Both USB and Relay Shield for power

As one who is just starting out to explore the Particle IoT world, I want to be sure I don’t mess up the Photon.

My Photon will be powered from a ‘12V’ battery via the Relay Shield. I would prefer to use a Windows7 PC to do the programming via USB, but am concerned that when I’m doing that I’d be supplying power from two ends, both from the USB and from the Relay Shield.

Is that likely to cause a problem?

There is a protection diode between the Vin pin and the USB connector which prevents the power fed to Vin into the USB port.
Also the 12V will never make it to the Photon as the shield already has a regulator on board
Here are the schematics

@brettn, there is a protection diode on the Photon between Vusb and Vin. The Vin pin is used to supply the power to the Photon from the 12v to 5v converter on the shield. This diode will provide the protection you need.

Many thanks for the info. I’d hoped to hear it was something like that.