Fan-less DCDC module power supply needs a Vicor Module?.....not an "Open Frame" type DCDC module

[zenerbjt]

Dear Engineers,

We wish to design a modular power supply of the following spec:

Vin = 42-59VDC (14S LiPO)
Vout = 12V
Iout = 11A
Isolated (500V)
Not allowed to use fans to cool it….just heatsink.
Enclosure is a totally sealed carbon fibre box of dimension 50cm x 20cm x 10cm (high).
Max ambient outside of box = 45degC.

Given the non-use of fans, I believe you would agree with me that this more or less confines us to a Vicor module type solution? Due to the greater thermal conductivity of the material of the vicor modules.

For example, A Vicor PRM48AT480T400A00 cascaded with a Vicor VTM48ET120T025A00 would cover our spec. Their datasheets give the thermal resistance of their hottest component to the case as 1 degC/W. You simply can't get that low with "open PCB" type DCDC modules, because they use gap-pad to thermally couple to their little metal base-plate.

“Open PCB” type DCDC modules such as eg the Murata UEE-12/12.5-D48NB-C just can’t compete for such a fan-less application. Do you agree?

The power components of the UEE-12/12.5-D48NB-C are gap-padded to the metal base-plate. Clearly, gap pad isn’t as good a thermal conductor as the Vicor module material. The UEE-12/12.5-D48NB-C module’s datasheet doesn’t even provide any thermal resistance figures.

Clearly , the “open PCB” type DCDC modules must have a fan blowing over them in order for them to operate at anywhere near maximum power. Do you agree?

Vicor PRM48AT480T400A00 datasheet

http://cdn.vicorpower.com/documents/datasheets/PRM48AF480T400A00_ds.pdf

Vicor VTM48ET120T025A00 datasheet

http://www.vicorpower.com/documents/datasheets/VTM48E_120_025A00.pdf

Murata UEE-12/12.5-D48NB-C datasheet
http://www.murata.com/products/productdata/8807039893534/uee150w.pdf?1583754815000

Here is a picture of an “open-PCB” type , “non-Vicor” DCDC module…..
http://www.digikey.co.uk/product-de...2-12-5-D48NM-C/UEE-12-12-5-D48NM-C-ND/4747528
……You can clearly see that its meant to only be used with blown air. There is no high-thermal-conductance potting like you get in the Vicor modules.

Surely you agree, that our Fan-less spec predicates a Vicor DCDC module approach?

 

[gophert]

If you're sure about your charging voltage, you can get by, barely get by, with just a VTM48ET120T025A00 - Absolute Max voltage 60v.
But, it would be better to distribute the heat in the box over several modules so stick to your first idea.

Also, are you allowed to fill the box with heat-transfer silicone?

 

[ChrisP58]

If your sure about your charging voltage, you can get by, barely get by, with just a VTM48ET120T025A00 - Absolute Max voltage 60v.
But, it would be better to distribute the heat in the box over several modules so stick to your first idea.

Also, are you allowed to fill the box with heat-transfer silicone?

That would be true if the two converters were operating in parallel. But the op wants to run them in series.

So the power dissipated by each module isn't reduced or shared. The total power dissipated will actually double since all of the power has to go through each module.

Actually more than double since the first converter has to supply the output power plus the inefficiency of the 2nd converter.