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'capacitor ripple current'
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2005\08\14@014014
by
Vasile Surducan

> Hello all,

> If a capacitor is rated at 1A ripple current at 50kHz, is this a

> continuous rating based on power dissipation due to internal resistance?

Yes it's a continuous rating at a maximum temperature, based on the

capacitor reactance.

>

> I'm designing a motor controller that should be able to handle peaks of

> 100A or more for fractions of a second and I'm trying to figure out what

> the capacitors can handle.

Will need special capacitors, and I'm guessing that will be more than

one. The problem might be also the voltage level of this capacitor.

cheers,

Vasile

> Thanks

>

> --

> Martin Klingensmith

> http://wwia.org/

> http://nnytech.net/

>

> --

2005\08\14@022412 by David Van Horn

-----Original Message-----

From: .....piclist-bouncesKILLspam@spam@mit.edu [piclist-bouncesKILLspammit.edu] On Behalf

Of Vasile Surducan

Sent: Sunday, August 14, 2005 12:40 AM

To: Microcontroller discussion list - Public.

Subject: Re: capacitor ripple current

On 8/14/05, Martin Klingensmith <.....martin-distlistsKILLspam.....nnytech.net> wrote:

> Hello all,

> If a capacitor is rated at 1A ripple current at 50kHz, is this a

> continuous rating based on power dissipation due to internal

resistance?

Yes it's a continuous rating at a maximum temperature, based on the

capacitor reactance.

Jim Williams of Analog Devices, has a good formula for this.

Several terms, and the results can be quite interesting.

I used the formula for a particularly difficult thermal printer design,

and it suggested that three really cheap caps would be better than one

expensive "low ESR" model. I went with the guidance, and that worked

out very nicely.

There are scads of systems in the field now, but essentially no

failures. :)

I don't seem to have the right book on hand, so I can't quote it

directly.

Perhaps someone else out there does?

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