from USB. I only want to use usb to transfer data, 12V is the power to the entire system.
The point is that whether the power is from 12V only, USB only, or both, the total current should not go up. eg, if USB powers some logic in the system then 12V load should drop accordingly. I can not explain why total current jumps when USB is connected.
So you power a laptop from the same 12volt battery.
Are you sure the negative battery terminal of the laptop is internally connected to ground.
If you connect a DMM between Arduino ground and e.g the exposed ground of a USB socket, you measure almost zero ohm, or no current when on?
Leo..
I connected laptop DC charger to computer, and computer to arduino using USB, the resistance between DC charger ground to arduino ground is almost 0.
Are you suspecting some grounding issue? I could try AC charger to see if it makes any difference.
And is there any way to shut off laptop USB hub power?
blackdragon72:
And is there any way to shut off laptop USB hub power?
Yes.
Wawa:
A laptop/PC does not normally switch off USB power when on standby or sleep.
Turn it off.
TLDR but ... The problem is not in the grounds.
Wawa:
If the Nano would draw 0.4Amp, you would know. 0.4A is 2watt on 5volt, and 4.8watt on 12volt. Something will get hot.
Post a hand drawing of your wiring.
Or in fact, a perfectly focused photograph of your set-up with all wires clearly visible as they terminate on the modules and show that as a link in the text, not an attachment.
