Re: [coreboot] Will a KCMA-D8 boot without the 8pin EPSV12 cable if you are using a 35W CPU?

[Nico Huber]

On 10/18/18 3:16 PM, Angel Pons wrote:
> I believe the power traces are different, so the CPU VRM feeds only through
> the EPS12V connector. However, if your PicoPSU is large enough, I guess a
> EPS12V cable can be attached to it.

Probably not for a 35W CPU, but generally: Using adapters for the
EPS12V connector is dangerous. They have more than two pins for a
simple reason: The electrical current through each pin/connection must
not get too high. There are adapters that route the whole current
through a single pin on the other end (e.g. a single old-school PATA
drive connector). Never use these unless you know they can take the
current you expect! (e.g. not much more than 3A for a 35W TDP, that
might be ok for a single pin, but you should read each connectors
specs)

Same applies to the tiny connectors for (hard)-drives on the PicoPSU,
if the current goes through less pins on the PicoPSU side, don't do it
(unless you know what you are doing).

There are PicoPSUs that have a 4-pin EPS12V connector btw. So I'm not
sure what the original question was; would it work w/o full 8 pins? or
would it work w/o any? The former likely yes, the latter likely no.

Nico

Will a KCMA-D8 boot without the 8pin EPSV12 cable if you are using a 35W CPU?

[Angel Pons]

Hello,
> Probably not for a 35W CPU, but generally: Using adapters for the
> EPS12V connector is dangerous. They have more than two pins for a
> simple reason: The electrical current through each pin/connection must
> not get too high. There are adapters that route the whole current
> through a single pin on the other end (e.g. a single old-school PATA
> drive connector). Never use these unless you know they can take the
> current you expect! (e.g. not much more than 3A for a 35W TDP, that
> might be ok for a single pin, but you should read each connectors
> specs)

Agreed. I have seen a cheap power supply whose ATX12V wires got warm
because of this. I oblviously rebuilt the power supply, including replacing
said wire.
> Same applies to the tiny connectors for (hard)-drives on the PicoPSU,
> if the current goes through less pins on the PicoPSU side, don't do it
> (unless you know what you are doing).

I have some SATA DVD units that can use up to 2.5 A on the 12V line, and
another PATA unit (with a Molex connector) which uses the same. Using two
+12V wires from two different connectors should be enough to power the CPU.
> There are PicoPSUs that have a 4-pin EPS12V connector btw. So I'm not
> sure what the original question was; would it work w/o full 8 pins? or
> would it work w/o any? The former likely yes, the latter likely no.

I think so. In fact, I have a 95W CPU on a 8-pin motherboard powered by a 4-pin
power cable, and the computer runs fine. And none of my boards run without
the 12V CPU power cable (I forget about it too often).

I found the w.r.t. power supplies and connectors:
 - https://www.hardwaresecrets.com/everything-you-need-to-know-about-power-supp...
   (page 3 is probably the most relevant)

- http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=20...
   PicoPSU roundup (from 2010, somewhat old, but still interesting)

Best regards,

Angel Pons Pons

Will a KCMA-D8 boot without the 8pin EPSV12 cable if you are using a 35W CPU?

On 10/19/2018 05:15 AM, Nico Huber wrote:
> On 10/18/18 3:16 PM, Angel Pons wrote:

Thanks for replying all!
> > I believe the power traces are different, so the CPU VRM feeds only through
> > the EPS12V connector. However, if your PicoPSU is large enough, I guess a
> > EPS12V cable can be attached to it.
>
> Probably not for a 35W CPU

In comparison I have various other boards with higher wattage CPU's that
lack EPS connectors such as an AM1 for a 40W CPU...what is different? I
mean the 8pin one not the 4pin cpu cable.
> but generally: Using adapters for the
> EPS12V connector is dangerous.

I know - I am the one who added that on the wiki :D but it is always
good to repeat it :D
> They have more than two pins for a
> simple reason: The electrical current through each pin/connection must
> not get too high. There are adapters that route the whole current
> through a single pin on the other end (e.g. a single old-school PATA
> drive connector).

Oh man that is bad

I wanted to either not connect a 8pin cable at all since a very similar
platform on the AM1 series doesn't need or come with one or use one of
my adapters that combines a 4PIN CPU cable and a molex cable which has
worked fine on my H8SCM with the same CPU before I got a new PSU for it
(H8SCM only $40 - I don't want to risk this $300 brand new KCMA-D8
although they are going for only $90 china used on fleabay atm)
> Never use these unless you know they can take the
> current you expect! (e.g. not much more than 3A for a 35W TDP, that
> might be ok for a single pin, but you should read each connectors
> specs)
>
> Same applies to the tiny connectors for (hard)-drives on the PicoPSU,
> if the current goes through less pins on the PicoPSU side, don't do it
> (unless you know what you are doing).

I always check the ratings.
> There are PicoPSUs that have a 4-pin EPS12V connector btw.

I know I have one :D

But dont I still need 8 pins total?
> So I'm not
> sure what the original question was; would it work w/o full 8 pins?

I just want to make it work with a normal CPU 4pin cable
> or
> would it work w/o any? The former likely yes, the latter likely no.
>
> Nico

Will a KCMA-D8 boot without the 8pin EPSV12 cable if you are using a 35W CPU?

[Angel Pons]

Hello,

On Sat, Nov 17, 2018 at 8:06 AM [e-mail]  wrote:
> I just want to make it work with a normal CPU 4pin cable

With a 35W CPU, I don't think anything bad would happen if you use a
4pin ATX12V cable (better try a regular ATX PSU first) then try to
power up. At most, the board may not boot because the CPU is not
powered. If it works, swapping the ATX PSU with a PicoPSU should work
too.

Best regards,

Angel Pons Pons