60 Hz inductor design?

I want to reshape the output of a 115v "modified sine wave" inverter so
as to allow it's use with a 19.2 v NiCad battery charger which refuses
to work with the raw inverter output. Using Spice I find that an
inductor input singly loaded Tchebeyscheff filter would give a much
improved sine waveform. The current thru the 237mH inductor appears to
be 3amp pk with of course a very distorted voltage wave of some 190 v
pk. Is it ok to use power transformer core of the above VA and assume
that since there is no secondary there will be twice the winding area
available. Since the inductor Q is max when conductor loss = core loss
does this mean that the optimum core for an inductor will have a
smaller winding window than that of a trnsformer of the same VA?
I use a 19.2 v Sears drill to raise the sail on my boat and want to
recharge the battery from ship's power (12v).
Dick

I want to reshape the output of a 115v "modified sine wave" inverter so
as to allow it's use with a 19.2 v NiCad battery charger which refuses
to work with the raw inverter output.

It would be simpler to convert the inverter output to DC, voltage
doubling if necessary.

[snip]

I use a 19.2 v Sears drill to raise the sail on my boat and want to
recharge the battery from ship's power (12v).

What does that have to do with anything other than to boast about your
economic status?

rqlhgl@ieee.org wrote:

I want to reshape the output of a 115v "modified sine wave" inverter so
as to allow it's use with a 19.2 v NiCad battery charger which refuses
to work with the raw inverter output. Using Spice I find that an
inductor input singly loaded Tchebeyscheff filter would give a much
improved sine waveform.

How did you model the battery charger as a load on the filter in spice?

The current thru the 237mH inductor appears to
be 3amp pk with of course a very distorted voltage wave of some 190 v
pk. Is it ok to use power transformer core of the above VA and assume
that since there is no secondary there will be twice the winding area
available.

In most transformer designs, the primary and secondary windings each
use about half of the window area, if that is what you are asking.

Since the inductor Q is max when conductor loss = core loss
does this mean that the optimum core for an inductor will have a
smaller winding window than that of a trnsformer of the same VA?

A better way to look at the Q problem (since you may not have all
variables available, like arbitrary core size) is that highest Q
occurs at lowest total losses. For a given core, the copper losses
are lowest by filling the window with copper. Also for a given core,
the losses are lowest for lowest core flux swing. So adding air gap
to the flux path should give the lower core loss. But that also
lowers the inductance, requiring that filled window to have more turns
(of thinner wire) to restore the inductance, which raises the copper
losses. So the main balancing act is between lowering the core losses
with gap while raising the copper losses.

Hitting close to the true minimum loss takes either some experiment or
considerable math.

I use a 19.2 v Sears drill to raise the sail on my boat and want to
recharge the battery from ship's power (12v).
Dick

I doubt that a good sine wave is needed to make the charger work. I
suspect that the fast edges of the modified sine wave inverter are
just confusing the control circuit in some way, and just some simple
low pass filtering will suffice. But I have been wrong lots of times.

To Fred:
I want to take advantage of the existing (already paid for) quick
charger which has 4 contacts to the NiCad battery and senses battery
temperature. I suppose I could build a 12/~24 v dc-dc converter, say
one that adds 12v to the existing 12v but then I would have to also
build in temperature and float voltage programming to match the
existing charger.
The bit about the boat is relevant to the fact that 115v sinusoidal
suppllies for boats start at about $600 and the drill plus charger was
only $99, it is thru making such choices that I preserve my "economic
status".

To John:
I assumed that the charger input impedance was V*V/W where the charger
power is stated to be 75w, this gives 176 ohms. I figured that
non-linear deviations from this assumption would be mitigated by the
20uF shunt capacitor of the filter. I just bought an old Kiusui 'scope
on EBay and hope to take a look at the inverter output and the charger
input current via a home-brewed current transformer. I've been retired
15yrs and sure miss having a lab full of equipment.
Thanks for your interest, Dick

On 3 Dec 2005 21:57:35 -0800, rqlhgl@ieee.org wrote:

I want to reshape the output of a 115v "modified sine wave" inverter so
as to allow it's use with a 19.2 v NiCad battery charger which refuses
to work with the raw inverter output. Using Spice I find that an
inductor input singly loaded Tchebeyscheff filter would give a much
improved sine waveform. The current thru the 237mH inductor appears to
be 3amp pk with of course a very distorted voltage wave of some 190 v
pk. Is it ok to use power transformer core of the above VA and assume
that since there is no secondary there will be twice the winding area
available. Since the inductor Q is max when conductor loss = core loss
does this mean that the optimum core for an inductor will have a
smaller winding window than that of a trnsformer of the same VA?
I use a 19.2 v Sears drill to raise the sail on my boat and want to
recharge the battery from ship's power (12v).

