1500W SMPS Inverter Heatsink Temperature?  - Page 1
Forum section: electronics / projects

author: AJ3G
author_rank: Regular Contributor
timestamp: December 14, 2020, 04:31:34 am
content: All:I am using a 65V, 1500W Switch Mode Power Supply to drive two RIDEN 6018 controllers. Both RIDEN Controllers have a thermocoupler to monitor temperature inside the enclosure. I have opted to attach the thermocoupler to the heat sink of the SMPS. This is a rather large SMPS built in the 90’s. When sitting at a light, or no load at all, the Heatsink seems to be stabilizing around 105 Degrees F. When I increase the load to 30W I see something around 110 Degrees F.I have a fan control circuit, which I would like utilize for quieting the supply down when using light loads. The question I have is what would be normal temperatures to expect for a SMPS of this vintage and power on the heat sinks of the switcher? I did not expect 105 Degrees F stable with no load, and I have not yet really exercised the supply. These are parameters I have never measured before, so I am hoping someone could give me idea of what would be normal, so I can work on setting up the fan control circuit.The supply seems to operate well, so I doubt there is an issue, and this type of temperature on the heatsink is normal at a light or no load. Tomorrow I hope to utilize a 400W Electronic DC Load to make adjustments to the Fan, so I am hoping that I can get some feedback as to what might be expected. I do not need precise, but any rough order of magnitude to start from would be most helpful!Thanks in advance!Rich

author: Whales
author_rank: Super Contributor
timestamp: December 14, 2020, 05:14:06 am
content: A 'normal temp' is somewhat arbitrary tradeoff of lifetime versus noise+dust+size. Some things run almost to 100degC so size & cost of the cooling can be minimised, others run only to +30degC above ambient using big heatsinks and large, slow fans; so they're quiet and reliable.Instantaneous deathAll of the semiconductor parts will have a max junction temperature (TJmax) that you can calculate based off the temperature of the heatsink (right where they attach) and the wattage you think they are dissipating. Datasheets provide the relevant thermal resistances to calculate this. Dave has made some videos on this.Slow deathMost high-current silicon semiconductors are rated to 100degC or higher. This includes large FETs and diodes. Most electrolytic capacitors are rated to 85degC or higher.This 'rating' comes along with an expected lifetime in hours. Eg a capacitor might be rated to last 1000 hours at 85degC. As an approximate rule: every 10degC cooler than this rating doubles the life expectancy.

author: AJ3G
author_rank: Regular Contributor
timestamp: December 14, 2020, 05:33:40 am
content: Hi Whales:Thanks for the response. Tomorrow I will attempt to see if I can identify some of the components so I can pull a spec sheet of the device's. The SMPS is very densely packed and its very difficult to see all of the components without tearing the whole thing apart. How they managed to pack so much stuff into a small space is a marvel in itself.It appears to settle in at 105F, so I will be curious what happens under some reasonable load testing.Rich