I bought this 12 volt 25 amp DC DC converter, which has a input current range of 36 - 75 volts. I plan to use this for a project.

When using 73 volts input, I noticed the DC DC converter was getting super hot.

I thought I had a possible short, but I hooked up my fluke and checked the amps. With "no load" it was pulling 90 mA at the 73v input.

That is a whopping 6 watts of power with no load on the DC DC converter.

I thought there was something wrong until I checked the specifications and found that it is rated to draw between 80 mA and 140 mA with a typical 110 mA draw.

I was very suprised about this high draw and no load.

Is this normal for DC DC converters? Should I have bought something else?

Here is the data sheet below of what I bought with full specs.
http://www.mouser.com/ds/2/632/DS_Q48SC12025-372467.pdf

 

Just off the cuff, as a technician, I don't think the inverter is faulty, since it is brand new. It is 91% efficient at 300 W, leaving 10% power lost. 10% of 300 W is 30W lost. 6 W isn't too bad in standby mode. I think your inverter is fine, but don't quote me on that.

 

The short answer: because you're supplying it with a high (least efficient) input voltage and you've done no thermal management.

 

The design of DC-DC converters always requires some compromise- it's impossible to design one that is super-efficient across all possible loads and input voltages, so they optimize it for a reasonable load scenario.

When it's unloaded, the efficiency is terrible, load it up and that 90 mA becomes insignificant.

 

Just off the cuff, as a technician, I don't think the inverter is faulty, since it is brand new. It is 91% efficient at 300 W, leaving 10% power lost. 10% of 300 W is 30W lost. 6 W isn't too bad in standby mode. I think your inverter is fine, but don't quote me on that.

I am quoting you on that because I agree with your analysis