MOV curve...

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On Sun, 9 Aug 2020 17:10:16 -0400, M Philbrook
<jamie_ka1lpa@charter.net> wrote:

In article <8nq8if153h9ivuqtpeobrg2v3foir3ou4b@4ax.com>,
jlarkin@highland_atwork_technology.com says...

I always thought MOVs were sloppy, but they are actually pretty cool.

https://www.dropbox.com/s/9axwbhmmnd460n5/Littlefuse_V25S150P_EI.jpg?raw=1

We blew up a channel in our alternator simulator, probably some crazy
flyback voltage from the simulated load, so I\'m going to add an MOV
across each of the output phases. This one can absorb 22,000 amps and
300 joules.

390 volts max at 100 amps.

The low part of the curve looks very exponential. Someone once sold a
MOV type part as an analog computing element.

I work with big power at times and if that is truely an alternator
(Hardware rotor etc) Then you must be removing loads during critical
cycle times where as the regulator does not have a chance to redcuce the
field..

Alternators are current devices so removing the load abruptly is going
to produce some interesting results if the field was energized at some
higher levl.

I\'m working with/simulating permanent-magnet aircraft alternators. The
regulator is a diode-mosfet 3-phase bridge rectifier that shorts the
alternator windings to regulate the DC out.

Getting a lot of voltage across the alternator windings shouldn\'t
happen in normal use.

Our run of the mill generator had such issues with the way we were
using it. It would at times cause a little damage to Mov\'s, fuses for
small devices when a large load was removed.

The fix was to figure out the L of the generator output, I used a meter
for that and then put some AC caps of good amp service across the
output. Using Welding caps are good for this, they should be low ESR
types.

But the results are the caps will absorb the sudden fly back effects
which is really an effect of unloading the alternator abruptly.

It isn\'t the best but but its better than nothing.

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Tim Williams]

<jlarkin@highlandsniptechnology.com> wrote in message
news:3jp0jf9e93j11imqq1e50aptgc21kpk0bq@4ax.com...

I\'m working with/simulating permanent-magnet aircraft alternators. The
regulator is a diode-mosfet 3-phase bridge rectifier that shorts the
alternator windings to regulate the DC out.

Magnetos*.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[M Philbrook]

In article <3jp0jf9e93j11imqq1e50aptgc21kpk0bq@4ax.com>,
jlarkin@highlandsniptechnology.com says...

On Sun, 9 Aug 2020 17:10:16 -0400, M Philbrook
jamie_ka1lpa@charter.net> wrote:

In article <8nq8if153h9ivuqtpeobrg2v3foir3ou4b@4ax.com>,
jlarkin@highland_atwork_technology.com says...

I always thought MOVs were sloppy, but they are actually pretty cool.

https://www.dropbox.com/s/9axwbhmmnd460n5/Littlefuse_V25S150P_EI.jpg?raw=1

We blew up a channel in our alternator simulator, probably some crazy
flyback voltage from the simulated load, so I\'m going to add an MOV
across each of the output phases. This one can absorb 22,000 amps and
300 joules.

390 volts max at 100 amps.

The low part of the curve looks very exponential. Someone once sold a
MOV type part as an analog computing element.

I work with big power at times and if that is truely an alternator
(Hardware rotor etc) Then you must be removing loads during critical
cycle times where as the regulator does not have a chance to redcuce the
field..

Alternators are current devices so removing the load abruptly is going
to produce some interesting results if the field was energized at some
higher levl.

I\'m working with/simulating permanent-magnet aircraft alternators. The
regulator is a diode-mosfet 3-phase bridge rectifier that shorts the
alternator windings to regulate the DC out.

Getting a lot of voltage across the alternator windings shouldn\'t
happen in normal use.


Our run of the mill generator had such issues with the way we were
using it. It would at times cause a little damage to Mov\'s, fuses for
small devices when a large load was removed.

The fix was to figure out the L of the generator output, I used a meter
for that and then put some AC caps of good amp service across the
output. Using Welding caps are good for this, they should be low ESR
types.

But the results are the caps will absorb the sudden fly back effects
which is really an effect of unloading the alternator abruptly.

sounds like a poor system to me...

I guess it would be great if you were stuck in the middle of nowhere and
you needed some power, you could at least hand crank it or build a
Gilligan\'s Island genetor..

Putting that aside. The old magnetic amplifier design can work for that
where by you can bias the coils with small amounts of current to ramp up
the output.. In this case a 3 phase one..