I’ve seen the same thing. I had placed a second order for a 014 and that arrived yesterday. On it’s own the 016 works fine, when I have the 2 connected one will fail to respond quite frequently. I too checked and played with the cable type, lengths, shield and termination resistors to no avail, what I also noticed using the debug mode in minimalmodbus was that once the device failed to respond immediately, it was never going to respond. That is that no matter how high I set the timeout, it didn’t impact the fails. I noticed there were only 2 conditions, either the device responded and total round trip time was 60 to 80ms, or the timeout limit was reached.
I successfully fixed this by setting the timeout low and puting the read command in a looped try catch to allow up to 5 retries without raising an error
for i in range(5):
try:
data = self.read_registers(0,10,4)
break
except IOError as e:
pass
if data:
. . .
what I found is if it doesn’t succeed the first time it always succeeds on the second try, this takes a maximum of 160ms round trip where as even a 1.5s timeout often failed.
I suspect there is a glitch in the FW which causes a stall if a read is tried when something else happens to be going on, a clash of some sort, no matter how long you wait it will never recover, it just times out. Since it only occurs with multiple devices connected, I suspect these might just be a bit too sensitive to noise or certain cable/connection characteristics perhaps.
Totally, I was actually looking to use these more for some per consumer monitoring, eg a ring main of MVHR units, having one of these installed at each MVHR unit rather than having to individually wire each MVHR unit back to the dist board to monitor individually.
For “monitor device per breaker” monitoring I think I would prefer to see them din rail mounted in the dist board, but I’m particularly thinking about new builds here, choice is always limited when retro fitting.
An average DIY’er could (quite) easily add one of these behind a power outlet (in the floor, ceiling or hollow stud/partition wall etc) to measure (for example) the consumption of a washing machine or dishwasher etc. It costs not much more than a CT and needs no power supply, It’s not RF or WiFi it just needs a simple signal cable.
BUT - It needs to be said since these are mains powered, they are not as “DIY” as the usual low voltage OEM kit. Caution and confidence in what you are doing is very important when using these devices, especially the pzem014 that sits in-line with the circuit being monitored.