Removing impedance protection from MOEPED #3

[DGoncz 22044-0394]

MOEPED #3 is mechanically stable and more than half of the onboard 110 VAC
systems are on line.

MOEPED stands for MObile Experimental Physics Educational Demonstrator. It's
my project for one repeated credit at the community college Seminar and
Project in physics, PHY 298, with Dr. Majewski. It is a 2004 Lightning Cycle
Dynamics (www.lightningbikes.com) Thunderbolt recumbent, their base 7-speed
model, with several transmission changes.

First, there is the tandem crankset. Providing a 51 tooth cog on the left
side lets me drive a modified Surplus Center (www.surpluscenter.com) 10-1134
"impedance protected" (stall proof) ceiling fan motor with bike chain at
about its design rpm, or drive the pedals from the motor. Driving the pedals
from the motor helps debug the wide-range 24-35-51 / 11-34 gearing. Driving
the motor from the pedals should produce AC when patched correctly but it
doesn't and that is what this post is about. Pics are at
ftp://users.aol.com/DGoncz/Bicycle/ACMotorGenerator/

Second, the rear hub has been replaced and relaced with an 8 speed disc hub,
7 cogs, a spacer, and a Big Cheese spider to carry chain rings on the left
side. A 48 tooth cog drives an Ametek servo motor from C&H sales
(www.candhsales.com) rated 30 VDC, 12 A stall, 900 rpm, which drives a Radio
Shack inverter (www.radioshack.com) rated 140 W, 10-15 VDC, 2.4 W idle. The
pinion is 8 teeth, comes from Northern Hydraulic, who I think are at
(www.northerntool.com) and has been thinned to 2 mm and chamfered. The motor
mount is made from plastic drain pipe, hangs from the seat stay clamps, and
is tensioned from the seat brace. An aluminum motor mount is in the works.

The bike has been fitted with an ESGE dual leg kick stand, *backwards*.
Lighning has accepted this recommendation for their customer tip file. I
have not seen it in print. The bike stands on its own, and a bit of wood
underneath with two pocket holes captures the legs when you want to pedal
and prevents spreading of the kickstand legs. Two extra long spokes will soo
n be fitted to the stand legs to snag the chain stays with the spoke heads,
and wing nuts will tighten the spokes to lock the stand, allowing seated
pedaling. It will take five minutes to set up once parked.

To proof the power generating ability of the system I plugged the motor into
the inverter and went for a ride. As expected, it was a dynamic brake, but
nothing blew up. The system could generate say 20 watts all night long while
riding and you'd hardly notice it. I've run a fluorescent lamp from the
inverter. I could run my laptop from it but I don't have a padded case yet.

My question to the readers of alt.engineering.electrical,
rec.crafts.metalworking, sci.electronics.design, and sci.electronics.repair
is:

Given this is an impedance protected ceiling fan motor with many turns of
fine wire, and I have invested four years of effort, and the system is
stable, is it now time to rewind the stator with fewer turns of thicker wire
to optimize generator function, as it is not likely that this motor will
ever be stalled, or should I continue to try various cap combinations,
driving the AC motor/generator from the DC motor in reverse, or should I run
a sweep to find out what is going on and *compute* an optimized cap? I'm
leaning toward rewinding the stator. It seems like an idiot proof motor
would make a lousy generator.

The motor run cap is currently 5 microfarads. The self-excitation cap is
currently 30 microfarads. Currently the motor runs right as a motor, but
only generates 0.1 VAC at best speed when patched as a generator, even when
I "whack" it with DC while cranking as described in Lindsay's "Alternator
Secrets". I suspect there's just too many turns of wire in there. I have an
audio amp and can download Daqarta again for a sweep. I have a Tek 541 scope
with CA plug in. Soon all these and the bike will be under one roof.

