Man, all this MOT talk is making me want to build another MoFo.
Making me a little hungry too. 🙂
Making me a little hungry too. 🙂
What magnetic shunts? There is nothing removable with the MOTs - the steel plates are air-gapped and welded together with a thin bead on two of the edges.
No, but nothing immediately audible. If there is any, a simple orthogonal orientation like how two coils on a crossover are oriented should take care of that.
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No, can’t say I ever opened up a MOT with chisel, hammer and hacksaw. The design called for a circa 50mH to 67mH inductor with low DCR and > 4A capability so I think it fits the bill as is. I would not want to chance ruining the primary by hacking/hammering into it. We are only using the primary.
Interesting video though. The guy replaced the shunts when he wound the secondary. So they are not needed when only using the primary?
Interesting video though. The guy replaced the shunts when he wound the secondary. So they are not needed when only using the primary?
yes, he completely removed the shunts.....
the shunts were used to limit currents....
i would have wanted him to measure inductance with and without those shunts...
what makes me iffy with MOT's is the lack of air gaps, they are butted.....
other than that, i think they are fine...
primary wires on that MOT are like #16 so the low dcr.....
50 to 67mH air coils are possible..
there are online coil designers that can be used...Coil design and inductance calculator
the shunts were used to limit currents....
i would have wanted him to measure inductance with and without those shunts...
what makes me iffy with MOT's is the lack of air gaps, they are butted.....
other than that, i think they are fine...
primary wires on that MOT are like #16 so the low dcr.....
50 to 67mH air coils are possible..
there are online coil designers that can be used...Coil design and inductance calculator
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The steel E plates themselves have a very thin airgap (maybe 0.3 to 0.5mm). Probably used shim stock to set the gap, welded them and then removed the shims. The gap is right below the little weld bead.
at a current levels of upwards of 1A, the air gaps could be in the 1/8 inch or 3 mm, more with more currents, so that the actual gap is in the 1mm since there are three gaps..
i deal with MOT's a lot, but the one thing i disliked about them is the very high magnetizing currents, so i would not use them for more than 30 minutes at a time,
use them lots of hours and they will fry eggs, sunny side...
but for this MOFO project, they will be probably okey to use..
i deal with MOT's a lot, but the one thing i disliked about them is the very high magnetizing currents, so i would not use them for more than 30 minutes at a time,
use them lots of hours and they will fry eggs, sunny side...
but for this MOFO project, they will be probably okey to use..
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One reason for a MoFo to die is disconnecting the DC power supply at the amp. This causes the magnetic field in the coil to collapse and sends a kickback voltage through the zener and the mosfet, killing both of them. This can be solved by adding a 1,000uF cap at the DC input to the amp (prevents the rapid coil collapse), or switching the AC mains off rather than abruptly removing the DC power supply.
Some exploration of this is here: Build This MoFo!
Some exploration of this is here: Build This MoFo!
it was never a good practice to switch off dc manually in the first place...
plasma effects (a huge current dumping into an infinite resistance) reared its ugly head that way....don't do it...
plasma effects (a huge current dumping into an infinite resistance) reared its ugly head that way....don't do it...
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I’ve always had a cap multiplier feeding a CRC on mine. It must be the last C on the CRC (22,000uF) that keeps mine alive. Since it is powered with a SMPS, that’s the only way to turn it off - by shutting off the DC.
currents in the 120 or 240 volts line will always be smaller than the currents on the dc lines, so it made more sense to me to use a switch on the ac line and turn on/off from there there....beside it is a fire/safety requirement anyway...
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Funny thing is,
It will always fry the mosfet immediately when i try using big pure 10A transformer.
But normal behavior when using 3-5A transformer with same voltage.
I followed the schematic as is. 🙄
It will always fry the mosfet immediately when i try using big pure 10A transformer.
But normal behavior when using 3-5A transformer with same voltage.
I followed the schematic as is. 🙄
ok, this is very cheap but are you sure this have air-gap to support the DC current without saturation ?
Schematic? cap bank size/configuration, mosfet - IRF250? choke? just thinking of the current pulse...
my thoughts too, but the presence of magnetic shunts in the MOT prevents core saturation, it looked to me, that he did not bother to remove those, even the high voltage and the filament windings, the hv windings pose a huge hazard if not properly taken care of....so every one who wanted to use MOT's are properly warned...
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schematic same as MR pdf file.
mosfet IRF240
cap bank 2x 10mF
choke 12mH 0.2ohm
even when i try to put fuse from positive rail to the drain, it will blow the fuse and also break the mosfet in 1 second, with 10A transformer.
but that not happen with 3-5A transformer and singing well too.
do you have protective zener for gate ?
it is shown in parts list but not on schematic ...... and I believe it's put on pcb for that exact purpose
in short - zener from 7V5 to 15V , cathode to gate , anode to source , will prevent gate to fly too far from source and cause BigBadaBooom
it is shown in parts list but not on schematic ...... and I believe it's put on pcb for that exact purpose
in short - zener from 7V5 to 15V , cathode to gate , anode to source , will prevent gate to fly too far from source and cause BigBadaBooom