Setting up OCP on the AX1500i

By Jonny Gerow, on May 9, 2014

The AX1500i features OCP (over current protection) on each PCIe and EPS12V connector (the 8-pin connectors on the modular interface).  The OCP in an AXi product works in a very similar way to that of any other PSU with OCP.  Voltage goes across a shut located at the connector, this is measured by an op-amp that sends a signal to an IC.  In the case of an analog PSU, the IC is your supervisor IC.  In a Digital Power Supply, like the Corsair AX1500i, the IC is the MCU.

The primary difference this creates between the OCP in an AXi Digital Power Supply Unit and one in a typical analog PSU is that the AXi's OCP can be controlled, or even turned off, by the user. By default, OCP is enabled and set to 30A. This article talks about what OCP is and how to adjust it for extremely power hungry graphics cards.

OCP is an intentional limiter that prevents more than a predetermined amount of power to get delivered by a particular connector. By having this OCP in place, any shorts that create a resistive load that can overload and overheat the pins, wires or connectors of the power supply are cut short as the power supply is forced to shut down if the OCP value is exceeded. While each connector can easily handle 40A of current or more, we have set the default OCP limit to a conservative 30A on each connector of the AX1500i.

The current version of Link does not poll the power supply for its current setting. So initially, you will see a power tab with all OCP check boxes unchecked and all of the OCP sliders set to 20A.

While future versions of Link will have a polling feature that will read the PSU's settings, currently this information is incorrect. If the AX1500i was actually being polled, the settings you would see in the power tab in Link would show all of the OCP check boxes checked and all of the sliders set to 30A.

When benchmarking AMD R9-295X2 graphics cards, we found that the cards can overload the preset OCP of the AX1500i and cause it to shut down. So once your PC is built and you have powered everything up, installed Windows and made sure everything is working correctly, it will be necessary to install Corsair Link if you wish to maximize the performance of your 295X2 card.

In Link, there are one of two methods that can be used. One is to check all of the OCP check boxes and turn the OCP up to the maximum of 40A.

The other method that can be used is to turn off the OCP altogether. To do this, you must check all of the boxes for OCP and then uncheck them. After no more than 15 seconds, OCP will be disabled on the AX1500i power supply.

Using either of these methods should ensure troublefree operation of one, or even two, AMD R9-295X2 graphics cards in your PC.