What are you running the inverter from?

Might it not just be easier to charge batteries from the original
source? This is a simple boost converter.

There are also lower-voltage drills.

RL

The battery charger probably just wants to see something with slower
risetime....I doubt that you need to provide it with anything like a
good sinewave. Why not start with a couple of inexpensive toroidal
inductors rated for 5 Amps DC or so, one on each leg of the mains? Of
course, one of twice the inductance will have nearly the same effect.
Then, add an X capacitor of a microfarad or so in parallel with your
charger mains input. I'll be surprised if this combination doesn't do
the job.
It's also possible that a cheap isolation transformer, especially a
c-core or a split bobbin type, might have enough leakage inductance to
do the job.
In case there's some type of common mode coupling problem that's
bothering the charger, you can try inserting one of those 'Corcom' type
line interference filter modules, too.
Paul Mathews

rqlhgl@ieee.org wrote:

I want to reshape the output of a 115v "modified sine wave" inverter so
as to allow it's use with a 19.2 v NiCad battery charger which refuses
to work with the raw inverter output. Using Spice I find that an
inductor input singly loaded Tchebeyscheff filter would give a much
improved sine waveform. The current thru the 237mH inductor appears to
be 3amp pk with of course a very distorted voltage wave of some 190 v
pk. Is it ok to use power transformer core of the above VA and assume
that since there is no secondary there will be twice the winding area
available. Since the inductor Q is max when conductor loss = core loss
does this mean that the optimum core for an inductor will have a
smaller winding window than that of a trnsformer of the same VA?
I use a 19.2 v Sears drill to raise the sail on my boat and want to
recharge the battery from ship's power (12v).
Dick

Reply to Legg:
I guess my Dec 4 1:38 pm reply crossed your's, I have 2x 115 ah 12v
batteries.
I need the 450 in lb torque of the higher voltage drills even running
it in low gear and reverse to take advantage of the 2:1 gear ratio of
the 2 speed winch.
Reply Paul:
I am going to wait and see what the 'scope reveals,(if it works at the
@21.50) I paid. For the Spice simulation I assumed that the "modified
sine wave" inverter output would have a 115v rms value which
translates to about 150v pk. Surplus 2amp Corcom line filters can be
bought for <$10 but would not transmit the full 115v rms that the
modeled LPF does.
Dick

rqlhgl@ieee.org wrote:

I want to reshape the output of a 115v "modified sine wave" inverter so
as to allow it's use with a 19.2 v NiCad battery charger which refuses
to work with the raw inverter output. Using Spice I find that an
inductor input singly loaded Tchebeyscheff filter would give a much
improved sine waveform. The current thru the 237mH inductor appears to
be 3amp pk with of course a very distorted voltage wave of some 190 v
pk. Is it ok to use power transformer core of the above VA and assume
that since there is no secondary there will be twice the winding area
available. Since the inductor Q is max when conductor loss = core loss
does this mean that the optimum core for an inductor will have a
smaller winding window than that of a trnsformer of the same VA?
I use a 19.2 v Sears drill to raise the sail on my boat and want to
recharge the battery from ship's power (12v).
Dick

That charger might run on 160 volt DC. It probably just takes mains
power, runs it through a bridger rectifier and runs off that.

Any decent charger should work over a range of mains voltages, usually
down to 100V or less for a 120VAC charger. Consequently, I'll be
surprised if slightly less peak voltage poses any problems. If you end
up needing to do heavy filtering for some reason, there are passive PFC
chokes readily available, possibly in surplus. If you get desperate for
sources, let me know, and I'll send you some large powdered iron cores
and instructions for winding suitable inductor(s). I'm a boater on a
budget, myself, and it cracks me up how people assume that anyone with
a boat must be wealthy.
Paul Mathews

I use a 19.2 v Sears drill to raise the sail on my boat and want to
recharge the battery from ship's power (12v).

One of the significant factor in my purchasing Dewalt cordless tools some
years ago was the availability of a 12V DC input charger that works with most
all of their batteries, including the 14.4V ones, as I was going to be
spending time out in the middle of nowhere, I mean, New Zealand :-), with all
of a 50W 12V solar panel for power.

Something to keep in mind if you start losing enthusiasm for your initial
approach here... (and since it's a sailboat, power efficiency probably is a
concern as well -- I'd rather go through one power conversion than two...)