Anyone used alternatives to electrolytic filter caps? How were the results?

[diagrammatiks]

Just be aware that film caps can get big. Even the Wima's grow to gigantic proportions. I've got 2.2uf 630vdc that just came in that are the size of fig newtons. They are hard to use too since the leads on the box caps are meant for pcb construction and don't get any longer.

that being said 630vdc is pretty much the standard in a high capacity axial leaded metalized film cap. There's really no reason to use less then 630 in the power supply.

This is the last time I restocked.



A 47uf Solen 630vdc is about the side of a half used roll of toilet paper.

The 10s and 15s are much more manageable.

The 10uf 630vdc is barely bigger then a 22uf F and T or IC electro, about the same length but just a little bit thicker.

Oh ya, I got a chassis in the other day that I threw a bunch of things in to see what all could fit...it's my first time working in a full size chassis.



There's plenty of room in there for all sorts of stuff it seems.

[greengriff]

The motor run caps don't seem to have a very long lifespan compared to other poly caps I've been quoted between 3000 and 10000 hours by various suppliers of motor run caps, whereas the Vishay poly caps on the farnell website are quoted at 100,000 plus. They are 3 times the price but with 10 times the quoted lifespan.

For a comparison, what is the expected life in hours of an electrolytic? I can't say I've ever come across that information as it applies to amps - I just change them if they are getting towards 10 years old or if I hear any ghost noting.

[diagrammatiks]

There is no reason to use motor starts. They are terrible for audio and are bigger and bulkier then the current crop of film caps.

If you want oil asc and obligatto make oil filled film caps.

If you need radial leads mundorf makes their tube cap series which are can type film caps.

[greengriff]

R.G. had suggested motor run caps as a sensibly priced poly alternative to lytics. Have you used them and had bad experience with them then?

[Steve Conner]

There is no reason to use motor starts. They are terrible for audio and are bigger and bulkier then the current crop of film caps.

Let's see some evidence for that statement.

(You probably meant motor run caps anyway: motor start caps are non-polarised electrolytics.)

The lifetime of electrolytics depends on operating voltage and temperature, like most components. The life rating given by the manufacturer is for operation at the rated voltage and temperature, and running them cooler can extend it a lot. The main difference is that unlike film caps, electrolytics go stale if unused for a long time.

[greengriff]

Hi Steve. Thanks for chipping in again. So realistically then, the only advantage of poly over electrolytics is that they don't dry out if not used? That is obviously a useful advantage as many owners of loud valve amps may own several and not use any particular one that often. However I was attracted by what I thought would be the much longer service life of polys (all other things being equal). Are you saying that was an incorrect assumption on my part?

[J M Fahey]

I think motor run caps aren't quoted as having a long life ... when used with motors which are an incredibly abusive load.
With gentle electronics use they should last 10X that, similar to what their "brothers" quote.
As far as electrolytics, rather than an "hours" rating they should be rated in years running since they were made, electrolytic chemistry "eats" them (or degrades, if you want a more polite word) whether they are in use or sitting in a shelf, not too dissimilar to what happens to batteries, and approximately for the same reasons.

[Steve Conner]

That seems about right.

Failures in electronic components are caused by chemical degradation. So, they all have a failure rate that varies with temperature, approximately according to the Arrhenius equation. This is an exponential, so for every x degrees increase, the life is halved. The value of x depends on what kind of component it is, and the manufacturing quality.

Electrolytics also have a fixed shelf life in addition to that.

Motor run caps, and these new-fangled DC link caps for power electronics, both carry high AC currents and run hot. I imagine this is what limits their lives. The manufacturer can print any life spec he wants by altering the temperature the life test is done at. As JM says, in your guitar amp they will all probably last for ages.

[greengriff]

Right then, motor run caps it is. The discounts offered by ebay sellers if you buy a few are pretty generous too, taking a 100uf pretty near to the price of a 50uf+50uf electrolytic, which seals the issue for me! Many thanks for all your responses, they have been extremely helpful.

[diagrammatiks]

I had read an article about the big motor run caps at some point. I recall that they didn't have a significant improvement over electrolytics. I'll try and find it.

However, griff if you find some nice ones lemme know and I'll try it out myself.

The issue I had when I was looking was that the 100uf's were huge and heavy and I didn't really find any that were that cheap.

[greengriff]

Hi,

I found loads on ebay and the sellers were willing to discount them quite heavily if I bought a few. The price is comparable with electrolytics. I don't mind if they are no 'better' than electrolytics - I just want a long life out of them.

[seess]

Certain builders do use non-electrolytic caps, (I believe Carr do in some models at least?) limiting factor is often the physical size of the caps, e-caps can usually be found to fit in any existing amp...try finding r430-40uf's worth of non-electrolytic caps to stuff into a 5F2r4A right after the rectifier, or fitting them in space left by 2x 350/500v electrolytics as main filters for a BF/SF Fender.

If you gen up on physical cap sizes, then build in adequate space from scratch with a suitable chassis, then you should be fine. In a lot of cases though it still makes sense to go with long life e-caps & just anticipate a reasonable part life.

you are right. But sometimes it is a good idea not to use any amps.

[R.G.]

I had read an article about the big motor run caps at some point. I recall that they didn't have a significant improvement over electrolytics.

If the comments were about the sound of them, no there would not be a huge improvement in sound over electros. However, they have no built-in degradation/failure mode like electros, so they will *never* need periodic replacent like all electros will.

That is, there is a significant improvement in lifetime.

[Chuck H]

Just looking at Mouser I narrowed some search fields and came up wit these Epcos caps:

EPCOS motor run

Looks like they target the same 60,000 hour life expectancy as most motor run caps (probably much longer in a guitar amp, as noted) and cost about the same as Sprague Atoms. Not quite as large as many other motor run caps. Of course, due to the typical application for these caps there are no impedance/ESR or ripple figures given in the data specs. But being film caps I would guess that they stack up against any aluminum electrolytic.

[diagrammatiks]

true.

I just grabbed a few of the asc motor runs for a project of ebay for pretty cheap.

They are really big though.

The 15ufs I got have a 1.75 inch diameter.

The 40uf of those is almost 2.8 inches round.

I'm really hoping that DC link capacitors come down in price soon.

I was searching around and found this company

Electronic Concepts, Inc. - Manufacturer of Film Capacitors

that seems to sell pretty compact film caps but they don't sell to the public.