+12V on Macron MPT-301

[TELVM]

Re: +12V on Macron MPT-301

And how about three 10A bridge rectifiers inside a 1275W platinum PSU?:

http://www.techpowerup.com/reviews/T...X-1275M/4.html

That's theoretically enough rectifying for 7KW @230VAC . But I don't think max total power is what that mega-overkill trio is about, but efficiency.


I bet in the not too distant future we'll begin to see mosfet bridge rectifiers inside top-notch "80+ Unobtainium" PSUs.

[Wester547]

Re: +12V on Macron MPT-301

It's another 250W unit... one of the newer 250W ones.
But keep in mind it's running a Dell OptiPlex GX170L with a 2.8 GHz P4 Prescott CPU. Those things have a TDP of 89W and can pull a max of 100 W. With nearly no load on the 5V rail, you can see why that is. If it was the other way around with a large load on the 5V rail and almost none on the 12V, I think the PSU would cross-load a lot less.

Good point. IIRC you had tested your HP-P2507FP3 with a R300/Radeon 9500 Pro and because of the fact that the card puts a good load on the +3.3V, +5V, and +12V rails (despite not really being a power hungry card at all, even for its time), it keeps the rails balanced very well in terms of voltage regulation, so that probably helped lots.

[momaka]

Re: +12V on Macron MPT-301

but some of the later models had no ferrite coil at all and two 3300uF 16V capacitors and a 1000uF 16V capacitor in parallel on the +12V output) was better than that. I remember you saying you couldn't get your HP-P2507F3P to crossload... unless you're talking about another unit?

It's another 250W unit... one of the newer 250W ones.
But keep in mind it's running a Dell OptiPlex GX170L with a 2.8 GHz P4 Prescott CPU. Those things have a TDP of 89W and can pull a max of 100 W. With nearly no load on the 5V rail, you can see why that is. If it was the other way around with a large load on the 5V rail and almost none on the 12V, I think the PSU would cross-load a lot less.

Is that because the further they are apart, the greater the difference in temperature

Yes.
Behind each other with a heat sink in between is the best way to do it.

800W, that is about 6.67A of current, Vf of the power rectifier can be as high (or more) as 1V, two diode Vf drop in each 1/2 of AC cycle, so power will be about 13.33W/2 = 6.67W (for 2 Diode Vf which will conduct only 50% of the cycle). The other 2 Diodes in the bridge will dissipating heat in another half of the AC cycle. So it can get hot.

Woops, big brainfart on my part there. Yes, without a heat sink, they will.
I think what i meant to say was that having two bridge rectifiers is a gimmick, not that the heat sink is (don't even know why I said that.... the microwave ovens I opened all had their bridge rectifiers heat sinked... what I wanted to point out is that they all had just one bridge rectifier).

[TELVM]

Re: +12V on Macron MPT-301

... I don't think it matters here this much anyways because even one of those bridge rectifiers will be sufficient to handle the full load from the PSU. I've seen microwave ovens rated for over 1 kW with just one of these bridge rectifiers. I think it's more of a gimmic/hype that they have bridge rectifier heat sinks in those PSUs.

I suspect this pairing of way oversized bridge rectifiers may have something to do with overall efficiency. The pic comes from a 80+ Platinum PSU, and the same can be seen in many gold/platinum PSUs.

It maybe not critically neccessary on some PSUs, but I think heatsinking the bridge rectifier is a healthy custom, it wouldn't harm .

[c_hegge]

Re: +12V on Macron MPT-301

But I don't think it matters here this much anyways because even one of those bridge rectifiers will be sufficient to handle the full load from the PSU. I've seen microwave ovens rated for over 1 kW with just one of these bridge rectifiers. I think it's more of a gimmic/hype that they have bridge rectifier heat sinks in those PSUs.

The reason is that bridge rectifiers are generally rated for what they can deliver with a heat sink installed, unlike discrete diodes.

[Wester547]

Re: +12V on Macron MPT-301

Synchronous rectification helps even more as far as secondary side efficiency goes.

Nothing to worry about. Just about every brand-name computer from the Pentium 4 era does this. On my Dell OptiPlex GX170L, for example, the bounce on the 12V rail is so bad that you can hear the system fan revving up and down when the CPU load changes (this is with a 250W HiPro PSU). IIRC, the voltage on the 12V rail is bouncing between 11.88V and around 12V.

Really? I thought Hipro's voltage regulation (in those 250W Dell units with a 3300uF 16V capacitor before and after the ferrite coil and either a 20A or 30A schottky on the +12V rail.... but some of the later models had no ferrite coil at all and two 3300uF 16V capacitors and a 1000uF 16V capacitor in parallel on the +12V output) was better than that. I remember you saying you couldn't get your HP-P2507F3P to crossload... unless you're talking about another unit?

