Long lead time on X1 Capasitors - Page 1
Forum section: electronics / projects

author: Bloch
author_rank: Unknown
timestamp: April 07, 2011, 01:32:43 pm
content: HiDo you know there i can buy 100nF X1 760vAC size is not important. Likehttp://www2.mouser.com/ProductDetail/Kemet/PHE845VD6100MR06L2/?qs=sGAEpiMZZMvQAn3cSZoTr5GrNz0LKpDovCUxxaM%252bXts%3dThe reason I ask here is that i nead them now and All the places i do know have lead times between 26 and 52 Weeks !!RegardsLars

author: deephaven
author_rank: Frequent Contributor
timestamp: April 07, 2011, 01:40:42 pm
content: Farnell has thesehttp://tinyurl.com/3up2n69

author: Bloch
author_rank: Unknown
timestamp: April 07, 2011, 01:48:56 pm
content: Quote from: deephaven on April 07, 2011, 01:40:42 pmThanksBut I do need a Rating of 760Volt AC.And i cant see that on the list you did give meRegardsLars

author: Zero999
author_rank: Super Contributor
timestamp: April 07, 2011, 05:45:32 pm
content: Can't you put two 400V capacitors in series?

author: Bloch
author_rank: Unknown
timestamp: April 08, 2011, 08:45:09 am
content: Quote from: Hero999 on April 07, 2011, 05:45:32 pmIt's not a perfect solution. But it seems to be the solution this time.I wonder why everyone's stock has gone to zero and firms are up to six months to do the next batch ?Regards,Lars

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2011, 04:02:30 pm
content: Just another thought, you probably want to use 440V capacitors. if you're going to put them in series, the tolerances could mean the voltages across one of them is >400V so go for 440V of more as an insurance policy.

author: Rufus
author_rank: Super Contributor
timestamp: April 08, 2011, 04:59:45 pm
content: Quote from: Bloch on April 07, 2011, 01:48:56 pmX? capacitors are very conservatively rated. Some manufacturers closer to what they can stand, others just call them 250vac for their intended application.Your 760v capacitors are tested at about 4.2kv dc, one of the capacitors in the Farnell list for exampleis rated at 275vac and tested at 3.4kv dc. So your 760v capacitor is rated at 2.7 times the voltage but only tested at 1.2 times.Depends on your application but you might be reading more into that 760v rating than is really there.

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2011, 05:24:02 pm
content: Yes, didn't think of that but I thought the whole point of X2 capacitors was that they're overrated?Check out Y1 capacitors which will be tested to 8kV yet rated for under 500VAC.

author: Bloch
author_rank: Unknown
timestamp: April 08, 2011, 06:46:57 pm
content: Quote from: Hero999 on April 08, 2011, 05:24:02 pmIt is hard to find the definition.But from herehttp://capakor.com/product/pdf/(21)General_technical_information.pdf?An X capacitor is used in Across-the-line applications?In this location,a failure of the capacitor will not cause anybody to electrical shock hazards and usually will open the fuse and turnthe equipment off.?Class Y capacitor is used in Line-by pass applications?In this location,a failure of the capacitor will cause anybody to electrical shock hazardX1 >2.5Kv,<4.0Kv High pulse:industrial printer,lighitng ballast or minicomputer which is connected to a 3-phase lineX2 <2.5Kv The most common class. General purose:Computer,hair dryer,FAX,hand power tool which are plugged into ordinary wall outlet.X3 <1.2Kv - General purposeY1 8.0Kv For bridging double or reinforced insulation.Y2 5.0Kv For bridging basic and supplementary insulation. Application:power supply used in data processing equipment.Y3 none For bridging basic and supplementary insulation.Y4 2.5Kv For bridging basic and supplementary insulationSo It is all about safety !.And there i use them I really dont want to experiment to much.The power lines to there they are connected are 20*8 mmand a voltage 690VRegards,Lars

author: Neilm
author_rank: Super Contributor
timestamp: April 08, 2011, 07:05:51 pm
content: Quote from: Bloch on April 08, 2011, 06:46:57 pmThey also have to be able to withstand any voltage surge they might get on the mains. Hence the reason they will quite often have many kV surge ratings.Neil

author: Wim_L
author_rank: Regular Contributor
timestamp: April 08, 2011, 07:50:05 pm
content: Quote from: Hero999 on April 07, 2011, 05:45:32 pmThis may or may not be safe. If the two capacitors are used near their maximum ratings and have different leakage, a charge imbalance can develop that far exceeds that of the ratio of capacitances of the two, and might exceed the rated maximum.

