Bestec ATX-300-12Z REV.EHR

[370forlife]

Re: Bestec ATX-300-12Z REV.EHR

A forum member on here named big pope is near you, china i believe, he is a supplier of samxon caps, which are good for the most part.

[POM_MJ]

Re: Bestec ATX-300-12Z REV.EHR







voltages with small loads are 4.95(5Vsb), 4.90(5V), 3.32(3.3V), 11.78(12V) ???

Any suggestions?

[Toasty]

Re: Bestec ATX-300-12Z REV.EHR

The 5v and 12v are "group regulated" and are supplied through the same toroid (the one to the right). Because of the co-mingling in that toroid, they are both off by the same percentage: -2%.

The 3.3v is independently regulated and goes through the smaller one to the left.

Load the 5v and 12v with 5A and 6A respectively and put 6A on the 3.3v. Then see how it runs.

12v and 6v Headlight bulbs make good loads.

Toast

[Toasty]

Re: Bestec ATX-300-12Z REV.EHR

EDIT: Everell should join us.
He's been more *ahem* "intimate" with the Bestec's....



Saying that:
I'd like to find out how to build a 750w-1000w MOSFET based load bank for the PSU's. Something you can dial-a-load in and have it do it.
I 've read some of the explanations, but I want someone to give up the specs needed. The boards are a piece of cake anymore.

I'm not spending $1000's on it either. Should be doable for $400-$600, with room to expand.


Toast
Nitey-nite!

Meds are kickin..........zzzzzzZZZZZZZZZzzzzzzzz

[POM_MJ]

Re: Bestec ATX-300-12Z REV.EHR

Sorry, wrong caps name again.
1000/16V and 2200/16V on 12V rails was JAMICON before changed to both 1500/16V Rubycon.

Ok, I will try to find some bulbs to load test.

[370forlife]

Re: Bestec ATX-300-12Z REV.EHR

Ahhh, rubycons, much better.

When Oklahoma Wolf tested a bestec ATX-250-12E, it never got the 12v rail over 11.84 except on the crossloading test, where it shot up to 12.54.

http://www.jonnyguru.com/modules.php...tory2&reid=154

May be part of bestec's OVP design or something.

[everell]

Re: Bestec ATX-300-12Z REV.EHR

OK Toasty - I'll take a shot at it!

First I would like to say that most of my work with the Bestec power supplies was problems in the 5vsb circuit. My solution to the Bestec ATX-250 12E was a bit extreme, but it worked. As for the other Bestec models - I have not seen the same kind of 5vsb failures due to the pwm chip in the later models. Most of these failures have been bad caps - just like the other brand power supplies.

The Bestec ATX-300 12Z we are discussing here does not appear to have a 5vsb problem. One more piece of proof that the later models are indeed good power supplies when recapped.

The problem here is that both 5v and 12v rails are low. They are both regulated by the same regulator chip IC3 which is a AZ431 (or equivalent). The resistor from the 12v rail to the reference pin is R57 which is 24K. The resistor from the 5v rail to the reference pin is R61 which is 5.1K. The resistor from reference pin to ground is a parallel combination of R59 and R60. R59 is 3.00K and R60 is 27.0K. This parallel combination calculates to 2.70K.

So why two resistors in parallel between reference pin and ground? As a cost savings, rather than putting in a variable resistor to set the 5v and 12v voltage values, they put in a higher resistance than what is needed (in this case R59 which is 3.00K). Then they bridge a parallel resistance to bring the voltages into spec. So if you play with the R60 value, you will probably be able to put those voltages where you want them.

These resistors are surface mount resistors on the bottom of the pc board. You may or may not want to attempt changing them. Also, the R60 value on your board may or may not be 27.0K. The R59 value probably is 3.00K.

[POM_MJ]

Re: Bestec ATX-300-12Z REV.EHR

Oh, very great regulator circuit descriptions.
I understand if I've changed R60 up/down I can get more/less 5V and 12V, right?
Thankyou very much everell, This is exactly answer I waiting for.





The R60 is very small (I think it's 0603 chip resister), but I will try.
Thankyou again for every suggestions.

[everell]

Re: Bestec ATX-300-12Z REV.EHR

If you want to try it.............remove R60. Solder a 27K resistor and 20K potentiometer in series (or a 27K resistor and 10K potentiometer in series). Adjust this series resistance to about 27K. Solder this series combination where R60 was. Apply power to the psu. Adjust the potentiometer to the voltages you want. Turn off psu. Remove the series combination and measure its resistance. That's the value you need. Now just find itty bitty small SOT resistor with that value resistance, solder it in R60 location, and you should have what you want.

Notice that R60 value on my psu and on your psu is different. I expected this....it is being used for calibrating the 5v and 12v rails.

Have fun .... be EXTRA careful .... always wear safety glasses when working with these power supplies.

[POM_MJ]

Re: Bestec ATX-300-12Z REV.EHR

Yeah, I was changed R60 to 33K (from an old PCI card), then I've got 12.02V finally and 5.06V and 3.33V while loading with same test system.
Thankyou very much to everyone especially everell.