Exactly. It's crucial to have the rectifiers near each other AND on the same heat sink.

Is that because the further they are apart, the greater the difference in temperature (IE, paralleling them on a heatsink where they're right next to each other is better than paralleling them where one is on one side and the other on the other side of the heatsink)?

[budm]

Re: +12V on Macron MPT-301

800W, that is about 6.67A of current, Vf of the power rectifier can be as high (or more) as 1V, two diode Vf drop in each 1/2 of AC cycle, so power will be about 13.33W/2 = 6.67W (for 2 Diode Vf which will conduct only 50% of the cycle). The other 2 Diodes in the bridge will dissipating heat in another half of the AC cycle. So it can get hot.

[momaka]

Re: +12V on Macron MPT-301

Even using schottkys with 100 reverse voltage I have horrible luck, they usually don't start up. Is there something not suitable with the VF30100S?

The only thing I can think/guess might be the problem is relatively slow recovery time. If the rectifier is still "ON" when the voltage from the transformer reverses in the second half-cycle, then the rectifier might appear shorted to the PSU's SC protection.

Since the VF is lower, I assume it'll still increase the efficiency.

Yes.
Vf times the current through the rectifier gives you the heat which the rectifier has to loose. So for example, if you have a rectifier with Vf = 1.3V and the current going through it is 10A... then it has to dissipate 1.3 x 10 = 13 Watts. That's quite a bit. Compare that with a 0.5V schottky passing the same current: 5 W - almost 1/3 the heat output just from that rectifier.

I believe Momaka has the same power supply (with a 16A ultrafast or fast recovery on the +12V output), and with an AMD 95W TDP CPU he couldn't get it to kick out any noticeable heat even in hot weather, even at full load.

Correct. It was actually with a 105 W TDP AMD FX-57 CPU. I also tested a friend's i7 quad-core with a 95W TDP. Although, I should note that my tests weren't longer than an hour or so and not under 100% CPU load all of the time. I just tested a few games for a little bit. I should also note that I have drilled a few extra holes in the case of my Macron PSU.

When idling, the 12V sits at 12.20V, at 100% load it drops to 12.02V. I thought that was bad but I guess that's just typical group regulation. When the CPU usage is jumping up and down a lot, the 12V does bounce around quite a bit...not sure if I should worry about that or not.

Nothing to worry about. Just about every brand-name computer from the Pentium 4 era does this. On my Dell OptiPlex GX170L, for example, the bounce on the 12V rail is so bad that you can hear the system fan revving up and down when the CPU load changes (this is with a 250W HiPro PSU). IIRC, the voltage on the 12V rail is bouncing between 11.88V and around 12V. But this is not my only computer that does this. In fact, I think my HP Pavilion 8756c is even worse - and that thing is an ancient Pentium 3 -based system that I still use today when at home and not in college. Works perfectly fine to this day with its original IBM Deskstar HDD.

You'd think HDDs hate the bouncing on the 12V rail, but what they actually hate the most (in my experience, anyways) is high ripple. I had an HDD nearly cook itself from a crappy L&C PSU. Same HDD ran just normally warm with a decent PSU.

^ That's if you parallel them without a heatsink. If they're in parallel on a good heatsink (if they're on opposite ends of the same heatsink and have adequate thermal pads), they probably won't be more than a couple of degrees apart in temperature (celsius), so it shouldn't be a problem.

Exactly. It's crucial to have the rectifiers near each other AND on the same heat sink.

^ Two 15A bridge rectifiers inside a 800W PSU, both on the same side on the heatsink . Wouldn't the external one get much hotter?

Probably.
But I don't think it matters here this much anyways because even one of those bridge rectifiers will be sufficient to handle the full load from the PSU. I've seen microwave ovens rated for over 1 kW with just one of these bridge rectifiers. I think it's more of a gimmic/hype that they have bridge rectifier heat sinks in those PSUs.

[goodpsusearch]

Re: +12V on Macron MPT-301

The bridge rectifier rarely gets even warm. I don't really get why they put heatsinks on them to be honest....

[TELVM]

Re: +12V on Macron MPT-301


http://www.techpowerup.com/reviews/F...R3_800W/4.html

^ Two 15A bridge rectifiers inside a 800W PSU, both on the same side on the heatsink . Wouldn't the external one get much hotter?

