What's the rule for Poly mods? (Half the capacitance?)

[TheLaw]

So my onboard LAN died, so I had to get a new LAN card. It's a decent card. I even outfitted a VGA RAM heatsink on the main chip. The problem I have most with it are these crappy little lytics it has. Capacitor selection has become an obsessive disease lately. Something that I might have considered in the past is now becoming inferior with my new knowledge of capacitors.

Anyway, just for the hell of it, I want to replace these caps.

I can't find that thread I think either PCBONEZ or someone else made that had a lot of info on that. Maybe someone could direct me?

Otherwise, what is the rule for replacing electrolytics with polymers? Half the capacitance?

The card was only $10, so if it doesn't work, It's not that much off an offset.

Thanks.

[Topcat]

Re: What's the rule for Poly mods? (Half the capacitance?)

Half capacitance of the lytic is a good rule of thumb, but sometimes its just trial and error.

I just got done polymodding some GX745's, good trial, no error.....and they should last damn near forever!

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

Thanks Topcat!

By trial and error, you mean: It might actually be closer to the lytic capacitance than you think?

[Topcat]

Re: What's the rule for Poly mods? (Half the capacitance?)

When I say trial and error, I mean using what you have on hand, as long as you aren't over-volting them. Then seeing how it works, measuring ripple, and the best test of all, seeing how stable the system is afterward.

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

When I say trial and error, I mean using what you have on hand, as long as you aren't over-volting them. Then seeing how it works, measuring ripple, and the best test of all, seeing how stable the system is afterward.

Oh...Well, maybe I'll just get some Nichicon HZs or something. Should last just as long. Maybe not theoretically, but for its own lifetime.

How do you measure ripple? O-Scope?

[PCBONEZ]

Re: What's the rule for Poly mods? (Half the capacitance?)

It's not that easy.
-
The 1/2 the uF as a thumb-rule only applies to VRM's and it's based on a tech doc discussing VRM's.
IIRC it was an application guide for a VRM controller IC chip. Kc8 posted it here a few years ago.
In essence, he was doing poly mods and I asked him how he knew how much uF to use.
He answered saying 1/2 the uF and posted that PDF file as the proof.
-
The '1/2 the uF thumb-rule' is also based on lowing the ESR more than a little bit.
There are now some lytics that have lower ESR than some polys.
That is due to lower grade polys coming into the market since the rule was 'invented' when I asked kc8 for one.
Any ole poly won't do.
You STILL have to check specs on new and old just as you do with lytics.

IOW: The rule -assumes- you are working on a VRM.
It does not blanketly apply to any application because in some the uF might be critical to the circuit's operation.

If it's not in a VRM you either:
- trace the circuit, look up the chips coils and caps, and then do the math.
- cross your fingers and jump in a blind leap of faith.
.

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

It's not that easy.
-
The 1/2 the uF as a thumb-rule only applies to VRM's and it's based on a tech doc discussing VRM's.
IIRC it was an application guide for a VRM controller IC chip. Kc8 posted it here a few years ago.
In essence, he was doing poly mods and I asked him how he knew how much uF to use.
He answered saying 1/2 the uF and posted that PDF file as the proof.
-
The '1/2 the uF thumb-rule' is also based on lowing the ESR more than a little bit.
There are now some lytics that have lower ESR than some polys.
That is due to lower grade polys coming into the market since the rule was 'invented' when I asked kc8 for one.
Any ole poly won't do.
You STILL have to check specs on new and old just as you do with lytics.

IOW: The rule -assumes- you are working on a VRM.
It does not blanketly apply to any application because in some the uF might be critical to the circuit's operation.

If it's not in a VRM you either:
- trace the circuit, look up the chips coils and caps, and then do the math.
- cross your fingers and jump in a blind leap of faith.
.

Thanks for the explanation but I think I'll just use some high quality lytics.

[c_hegge]

Re: What's the rule for Poly mods? (Half the capacitance?)

https://www.badcaps.net/forum/showthread.php?t=9466

I gave two GA-7VA motherboards a FULL poly-mod (replaced EVERY single cap with polys). I used half the capacitance for the VRM caps, but for the others, I reduced it slightly, but not down to half. Where there were originally 1000uF caps, I used 820uF polys.

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

Hmmm...I am intriguing.

However, even a bunch of OSTs would be an improvement over whatever rubbish is on this card right now.

But VERY nice job on the full poly mod.

AH! So confusing. Maybe I'll buy a trial card. (It was like $10 on Newegg) I'll try some polys on those.

If I don't burn the card into oblivion when soldering it 6000 times, I might try it for real on the good card.

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

Shucks...I have a Weller WLC100 station and the stock iron it came with (that I am using), doesn't have a grounded tip. According to the badcaps FAQs, I need. One.

Anyway to ground it?

[PCBONEZ]

Re: What's the rule for Poly mods? (Half the capacitance?)

That's fine.
Concern over static on the tip when you are working on caps is rather silly.
Caps charge and discharge by design. Static won't hurt them.
.

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

Ah...Good. Though that Weller isn't considered to be one of their professional units, it still wasn't all that cheap...and to see my investment not be able to do something would make me sad.

I'm just curious why that is written up on this website under the Recapping tutorials...Hmm...

So let's try to find some decent caps and give it a whirl!

Thanks.

[PCBONEZ]

Re: What's the rule for Poly mods? (Half the capacitance?)

For the same reason you shouldn't use a cell phone in a gas station.
We wouldn't want that little Ultra High Frequency "UHF" transmitter [that you hold right against your head] to set the gas on fire, now would we?

