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Re: [TCML] Mot Help needed
Hi Jim,
I'm no MOT expert, but you certainly need to get the MOT's phased
correctly. I personally would go about that simply measuring the output
across the two MOT's feeding a "low" voltage into the primary (low
enough that a typical AC meter is capable of measuring the output). When
phased correctly the voltage won't cancel. To change phase on the MOT's,
simply reverse the primary feed on one of the MOT's. Be careful with the
core. Because one end of the secondary is tied to the core, you can get
shocked or worse if the core isn't grounded.
Here's some ascii art that may help regarding secondary core connection.
The first art is a center grounded full wave rectification scheme. This
would actually be the safest and easiest as it requires no need to
remove the secondary winding from the core, however, if your are out to
double up on the secondary voltage, then you need to isolate the
secondary MOT to MOT connection or float the core. The second art is a
full wave rectification scheme with the core floating. This will allow
the MOT's to add.
Full wave rectification with the center tap grounded:
Output voltage is Vp/2:
(+Vac)
Neutral-----O*|| o--------(+)DIODE(-)----|
O || o |
O || o MOT-1 |
O || o |
|--O || o--| | Load
Hot--| |-GND(Core) |--(DC+)----/\/\/\/\----(DC-)--|
|--O || o--| | |
O || o | |
O || o MOT-2 | GND
O || o |
Neutral-----O*|| o--------(+)DIODE(-)----|
(-Vac)
Full wave rectification with with cores isolated (not tied to ground):
Output voltage is Vp:
(+Vac)
Neutral-----O*|| o------------(-)-----------------------------(+)
O || o D D
O || o I I
O || o MOT-1 O O
O || o D D
O || o E E
|--O || o--| (+) Load (-)
Hot--| | |--(DC-)----/\/\/\/\----(DC+)---|
|--O || o--| (+) (-)
O || o D D
O || o I I
O || o MOT-2 O O
O || o D D
O || o E E
Neutral-----O*|| o------------(-)-----------------------------(+)
(-Vac)
I'm not sure if it matters if the cores are floating or if you simply
disconnect the secondary connections from the core. One may be more
feasible than the other. I think I would simply try to isolate the cores
from the case if there's room so that the individual MOT's see their
normal stresses between core and winding.
Again, I'm no expert so others may want to double check my art and
comments. I'm under the assumption that your not going after a MOT
doubling scheme using caps, but simply using the MOT's themselves to
double up the voltage. I think you can get plenty of power with the
shunts installed. You might want to keep the shunts in for now and
remove them later if needed.
Take care,
Bart
Jim Mora wrote:
Hi MOT folks,
I have 2 MOTS ready to submerge in a ammo box of transformer oil. It crossed
my mind that I may have a phasing issue. Clearly, on the 120/240 feed side,,
the winding on the inside needs to go to the other outer winding to series
them for 240 volt op. I plan to do a FW bridge so I believe I have to
disconnect the grounds at the cores. Do I have to take the output of one and
tie it to the internal winding of the other as in the LV phasing? This will
be stressful for both windings but I can't seem to get my head around if I
can connect the two inner turns. In the least this would create a reverse
mutual inductance if not null output.. In the scenario of traditional series
both inner cores will see the full 2200v. I guess this is ok under oil?
Lastly I have been wondering if I should remove the shunts. I'll probably
need to split the cores to get them out. This may be worthwhile as I may be
able to get some transformer paper under the cores designed for oil. I'm new
to the MOTley crew;-)
Jim Mora
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