Capacitors

Background

Examples of Bad Caps

These are related to using the ESR-Cap meter.

Heathkit GC-1000 Most Accurate Clock

This had nearly all the electrolytic caps bad.  It's now working great on the built-in whip antenna. 

Oven Controller

See Hints and Tips: Cold Oven Robertshaw Controller in GE Electric Oven
Two caps in the analog temperature control circuitry, both marked 4.7 uF 35 V, tested C: 000 ESR: ---.  The interesting thing is that the replacement caps, rated 4.7 uF 25 V, are larger.  This means the capacitors the factory used were faulty in that you can't get that much capacitance in that small a package with that voltage rating.

I didn't determine the working voltage of the 4-bit micro controller but expect it runs on 5 volts.  The LM324 op amp might be running as high as 32 V, but I very much doubt it, +/- 15 would be the max expected, so getting 25 V replacement caps seems to be conservative.

The bad C1 and C17 caps were punched into a copy of the board photograph to keep track of them and then bare wires were soldered on to allow them to fit in the SR LCR meter or HP LCR fixture.  You can see that the new caps are much bigger. Cap WVDC dia mm height mm pitch mm Old 4.7 35 4 6 1.5 New 4.7 25 5 11 2 The height needs to be short in order to allow for the relay board that's mounted directly above this board (see the Hints and Tips web page).  The replacement parts were installed laying on their sides out of general principles.   But it turned out it was required for vertical clearnace. The volume of an electrylytic capacitor depends on both the capacitance and on the working voltage and since the new part has a lower working voltage there's a huge difference in volume.

The SR 715 (1 kHz & 1V drive) shows the bad caps as about 20 nF (0.02 uF) not the 4.7 uF they should be and with a series resistance of about 40 k Ohms.  This is consistant with the electrolyte evaporating.  Note that total hours of use this oven has seen is probably under 10 so the problem was not heat.  But the controler board (clock) is powered 24/7/365 minus the occasional power failure.

Super Capacitors

There are three general types of super capacitors (Wiki: Capacitor).  They are also known as Double Layer Capacitors (Wiki)

Memory Hold Up Super Caps

These typically have an internal resistance that's 10 or more Ohms.  Because of the high internal resistance they're good for very low current applications, but can not be used for powering motors or other high energy applications.
See 24 and 25 below.

Commercial/Industrial Super Caps

20 Farad 2.7 Volt Kamcap

Miller Solar Engine 0.35 F, 2.7V

These are typically single units and so have a breakdown voltage under three volts.
Measuring (see below) a 20 Farad 2.7 Volt capacitor by setting the HP E3617A bench top power supply for 2.5 Volts (below the 2.7 V max) and with the clip leads shorted setting the current to 0.5 Amps.

Connecting the second clip lead when the clock is at the top of a minute (23:32:00) and watching the voltage on the power supply climb.
It gets to 2.0 volts at 23:33:25, i.e. after 85 seconds.
So the total Coulombs moved is I (Amp)* t (sec)= 0.5A * 85 seconds = 42.5 CoulC = Q / V = 42.5 Coul / 2 Volts = 21.25 Farads

Automotive Audio Super Caps

These start at about 1 Farad and are rated for "12 Volt" automotive electrical systems and so can be charged.
The built-in voltmeter shows Lo from about 5 volts to 8.34 Volts then shows the voltage up to 15.9 Volts, and above that shows Hi.
The meter draws 17 ma at 16 volts, which is a large part of 100 ma, which I'm using to measure the capacitance, so for measuring the capacitance it's best to remove the meter.

It's probably also a good idea for automotive users to remove the voltmeter so that the battery will hold it's charge for a longer time.  With the voltmeter connected the cap drains very quickly, but without the meter the battery takes a few days to discharge to 9 Volts.  If the cap discharges too far it may blow a fuse in an automotive application.

1 Farad Cap with Voltmeter removed

Measuring the Capacity of a Super Capacitor

The method is known as Coulomb (Wiki) counting and is commonly used to measure battery State Of Charge (Wiki: SOC Coulomb counting).

For example for the 1 Farad Truconnex super capacitor above I started with the terminals shorted for a little while so the voltage was zero.

