Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site kitty.UUCP
Path: utzoo!watmath!sunybcs!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: net.analog
Subject: Re: One farad Caps
Message-ID: <168@kitty.UUCP>
Date: Sun, 28-Jul-85 18:34:48 EDT
Article-I.D.: kitty.168
Posted: Sun Jul 28 18:34:48 1985
Date-Received: Mon, 29-Jul-85 06:59:49 EDT
References: <102500002@hp-pcd.UUCP>
Organization: Recognition Research Corp., Clarence, NY
Lines: 35

>    Recently I have seen data on a new type of capacitor called the Maxcap(tm)
> double layer capacitor. A 1 farad maxcap is 1.1 inches wide and .55 inches
> high. It looks like its some sort of a very weak battery that can be fully
> discharged or even reverse charged without harm.
> 
>    Has anyone ever used these? It would seem that the initial surge current
> if you connected one to a 5 volt supply could easily overload most supplies.
> Any experiences and or horror stories would be appreciated.

I have on occasion used some large capacitor arrangements (around 1 Farad)
on process control instrumentation to provide a simple solution to short
duration power line voltage drops (like starting motors).  I simply use a
low resistance (0.5 to 1.0 ohm) between the rectfier diode bridge and the
capacitor to limit the charging current and thereby avoid transformer and
diode stress.  My loads are only in the couple hundred milliampere range,
so the 1 Farad capacitor gives me pretty decent protection without the
maintenance worry and added circuitry required to charge a nicad or gel cell.

Actually, the current limiting resistor is not even necessary unless the
transformer is vastly oversized with a very low impedance and high short
circuit current.  If you consider the total amount of the charging energy
going into the capacitor (0.5*C*V**2) and figure out the watt-seconds, it
presents a miniscule momentary overload for the transformer and rectifier
diodes.

	Larry Lippman
	Recognition Research Corp.
	Clarence, New York
	UUCP	{decvax,dual,rocksanne,rocksvax,watmath}!sunybcs!kitty!larry
		{rice,shell}!baylor!kitty!larry
		syr!buf!kitty!larry
	VOICE	716/741-9185
	TELEX	{via WUI} 69-71461 answerback: ELGECOMCLR

	"Have you hugged your cat today?"