[Wester547]

Re: +12V on Macron MPT-301

^ That's if you parallel them without a heatsink. If they're in parallel on a good heatsink (if they're on opposite ends of the same heatsink and have adequate thermal pads), they probably won't be more than a couple of degrees apart in temperature (celsius), so it shouldn't be a problem. The reason why you won't get the full ratings is because the rest of the PSU has to be capable of it too, and often the greatest limiting factor of the PSU is how much power it can output as a whole (without the main switcher[s] exploding or the toroidal coils burning). That depends on a number of other things - how well it's ventilated and cooled, the width of the PCB traces, the ability of the main transformer, the bulk capacitance, the main switching transistor(s) and how well they're driven, the switching frequency, keeping input and output ripple and voltage regulation in spec, keeping efficiency above 70%, the core losses of a toroid in a magamp circuit, etc... all of those things translate into a lower ambient temperature if done well.

More than anything, when I see a really overspec'd secondary, I think high output power rather than "there's 60A on the +5V rail!" (which isn't really true, especially if you consider how power is distributed in +12V heavy PSUs especially, as well as OCP). Really overspec'd and low VF rectifiers means the voltage drop (as a whole) on the secondary side is much lower (higher overall efficiency and less heat output), which means the main switcher(s) have to handle less load, which means more a greater maximum power output. And when I see a really anemic secondary side in terms of rectifiers, I think low output power (which is probably true, especially on lesser heatsinks). The contact area of the heatsink is important, that's also why TO-247 parts are theoretically capable of more current than equivalent TO-220 parts on the same heatsink (their thermal resistance is better, because they cover more surface area so it's easier for the heat from the rectifiers to reach the top).

More on topic on my part, I think paralleling rectifiers if done properly isn't a bad idea, especially in a Macron PSU where the original rectifier was a 16A ultrafast or fast recovery.

[ben7]

Re: +12V on Macron MPT-301

You never get the full ampere rating of those rectifiers regardless of being single or in parallel anyway.

Yeah.
Running them in parallel is a bit dangerous, BUT, as long as they have good thermal contact to each other, they shouldn't be too much of an issue.

What happens is one diode gets hotter for whatever reason, and it's resistance goes DOWN, making more current take the path through this diode, and increasing the heat even more.... thermal runaway!

[goodpsusearch]

Re: +12V on Macron MPT-301

You never get the full ampere rating of those rectifiers regardless of being single or in parallel anyway.

[TELVM]

Re: +12V on Macron MPT-301

You double the contact area of the rectifiers with heatsink and double the total rectifying amperage ...

I know nothing but, from what I read elsewhere, assuming that two 16A in parallel will automatically grant us the full 32A total might be a bit in practice ...

[eccerr0r]

Re: +12V on Macron MPT-301

I don't use my PresHot anymore, I only have a cheap aluminum hs/f and IIRC is stayed around 60C... though I should check again.
No overtemperature problems at least. The video card, however...

[TELVM]

Re: +12V on Macron MPT-301

let me ask.. how many fans have you got in there? i have honestly lost the count

Just seven (there's also a 92 at lower front blowing on the HDD) because the ancient GPU doesn't draw much juice.

We need a critical mass of fans if we want hot systems to run cool & quietly:

Forumer Pentium4's Preshott idles @ 57C. Mine idles @ 37C, and burns @ 45C. The fans never go above 78% rpm and thus make little noise (I hate noisy comps ).

[domas]

Re: +12V on Macron MPT-301

I'd work on improving case ventilation, all the heat from the Preshott flamethrower is cooking the PSU.


We need to let Preshotts know, in no uncertain terms , that we're serious about cooling for them to behave.

let me ask.. how many fans have you got in there? i have honestly lost the count

[goodpsusearch]

Re: +12V on Macron MPT-301

You double the contact area of the rectifiers with heatsink and double the total rectifying amperage. But the parts have to be identical. Every minor difference in the voltage drop or the internal resistance of the rectifying diodes would result in losses. I hope someone can explain it better than me

[rogfanther]

Re: +12V on Macron MPT-301

Little bit of curiosity : if a psu has the place for another rectifier in parallel with the already installed one, is there some other thing to take care of , or could one just add another rectifier in paralle, provided it is the same part ? I´m thinking in the lines of making a psu more stable as each diode has to work less....

[goodpsusearch]

Re: +12V on Macron MPT-301

My Macron psus:
https://www.badcaps.net/forum/showthread.php?t=12348

https://www.badcaps.net/forum/showpo...86&postcount=3 (before recap)
https://www.badcaps.net/forum/showpo...5&postcount=48 (my first recap )

https://www.badcaps.net/forum/showthread.php?t=22916

As you can see on the last link my treatment was to add a F16C20C in paraller with the original F16C20C my Macron had at 12V.

Recently I've done the same to the other Macron I own. I replaced the original F16C20C with 2 x U1620G. Both psus run perfectly fine

I forgot to mention that I did those improvements without removing the secondary heatsink. I avoid removing heatsinks in psus unless I have to.