Fortron Zen300, max combined Power?

[metalfan2]

Hi,

the manual says:

+5v and +3.3v is 120w max. total output power is 300w
12v1 can do 8a and 12v2 can do 14a

does that mean that if i max out 12v1 (96W) and 12v2 (168W) i can only use 36w from 5v + 3.3v ?

greets

 

[mpilchfamily]

No, the max will be about 180W or less. Most likely it will be a little less then that. So it offers a max amperage of about 15A. Yes that is correct only 15A. The amperage rating listed for each of the 12V rails is the max amount it will allow before the PSU shuts down for saftey reasons. But its not how much power is availible to each rail. At most the 1st rail will get about 6A while the 2nd rail only gets 9A.

 

[metalfan2]

How do you know that?

 

[mpilchfamily]

The PSU isn't able to output more then 300W max. So if the 5v and 3.3v rails are using 120W of that then there is only 180W left for the 12v rails to use. well 180W divided by 12V gives us a total of 15A the 12V rails can work with. Now that 15A has to be distributed between both 12v rails.

You can also look at other PSU labels and see that they list a certain amount of wattage dedicated to just the 12V rails. You'll also notice that that amperage is less then the combined amperage ratings of the rails. This is because the ratings of the rails are just that, ratings. The actual output varies based on the load the PSU is receiving. Now if you have too much connected to one of the rails and it either A) surpasses the combined power offered tot he 2 rails or B) surpasses that rails amerage rating the PSU will sut itself off.

Bottom line all this information is in the stickies that are at the top of this section. jonnyguru has spent many years in the PSU game and spent allot of time writing them out and trying to simplify the information for everyone. So take some time and read threw them.

 

[metalfan2]

Ah, youre right. In one Sticky he says:

Just to clarify, "500W", for example, means the PSU can put out, as in "DC Output", a total maximum of 500W regardless of how the load is distributed across the several voltages.


so if the pc does not require the full 120w (in my case) for 5v/3.3v it can be used as 12v power right?
The PSU would than be capable of 264w (12v1 and 12v2 at max) if it only uses 36w on 5v/3.3v

 

[mpilchfamily]

No

There is 120W going to the 3.3V and 5V rails. That power is not able to cross over to the 12V side. So whatever isn't used is basically lost. And the 3.3V and 5V rails never get fully utilized. At most that PSu is only able to supply 180W to the 12V rails. Its actually less then that because there are a few amps going to the 5VSB and the -12V rails. But we're only talking about maybe 2A (about 20W) tops for those 2 rails. So you looking at about 160W for the 12V rails.

See the components in the PSU used to produce the 3.3V and 5V rails are generally separate from those that produce the 12V rails. If you where to open the PSU up you would see 2 or 3 large square looking objects. Those are call transformers. There job is to take the AC voltage from the wall and convert it into the DC voltages needed for your PC. The largest one takes care of the 12V rails. If there is only 2 of them the smaller does both the 5V and the 3.3V rails. If there if 3 of them that are all different sizes then the smallest is the 3.3V and the mid range one is the 5V. Some larger PSU like the 800W and higher ones have 2 of the large transformers to produce 2 dedicated 12v rails. Anyway thats going a bit deeper into it then needed. But all the other components in there are for regulating the voltages. Making sure they are smooth and steady. They also offer Over Voltage Protection (OVP) and Over Current Protection (OCP).

Ive been working with PSUs for a while now. For a time i was going to start doing my own PSU reviews for another form. Even went as far as building my own load tester. But i don't have the time to do that now days. But you can check out the load tester build in the first link listed in my sig.

 

[metalfan2]

A transformer does not change AC into DC

 

[HOOfan 1]

transformer steps down the voltage...rectifiers and diodes change AC to DC.

 

[metalfan2]

Just received the answer from the support.
Yes, it is possible to max out 12v1 (96w) and 12v2 (168w) if you only need 36w 5v/3.3v

 

[HOOfan 1]

Originally posted by: metalfan2
Just received the answer from the support.
Yes, it is possible to max out 12v1 (96w) and 12v2 (168w) if you only need 36w 5v/3.3v

more like 12v1 OR 12v2

I doubt VERY VERY VERY seriously that unit is capable of 88% of its rated power on the 12V rail alone. Either that or Tech support is lying to you.