Day yesterday I was talking about a kit whose main element is the Raspberry pi, which is focused on the market for children who have an interest in building their own computer.
Well, a little over a week ago, many Raspberry Pi users who purchased the PoE HAT plugin started making a number of claims in various forums and even within the Raspberry blog.
Because multiple users reported issues with the recently released Raspberry Pi Power-over-Ethernet HAT, the Raspberry Pi Foundation is offering to refund customers who bought the faulty board.
In the days after its release in late August, users had been reporting limitations in the power delivered by Raspberry Pi PoE HAT.
The HAT is a complement to the popular Raspberry Pi 3 Model B + SBC that has a fully isolated switching power supply with 37-57V DC, Class 2 input and 5V / 2.5A DC output.
La HAT connects to the 40-pin connector and the new PoE-specific 4-pin header introduced with the B +, located near the USB ports.
El PoE HAT is provided with a 25 x 25mm brushless fan to cool the Broadcom SoC.
But unfortunately, this accessory could not be well received by the market due to the aforementioned problem.
During the intervening weeks, engineers at the Raspberry Raspberry Pi Foundation have been scrambling to discover the nature of the problem. An interesting move can be followed on the Raspberry Pi forums.
About the problem
In an article in The Register , the problem was explained by Eben Upton, co-founder of the foundation and CEO of Raspberry Pi Trading.
According to Upton:
"This is an interaction between the low frequency switching regulator on the HAT and one of the two brands of USB current limiting switch we use on the main board."
Upton explained that because the regulator operates fairly in low frequency, each time you change it, you move a large amount of power to the three USB reserve caps through the current limiting switch.
This large instantaneous current is tricking the switch into thinking that a true overcurrent event is occurring.
“We lost it in product testing because (dumb luck) our heavy load testing was done on boards with the other brand of switches, and most of our field testers only used the board to power mice and keyboards, which works fine. on all the HAT / Pi pairs we've tested, ”said Upton.
The Key Points of Raspberry Pi PoE HAT Problems, and the steps being taken were detailed in the letter Upton sent to The Register, and were also posted on the Raspberry Pi forums.
They are the following:
- “A significant proportion of the HAT / Pi pairs are limited to delivering less than 200 mA of downstream current to USB. This is generally sufficient for mice and keyboards, but not for hard drives, for example «.
- "We will fix this in a later twist on PoE HAT."
- "In the meantime, we will add a note where the HAT is sold, documenting this limitation."
- “We will provide a couple of manual mod options for adventurous users. They are likely to be:
- "Removing the tank caps from the main board (a simple and clean way if you can use a soldering iron, but it limits the USB connection)."
- "Insert a small amount of series impedance into the current path from the HAT (this will be a bit difficult to implement)."
- The key points of the Raspberry Pi PoE HAT problems, and the steps taken, were written in the letter Upton sent to The Register, and also posted on the Raspberry Pi forums.
The original blog post, announcing Raspberry Pi PoE HAT can be find here . The product page with links to resellers it's here .