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201.51.142.180
Would a polypropilene motor run capacitor of 250Vac (Epcos B32320) work in a PSU of 360Vdc?
thanks
Follow Ups:
Peter,100-330VAC can be operated at 450VDC
330-400VAC can be operated at 600VDC
401-440VAC can be operated at 750VDC.Now under no circumstances can the steady state current exceed 15Amps, due
to the nature of the internal connections.Best Regards,
Stacey G. Bauer
Director AC Engineering
ASC Capacitors
301 W. O Street
Ogallala, NE 69153
(308)284-3611
fax (308)284-2708
Hi.330VACx1.4142=466.6VDC
400Vx1.4142=565VDC
These two calculated figures go inline with what ASC quoted (+/-5% tolerance).But 440Vx1.4142=622.248V or 653VDC including the +5% tolerance.
Much below the quoted figure.But anyway, it better plays safe than regrets.
As I said, caps tend to shorten their service lifespan bigtime on overrated operation. It may work OK today, but who knows what would happen in long run?
...much better to use a manufacturer's specification.Rating a cap for AC motor usage is a lot more complex than just a simple RMS-to-peak calculation. A motor run cap is not used across the line; it is in series with a motor winding to cause phase shift. You have to consider transients, overloads, motor inductance and back EMF, etc., etc.
That's why I asked ASC in the first place.
These ratings may or may not apply to manufacturers other than ASC, but I would expect similar responses.
Unlike electrolytics, film caps don't have a very strong correlation between vapplied voltage and lifetime.
Hi.such figures were taken from someone's mouth? You gave the impression that someone just gave you some numbers out of his head.
If all those figures you quoted were manufacturers' printed specs, then we got to abide. No question about it.
I agree one caps differ from make to make even using same dielectric materials.
c-J
PS: One time I called up the application manager of a major schottky diode maker on basic specs, & I was not impressed at all with his answer.
I find it interesting that you should miss the person who sent the mail...Stacey G. Bauer
Director AC Engineering
ASC Capacitors
301 W. O Street
Ogallala, NE 69153
(308)284-3611
fax (308)284-2708That's just about as official as it gets, and should probably preclude any further debate about voltage tolerances.
...running on them, not just HALF the waveform that's used to calc the RMS value? So a 250VAC MR cap sees, continuously, 250VACRMS times 1.4 to get it to the zero-to-peak half of the P-to-P waveform and then times 2 to get it the entire AC waveform the cap's exposed to. That's c. SEVEN-HUNDRED Volts that must be contained by the layers of film.I've seen many MR caps with both AC and DC ratings that have DC ratings FAR in excess of 1.4 times the DC number; sorry I wasn't keeping notes or I could send you to some.
I have a pair of 805-based SETs using ASC-brand 440VAC MR caps on a 920VDC rail that's SS rectified and surges to some 950VDC - 970VDC on turnon; they've run for a couple years just finely.
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
IF and only if you KNOW that the AC rating is RMS, yes, then you can use 2.8 as the multiplier. Seems I found out some AC-rated caps are rated with peak AC Voltage.I guess if you want to be conservative, use 1.4.
But I'm not removing those 440VAC MRs from those 805 SETs. :-)
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
I agree with you.
I think AC capacitors are very robust capacitors.
I imagine a capacitor capable of running 250Vac with high currents will see 360Vdc or even 450Vdc as a easy job.
Who else agree with this?
...that the multiplier is 2.82, not 1.41.
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
Hi.So how many hours you ACTUALLY switched on your amp in these "couple years" ?
...my 1.4- v. 2.8-multiplier question, or are you just trying to be a smartass?
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
Though the DC equivalent rating is close (1.4 x 250) don't forget the full AC current rating is massively beyond what this cap will experience in your application. Motor run applications are also designed for harsh environments and undoubtedly have very large safety factors regarding spikes, pulses, etc. to meet UL requirements. I would have no hesitation.
Thermionically addicted.
Hi.Mathematically, 250VAC should be OK for 250x1.41421=353.55VDC.
But it can be risky unless you make it damn sure the tube heaters are all heated up well before you switch on the HV to avoid damaging surges. Is it a CLC or LCLC PS?
CLC.
rectifiers, 20uF electrolyte, 6H, 50uF motor run.
Hi.But ...for CLC where the cap charges up a surge well exceeding the theoretical DC voltage for the cap in question, I would suggest you to replace it with a higher rated DC voltage cap for long safe operation. Or serie up another cap of double the capacitance to boost up the DC safety margin.
only half the capacitance, . but twice the voltage rating . You may need to strap a couple of high value resistors across the caps for safety. Look at the example in Morgan Jones' book, if you have it.
Hi.Besides, any caps working on max. load will shorten their life span.
The motor-run oil cans I've been using got stipulation on the can body the estimated service hours on operating specified voltages.
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