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Old 11-29-2017, 08:01 PM   #1
TechGeek
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Question Good motor capacitors for an MOT?

Hello. I'm looking to build a resonant MOT bank, and I'm looking for capacitors for the MOTs. I don't really know where I should look for capacitors for this task (besides Digikey, Mouser, etc) or what brands I should look for and stay away from. I'm pretty sure the 2 sites I listed (and probably a few more) will be good places to look.

Also, what should I get in terms of capacitance and voltage rating? I assume that voltage should be in the 300-400VAC mark, but have no clue about capacitance.

If you could answer these questions for me, that would be great! Thanks!



EDIT 1: I'm planning on building 10 MOTs into the bank. How many capacitors would I need? Also, will I need to ballast the bank? (I assume yes.) If so, what should I use to ballast them?
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Old 11-29-2017, 10:41 PM   #2
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Default Re: Good motor capacitors for an MOT?

Are you trying to build something like this?
https://www.youtube.com/watch?v=3r8ZP4XOkYI
http://4hv.org/e107_plugins/forum/fo...opic.php?38015
http://stevencaton.com/Resonant%20MOT%20Bank.html

The caps will not be 400V caps for sure.
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Last edited by budm; 11-29-2017 at 10:46 PM..
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Old 11-30-2017, 05:05 AM   #3
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Default Re: Good motor capacitors for an MOT?

Something like that, but scaled up to 10 MOTs.
Why? For destruction purposes. My plan is to have the high-voltage secondaries wired in series for a total output voltage of somewhere around 25kV with enough current to annihilate anything I connect to the output terminals.

I also assume that this will eat loads of current from the wall.

What voltage of caps do I want to look for?
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Old 11-30-2017, 10:00 AM   #4
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Default Re: Good motor capacitors for an MOT?

^ Well, let's run those numbers shall we? 12 MOTs are around 25kv. Ive noticed MOTs idle around 6 amps. 12*6=72. 72 amps. Keep in mind the common US household power feed is 100 amps.

Now under a transient short (i have tested this) MOTs will pull around 27 amps. A Bolted short will pull closer to 25 amps. we will use bolted numbers. 12*25=300 amps.

You could do 200 amps using both phases of a 100 amps service, so let's do that real quick. 200/25=8 8*2=16.

So, ignoring the standard safety margins of 95% rated load, you are looking at 16kv. You will need High Voltage Doorknob Caps for this. And lots of them since they are <uF.


Now for safe margin numbers.

(100*.95)*2=190, 190/25=7 7*2=14. 14kv is all you will get if done safely and realistically.


Now, lets assume you live in the big shitty, in some new HOA. You have a 200 amp feeder.
(200*.95)*2=380
380/25=15
15*2=30

30kv is what you can get.

Or, like me, you are out in the sticks, in a state that still runs on coal.

(50*.95)*2=95. 95 amps. 95/25=3.8 Im rounding this to 4 for sanity sake. 4*2=8. 8Kv is what you (i) can get.


Now, this is all assuming you take your whole home home offline to do this, Which is very, very impractical. Also keep in mind i do round. Usually down to account for losses, and these numbers are destructive to the MOTs which are rated at 15 amps under normal operation. You need to ballast them to keep them from destroying themselves. 1.5Kw incandescent bulbs are my choice, but a submersion heater at 1.5kw is just as well.


EDIT: OK. So you want limited power? Easy. You won't get the full output voltage under short, but here we go. 10*15=150. You will draw 150 amps. Still need to take the house offline. 10*2=20 20Kv. 1500/2000=0.75.

20Kv OR 750mA. output.

For output capacitance... In the article budm linked to with the 4 MOCs in series-parallel, the capacitance is the same as one MOC. 1uF being a good round number. 1 25kv 1uF cap will do. otherwise, MOCs are ususaly rated for 2.2Kv. 10 MOCs in series will do, but it will only have 1/10th the capacitance. It will be a 0.1uF 22kv cap bank at this point, so you may want 10 of them in parallel. Or go with the 0.1uF bank. Its a nice number...
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Last edited by goontron; 11-30-2017 at 10:42 AM..
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Old 11-30-2017, 12:45 PM   #5
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Default Re: Good motor capacitors for an MOT?

Is someone going for a Darwin ?
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Old 11-30-2017, 01:30 PM   #6
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Default Re: Good motor capacitors for an MOT?

^ And inefficacy.....
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Old 12-15-2017, 05:21 PM   #7
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Default Re: Good motor capacitors for an MOT?

Quote:
Originally Posted by TechGeek View Post
Something like that, but scaled up to 10 MOTs.
Why? For destruction purposes. My plan is to have the high-voltage secondaries wired in series for a total output voltage of somewhere around 25kV with enough current to annihilate anything I connect to the output terminals.
Just get a 10kVA or similar size distribution transformer (or two!). Much easier, plus those can handle a larger amount of power. MOTs will overheat easily if you don't ballast them.

Also keep in mind that one end of the MOT HV winding is often connected to the core of the transformer, so if you place them on something like wood, you will possibly end up with unexpected arcing.

Quote:
Originally Posted by goontron View Post
Ive noticed MOTs idle around 6 amps.
You sure that is correct? It seems more like that would be apparent power rather than true power, given that MOTs are [obviously] inductive. Then again, I do know that they tend to run at a high-ish flux density. (Making it less efficient electrically, but the manufacturing cost is lower because it is physically smaller for the same power output, and this is okay because the transformer is only used intermittently and with fan cooling.)

Quote:
Originally Posted by goontron View Post
So, ignoring the standard safety margins of 95% rated load, you are looking at 16kv. You will need High Voltage Doorknob Caps for this. And lots of them since they are <uF.
Another option would be to get your hands on a large oil-filled capacitor as are used in electrical distribution. You can get large ones that are like 10uF and rated for more than 34.5kV. (Which is a somewhat common distribution line voltage used here in the USA.)
(Note that they are used for PFC, and often are rated in kVAR rather than microfarads.)

-Ben
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