Will a 30uf Polypropylene Cap Make My AC Sound Better?

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I have some spare 33uf Vishay and some 60uf ASCs that are larger than a grenade.

Any advantage over a motor run? They’re both rated over 400V and my AC runs off of 240V.

Any benefit to a higher quality motor run a la ASC?

Also any thoughts on a hard start kit?

I have a feeling someone out there must have tried using one of these.
 
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This is what is in there now. Seen better days.

eOpaB27.jpg
 
They do make polypropylene motor run caps. They come with 1/4” faston terminals. And they show up on the surplus market from time to time. I have also seen smaller ones supposedly made for ceiling fans - that are *not* X or Y rated.

They make great speaker crossover caps, regardless.
 
I am puzzled why you want to listen to AC. I suppose it does sound a bit like some drum'n'bass music, though.

Any capacitor put across the mains supply must be mains rated i.e. X or Y. If not, you may have some explaining to do when your house burns down. If you want the capacitor to do something useful then it should be part of some circuit, not simply slapped across the mains.
 
Any capacitor “slapped across the mains” would either be in some noise filter or for power factor correction. A motor run/start cap is in series with one of the windings - usually seeing less current than the main one. The one in my AC isn’t X or Y, but does have all 3 safety cert stamps on it. The batch of MKP motor caps I bought for speaker crossovers has the same safety certs. My AC needs more than 15uf, unfortunately, because every 5 years my AC needs a recap - usually on the hottest day of the year. At the same time I got the other caps, I scored some 5 uF/ 250 VAC MKP’s that we’re supposedly for ceiling fans. No certs or anything, but at two bucks a pop they work just fine in vocal wedge crossovers. I have blown electrolytics to kingdom come in the same application.
 
I am puzzled why you want to listen to AC. I suppose it does sound a bit like some drum'n'bass music, though.

Any capacitor put across the mains supply must be mains rated i.e. X or Y. If not, you may have some explaining to do when your house burns down. If you want the capacitor to do something useful then it should be part of some circuit, not simply slapped across the mains.

Not disagreeing, but I think 2 different ratings/end use are being mixed.
In my view, X and Y rated caps are a modern thingy invented specifically for *consumer* everyday use power supplies, most often but not necessarily SMPS filtering where they are *needed* because they are a powerful source of interference, and where often, at least in Audio stuff, consumer touches the metallic chassis or parts connected to device ground.
And device , Audio/TV/Computer lives in a living room surrounded by flammable curtains, furniture, books, etc.

While ugly but incredibly robust "AC rated" caps as shown above exist since forever and are used in a more "industrial" way, which routinely subjects them to high stress.
So they are as large as needed, no space constraints, dielectric can be as thick as designer wants.

No need to design them to "fail-safe" .... in principle they are designed "not to fail" .... period :)

So yes, I would connect an industrial type AC rated capacitor across Mains any day of the week: they are *designed* and *tested* for that.

And most important: consumers are NOT supposed to touch any part of the motor or inductor wiring :)
 
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AC compressors are noisy. I'm surrounded by them, they drone on and on night and day. That's Florida in the summer. If anything can quiet that, I'm all for it.



Pano understands.

I’m in the United States, near Pano. I can’t remember the last time I turned on heat.

The title of my post was tongue-in-cheek.

Air conditioners run all year round 24/7 here at noise pollution levels.

Lots of problems related to the motor run / motor start caps just not having the long term stamina.

Seems the AC units are pretty specific about how much capacitance they want for the run cap- mine specifically says 70uf. I’m not sure what the results of more or less precision are.

Then there are hard start kits designed to mitigate this by putting an additional cap and potential relay in the start circuit. It’s unclear to me how they work precisely and under what circumstances they should be used or not used. There’s names like 5-2-1 and Suppco that make them.

The “hard start” used to come with A/Cs apparently but not anymore due to cost cutting.

Perhaps it’s called something else where you live. See here:

YouTube
 
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AFAIK it's the compressor itself making that noise and drowning out any other noise sources such as the motor.


The compressor makes the noise, yes.
However the cage is usually the culprit of general vibration.... loose screws etc. You can line it with damping sheets.

Then there’s compressor noise due to it overextending itself. Many get noisier over time as they approach failure.

Also it’s deplorable how cheap companies have gotten.

AC’s are relatively simple circuits but in 9/10 cases around here they are malfunctioning / not operating to specification due to poor build quality and lack of regular maintenance.

I was tossing around the idea of polypropylene to not have to concern myself with whether the start or run cap was dying or leaking or what have you.
 
He wants to listen to his air conditioning?



I would like to NOT listen to my air conditioning.

I’d like to reduce strain on the compressor / high current pull on startup as well.

Preferably long term.

See here: Understanding & Selecting Capacitors | Industrial Equipment News (IEN)

Oil caps here in Florida, at least those commonly used in HVAC and under constant use, don’t seem to last long. Especially those in outdoor units which are subjected to high heat and humidity.

The start cap is 5uf and the motor run is 70uf.

Hard start kits are $50. HVAC repairmen are upwards of $100/hr.

Vishay MKP1847H Polypropylene High Humidity Film Caps would cost about $50 for the 70uf required and are rated for 250V AC.

They are rated for 100,000 hours!


MKP1847H Vishay Datasheet

Of course we probably want to go with 370AC or 440AC. Perhaps this:

MKP1847625354Y5 Vishay / Roederstein | Mouser

Kemet C3B films I can pull off 70uf for about $30 or so.

Kemet C3B Datasheet

So replacing both with Film caps should cost less than a service call.

Probably even saving money compared to how many motor runs would get swapped out in the time it takes for the film to die.

On a 10k + AC I think it would be wise to consider, as this is a major point of failure in these devices where I’m located (high temp, high humidity, all year round operation).
 
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In contrast a 70uf motor run from CDE is $47, about the same.

So, then I suppose the question is what does an oil filled motor run have on a dry film cap?

An apparent problem is that Motor Run oil caps are frequently run at temps in excess of their ratings. My Aerovox is rated only for 70C.

It’s 89 F / 31.5 C ambient and 68% humidity today where I am. The AC is in full sun in essentially a big metal sauna running 24/7.

Failure rate for the CDE oil cap is 6% at 60k hours, but scales as temp increases.

See charts here: https://www.mouser.com/datasheet/2/88/MPF-611103.pdf
 
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I wonder how much difference it would make to the overall noise? I know that the turntable fanatics here are always tweaking the motor caps for quieter running, but how much would that matter to the compressor. I do know that during brief brown outs here caused by storms, the A/Cs run very rough until power stabilizes. I turn ours off to prevent damage.

Of course there are a couple of other motors that should have run caps, the condenser fan and the blower fan that moves air.
 
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