Revision as of 23:46, 6 December 2010

Introduction

This page is a work in progress, describing the steps people have taken to resolve power issues related to the 'new' Mikrotik R52hn and R52n cards.

The Problem

A typical Mikrotik RB433 will quite happily power 3 R52 or equivalent cards on a standard 18v 0.5A POE injector over more 30m or more of Ethernet Cat5e cable. Unfortunately once an 'n' card is added, this is no longer the case.

The standard issue that arises once 'n' cards are added is that the router board reboots at regular intervals. The problem can be triggered by running scans on all of the wireless interfaces at the same time and waiting up to 10 minutes.

Other symptoms include:

• router config reset after reboot
• instability in previously stable links, especially during periods of high load
• high pitched whining noise coming from the rb
• POE network port jabbering and loss of ethernet connectivity, with the wireless links remaining active

Causes

The cause of these problems is a lack of power to the routerboard's CPU and wireless slots, which is in turn caused by either a lack of power to the power converter, or the power converter being overloaded and mis-behaving.

Lack of input power

This seems like an obvious one - if the routerboard isn't provided with a clean, on-spec power supply, it will mis-behave. Unfortunately the use of POE can hide this. Cat5e cable is 0.x mm thick and as such will lose x volts/m @ x A. In other words, a 24v 1A POE injector will only provide the routerboard with x W of power after running along 30m of Cat5e cable. Increase that to 60m and you've got a serious, but hidden problem.

Start by reducing the network cable length as much as is feasible, then try a higher rated POE injector. Finally, you should go for direct DC power to the rb.

HINT Sometimes POE efficiency can be reduced by poorly crimped connectors or damaged network cable - check or re-crimp if possible.

Overloaded on-board power converter

This is what gives the 'n' cards a really bad name - the onboard power converters for the routerboards are limited by design and in most cases cannot supply enough power to both the wireless cards and the CPU. Once this limit has been reached, the power converter should shut down the board, but it would appear this is not always the case - so presenting the user with the above-mentioned set of issues. It also appears that occasionally under these circumstances the power converter outputs unsafe voltages, which cause the on-board flash to be erased or the board to be permanently damaged.

Power converter ratings

Power ratings

Solutions

RB power configuration matrix

This is a matrix of real-life configurations, what worked and what didn't. Please add your experiences and solutions to the problems here.

PLEASE BE AS SPECIFIC AS POSSIBLE - mention at least the following:

• rb type
• RouterOS version
• the number of cards
• the type of cards (R52/R52n/R52hn/XR71 etc)
• the power supply (POE/Direct DC)
• If using POE

* cable type (Cat5e normal/shielded/Cat6 etc)
* distance between injector and rb

• measured voltage

* at supply
* at RB

• how many RBs on the same power supply

RB433AH RB493AH

R52 R52hn R52n