Then setup an HP/Agilent E3617A bench top power supply for 16.0 Volts open circuit and with the leads shorted together set the current to 100 mA.

At the top of a minute I connected the power supply to the super capacitor and watched the voltage meter on the supply climb up to 14 Volts and noted the time again (it was right at 2 minutes.

The number of coulombs delivered to the capacitor is 0.1 Amps * 120 Seconds = 12 coulombs

Note:  The reason for using a current source rather than a common power supply that's close to a constant voltage source is that if a voltage source is used the current will be constantly changing to reflect the voltage difference between the fixed power supply voltage and the increasing capacitor voltage.  That makes it very hard to count the charge transfer (coulombs).

C = Q / V = 12 coul / 14 V = 0.857 Farad

Plotting in Excell the time vs. voltage and fitting a straight line that goes through 0, 0 gives the following slope & quality of fit:
Volts on the Y axis and Seconds on the X axis.

C = dQ / dV
dQ is the change in one second and since the current is 0.1 Amp that's 0.1 coulomb.
dV is the slope of the line and that's 0.0776 so:

C = 0.1 / 0.0776 = 1.288 Farads
This may be a little more accurate than basing the capacitance on a single measurement, like above.
There is a little curvature in the actual data compared to the straight line, not sure why.

Next try this with a different current to see if it results in a similar answer.

Table

Tested in # order using all the testers, then the next #.  A Lazy Susan helped.
SR 715 at left then counter clockwise Micro ESR-Cap meter, EVB ESR (only) meter, Fluke 87 DMM