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2011, 08:27:52 pm
content: Quote from: Wim_L on April 08, 2011, 07:50:05 pmThat's why I followed up with a post recommending 440V capacitors which should be overrated enough to avoid that problem.

author: Unknown
author_rank: Unknown
timestamp: April 08, 2011, 08:52:19 pm
content: Depends on the tolerance of the capacitors, if they're +/- 20%, worst case is 60% of the voltage across the one with the highest value (assuming the reactive impedance is more significant than the leakage), or about 460VAC at 760VAC. This is without accounting for tempco or aging. I think playing these kinds of games with safety-critical components is a bad idea, you're not allowed to just use any old capacitor for a reason. If one of the X1 capacitors shorts, the other will be subjected to the full voltage until the shorted one heals (or melts/blows).If I had to do a bodge job, I would use three capacitors in series to get some extra safety. Note that capacitance decreases if you put capacitors in series.

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2011, 09:13:20 pm
content: X capacitors aren't so critical as they only bridge live and neutral they only have to have functional insulation so no one will be electrocuted if they fail.The most important thing is they're flame retardant and self healing (unlikely to fail short circuit), as far as I can tell the impulse ratings are as much about reliability as anything else.440V should be fine if the capacitors are 10% tolerance, use 470V for 20% tolerance. It's very unlikely one capacitor will be as bad as 10% under tolerance and the othy 10% over and if they're both installed at the same time, they should age at roughly the same rate sand therefore degradation should be similar too.

author: RayJones
author_rank: Frequent Contributor
timestamp: April 08, 2011, 11:53:52 pm
content: Is there any problem in using a few hundred K in parallel with the caps for the express purpose of load balancing?That's what we were taught way back.

author: PetrosA
author_rank: Frequent Contributor
timestamp: April 09, 2011, 02:52:03 am
content: I recently read an article about long lead times for lighting fixtures here in the US. Evidently it's mostly the specialty high efficiency stuff with electronic transformers/ballasts required by new laws in commercial/industrial settings that are affected and the problem is bad. Contractors are bidding jobs and can't get the fixtures in time to meet the deadline. Supposedly the problem is that a large number of small electronic component manufacturers went out of business during the peak of the economic crisis and the big players slowed down production to the point where now they can't keep up. Some suppliers claim the lead time is better than it was - down from 8-12 weeks to 6-8 weeks, but still way too long for bid projects.I don't know if you'll be able to read this without being logged in, but here's the article:http://ecmweb.com/lighting/ballast-shortage-20110201/

author: Bloch
author_rank: Unknown
timestamp: April 09, 2011, 03:22:34 am
content: Quote from: PetrosA on April 09, 2011, 02:52:03 amThank you for the link.First economic going to fast then slow and now faster again.Why is that my problem

author: Zero999
author_rank: Super Contributor
timestamp: April 09, 2011, 08:05:32 am
content: Quote from: RayJones on April 08, 2011, 11:53:52 pmThat works better with DC than AC. For DC, the divider just needs to draw a bit more current than the leakage through the capacitors so very high value resistors will do. With AC, the resistors still need to have a lower impedance than the capacitors but it's much lower with AC flowing through them. In this case 220nF capacitors (required for just over 100nF when connected in series) have an impedance of 14.5k at 50Hz so resistors with and lower value would dissipate too much power.

author: Unknown
author_rank: Unknown
timestamp: April 09, 2011, 12:01:59 pm
content: You'll also have to make sure that your resistors are specified for the working voltage and transient voltage, and will fail safely.