Why are today's caps smaller?

[berniedd]

I am trying to fix a 40-year old Hewlett Packard medical electrocardiograph machine. Main symptom is hum, evidenced by the writing stylus that's constantly vibrating - can't get rid of it. So naturally I'm replacing the electrolytic capacitors. I'm just amazed that today's capacitors are 5 to 10 times smaller than those old ones of the same capacity and rating. What's the reason for this? Better electrolyte? Or are the old ones beefed up or of special construction somehow, hence their size?

Example: I just replaced a pair of upright Sprague electrolytics, 3200 ufd/25 volts each. Main filters after the rectifiers. Each unit is about 2 inches tall, and a little over 1 inch in diameter. Yet the replacements I used are pygmies compared to these hulks. Also, am I correct to assume that the lug on the can is negative, and the slightly off center terminal is positive?

[washu]

Re: Why are today's caps smaller?

It's likely a combination of both improved electrolyte and beefed up construction. HP made good stuff back then so it wouldn't surprise me that they used caps that were "beefier" then absolutely required. When new they could likely stand a fair bit over their rated voltage without failing.

Better manufacturing techniques probably has some role as well. Caps made today can be made to tighter tolerances and thus smaller.

I have an old cap that is about 6" tall by 1" diameter. It's rated at a whole 8 uf. It was also made in the 30s so improvements have been made since then.

[Toasty]

Re: Why are today's caps smaller?

That caps comes from an era when those type of caps were everywhere in everything electronic. It remained so up into the 80's. As progress was made in the electronics industry, the demand dropped literally overnight. Within about 5 years, you just didn't see them anymore in new equipment. The manufacturers backed way off in production and cuts of 70-90% of prior production were common. That dropped to zero for many manufacturers as the demand shifted to smaller, higher performance devices.

Sprague, Mallory, and Cornell-Dubilier (CDE) were common makers.

These were available as single section, as you have, to multi-section caps with 2-4 values and voltages per can.

That style of cap is still available in a limited range of values, but they are primarily focused on the antique radio and television markets. Where there used to be hundreds of values and voltages, there are perhaps < 50 now, and that may be optimistic. Those that remain are typically in the 150v-450v range and 10-200uF range.

The polarity as you surmised is correct and should be indicated on the original can in some manner. Such as: CAN COM. NEG.

If you use axial leaded caps, make sure you mount it with the positive lead down on the board and the negative up from the top and bent over and down to the board.

>>What's the reason for this? Better electrolyte?<<
Yes, and overall better chemistry/engineering/manufacturing processes of the materials used in construction. Higher purity materials than previously available.

Toast

[Wizard]

Re: Why are today's caps smaller?

Ceramic capacitors have now achived 1uF in sand grain sized in that decade. Now some of them are now 10-200uF found in T-CON boards due to height limitations. (T-CON stands for timing control to take LVDS data, translate and output correct timing & route AC pulses to correct X & Y lines on LCD via driver ICs.).

Before that it was small values.

Cheers, Wizard