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Registered Member #1054
Joined: Wed Oct 10 2007, 10:51PM
Location: Bulgaria
Posts: 29
Hello guys, Today I obtained a big MOT (2300V/1500W), but I figured out that my MOCs are rated for 2100V (except for one) :( The question is can I run them at 2300V or they won't withstand it?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
MOCs have a lot in hand. You can't field components by the millions and keep happy customers without them being conservatively rated (the components that is, not the customers). The difference between 2100 and 2300 is sufficiently small you should be OK. Unless you are returning a repaired MO back to your rich in-laws with a claim that it will work for ever.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Microwave oven capacitors are tested under much harder conditions than what they are running at. I got a example datasheet snippet here:
A typical data sheet for a common microwave oven capacitor is as follow. Technical Specifications Values Capacitance 0.8 ~ 1.2 uF. +/-3% Rated Voltage 2,100 VAC Frequency 50/60 Hz. Dissipation Factor 0.0035 maximum Operating Temperature =â€-10 ~ +85 C.†Insulation Resistance : T- C 1,000 MOhms Test Voltage: T – T T – T: 9,030 VDC for 60 seconds Test Voltage: T – C T – C: 9000 VAC 10seconds
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
I had started the construction of a high voltage / high current supply using a MOT. First thing I did was test the MOT under NO load--after a while it got HOT--to HOT. I had more...same test (MOT just sitting there) same thing happened. I haven't trusted them since (for any long term use) I try to go with the NST: more voltage, less current, way less amps, more safe, great with a variac. ...my 2 cents...
Registered Member #39190
Joined: Sat Oct 26 2013, 09:15AM
Location: Boise National Forest
Posts: 65
The problem with most modern MOTs is that they were designed and built in a climate of tremendous price competitiveness and very slim margins. So, for example, the transformer laminations are thick, they aren't grain-oriented, they're welded (can you say eddy current?!), and they're operating right up against the material's saturation limit. Reduce your operating voltage even by ten volts and they will idle cooler. But you can't make a silk purse out of a sow's ear. These transformers were clearly a compromise, intended for both low duty cycle operation and forced convection.
OTOH, some of the older name-brand units, that sold for hundreds of dollars originally, have great transformers. That may be the place to start.
Personally, I hate NSTs because of their intentional flux leakage (to limit secondary current). Great for neon tubes. :) Lousy for my uses. :(
Registered Member #1054
Joined: Wed Oct 10 2007, 10:51PM
Location: Bulgaria
Posts: 29
Thanks for the answers! I'll test them out then :)
@Dr. Slack, It's for the power supply of my GU-81M VTTC :) Currently it produces 45cm to ground sparks (with smaller MOT), but I think there's a room for more tuning.
@Signification, Yes, the MOTs can get really hot especially if they're rewound for different purposes. I think the best decision is to put some ballast in series with the primary. I'm using a 400W inductive ballast (from a neon lamp starter) for my rewound MOT (12,6V/10A for the tube's fillament) and it gets barely warm within few minutes.
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Question about MOT/MOCs