Yours,

Doug Goncz
Replikon Research
Seven Corners, VA 22044-0394

 

[Dimitrios Tzortzakakis]

There are not too many turns in it, in reality (despite theory) an
asynchronous motor cannot be a generator.Sorry to be the messenger of bad
news, but that's it.That's a reason why (I think so) wind-generators coupled
to the grid in fact work as motors, dissipating power than producing it as
generators.To produce ac, you need a *synchronous generator*, found
everywhere from small heads (650 W) to the largest one, 2000 MVA, operated
in a nuclear power station.Or, a dc *generator* (not motor).Either with
shunt, series or compound excitation.Usually it's shunt.

 

[klasspappa[remove]]

Asynchronous motor CAN be a generator...
It must turn faster than the magnetic field and you may apply some power
to it, then it will transfer power back to source...

 

[daestrom]

There are not too many turns in it, in reality (despite theory) an
asynchronous motor cannot be a generator.Sorry to be the messenger of bad
news, but that's it.That's a reason why (I think so) wind-generators
coupled
to the grid in fact work as motors, dissipating power than producing it as
generators.To produce ac, you need a *synchronous generator*, found
everywhere from small heads (650 W) to the largest one, 2000 MVA, operated
in a nuclear power station.Or, a dc *generator* (not motor).Either with
shunt, series or compound excitation.Usually it's shunt.

Sorry, but you are wrong. Asynchronous induction motors can be used as
generators. They have to be driven at a speed higher than the synchronous
speed. The winding must be excited from an external source of reactive
current (the utility line or capacitor bank will do). They are much harder
to regulate/control than synchronous when in an isolated 'island'. But when
connected to a grid they can work quite well.

And a DC motor can often be used as a DC generator as well. In fact, many
large un-interruptible power systems use DC machines that act as generators
to charge/float station batteries normally, yet can instantly change roles
to act as motors to drive the AC generator from the batter when the normal
power is lost.

daestrom

 

[Dimitrios Tzortzakakis]

--
Tzortzakakis Dimitriïs
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

message Sorry, but you are wrong. Asynchronous induction motors can be used as
generators. They have to be driven at a speed higher than the synchronous
speed. The winding must be excited from an external source of reactive
current (the utility line or capacitor bank will do). They are much harder
to regulate/control than synchronous when in an isolated 'island'. But when
connected to a grid they can work quite well.

That's what the theory says anyway.But here we have many problems from these
"wind generators" coupled to the grid;lights "flickering";grid
instability;many power outages.

And a DC motor can often be used as a DC generator as well. In fact, many
large un-interruptible power systems use DC machines that act as generators
to charge/float station batteries normally, yet can instantly change roles
to act as motors to drive the AC generator from the batter when the normal
power is lost.

Yes, of course but they don't have such great efficiency when working on the
opposite role.A generator has the best efficiency when used as a generator,
and a motor when used as a motor.

 

[Dimitrios Tzortzakakis]

--
Tzortzakakis Dimitri?s
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

Asynchronous motor CAN be a generator...
It must turn faster than the magnetic field and you may apply some power
to it, then it will transfer power back to source...

I just run through the book of electrical machines I, one of my old
subjects, and it doesn't mention asynchronous generators at all.It only
mentions alternators.If one generator needs applying power to it to generate
electricity, it loses the purpose of being a generator.The proof of this is
our friend's experience;in his post he mentions the asynchronous motor when
operated as a generator has an output of only 0.1 V RMS, which is useless
for any purpose at all.In no lab have we had a project of converting a motor
to a generator;always in motors and generators the apparatus was
separate.Talking about asynchronous generators.

 

[daestrom]

--
Tzortzakakis Dimitriïs
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr

That's what the theory says anyway.But here we have many problems from
these
"wind generators" coupled to the grid;lights "flickering";grid
instability;many power outages.

Grid instability and 'flickering' is not inherent to a particular machines
design. It is more a case of poorly designed grid. When adding any new
generation to a grid, proper studies must be done on its impact to the
existing grid. You don't just 'slap' another generator onto a grid if it's
output is any appreciable percentage of the local load/existing-generation.
Regardless of its internal design or prime mover.