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

For the same reason you shouldn't use a cell phone in a gas station.
We wouldn't want that little Ultra High Frequency "UHF" transmitter [that you hold right against your head] to set the gas on fire, now would we?

Liability?

[PCBONEZ]

Re: What's the rule for Poly mods? (Half the capacitance?)

Well meaning yet clueless 'rule makers'.

I the entire existence of mankind there has not been a single instance of a cell phone transmission causing a fire.
[Walkie-Talkies either for than matter.]

- Know why?
.. It's not physically possible for that little bitty x-mitter to put out enough energy to get anything hot or make a spark.

- But damned it! - We have a law just in case!
.

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

I understand.

I need a 10uF cap and 4 22uF caps.


They are all rated for 25V currently, though my multimeter shows that <5V are running through them at any given time. But I suppose, what's the difference...

So for replacements. For the 10uF, I'm looking at a 50V Nichicon PM and for the 22uFs, I'm looking at some 50V Panasonic FRs.

Are Nichicon PMs any good for motherboard/PCI card use?


The name of the capacitor company on the card is TWBOR. Not sure if you've heard of them. http://www.twbor.com/Enproduct.asp

In regards to ESR, the bigger the capacitor, the less the ESR?

[yyonline]

Re: What's the rule for Poly mods? (Half the capacitance?)

Are Nichicon PMs any good for motherboard/PCI card use?

Nichicon PM are low ESR, but not very low ESR. In other words, they're on the high ESR end of the low ESR range. They may be usable for specific applications, but I wouldn't say they're the best choice in general for motherboard use. See the next point below...

The name of the capacitor company on the card is TWBOR. Not sure if you've heard of them. http://www.twbor.com/Enproduct.asp

What series is the existing capacitor? With that info, we can look up the specs of the original capacitor to see if your proposed replacement is good enough. You want the same or lower ESR, the same or more ripple. I usually try to keep it with reason...going from a general purpose cap to a low ESR cap with many many times the ripple handling ability and a fraction of the original ESR may cause issues in certain circuits. Generally, I assume the existing capacitors are good enough as far as ratings go. I try to find a replacement with better real-world reliability, which is different than the lifetime spec.

In regards to ESR, the bigger the capacitor, the less the ESR?

I'm assuming you mean bigger as in larger physical size, as opposed to a larger capacitance rating. Within the same series (and more strictly the same voltage rating, but we'll ignore that for now), this is true. Taking Nichicon PM, since you mentioned that earlier... a large Nichicon PM will have less ESR and more ripple handling ability than a small Nichicon PM.

Comparing size to ESR relations across different series does not work. A large Nichicon PM may have more ESR than a smaller Rubycon MCZ or other ultra low ESR capacitor. (Disclaimer: I did not actually compare the specs, it's just a hypothetical example.)

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

Nichicon PM are low ESR, but not very low ESR. In other words, they're on the high ESR end of the low ESR range. They may be usable for specific applications, but I wouldn't say they're the best choice in general for motherboard use. See the next point below...



What series is the existing capacitor? With that info, we can look up the specs of the original capacitor to see if your proposed replacement is good enough. You want the same or lower ESR, the same or more ripple. I usually try to keep it with reason...going from a general purpose cap to a low ESR cap with many many times the ripple handling ability and a fraction of the original ESR may cause issues in certain circuits. Generally, I assume the existing capacitors are good enough as far as ratings go. I try to find a replacement with better real-world reliability, which is different than the lifetime spec.



I'm assuming you mean bigger as in larger physical size, as opposed to a larger capacitance rating. Within the same series (and more strictly the same voltage rating, but we'll ignore that for now), this is true. Taking Nichicon PM, since you mentioned that earlier... a large Nichicon PM will have less ESR and more ripple handling ability than a small Nichicon PM.

Comparing size to ESR relations across different series does not work. A large Nichicon PM may have more ESR than a smaller Rubycon MCZ or other ultra low ESR capacitor. (Disclaimer: I did not actually compare the specs, it's just a hypothetical example.)

Thanks for the response.

There are no markings on the TWBOR capacitors other than capacitance, voltage, and 105C. They are black and grey...Sorry.

Alright, I'll try to see if I can find some capacitor other than the PMs. I can't find any 10uF Panny FRs but I did find a 10uF Panny FC. How about one of thise?

And thanks for clearing up the general theory of ESR/physical size. And yes, I meant physical size.

[yyonline]

Re: What's the rule for Poly mods? (Half the capacitance?)

Alright, I'll try to see if I can find some capacitor other than the PMs. I can't find any 10uF Panny FRs but I did find a 10uF Panny FC. How about one of thise?

FC is slightly better than Nichicon PM, but not much. It might be a perfectly good replacement, but without knowing what the originals were, I can't say for sure. FR would likely be an excellent replacement, as it has excellent specs. If you can't find them...what is your location? We may be able to suggest somewhere you can purchase appropriate replacements online.

[TheLaw]

Re: What's the rule for Poly mods? (Half the capacitance?)

FC is slightly better than Nichicon PM, but not much. It might be a perfectly good replacement, but without knowing what the originals were, I can't say for sure. FR would likely be an excellent replacement, as it has excellent specs. If you can't find them...what is your location? We may be able to suggest somewhere you can purchase appropriate replacements online.

New Jersey, USA.

Maybe I'll try to see if I can find some Rubys or continue my search on Mouser. I'm no pro with capacitors yet, though I do have a bit of an understanding.