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Registered Member #5208
Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86
Hi, I was wondering if I could use a MOT PSU (currently 22 turns of 18AWG wire,230V) as a ballast for another MOT with secondary intact. If yes, how to do it?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The best way to use a MOT as a ballast is to grind off the weld on the core, remove the I-part and reassemble with an air gap. Leave the secondary winding disconnected.
Registered Member #5208
Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86
Thanks for reply Dr.DarkCurrent. I don't have the suitable tools to grind off the weld, I barely removed the secondary, these things are quite tough (are you Jmartis2?). I used a heating "coil" from a kettle, it works but it get's really hot. BTW, if I get it right, the kettle was rated at 2kW, so, 2kW/2100V=2100V@95mA, right? EDIT: Merry Christmas everyone!
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
zippotix wrote ...
Thanks for reply Dr.DarkCurrent. I don't have the suitable tools to grind off the weld, I barely removed the secondary, these things are quite tough (are you Jmartis2?). I used a heating "coil" from a kettle, it works but it get's really hot. BTW, if I get it right, the kettle was rated at 2kW, so, 2kW/2100V=2100V@95mA, right? EDIT: Merry Christmas everyone!
The kettle coil gets hot becuase its designed to be run underwater
You are on the right track with the wattage, however the actual power to the MOT may be slightly lower due to other looses.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You can break the welds on a MOT core with a hacksaw.
When using a MOT as a ballast I like to remove the secondary completely. It can be replaced with a primary from another MOT to get more inductance options.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Steve Conner wrote ... You can break the welds on a MOT core with a hacksaw.
Yup, I've done that and it took only a minute or two. The thin kerf lets you retain some weld bead on each stack of laminations, so they don't fall apart.
If your objective is just to separate the copper from steel, a hammer and chisel can break the welds in a few seconds.
Registered Member #4081
Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139
I think 2100VAC is the open circuit voltage, it drops down under load because of something called secondary impedance (it's a bit like internal resistance in batteries). Assume it puts out 1000mA, so with a 2kW power out we get 2kV. Realistically it will be less as MOT's have very poor efficiency (~60%). Also with a 2kW ballast you have to take into account the power draw of the MOT (say 3kW?) as it has it's own impedance.
Registered Member #5208
Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86
Yeah, I know this transformer is lossy and generally crap :). I will try to hack through the welds. Dr.DC, you helped me with the halogen flyback driver, remember :D? But do you mean 950mA output even with 2kW ballast? That would suck, I was hoping it would be somewhat safer to mess around with. I'm seriously careful with MOTs, even the noise it gives is malevolent.
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Quick MOT question.
