Maximum cortex voltage - from official Q&A

[jpearman]

A question was recently asked in the official Q&A.

@marccenter

Dear VEX,
I would like to do some bench programming with the Cortex without having to worry about charging the 7.2 volt batteries. I would like to use a 12 volt , 5 amp power supply. I see that the maximum voltage for the Cortex in the documentation is 12 volts. I am a little concerned that if the 12 volt supply drifts upward that I may damage the Cortex. Can you comment on how much headroom I have on the 12 volt maximum voltage input to the Cortex?

The answer from VEX tech support is as follows.

@Eli Osornio

Hello Marc,

A 12V power supply will not damage the Cortex even if you drift up a few volts.
Please be aware that any kind of operation outside of the recommended range may not damage the Cortex, but will void the factory warranty.

15V will damage the Cortex.

Not to nit pick, but this answer first says that it’s OK for the voltage to drift above the 12V spec by “a few volts” and then says that 15V will damage the cortex. I guess 3V is more than a few volts. A real spec with qualification would be useful.

In this thread I discussed the power distribution in the cortex as I understood it.

https://vexforum.com/showpost.php?p=326053&postcount=1

There are two main 5V power regulators running from the input power. The LM2940 datasheet shows maximum input as 26V, the L5973D has a maximum input of 36V, however we have no idea of the rating of the surrounding components. A typical value for capacitors used in this application may be 16V so I suspect anything above that would cause harm and would be the reason why the spec for the cortex has maximum input at 12V.

Another consideration has to be motors that may be connected to the cortex. The spec given for these is when they are driven at a nominal 7.2V and I’m not sure I would want to run them (continuously) much beyond 9V without more information. Input power to the cortex is fed directly to the motor ports and is a good reason not to be powering the cortex from 12V.

Bottom line is that a 9V bench supply would be more suitable and ideally an adjustable one set for 7.2V.

[JVN]

Hi James,
Eli updated his post. We agree with your comments.
In general we will stick with posting the MFG rating, and allowing the community to provide “what you can actually get away with” type comments.

-John