Executive summary
It was found that BalenaFIN boards did not perform well in elevated ambient temperatures.
Balena did an root cause analysis and issued an fix.
We did some tests (described in this post) that verified that fixed boards work ok at least in ~73 C ambient temperature for 8 hours.
Description of project
It was found that our BalenaFIN based products are not working correctly at elevated ambient temperatures. This was also the case in deployed installations at our client sites where elevated temperatures are often found due to hot process environment. During summer 2020 we were forced to add extra cooling to deployed devices at field as quick fix for the problem.
As soon as our clients reported possible temperature problems, we did small change to our deployed software to read internal temperature from BalenaOS /sys/class/thermal/thermal_zone0/temp and send it to our cloud. So we have temperature data from failed units and can thus compare readings.
These pre-fix boards have failed when this internal temperature was between 60-70 C. Unfortunately we don’t have any ambient measurement data available for those deployed pre-fix boards.
After extended testing Balena found an issue on their board that affected board stability at high temperatures. An resistor value was found to be wrong and thus resulted to wrong voltage levels that resulted in internal components being powered off. Based on testing Balena changed the resitor value to more suitable value. Detailed root-cause analysis can be found from https://www.balena.io/blog/usb-issue-rca/.
We ordered new boards immediately when they were available after Balena released information about this fix.
Test aim
- Phase1
- We shall test that ambient temperature of ~70C is not an issue for BalenaFIN by heating bare BalenaFIN in heat-chamber to ~70C ambient and log the performance for one full workday (8h).
- Phase 2
- If phase 1 succeeds, we shall test with ethernet sensor connected
- Phase 3 (optional)
- When we have new batch of mPCIe modems, we should test with the modem we are using to verify out also mPCIe working
Test setup
- BalenaFIN board (new fixed revision, received from Balena 2020/08)
- Memmert UM200 laboratory heat-chamber
- Fluke T3000FC temperature logger
- IFM AL1350 industry IoT ethernet-board
- IFM TV7105 IO-LINK temperature probe
- AIM TTi laboratory bench power supply with 24V output
- Software to read and log /sys/class/thermal/thermal_zone0/temp temperature reading

Test decription
Phase 1: Bare BalenaFIN – board 8 h
- Laboratory heat-chamber was heated to approximately 73C
- BalenaFIN was put inside chamber to FR4 base
- Fluke-temperature probe was put inside chamber and logging was started
- BalenaFIN started to send temperature values to cloud and these were monitored and logged for 8 hours.
- Graphs were drawn with ambient temperature from Fluke temperature logger and internal temperatures sent by BalenaFIN and checked that Balena did send temperature to cloud whole time.

Fig 1: Test chamber temperature readings of 73 C during 8 hour test period.

Fig 2: Internal temperatures reported by Balena. About 91 C.
It was found that Balena worked correctly during this test so proceeded to phase 2.
Phase 2: With ethernet connected, 3 h
- Same setup and test procedure as in phase 1 but heat chamber temperature was measured also with IFM IO-link industrial sensor connected to ethernet. If USB power is missing, this should show in data as per Balena’s report, ethernet bridge is also USB-based.


Fig 3: 3 hour heat chamber temperature and balena internal temperatures. Heat chamber temperature measured with ethernet sensor to see if ethernet is stable.
BalenaFIN was found to be correctly sending both values whole time.
Conclusions
We verified that at least BalenaFIN unit we tested was successfully able to withstand 73 C ambient temperature without failing.
So the fix that Balena did seems to be working.
Possible next steps
To replace every distributed board at customer sites with a fixed board and send broken boards back to Balena for RMA repair.
If needed, heat chamber tests with mPCIe modems used in application could be done also.
Test time, location and participants
2.-4. Sep. 2020
PalonenLABS Oy workshop, Tampere, Finland
Henry Palonen / PalonenLABS Oy