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I need to supply an evaluation kit with 32 VDC ±10 % from a 48 VDC battery. The power supply of the kit is rated at 60 W with spikes at 150 W lasting 100 ms (it controls motors).

I have choosen the following DC/DC converter: RPA300E-4832S/N/H (RECOM Power). The datasheet can be found here, or the manufacturer's data sheet here.

Here is my schematics:

enter image description here

I do not use the Sense and Trim functions. CTRL needs to be tied to GND for the DC/DC converter to operate, otherwise it is in standby mode.

The DC/DC converter is soldered on a veroboard with the heat spreader facing up. I have not added any heat sink and I cannot use air flow from a ventilator.

What I observe seems strange to me:

  • In standby mode, the DC/DC converter heats up a little: 35°C after 10 min. approximatively. It consumes around 30 mA.
  • When it operates, with a small load of 1 kΩ (and even without load!), it consumes around 100 mA and it gets hot really quick: after some minutes it is at around 60°C.

I can't imagine how hot it will get when the kit will draw some amps from it over a longer period of time.

Do you think it is a normal behavior or is there something strange with it? Do you have any advice to handle the situation?

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    \$\begingroup\$ Typical quiescent current is 100 mA so that sounds normal according to the datasheet but it is high compared to what’s considered good no load performance. Give it some more load? Also, airflow is required as per the datasheet. \$\endgroup\$
    – winny
    Commented Dec 17, 2021 at 18:20
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    \$\begingroup\$ It may have something to do with leaving +Sense and -Sense floating. Every other converter I've seen with that feature requires you to tie them to +Vout and -Vout respectively (if you're not using them for remote load sensing). \$\endgroup\$
    – vir
    Commented Dec 17, 2021 at 18:24
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    \$\begingroup\$ I can't imagine how hot it will get when the kit will draw some amps from it on a longer period of time. - try it? \$\endgroup\$
    – Andrew Morton
    Commented Dec 17, 2021 at 18:28
  • \$\begingroup\$ Also, try putting it in STANDBY mode (if possible) and see if it cools down. If not, it could be a defective part or not wired properly. \$\endgroup\$
    – icodeplenty
    Commented Dec 17, 2021 at 18:29
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    \$\begingroup\$ as @vir said, +Sense and -Sense must be connected, either directly to +Vout, -Vout or to the load if you want more precise regulation. \$\endgroup\$
    – Maple
    Commented Dec 17, 2021 at 21:22

1 Answer 1

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Similar modules that I have used require significant amount of cooling air flow or they run very hot even at low loading.

There is a derating graph on page 5 of the datasheet.

With natural convention cooling it is rated at just over 80% of full output provided the air temperature is 25°C. To achieve full output requires at least 1m/s at a more reasonable temperature of 40°C.

enter image description here

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  • \$\begingroup\$ Also, some modules will run hot even unloaded. We have a 1kW AC/DC that will get up to 60C with essentially no load. \$\endgroup\$
    – vir
    Commented Dec 17, 2021 at 20:39
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    \$\begingroup\$ Page 2 shows that the module dissipates 4+ watts with zero to very little load with a 48V input. You need forced air cooling. Even a whisper of moving air will make a big difference. The diagram on the bottom of page 6 implies moving air. Or, attach the module to a larger heat sink. \$\endgroup\$
    – qrk
    Commented Apr 8, 2022 at 21:14

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