Lawrenceb Posted August 10 Share Posted August 10 Hi, A bit of background as an example. I have a Fujitsu AOTG18LVCC heat pump and I would like to use a Shelly PM Mini Gen3 to monitor energy use. The heat pump Max current is 13.5A The PM Mini Gen3 current rating is 16A max measuring current so appears to be suitable. Will this have enough safety factor and how hot could it get? Thank you Quote Link to comment Share on other sites More sharing options...
Members thgoebel Posted August 11 Members Share Posted August 11 (edited) The manufacturer specifies 16A rated current. Why not rely on this? Otherwise, the Shelly Mini PM has tightened circuit paths with the load circuit: There is one electrical component only in the load circuit: The shunt. It has 1mΩ. Thus, 256mW are dissipated in the shunt at a rated current of 16A. This is a lot of thermal energy with respect to the small case. But I suppose the developer has executed a thermal test with worst case environmental conditions. Unfortunately there is no extra NTC to measure the internal temperature. Only the CPU temperature is tracked - an ESP32 prerequisite… Edited August 11 by thgoebel 1 Quote Link to comment Share on other sites More sharing options...
tvbshelly Posted August 11 Share Posted August 11 It certainly depends on where you mount the Shelly mini. If air can move freely around it, i.e. there is no heat build-up, it is of course easier to dissipate the generated heat . On the other hand, according to Shelly, the minis are intended for in-wall boxes, where heat transfer is certainly rather limited in my opinion. The maximum current of 13.5 A for the heat pump certainly does not mean that this current is continuously flowing. Can you estimate how long this maximum load can occur or what the usual average loads are? This may help you with the estimation. In principle, you can of course always measure such loads with current transformer CTs, then you are always on the safe side with regard to the load. Shelly also has devices for this purpose: Shelly PRO EM-50 (one-phase, 2 CTs) / Shelly Pro 3EM (three-phase or one-phase, 3 CTs) and Shelly EM. However, these are more expensive than the Minis and are only intended for DIN rail mounting (PRO), with the exception of the Shelly EM. Quote Link to comment Share on other sites More sharing options...
Members thgoebel Posted August 11 Members Share Posted August 11 2 hours ago, thgoebel said: The manufacturer specifies 16A rated current. Why not rely on this? Sorry for this repetition. Give it a try! And feel fine with your warranty… 1 Quote Link to comment Share on other sites More sharing options...
Lawrenceb Posted August 12 Author Share Posted August 12 (edited) Thank you for all your comments 🙂 I expect that it will be ok but I have limited experience with these devices, so it made sense to ask. I agree that the heat pump will usually not run at full load for long, maybe an hour max, especially as my outdoors conditions are generally fairly mild being near the coast. My instinctive feel is that 0.25W dissipation should be fine as spread over some PCB area and has significant tracks/solder attached. Edited August 12 by Lawrenceb Quote Link to comment Share on other sites More sharing options...
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