my second raspberry has just passed away

@spllg said in my second raspberry has just passed away:

@bearer because the rpi died while printing i do not feel it could be reactivated by reflashing the boot eeprom but i will try it laster.

odds are indeed low, but seems the "simplest" option without having it sent off somewhere for more in depth analysis.

there are a couple of test points to check voltage rails, but afaik all are generated from the same chip, so odds are its okay as the green led blinks
https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_4b_4p0_reduced.pdf

spllg

@bearer isolator: so i assume that the duet is not isolated. unfortunately i did not find this info in the duet docs.

they're not isolated no; there is a series resistance to prevent damage; which seems to be sufficient for everyone else. (i drew the isolator to protect the pi when testing the duet 3, testing finished and duet survived before the board was finished so it was never made)

dc42

Here's an update of our perspective.

We originally designed the Duet 3 5V supply to be able to handle RPi 3B+ plus some power to USB peripherals. Since then, the RPi 4 has become the norm, and it needs significantly more power.
We've seen a few cases of the Duet 5V supply being overloaded. It turned out to be less resilient when overloaded than we designed for. So in revision 1.1 we made some changes, including adding a 3A PTC fuse.
For the future, we're considering uprating the maximum VIN voltage to 50V (so that you can use a 48V PSU). This will mean we need to reduce the 5V current rating, so we would remove the option to power the RPi from the Duet. I think this is reasonable, given the market switch to RPi 4.
We've no reason to believe that there is any problem with the original connection arrangement between the Duet and the RPi even when they are powered from different 5V supplies, subject to the caveat below. However, in order to eliminate any possible issues caused by differing supply voltages, we've added level shifters between the Duet and the SBC interface in Duet 3 revision 1.1; apart from the SS signal, for which we've increased the value of the series resistor to 1K.

Caveat:

It is mandatory that the Duet, RPi PSU, and any PC that the RPi is connected to via USB are powered from the same power distribution block, or double/triple socket outlet. If you don't do this then you may suffer from transients caused by other mains-powered equipment or lightning etc. and poor mains wiring. In addition, if the PSUs of two or more of the devices have a connection between mains ground and output negative, or you connect the RPi via USB to a PC or other device with a ground connection, and one of the output negative connections is poor, then there may be a substantial current in the Duet to RPi ribbon cable ground connection. In particular, if the VIN- connection between the Duet and its PSU is poor, then the bed current may try to flow through the ribbon cable. This is exactly the same issue as explained at https://duet3d.dozuki.com/Wiki/USB_ground_loops.

The RPi PSUs that I have seen do not have a connection between mains ground and output negative. PCs always do have a connection between mains ground and USB common. Laptops often do too, when running from mains power.

spllg

@dc42 clarification: i did not power the duet via the usb (i did with my forelast one). instead i powered the rpi using an original rpi psu and powered the duet via the ribbon cable (5v->sbc and sbc->5v both closed as instructed by dc42). i did this in order to be able to switch the 24v psu on and off using the web interface.

as i am not an electronic engineer, i considered to 5v-power the duet and the rpi using 2 distinct psus (with 5v->sbc and sbc->5v both open) but now i feel, the only safe way to use the duet with a rpi (3+ not 4) is to power the rpi3+ from the duet (with 5v->sbc closed and sbc->5v open).

i will power the rpi from the duet, ground the stepper cases and see how long my next rpi will stay alive.

spllg

@spllg if i power the rpi form the duet i will loose the ability to switch the duet psu on using the web interface. any suggestions?

@spllg said in my second raspberry has just passed away:

@spllg if i power the rpi form the duet i will loose the ability to switch the duet psu on using the web interface. any suggestions?

if you only have a single supply for the duet yes. if you have a dedicated 5v supply for the duet, no (can't be a dc/dc off the main supply ofc)

spllg

@bearer i was told )by a person who knows how to operate the duet device) to do it this way. just wanted to point out that i lose functionality when following his advice.

rgds.

and the suggestion is to use a dedicated 5v supply.

spllg

@bearer going to to it this way and hoping the next rpi will survive for longer than 4 months - otherwise i think it would be best to go without an rpi - lost functionality but no rpi.

sorry for any inconvenience ..