100uF Ceramics - Capacitance at higher voltage

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I disagree with your conclusions, the video explains why you are measuring low. dv/dt type hand held measurements are inaccurate.

Proper LRC meters change current levels to adapt to impedance of part and use a pure sine wave to measure impedance accurately. e.g. 3mA sine is inaccurate. 30mA sine is accurate in large C devices.

In very large UltraCaps, 300mA is more appropriate.
 
I don't dispute that these are 100uf, only that they are not 25v rated. More likely 6.3v.

Without the proper equipment is there an easy way to verify the voltage limit, i.e stick 6v in it, if it discharges normally great, try again with 10v, 16v until the discharge is rapid (cap damaged)?

What I do know is they are not 16v. Presently the board has 14v and they are damaged. I thought it was my soldering heat doing it.
 
Frankly, I doubt you can even come close to the reliability you expect with limited experience.

**broken link removed**
 

You would have recourse to correct the problem from reputable distributors. They don't sell without backing up with specs and traceability.
 
ACharnley said:
Ok here it is, I sent an email to the guy at TDK who wrote the presentation linked to earlier. He says the maximum capacitance they do at 100uF is 16V. In other words, my capacitors are fake!
Click to expand...

Yeah, I wondered about that because no where could I find the part number for your capacitor and the TDK main catalogue, attached to post #32, only lists 100uF @16V as you say.

spec
 
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Tantalum capacitors are not suitable for power supplies- see my post #32.

If space allows, I would suggest considering five 22uF 25V axial lead ceramic X7R capacitors.

But as Tony says, only buy from a main line distributor: Mouser, Digikey, RS, Farnell etc. This applies to all components including resistors.

spec
 
I'm investigating all options but it looks like with 330uF needed it'll have go outside the case. At least it makes it replacement when the electrolytic degrades...

Regards, Andrew
 
ACharnley said:
I'm investigating all options but it looks like with 330uF needed it'll have go outside the case. At least it makes it replacement when the electrolytic degrades...

Regards, Andrew
Click to expand...

I have forgotten the details but there are high grade high reliability electrolytic capacitors which would have a longer life. For example: https://www.vishay.com/docs/28318/048rml.pdf

Your application is intriguing: what exactly is it for- bicycle lighting?. You speak of relatively high volumes- are you marketing this item yourself?

spec
 
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It's been one hell of a day. My PCB manufacturer went back and found out the one on the board is also fake (probably 10V). It's a rip off of a Fenghua, so the Chinese are cloning high density Chinese ceramics!

Ah well, I'm learning.
 
Just to clarify,

There are two issues with your switch mode power supply.

(1) Low impedance and high self resonance for the capacitor feeding the switch mode power supply (350KHz) locally.
(2) High capacitance low impedance reservoir to hold up the voltages between peaks of the supply AC input (50Hz full wave rectified.

As the switch mode power supply is working satisfactorily with the correct voltage input it seems that item (1) has already been met, which only leaves item (2).

The solution would then seem to be a decent local ceramic of about 100nF to 470nF say (presumably already fitted to the PSU) and a 330uf remote electrolytic capacitor.

Is this a summary correct?

spec

PS: if you are not already using them, high current (compared to the rectified current drain) would reduce the voltage drop across the rectifier and lower the capacitance necessary for the reservoir capacitor.
 
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Yep, and there's a 10uF 25v ceramic X7R local to the buck (as per MP2307 datasheet). This is retaining capacitance after 20v so appears to be in spec.

For the reservoir, 220uF isn't enough, a 330uF works fine, but I'll go for 470uF to give some overhead.

**broken link removed**

10,000hr life, pretty cheap. Looks good to me.
 

Nice.
(1) Nichicon is a respected make.
(2) -40 deg C to 125 deg C is an excellent temperature range.
(3) Industrial grade = good.
(4) 10,000 hours life @ 125 deg C is excellent
(5) Price is reasonable too, as you say.

spec
 
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Yes, it was a mistake getting ahead of myself on the casing prior to having given the PCB a thorough workout. I was duped by the capacitors and the size of them and as I've found out there are limits. Attempting to get performance and reliability in minimal space has proven tricky.

Tony - thanks for baring with me earlier.
 
ACharnley said:
It's been one hell of a day. My PCB manufacturer went back and found out the one on the board is also fake (probably 10V). It's a rip off of a Fenghua, so the Chinese are cloning high density Chinese ceramics!

Ah well, I'm learning.
Click to expand...
Been there that painful path.

That is the reason large OEMs require that components are exclusively purchased from reputable vendors.
 
There are different business ethics to China which I'm now learning about. I left the sourcing to the components to my PCB producer (who has been excellent, can't fault him). He does this all the time and uses only his "reputable suppliers", one of which he's just found made a cock-up. Warranty doesn't exist, only unused returns. Technically I should claim $0.23 (price of fake capacitor) not to mention time from the price of each board and he claims it back from the supplier. In reality this isn't an option.

The 6,000 fake capacitors, the seller will take back the two reels but not the unopened one. She'll return them to her seller, who'll put them back into stock to be sold again. And so the wheel goes round!

All this has me wondering what else is cloned and what reliability issues could surface down the line because of it. Could they possibly fake an MP2307 - a complex DC-DC, and what about the PIC10f200 I'm using? Hmm...
 
ACharnley said:
For the reservoir, 220uF isn't enough, a 330uF works fine, but I'll go for 470uF to give some overhead.

**broken link removed**

10,000hr life, pretty cheap. Looks good to me.
Click to expand...

The SRF of such a capacitor will be much lower than 1 MHz or even 500 kHz. Here's a sweep of the impedance and ESR of a similar 470 uF aluminum electrolytic. The measurement is made with essentially zero lead length:



The SRF is at about 80 kHz. With an additional 1 inch of lead length this is the result:



Now the SRF is about 40 kHz.

Also, the ESR is a lot higher than what you're getting with your MLCCs. The rated maximum impedance at 100 kHz for the 470 uF cap in your link is shown as 75 milliohms. The ESR at the SRF shown in the first image I've posted here is about 30 milliohms. And if you look carefully, you can see the slight increase due to the extra 1 inch of lead length in the second image.
 
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