You could add a steam turbine synchronous generator of similar size onto
that sort of grid and still have instability, 'flickering' and many power
outages. Adjust the governor or line-compensation incorrectly and it will
drag the local grid all over the place causing all sorts of problem.

Yes, of course but they don't have such great efficiency when working on
the
opposite role.A generator has the best efficiency when used as a
generator,
and a motor when used as a motor.

Nonsense. A properly designed machine will work equally well in either
mode. Have seen many large (300 - 500 kw) machines used for just this sort
of thing.

daestrom

 

[daestrom]

--
Tzortzakakis Dimitri?s
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "klasspappa[remove]" <"klasspappa[remove]"@hotmail.com> ?????? ???
??????

Asynchronous motor CAN be a generator...
It must turn faster than the magnetic field and you may apply some power
to it, then it will transfer power back to source...

I just run through the book of electrical machines I, one of my old
subjects, and it doesn't mention asynchronous generators at all.It only
mentions alternators.If one generator needs applying power to it to
generate
electricity, it loses the purpose of being a generator.

Then you need to find another book. An asyncrhonous generator needs an
external source for reactive power / excitation. That is not the same as
'applying power to it to generate'. When properly excited, an asyncrhonous
generator can supply much more power to the electrical system than it draws
in excitation energy. Much like a large synchronous machine needs an
external supply to its field to operate, yet it results in a net input of
power to the electrical system.

The proof of this is
our friend's experience;in his post he mentions the asynchronous motor
when
operated as a generator has an output of only 0.1 V RMS, which is useless
for any purpose at all.

Because 'our friend' didn't supply an external excitation. A synchronous
machine with an electromagnet field (not permanent magnets) also outputs
very low voltage when spinning with no DC field current. Are you suggesting
that synchronous machines are 'useless for any purpose at all'? Of course
not. Yet you suggest that an *improperly operated* asyncrhonous machine is
proof that all such machines are 'useless'.

In no lab have we had a project of converting a motor
to a generator;always in motors and generators the apparatus was
separate.Talking about asynchronous generators.

Possibly because your lab just didn't bother to explore this area. An
async. generator operating in a stand-alone fashion has many drawbacks. The
voltage control is difficult unless you have either a wound-rotor machine
and control the rotor circuit resistance, or variable capacitance connected
to the line terminals.

Because of the torque/slip characteristics of induction machines, the output
frequency is also very difficult to control. If the prime mover speed is
held constant, the output frequency varies with the amount of real load and
the amount of slip (remember in an async. generator, the output frequence is
lower than rotor speed. To maintain the output frequency in a stand-alone
machine, you must increase the rotor speed as load is applied.

But, if the machine is connected to a 'stiff' grid that approaches the
theoretical 'infinite bus', then many of these issues fade. The bus
maintains a constant frequency and voltage and the real power output of the
machine is controlled by controlling the speed of the prime mover. As speed
is increased above the synchronous speed of the machine, more power is
supplied to the bus.

Work out how the torque and power vs speed curves of an induction motor
behave and simply extrapolate beyond the synch. speed.

daestrom

 

[Active8]

On Tue, 21 Dec 2004 16:25:34 +0200, "Dimitrios Tzortzakakis"

You know, posting that hyphen at the beginning of your post causes
everything below it to be *not quoted* in replies as if it were a
signature block.

What didn't get quoted:
*********
I just run through the book of electrical machines I, one of my old
subjects, and it doesn't mention asynchronous generators at all.It
only
mentions alternators.If one generator needs applying power to it to
generate
electricity, it loses the purpose of being a generator.
*********

Now think about that. I don't care if it's a "generator" or
"alternator". My alternator uses 12 V from the battery to suply
field magnetization.

