VRM experience and rule R43

Technical Electrical
1

Hello, we have a few questions regarding the practical usage of the VRM module. Rule R43 in the game manual states:

R43 The Wireless Bridge power must be supplied directly by the 12V 2A output of a Cross the Road Electronics Voltage Regulator Module (VRM) (P/N: am-2857, 217-4245) and must be the only load connected to those terminals.

Is the following interpretation of the above rule correct:

  • Do not use the other pair of terminals in the 12V 2A section of the VRM to supply power to any other devices (assume the radio will use the full 2A).
  • It is OK to use the 12V 500ma, 5V 2A, and 5V 500ma terminals for other purposes.

If it is OK to use the 12V 500ma, 5V 2A and 5V 500ma terminals, I then have the following questions:

  • Should you avoid doing so anyway and dedicate the entire VRM to the radio (I’d hat to lose the radio during a match).
  • Is it true that the 5V 2A connectors are for a total of 2A (not each pair) and that this is peak load only (they are limited to 1.5A continuous).
  • Is there a total output wattage one can use as an estimate for what the VRM is capable of reliably running at? If so, is it something like: 12V * 2A + 12V * .5A + 5V * 2A + 5V * .5A = 42.5W?

We are looking at powering a Axis M1014 (5V .6A) and D-Link small 5 port network switch (5V .5A) and are trying to determine if we should add a second VRM module or if its OK to load up the 5V connectors on the VRM that supplies the radio.

Thanks for any help or comments you can offer and I apologize if I didn’t use the correct terminology to describe my questions (I’m more of a software guy).

2

The 12V supply and 5V supply in the VRM are separate and independently protected. Issues up to and including a short on the 5V supply should not cause an issue with the 12V supply.

You are correct that it is 2A for both pairs, not 2A each. Last year’s VRM was definitely 2A peak, 1.5A continuous on the 5V. Beta teams tested a 2016 version of the VRM, but I’m not sure if the change was to tweak the 5V to actually be 2A continuous or not.

Regardless, at 1.1A continuous you should be fine running both devices off the 5V supply of the same VRM as your radio.

3

Just to reinforce, don’t put anything other than the OpenMesh radio on any of the 12v VRM outputs, since they use a shared rail.

4

Thanks for the replies. Based on what you have both said, I will recommend to our team that we be conservative and:

  • Limit the total current draw of the four 5V connectors to 1.5A.
  • That we only use the 12V side to power the radio (leave all three of the other 12V connectors disconnected).

Thanks again - appreciated your help.

5

While the 12 volt outputs share the same regulator they do not share the same output protection. The rail is split into two separate PTC’s, 500mA and 2amps. While a short to the 2 amp rail will cause the radio to drop out, a short to the 12 volt 500mA rail will NOT interrupt the radio’s supply rail.

The 12 volt LED will turn off anytime the 12v 500 mA rail is shorted, however this is not an indication of the 12 volt 2 amp rail dropping out.

So yes it is safe to connect secondary loads to the 12 volt 500mA rail.

6

I mistakenly thought that I remembered having been able to put a 500ma continuous load on the 12v/500ma and a 1.2ma continuous load on the 12v/2a outputs and after a few seconds browning out the whole 12v side (on the older v1.2).

Sorry for the misinformation.

7

On the older revs of hardware (<1.4) that was only true on the 2 amp rail and the limit was actually 1.5 amps. So if you are unsure which rev you have keep the total budget below 1.5 and you are good to go.

The latest rev (1.4) can be identified by removing the bottom cover and identifying the solder mask color. A black solder mask is the latest Revision.