#	Photo	Mouser p/n	Type	Cap	Voltage	$	ESR Micro		Fluke 87	EVB	SR715		HP4328
							ESR	Cap uf	Cap uf	ESR	R	C uf	ESR
1		647-UVR1C101MDD1TD	Al Electrolytic	100 uf				116	102			92.65
					16	0.03	1.2			1.0	1.85		1.45
2		647-UVZ0J153MHD	Al Electrolytic	15,000 uf				14750	OL			13670
					6.3	1.40	0.06			0.06	.036		0.043
3		647-UHM0J272MPD	Al Electrolytic	2,700 uf				2750	2944			2594
					6.3	0.34	0.06			0.07	0.018		0.025
4		647-UVR1H220MDD1TA	Al Electrolytic	22 uf				23.5	20.7			19.8
					50	0.02	1.5			1.1	4.3		2.4
5		647-UHD1A471MPD1TD	Al Electrolytic	470 uf				495	490			490
					10	0.08	0.09			0	0.14		0.096
6		661-PSA10VB100M	Al Organic Polymer	100 uf				105	106			103
					10	0.72	0.06			0	0.34		0.078
7		75-94SA226X0020CBP	Al Organic Polymer	22 uf				28.3	24.9			24
					20	1.55	0.3			0.06	1.0		0.263
8		647-PLF0J471MC06	Al Organic Polymer	470 uf				496	492			480
					6.3	1.15	0.2			0	0.02		0.0160
9		598-CD15ED270J03F	Mica	27 pf				0	Note1			27.8pf
					500	0.75	----		19.5	OL	93k		OL
10		810-FK26Y5V1A226Z	Multi Layer Ceramic	22 uf				15				14.7
					10	0.34	0.22			0.01	4	Note 3	0.08
11		810-FK22X7R1C226M	Multi Layer Ceramic	22 uf				25	23.3			24.6
					16	1.06	0.13			0.01	2.3		0.248
12		581-NOJC107M006RWJ	Niobium Oxide	100 uf				106.8	95.0
					6	0.67	0.16			0.24	Note2	Note2	Note2
13		581-NOJB226M006	Niobium Oxide	22 uf				32.1	27.1		Note2	Note2
					6	0.42	0.46			0.46			Note2
14		581-NOJE477M004	Niobium Oxide	470 uf				441	452
					4	4.30	0.08			0.01	Note2	Note2	Note2
15		140-PF2A472F	Polyester Film	0.0047				0	5mf			4.78mf
					100	0.51	----			OL	368		OL
16		80-MMK37.5226K250R06	Polyester Film	22 uf				25.4	22.0			21.9
					250	5.98	0.39			0.24	0.14		0.1
17		80-T520B107M4ATE35	Polymer Tantalum	100 uf				111.8	96.5		Note2	Note2
					4 ESD	0.94	0.07			0.06			Note2
18		80-T520A226M6ATE100	Polymer Tantalum	22 uf				25.4	22.6		Note2	Note2
					6.3 ESD	0.72	0.14			0.13			Note2
19		80-T520D477M004	Polymer Tantalum	470 uf				441	439		Note2	Note2
					4 ESD	1.31	0.05			0.08			Note2
20		871-B32676E3226K	Polypropylene	22 uf				25.6	22.23			22.12
					300	10.85	0.12			0.03	-0.004		0.14
21		505-FKP233/1000/5	Polypropylene	33 pf				0	Note1		Note2	Note2
					1000	0.49	----			OL			OL
22		581-TAP226K016CRW	Solid Tantalum	22 uf				26.1	22.6			22.1
					16	0.53	0.48			0.43	1.4		0.76
23		71-597D477X0004V2T	Solid Tantalum	470 uf				495	486		Note2	Note2
					4 ESD	1.45	0.05			0.15			Note2
24		598-EDLSG105V5R5C	Supercapacitor	1 f					OL		Note2	Note2
					5.5	2.94	6.5			7.5			7.2
25		581-BZ015B603ZLB	Supercapacitor	60 mf				R ONLY	OL		Note2	Note2
					5.5	14.42	0.12			0.29			0.097
26		FRS CGC-10	Computer Grade	90,000				R ONLY	OL		98030
					10	1.75	0.03			0.02	.	-0.0025	0.0165
27		FRS MC-3.3	Polypropylene	3.3				3.9	3.41		3.4108
					400	2.00	0.51			0.52		0.050	0.78
28		FRS OMB1MFD	Orange Coating	1.0				1.2	1.006		1.0040
					630	1.96	2.0			1.7		2.77	4.2
29		647-UKL1E4R7KDDANA	Al Electrolytic	4.7								4.7
					25						3.3
30		Western Electric 21 BG dual 1 MF 21 AP 1 MF 1127513 Paper Condenser, Feb 9 1915 575653 Electrical condenser, Jan 19, 1897 449A-61   1 uF	Paper <0.2 uA5 0.1 uA5 < 0.2 uA5				5.0 4.6 6.5 5.1	1.46 1.54 1.33 1.17	1.31 & 1.41 1.16 1.055
No.	Photo	Mouser p/n	Type	Cap	Voltage	$	ESR	Cap	Fluke 87 CaP	EVB ESR			HP 4328 ESR

Variable

After a quick look at old patents I found this one where the capacity is not a linear function of tuning shaft angle.  This is aimed at crystal radios.
A variable condenser used for transmitting must have extremely low series resistance which is not required for crystal radio use.
Looking for design info for rotor plates for linear AM radio dial frequency.

		1525778 Variable condenser, Carl A Hellmann, 1925-02-10, - Fig 1. prior art linear & 180 deg rotation. Fig 2.  240 deg useful range Fig 3. 270 deg useful range Fig 4. useful range of 360 deg * n/(n+1) Fig 5 & 6. >180 deg range & non linear Fig 7. rotor smaller angular extent than stator Fig 8. like Fig 7 but different arrangement Fig 9. >180 deg range Fig 10 & 11. Cylindrical layout Fig 12. movable dielectric w/fixed paltes Fig 13. axial shift to change range Fig 14. detail for Fig 13. Fig 15. electrical detail for Fig 13. 1748345 Rotary variable condenser, Carl A Hellmann, 1930-02-25, - similar.
		1609006 Variable condenser, Clarence D Tuska, CD Tuska Co, 1926-11-30, - bearing alignment
		1709959 Variable condenser, John W Simmons, RCA, 1929-04-23, - rigid, fine adjustment,
		2123050 Variable capacitor, Marwin R Johnson, GE, 1938-07-05, -  slotted end plates to allow tweaking capacitance curve.

1525778 Variable condenser, Carl A Hellmann, 1925-02-10, -

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