Replacing ESC Caps

[Tommy3D]

Hi guys,

I really need your help. Can I replace these 3 caps for, let’s say, only one 35V 5000UF or even a 50V 3000UF?

Thanks in advance

[CraigP]

One cap doesn't work very well. There's too much current for the leads of just one cap, and it could just burn the leads up. Parallel caps help to spread the current out to avoid this problem and to reduce the impedance of the cap bank.

[ray schrauwen]

Just buy the same ones from Steve at OSE and get twice as many so you can parallel them up. There are tons of pictures on how to do this.

[CraigP]

The more caps the merrier! Remember to use that pre-charging resistor... It will bark at you if you direct connect without pre-charging first!

[Fluid]

Here's what I do. I prefer to eschew the resistor. I'm not afraid of a little pop, and it is that pop which lets you know the caps are still good. Caps are expendable items and do wear out without physical signs. Careful plugging of the plugs reduces damage, they are cheap and easy to replace. The pop is cheap insurance to help save an expensive ESC.

A single cap can work okay, I use a single large 1000 mFd cap on 100-150-amp setups and it works fine - no burned wires and decent ripple current suppression. But more, smaller caps with the same capacity work better to suppress ripple as they can charge quicker. On 200+ amp setups I use multiple smaller 1000 mFd caps.



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[CraigP]

Well, being an Electrical Engineer of 34+ years, I have to tell you that repeatedly exposing electrolytic capacitors to very high current surges will cause separation between the electrolyte and the plates. Meaning they go bad... It's the #2 reason for large capacitor failures, #1 being too high of operational temperature. I think if you look at the leads of a single capacitor, it becomes obvious that 150A isn't going to flow through it. If your not burning the leads up, then you have other resistances in the circuit, like wire and connectors, that is helping to moderate the ripple current. Because you've "gotten away" with doing that, doesn't make it good electrical practices. So that POP is also contributing to the eventual failure of your capacitors. Sorry, this is bad advice and I have to say something about it...

[Fluid]

You are entitled to your opinion of course, but I stand by what I do. Who cares if not using a resistor shortens the life of the cheap expendable caps - if the practice helps save an expensive ESC? It is recommended by the largest manufacturer of ESCs in the country, who has stated that the arc is your friend for the reasons I posted. It has worked for me for over a decade on a great many fast boats. (BTW long wires and excess impedence increase ripple, they don't reduce it. We use caps to help mitigate the ripple caused by long wires etc. Excess ripple is what kills so many ESCs, and bad caps don't protect the ESC.)

If you read my post, you know that all I did was state what I do, not what you should do. You are welcome to ignore my experience.




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[CraigP]

I leave you with something to ponder: You use the word ripple, but actually there are two ripples. There is voltage ripple, caused by current flowing over impedances, such as wires, connectors ect. This kills ESC's and motors by going over their voltage rating. Then there is current ripple, unseen unless there is a resistance to produce a voltage drop. I am specifically talking about current ripple. The manufacturers of ESC's are trying to provide a set of easy guidelines that folks can use, without having to talk college courses. But the fact is, if the caps are used to the point of not producing a spark, then they are really gone, and should have been replaced before that time. This problem is not near as much an issue on voltages up to 4s. But at 8s and higher, its a big deal. Also, I don't use cheap, expendable caps. Only very low impedance caps, which are not cheap. This isn't just FE experience, this comes from years of servo drive and KW level power conversion designs and debugging. And notice I'm not even bringing leakage inductance into the discussion, which is the other big circuit killer if not dealt with properly.

Didn't mean to get crossed up with you, but perhaps you should take into account the experience of others. I posted my initial response because the OP was interested in using HV solutions.

[Tommy3D]

Hi guys,

Thanks for all your replys. So, using higher Voltage Caps, doesn’t bring me any safety margins, right? I thought it would do.. lol

This is an Turnigy Marine 180A (I was checking, and right now the design is slightly different, so this should be a “V1” I believe), and I’m using 6S Lipos.

Well… for telling you the truth, I really don’t like that much of the connecting spark. If it is possible to eliminate, that would be great. Can you please point me a tutorial for adding the pre-charging resistor?

Should I be OK with 6 of these 35V 1000uf on parallel?

Thanks once again.

Regards

[CraigP]

Tommy, the pre-charging wire should be located on the ESC. It should be a smaller red wire. That wire is tied to a 50-100Ohm resistor which is tied to the large red wire, the +Input to your battery system. Before connecting the large wire, you should connect to small wire first, charging the caps on the ESC with the resistor. Then tie in the large red +Input wire. Do A google search for your ESC type and look for wiring diagrams, it should tell you the specifics.

There ARE advantages to using higher voltage rated capacitors, especially in applications like FE that have large current values in the system. I use 63VDC rated capacitors in ALL my ESC's. The higher rated voltage will allow the capacitor to work with the current better. You have to be real careful about WHAT capacitor you use. Selecting any ol' 1000uF cap can lead to big troubles. They need to be a low impedance, high ripple current, high temperature capacitor. Here's a Mouser Electronics PN so you can compare, or just get some of these. They are NOT cheap! But they work good! The following part number is for a 63VDC, 2200uF cap on Mouser: 661-EGPD630E222MM35H

You should only need 3 of these...

[CraigP]

BTW, small body caps are NOT usually high ripple current types. It takes capacitor volume, I.E. size, to make a high ripple current capacitor. Little dinky caps will not even "see" the current...

[RuntheraceAMC]

Is there a thread with pictures that shows how to set up parallel caps?

[ray schrauwen]

Search: Dr.Wayne

https://forums.offshoreelectrics.com/showthread.php?36868-Cap-banks-the-pre-emptive-answer&highlight=Dr.Wayne

[RuntheraceAMC]

That's one long thread. Thanks for the help