the Vin power is limited to 1A by the "reverse polarity protection diode" between it and the connector. It's limited to not much more than that by the current capacity of the connectors (probably 2A max for the "Power" socket, and no more than 5A for the Vin coaxial connector.) The PCB traces probably aren't good enough for 5A, either.
For 50A, you'll need a separate supply, with somewhat careful attention paid to connectors and such. Take a look at what the remote control people do for their high-power electric motors...