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Generators & Electric Motors General Discussion

AC capacitor types?


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Old 08-08-2019, 06:44:30 PM
Railroads Railroads is offline
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Default AC capacitor types?

I'm wondering what the general consensus is on resin vs oil filled AC motor capacitors?

For my induction generator control box I want to use stud mount AC caps. They are scarce as heck here in the states. I managed to find a source from the UK at a reasonable price. But they are resin filled type capacitors vs the more common oil filled motor capacitors.

I pulled up the basic specifications for both types from one of the manufacturers.

The stud mount resin filled caps, http://www.rifone-capacitor.com/upload/files/CBB60.pdf

The oil filled type caps, http://www.rifone-capacitor.com/upload/files/CBB65.pdf

When used for induction generators the capacitors are passing the full current of the winding sets on the 3 phase conversions to single phase output. In other words, The caps are under enormous stress all the time while in operation.

The caps both excite the generator and combine the different phases when wired C-2C to achieve 80% of the machines rating as a single phase output.

Robert
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Old 08-08-2019, 06:55:14 PM
Vanman Vanman is offline
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Default Re: AC capacitor types?

It's my understanding that capacitors last MUCH longer with either lower operating temperature, or operation below rated voltage. So my advice would be to source some ordinary American made run caps that are rated well above your operating voltage.

Keith
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Old 08-08-2019, 08:57:14 PM
Railroads Railroads is offline
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Default Re: AC capacitor types?

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Originally Posted by Vanman View Post
It's my understanding that capacitors last MUCH longer with either lower operating temperature, or operation below rated voltage. So my advice would be to source some ordinary American made run caps that are rated well above your operating voltage.

Keith
Yah but they won't work out for my needs. I saved from scrap a large Pass & Seymour data center box. I'm going to use it for my control panel. The ordinary caps we have would require some creative mounting and take up more room when compared to using the stud mount types. This control box is going to have quite a bit going on inside, so every bit of room counts. There is going to be several gauges, lights, switches, breakers, 2 PCB boards. Lots of fun stuff!

This weekend I will get a picture of the old data hub box I salvaged. I knew when I saw it that I was going to use it on my induction generator build. If I plan it out well, I can move the control center from my 3KW build to my future 15KW induction generator set powered by a 3 cyl diesel engine.

Robert
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Old 08-10-2019, 01:10:58 PM
Zephyr7 Zephyr7 is offline
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Default Re: AC capacitor types?

Vanman is correct that running the caps cooler than rated temperature will result in MUCH longer life (it’s not linear, either, half the temperature might give 16x longer life). Running at lower than rated voltage doesn’t affect lifetime, but it gives more margin for transients so less chance of a glitch killing your cap.

The regular oil filled caps in round and oval cans can be mounted either with base clamps or with a strap over the top. I’ve also seen them mounted to a plate with holes punched in it that clear the fan but not the rolled lip on top. Screwed down clips then clamp the rolled ring to keep the caps in place.

All that said, resin type caps should work just fine but won’t have the self healing capability of oil filled caps if you have any high voltage transients. If the caps have a ripple current spec then that is the max current they can safely pass in a series application too.

Bill
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Old 08-10-2019, 04:26:02 PM
Railroads Railroads is offline
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Default Re: AC capacitor types?

Quote:
Originally Posted by Zephyr7 View Post
Vanman is correct that running the caps cooler than rated temperature will result in MUCH longer life (it’s not linear, either, half the temperature might give 16x longer life). Running at lower than rated voltage doesn’t affect lifetime, but it gives more margin for transients so less chance of a glitch killing your cap.

The regular oil filled caps in round and oval cans can be mounted either with base clamps or with a strap over the top. I’ve also seen them mounted to a plate with holes punched in it that clear the fan but not the rolled lip on top. Screwed down clips then clamp the rolled ring to keep the caps in place.

All that said, resin type caps should work just fine but won’t have the self healing capability of oil filled caps if you have any high voltage transients. If the caps have a ripple current spec then that is the max current they can safely pass in a series application too.

Bill
Ok, Oil filled are better than what they use overseas. Anyone seen stud mount oil caps from a US supplier?

Robert
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Old 08-10-2019, 05:07:09 PM
Zephyr7 Zephyr7 is offline
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Default Re: AC capacitor types?

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Originally Posted by Railroads View Post
Ok, Oil filled are better than what they use overseas. Anyone seen stud mount oil caps from a US supplier?

Robert
I wouldn’t say “better”, just different. Each has their pros and cons. Resin caps are more physically durable, for example.

I’ve never seen a stud mound oil filled cap.

Personally, I’d try making the oil caps work in your application since they’re more readily available here.

Bill
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Old 08-10-2019, 09:25:18 PM
Railroads Railroads is offline
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Default Re: AC capacitor types?

Quote:
Originally Posted by Zephyr7 View Post
I wouldn’t say “better”, just different. Each has their pros and cons. Resin caps are more physically durable, for example.

I’ve never seen a stud mound oil filled cap.

Personally, I’d try making the oil caps work in your application since they’re more readily available here.

Bill
Bill, I've got heaps of oil caps. I will probably just use them. I've been collecting and saving every good AC motor cap I come across for a few years.

Robert
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Old 08-12-2019, 02:05:03 PM
Railroads Railroads is offline
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Default Re: AC capacitor types?

I didn't get a chance yet to dig out my enclosure that will be my Imag control center.

The panel I rescued is a residential gateway hub. P/N F7810L. There is a picture of one in their catalog on the front page. https://s3.amazonaws.com/cesco-conte...64-Catalog.pdf

robert
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Old 08-17-2019, 09:07:12 AM
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Jim McIntyre Jim McIntyre is offline
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Default Re: AC capacitor types?

If you want surplus N.O.S oil-filled run caps, these guys have a bunch, sometimes at decent prices:

https://surpluscityliquidators.com/t...32?clear_all=1
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Old 08-17-2019, 12:38:24 PM
Railroads Railroads is offline
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Default Re: AC capacitor types?

Surplus center has them cheap as chips too.

Robert
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Old 08-18-2019, 07:29:32 PM
dkamp dkamp is offline
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Default Re: AC capacitor types?

It would be best if your capacitors were NOT located in the same enclosure as the other electronics and switchgear...because when one fails, you'll have a huge mess. Keeping it in a dedicated enclosure separate from the rest, means that mess is contained.

Lesson learned in industry: blown-up capacitors sending smoke and innards all over safety circuits result in multi-point failures, thus, more serious things going wrong.

Add to that, the recovery time cleaning up, replacing all that mucked-up fess.

Regardless of resin vs. oil filled, if you've got motor run caps rated for over twice your system's working voltage, and they don't have some outlandish ESR, you'll have no problem making them last a long time. As noted, the oil-filled capacitor is inherently 'self healing' when subjected to unexpected transients. A static discharge making a wayward wander through your system will need someplace to go, and the dielectric is as good as any other, because at a million volts, there is 'no such thing' as an insulator... just a higher-value resistor.

I have stud-mount oil-filled motor runs in my Miller SRH-333 single-phase-converted welder... IIRC they came out of surplus center, and they're around 110uF @ 1800v... more than enough for the SRH's 240v primary supply (now). Stud mount is most commonly used in large busbar gangs, like what's found in traction inverters (on trains) and in other types of power systems. Probably find 'em in power supplies for broadcast transmitters (I originally bought my 333's cans for a quartet of 4CX250B's on 432mhz VSB video...
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