How to Choose Water Pump?

Take Maytech 300A ESC and MTSKR1905WF remote as example: 

We have 3 kinds 300A ESC: 

1. MTSF300A-WP with / without built-in receiver Waterproof & Watercooled ESC: 

This ESC is with waterproof case, it has 2 ways for water cooling:

1. Put it underwater directly.

2. Use water pump, and to use water pump, it can only use extra power supply.

 And to work with our MTSKR1905WF remote, can use relay switch on receiver to connect water pump, and suggest to use extra power supply to power water pump. 

This relay switch can withstand 30V 3A water pump, so as long as your water pump is under 30V 3A would be work. 

Wiring diagram for Internal receiver version: 

Wiring diagram for External receiver version: 

2. MTSF300A-OPTO Watercooled 300A ESC with 5V Output UBEC:

This version ESC include with a 5V UBEC to power for receiver, except for the above method to use extra power supply for water pump, here's another way to direclty use the 5V UBEC to power for receiver and water pump at once if you don't want to use extra power supply. 

But please noted: 

The 5V UBEC is 6W, the receiver is 0.5W. 

So the water pump you can use must be under 5.5W, voltage must be 5V, so water pump current must be under 1.1A. 

A. Wiring Diagram for MTSF300A-OPTO Watercooled ESC Use Extra Power Supply: 

B. Wiring Diagram for MTSF300A-OPTO Watercooled ESC to use 5V UBEC to power receiver and water pump at once: 

12V 30A Water pump and extra 12V Power supply, click below picture to check more specs: 

Above is the way to use water pump for watercooling, here's also another way to not use water pump for cooling: