Microwave oven high voltage 2.1KV AC capacitor - Page 1
Forum section: electronics / projects

author: paulc
author_rank: Contributor
timestamp: April 10, 2015, 03:12:39 pm
content: Does anyone have experience or knowledge about how much DC voltage they can handle CONTINUOUSLY ?Paul

author: German_EE
author_rank: Super Contributor
timestamp: April 10, 2015, 03:37:35 pm
content: 2,1KV DC would be a safe assumption as 2,1KV AC is nearly 6KV Peak to Peak.

author: paulc
author_rank: Contributor
timestamp: April 10, 2015, 04:04:18 pm
content: Sorry, this does not answer my question.I don't care about the P-P voltage, just need to know DC capability of the capacitor.

author: DanielS
author_rank: Frequent Contributor
timestamp: April 10, 2015, 05:30:58 pm
content: The peak of sinusoidal AC voltage is 1.41X the AC rating, so a 2.1kV AC capacitor should be good for about 3kV DC since it has to safely withstand the repetitive 3kV AC peaks plus whatever surges on top of that.So 3kV should be a reasonable upper limit. Whatever you do though, you probably want the capacitor contained within some sort of enclosure during use in case it explodes.

author: SeanB
author_rank: Super Contributor
timestamp: April 10, 2015, 05:52:53 pm
content: Just remember with using it for DC is that there is a large value discharge resistor inside the housing to discharge the capacitor in the oven. This may arc over at too high a voltage, and will always draw a current to discharge the capacitor. 33M is a typical value I have seen on capacitors I have opened to see why they failed. They often had large sections of the metallised foil missing inside on both electrodes. Just note the palm oil used is very smelly when they die, plus it is incredibly sticky.

author: paulc
author_rank: Contributor
timestamp: April 10, 2015, 08:11:11 pm
content: Didn't knew palm oil is used as the dielectric.It used to be some mineral oil, not so?Is it something new?

author: SeanB
author_rank: Super Contributor
timestamp: April 10, 2015, 08:21:13 pm
content: Higher dielectric constant than mineral oil, and when pure higher flashover voltage. No mixed chains in it either, so it is constant from batch to batch. not edible, but refined from palm kernel oil in a chemical factory.Many modern oils in sealed systems are no longer mineral oil, but either a plant oil or a synthetic organic salt based lubricant. Your car AC uses a organic salt PAG oil as lubricant, as it is miscible in the refrigerant more than a napthitic mineral oil, and aside from it turning into acid if exposed to moisture it works well. Drawback as well is it is slightly conductive, so in modern aircon it is replaced with POE oils, which are good insulators.

author: paulc
author_rank: Contributor
timestamp: April 10, 2015, 08:42:20 pm
content: WOW!!!Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 11, 2015, 08:05:40 am
content: Strange, I wouldn't think fatty acids would be anywhere near desirable, in or around anything electric (or most things mechanical, give or take of course).* T3sl4co1l files this away in the "possible but dubious" memory bankTim

author: Zero999
author_rank: Super Contributor
timestamp: April 11, 2015, 01:15:26 pm
content: I've done a bit of Googling. A variety of liquids are used for liquid dielectric capacitors, including other vegetable oils such rapeseed and caster oil so possible palm oil is used in some capacitors but not necessarily all liquid dielectric capacitors.http://my.execpc.com/~endlr/oil_filled.html

author: johansen
author_rank: Super Contributor
timestamp: April 11, 2015, 05:04:13 pm
content: I have seen "epoxidized soybean oil" on a number of pad mount 100-500KVA transformers