The alternator puts out more electrical power than it consumes. Gee,
I wonder if that extra energy comes from the mechanical energy
driving it.


-
Best Regards,
Mike

 

[Joel Kolstad]

If one generator needs applying power to it to generate
electricity, it loses the purpose of being a generator.

Hardly; you can make a pretty good case that the most efficient generators
often DO require some external power for the sake of field excitation,
monitoring/control equipment, etc. This initially comes from a bank of
batteries, a smaller 'starter' generator where you don't care about
efficiency since it'll only be used briefly, etc.

I was talking to a guy here in Oregon whose job is to maintain and monitor a
small (a half dozen or so MW, I believe) hydroelectric power plant; one of
the points he took pride in was that at _his_ plant he still had enough
equipment around that he could get the plant going without any external
power whatsoever. He said that many plants have been 'modernized' such that
almost all of the control is computerized these days, but the downside is
that they require external grid power to get the main generator going at
all. I can see that being a defensible engineering choice, although if I
had the guy's job I'd also be a little more comfortable knowing I could
re-start from an off-grid condition.

---Joel Kolstad

 

[daestrom]

Hardly; you can make a pretty good case that the most efficient generators
often DO require some external power for the sake of field excitation,
monitoring/control equipment, etc. This initially comes from a bank of
batteries, a smaller 'starter' generator where you don't care about
efficiency since it'll only be used briefly, etc.

I was talking to a guy here in Oregon whose job is to maintain and monitor
a small (a half dozen or so MW, I believe) hydroelectric power plant; one
of the points he took pride in was that at _his_ plant he still had enough
equipment around that he could get the plant going without any external
power whatsoever. He said that many plants have been 'modernized' such
that almost all of the control is computerized these days, but the
downside is that they require external grid power to get the main
generator going at all. I can see that being a defensible engineering
choice, although if I had the guy's job I'd also be a little more
comfortable knowing I could re-start from an off-grid condition.

In the industry, we say such a plant is 'capable of a black startup'. As
you say, many power plants today are *not* capable of starting up without
some external power. During the north-east blackout of 8/4/2003, one of the
priorities for the few plants that remained on-line was to supply power to
other plants so they could start up again. Many steam plants are not 'black
startup' capable as the myriad of circulating pumps and valves have to be
running before you can start rolling the turbine. Peaking plants such as
gas turbine or diesel often are capable of a 'black startup'.

I can certainly see how a hydro plant would be capable.

daestrom

 

[James Sweet]

I am confused about something. Even if a power plant requires external
power to start (say, fuel pumps should be operating for some time
before water heats up and boils), it would require a lot less power
than it produces. Probably many many times less. If so, then a power
plant can buy a generator of adequate size, say 1000 kW. It should
cost a relatively minuscule amount compared to the cost of the power
plant itself.

This is completely analogous to having an electric starter on an
engine. A small, cheap piece that can get stuff moving before the main
power plant starts up in a self sustained mode.

So, just what is the problem?Have them buy adequate generators and
that's all.

Any clarification will be appreciated.

i

They certainly could, however I think the issue is simply not wanting to
devote the money and space to a standby generator that might never be used
in the life of the plant. Not to mention maintenance of it, if a diesel
backup generator sits doing nothing for 25 years chances are it'll do
nothing right when it's needed most. I would still think it a good idea to
have one around, but I can see the resons for not having it.

 

[daestrom]

I am confused about something. Even if a power plant requires external
power to start (say, fuel pumps should be operating for some time
before water heats up and boils), it would require a lot less power
than it produces. Probably many many times less. If so, then a power
plant can buy a generator of adequate size, say 1000 kW. It should
cost a relatively minuscule amount compared to the cost of the power
plant itself.

This is completely analogous to having an electric starter on an
engine. A small, cheap piece that can get stuff moving before the main
power plant starts up in a self sustained mode.

So, just what is the problem?Have them buy adequate generators and
that's all.

