RC-Monster Forums - ESC Capacitors

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Having more of a smaller uF cap will have the least resistance, much lower than one large cap.

Quote:

Originally Posted by zeropointbug (Post 127639)

Having more of a smaller uF cap will have the least resistance, much lower than one large cap.

I wonder if the resistance is measurable with a simple ohm meter?

Hi Zeropointbug. Did you get your Quark ESC fixed?

You can't measure ESR with an ohmmeter. A meter outputs a small voltage and either measures current flow or measures the v drop on an internal resistor, and then calculates the resistance. If you put a meter on it, you'll see the resistance start very low and then rise until infinity.

This resistance, which should be called ESR for this discussion, can not be confused with Xc, which is capacitive reactance. Xc is a "resistance" as well, but the current is 90* out of phase with the voltage and the Xc "resistance" value changes with frequency (hence "reactance"). ESR is not Xc, but sorta like the 0* phase DC resistance.

Quote:

ESR Defined
ESR is the sum of in-phase AC resistance. It includes resistance of the dielectric, plate material, electrolytic solution, and terminal leads at a particular frequency. ESR acts like a resistor in series with a capacitor (thus the name Equivalent Series Resistance). This resistor can cause circuits to fail that look just fine on paper and is often the failure mode of capacitors.

To charge the dielectric material current needs to flow down the leads, through the lead plate junction, through the plates themselves - and even through the dielectric material. The dielectric losses can be thought of as friction of aligning dipoles and thus appear as an increase (or a reduction of the rate of decrease -- this increase is what makes the resistance vs freq line to go flat.) of measured ESR as frequency increases.

As the dielectric thickness increases so does the ESR. As the plate area increases, the ESR will go down if the plate thickness remains the same.

To test a Capacitors ESR requires something other than a standard capacitor meter. While a capacitor value meter is a handy device, it will not detect capacitor failure modes that raise the ESR. As the years go by, more and more designs rely on low ESR capacitors to function properly. ESR failed caps can present circuit symptoms that are difficult to diagnose.

This meter is something one can use to measure ESR: http://secure.transtronics.com/CAP-WIZARD.htm

Quote:

Originally Posted by BrianG (Post 127664)

Precisely! :wink:

sikeston34m.... nomods sent me a burnt out Quark with what a appears to be a good brains board on it, but unfortunately, i popped it onto my Quark, but no luck, doesn't even turn on. I noticed it has two little tiny caps missing from the board near the motor phase sensor end (where you solder it).

If anyone has a Quark they are willing to part with (that has overheated, or w/e) and knows the brain board is fine.... I am accepting them! :whistle::wink:

Excellant Information Brian! Thank you. I have attempted to measure them before and noticed how they charge up under the meter.

I was hoping to catch you Zeropointbug. I need a favor from you.

I am doing some research on the Quark line and what I need to know is this. I need to study the Gate Lead Driver circuits on the brain board of the Quark to figure it's amp carrying capacity. I do have an 80 amp Quark here, but this requires disassembly, and separation of the two boards to get the numbers from the driver fets. I'm not willing to take mine all apart, I'm using it.

I looked at your pictures and they are not close up enough to get the numbers. Do you have any extreme closeups of the Quark Brain?

Take a look at my thread on "Quark ESC Power Board Mods/Comparisons" to see why I need this. There may be some things there that interest you.

Yeah, I just got my internet connection back from it being down for a week! :no:

Do you need the reverse AND top pics of the brain board? I do have pics of them close up, but I am not sure if you can see any numbers... I will get some pics for you as soon as possible! Anything else? :smile:

I really need both sides of the brain board. Extreme closeups that will show the numbers on the components.

Some of the numbers are almost too small for me to see with my naked eye, but the camera has a way of really blowing it up.

Welcome back ZPB. I thought you were probably vacationing.

Okay, check out my pictures in my sig..... there will be 3 pics of the brain board at the end. :yes:

Great!

On the last picture, the 3 fets in a row are the gate driver fets. The top number looks like I1760. Is this correct?

The top number is the model number and the only one I need. The others are date codes and such.