# Dumb Q Re: DC-DC power supply



## chad1376 (Dec 27, 2012)

I think I know the answer, but looking for verification. 

I'm getting set to order a pico type DC-DC power supply for by build. These come in a range of power ratings. Since I'm still building and planning, I don't yet really know what my ultimate wattage needs are (and honestly, I'm to lazy to add up individual component needs and add them up.) To be on the safe side, I don't mind paying a little extra for a 150+/- watt supply.

I guess the question is: are larger supplies any less efficient when not operating at rated power. In other words, if my system only uses, say, 50-watts, would a 150watt supply draw more current from the cars 12v system than an 80 watt supply. 

Also, are there any benefits in reliability in going with a larger than needed supply.


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## Neil_J (Mar 2, 2011)

Larger wattage power supplies can in certain cases have a hard time with smaller (close to zero) current loads. It depends mostly on how the switching power supply was designed, and what kind (if any) protection circuits they used. Stop being lazy and just add your components up


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## basshead (Sep 12, 2008)

I always use double the recommended power for multiple reason. 

If a PS is designed for higher rated load it mean it can dissipate more heat than a smaller unit keeping its components cooler (as long that heat can go somewhere). Also some components might have some peak that a smaller unit might not handle well and cause voltage drop affecting other devices sharing the same power.

As far you question regarding the 50w load on a 80w VS 150w if they shared the same design the 80W would probably have a 10% efficiency advantage, but unless your power source is very limited I would still stick with the larger one. 

What's the project?


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## MarkZ (Dec 5, 2005)

Components these days are usually pretty specific about the peak requirements. You shouldn't have much problem sizing it up appropriately. It's hard for me to imagine what oversizing buys you in this context.


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## Neil_J (Mar 2, 2011)

I would also add, I would err on the side of quality, reputation, and reviews of a DC-DC supply, rather than going with a cheap one with a specific wattage. Look at what's worked for others, on this forum and others.


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## chad1376 (Dec 27, 2012)

Great info - Thanks everyone. I guess I'll suck-it up and at least get an estimate of power needs.

I'm building a PC based carputer (Currently Win 7 and Centrafuse). So far, I'm using: 
MSI E350IA-E45 motherboard
Samsung 840 SSD (120G)
2.5" WD HDD (1000G)

I talk a little about it just a few posts down:
http://www.diymobileaudio.com/forum/car-pc-forum/141734-all-digital-amp-using-nanodigi.html

Right now I'm getting the PC set up using a 120v supply. I'll ultimately end up with a lot of USB powered periphials, and was thinking of even tapping the 5V for a few non-usb 5VDC periphials.


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