Once a plant has started up, it certainly does produce more electricity than
it uses. A lot more. One plant I've worked at has a gross output of 880MW
electric. The 'hotel load' (the power needed to run the plant at full
power) is app. 30MW. So the net is 850MW.

But to start up, it needs about 15 - 20MW. And the main turbine is
producing zilch. Can you imagine how many diesel generator sets that would
take? A nice EMD V-16 can produce about 4MW. So, get about 5 or 6 of
those, connect them together with the correct switch-gear and controls and
have at it. But you will need this setup about once every 20 years, when a
major blackout such as 8/14/2003 occurs. That's a lot of hardware and
preventative maintenance for something you only need every 20 years. And 5
or 6 EMD V-16's with 4160V 4000kW output are not 'small, cheap pieces'.

So quite a lot of plants are not 'black startup' capable. The local grid
has to be 'up' to supply them with power to enable them to startup. Once
they *do* get on-line, it's a different story. But getting there is where
they need external power.

Take that nice diesel gen set you recently got. It's output is something
like 10kW right? And it just needs a nice 12V battery and electric starter
to get going. That's certainly affordable as opposed to a pull-rope. But
now imagine it scaled up by a factor of 100 000 so that you have a 1000MW
plant. In such a case even the 'cheap pieces' to start it would be very
expensive.

Some types of plants are much more easily made black start capable than
others. Hydro is perhaps the easiest. But even they need some
standby/emergency power for lubrication, gate-controls, cooling and such.
Modern gas turbines are probably also pretty easy to black-start. Steam
plants are some of the most demanding since they require a lot of pumping
power for the feed-water, and the boilers need quite a bit of auxilaries.

Then of course since most plants were built in the era of monopolistic
utilities with state regulation, you have to justify your plant's cost to
the regulators. The public service commission acknowledges that not *all*
the plants in a region need to be black start capable. They would not allow
such an 'extravagance' to be past on to the rate payers.

daestrom

 

[daestrom]

Aren't diesel backup generator typically exercised something like every
week or so for 15 minutes or somesuch in order to insure that they are
ready when actually needed?

Often it is a matter of past-performance. If they fail to start properly,
then the test frequency is increased. I've seen it as short as three days
on some really troublesome units. But if they perform well, then as
infrequent as once a month is common.

In addition to start tests, they are often 'load-tested' as well. The unit
is loaded to 100% and run for 3 hours or so to verify it can sustain full
load. This is done about quarterly. Or if the unit has been run unloaded
too much, they will be load tested in order to bring them up to full
temperature and burn out any soot problems. Depends on the unit.

daestrom

 

[Dimitrios Tzortzakakis]

In fact, for brown coal fired plants I have visited this is 10%.For a 300 MW
the auxilliary circuits need 30 MW.It's impossible to have a generator that
size;there is a special transformer supplied from the 150 kV grid for
startup.So, without 150 kV grid ->no startup.The generator itself supplies
the 400 kV grid (21kV/400 kV transformer).There was a hydro plant however,
that could be started with the 150 kV grid dead, by only a diesel generator
(here is where your idea comes) to open the valves for water.It has 3 125 MW
units;so is capable of supplying many brown coal plants at once.

 

[Dimitrios Tzortzakakis]

In fact, the plant "feeds its own auxilliary" as we were told;another
21kV/6.6 kV transformer takes power directly from the generator to feed
pumps, coal mills etc.Average power of 1 motor fed by 6.6 kV:1 MW.To
compare, a 30 MW generator with diesel engine prime mover is as large as a
mall.

 

[Dimitrios Tzortzakakis]

Field excitation comes from a small dc generator coupled to the same shaft
as the alternator (usually 220 V-1000 A dc for a 300 MW altenator,21kV,
10kA).Usually it's shunt excitation.THAT'S a case where a generator
generates without external excitation;there is some remaining magnetism in
the stator of the dc generator, so when it rotates the voltage
increases..and increases.