I didn't take a picture of the replaced R60 because hurry put the PCB back for test, but here are some pictures of voltages measurment.

[everell]

Re: Bestec ATX-300-12Z REV.EHR

Looks great! Good job there. Once you get everything put back together and working, you can check the voltages under actual load. If you need to tweak it any further, you know which resistor to change.

With bad capacitors changed and output voltages calibrated, looks like a great power supply.

[POM_MJ]

Re: Bestec ATX-300-12Z REV.EHR

When Panasonic caps has arrived, I will recaps again to original their values and voltages rated, may be try to change R60 to 27K same as yours also.

[370forlife]

Re: Bestec ATX-300-12Z REV.EHR

When Panasonic caps has arrived, I will recaps again to original their values and voltages rated, may be try to change R60 to 27K same as yours also.

Whats wrong with the rubycons?

Overspec'ing on a psu can actually be better for ripple.

[POM_MJ]

Re: Bestec ATX-300-12Z REV.EHR

Whats wrong with the rubycons?

Overspec'ing on a psu can actually be better for ripple.

Nothing wrong, but The Rubycon caps are rated 6.3V replaced original rated 10V on 3.3V/5V/5Vsb (after Pi filter),
two Rubycon 1500/16V replaced 2200/16V,1000/16V on 12V rails
and one Rubycon 1500/16V replaced 2200/16V on 5Vsb (before Pi filter).

Do I have any necessary to recaps them to their original values and rated by Panasonic caps or not?

[370forlife]

Re: Bestec ATX-300-12Z REV.EHR

6.3 on the 3.3v is fine, 6.3 on the 5v is a little close. I have seen it done on a lot of power supplies, but I don't know. I would think the bestec's OVP would kick in before that rail got that high.

[PCBONEZ]

Re: Bestec ATX-300-12Z REV.EHR

6.3v caps on +5v is fine.
They use 10v because at whatever uF the 10v version usually has a bigger can and so lower ESR.
You accomplish the same thing by switching to a better grade.
.

[PCBONEZ]

Re: Bestec ATX-300-12Z REV.EHR

6.3v is the limit for actual circuit voltage + ripple.
ATX spec makes the max actual voltage on +5v = +5.25v.
If you are at the max of 5.25v then to exceed the 6.3v rating you'd need 2.1v peak-peak Ripple floating on the +5v rail.
If you have 2.1v peak-peak Ripple on any rail then you have WAY WAAAAAAY more problems than new caps will fix.
.

[POM_MJ]

Re: Bestec ATX-300-12Z REV.EHR

6.3v caps on +5v is fine.
They use 10v because at whatever uF the 10v version usually has a bigger can and so lower ESR.
You accomplish the same thing by switching to a better grade.
.

Ok, I see.
10V caps has lower ESR and more rated ripple current than 6.3V caps with same capacitance,
then, replace 6.3V caps with 10V caps on 3.3V/5V rails would be better.

[PCBONEZ]

Re: Bestec ATX-300-12Z REV.EHR

Not quite got the idea yet.
I'll give explaining another shot.....

~~
Within a series the ESR varies with the can size.
In the cheap caps that end up in PSU's a ___uF 10v cap is usually physically larger than the same uF cap in 6.3v.
Because the 10v is physically bigger it has lower ESR.
-
That situation is so common that when they use cheap caps they tend to just use 10v by default.
-
But... By switching to a better 'grade' of cap [the MBZ in this case] the 6.3v cap now has lower ESR than the cheap 10v cap did and is a significant upgrade without needing a bigger cap.

Here's an example:
Look at the CapXon KF 6.3v and 10v 1500uF [A typical PSU type cap.]
6.3v is 10x16mm and ESR is 0.140
10v is 10x20mm and ESR is 0.062 [same series, bigger can, better ESR]

Now look at a better grade cap, the MBZ 1500uF
the 6.3v is only 10x12.5mm but ESR is WAY lower at 0.026

That's what I was trying to get across.
You don't need a 10v cap.
The grade change already accomplished the same thing....
.... and in fact upgraded you beyond why the 10v was used.

~~
And related.
~~
Now look at the MBZ chart again.
You will notice that REGARDLESS of the voltage....
All the 10x16mm have the same ESR and Ripple
All the 10x20mm have the same ESR and Ripple
All the 10x23mm have the same ESR and Ripple
- That's why I say -within a series- ESR changes with can size, not voltage or uF.
- That is typical of good brands of caps.
It's because their ratings are an 'at least' or 'no less than' kind of number with a realistic margin for error. Very good way to rate things for use in the real world. As a bonus, when they do things with a margin that way the true value is probably better than what you see in the table.

If you look at the same thing in the KF chart the ESR is all over the place for a given can size.
- That's typical of crap brands of caps.
It's probably due to the ratings in their table being an exact number for THAT cap with zero margin for error. Not a good way to do things because in the real world the actual conditions won't match the test conditions exactly.
.

[PCBONEZ]

Re: Bestec ATX-300-12Z REV.EHR

Sorry the KF table exceeds the wimpy upload size limit here.
Here it is. [If this will parse the Chinese characters in the file name....]