[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TCML] MOT Measurements

Hi Ted,
I agree that with filter caps or even stacked MOT's, the situation certainly changes and each circuit must be looked at. The situation in question was a single MOT and no filter cap added. That was the basic premise for why the measurements were performed due to a failure of the original transformer (not a MOT), but replaced with a MOT (and transformer resonance was hinted at but not known if this was the cause to the failure). If true, would the MOT suffer the same occurrence? Thus we measure and simulate a single MOT, 2 diodes, 2 caps at common ground with one side of the MOT output, and SISG switching circuit. In this case certainly no resonance issues, so that was at least removing that possibility.
Looking at the MOT as a transformer, by itself, is quite interesting. It is capable of some amazing power for it's size. As you begin DC filtering, you load the output, and as you impact the transformer impedance with the wrong or right C, you can really affect the current as it reacts with the MOT impedance, but filtering itself is impeded as you allow more current reaction to necessitate the needed current.
This is my first real look at a MOT from my own measurement perspective, so I am by no means an expert with this transformer. I have built a dual MOT ammo can supply some years ago, but never used it for a real coil (simply for a small flat secondary coil at the time) and no filter caps to deal with (and no measurements at the time to deal with either). It's been stuffed away in the corner of the garage ever since (under oil so probably good as gold).
Also, I'm uncertain how 50Hz 220V 1PH MOT's are designed in comparison to 60Hz 120V MOT's. Here in the US, we are back in the 1960's with voltages, and thus our appliances are so designed to accommodate. We at least have 60Hz going for us allowing for smaller necessary mass, but the 120V situation is the limiting factor here in the US. 

Happy 2009!
Bart




tesla wrote:

Hi Team

Couple of observations.
I agree in a standard AC design MOT resonance due impact of magnetic shunts generating leakage inductance is not an issue relating to resonating with the Tesla primary cap unless it is really really big. However in a DC system where MOT's are rectified and MOT's "see" filter capacitances or where secondary side capacitive ballasting is being incorporated all bets are off and the impact of the significant inductance needs to be considered (about 6Hy per MOT at operating currents and with primary side shorted which is equivalent cct when feed by mains). Worth noting in many stacked designs the MOT leakage inductances are all in series resulting in an even larger inductance thru which the equivalent voltage generator is required to "see" the load..
I've found it very difficult to get power out of a MOT (real grunt) unless they see a conjugate impedance (at least a moderatly capacitive load) and specifically designs requiring short pulses to charge the filter caps at the peak of the cycle have been unsuccessful for me. I interpret the situation as being one where getting short current pulses "thru" the leakage inductance simply results in the large reactance of that inductance limiting the charging current not to mention the high required currents thru the diodes and in and out of the filter caps)
The exception being the design (scopeboy et al) where the MOT is AC coupled to +ve and -ve peak clamps to generate 2 x pp which works well because those designs do provide a correct value capacitive component in the load seen by the MOT.
For those who may have interests I have looked quite closely at the impact on Secondary inductance in MOT's of DC in the winding for DC inductive charging use. (They saturate really quickly and must be gapped s if this is to be avoided and even then getting large L and high current capability is a real balance) 

Best
Ted in NZ

----- Original Message ----- From: "bartb" <bartb@xxxxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Wednesday, December 31, 2008 2:08 PM
Subject: [TCML] MOT Measurements



_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla


_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla