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I'm aware that motor efficiency (power out/power
in) increases with higher voltages - looking at the
power curves for just about any DC motor, be it a
series wound Advanced DC, an Astroflight Cobalt magnet,
or a LEMCO PM makes that abundantly clear. I also
understand high amperage draws are hard on batteries, and
limit the recommended depth of discharge. What I don't
understand is how, for example, pulling 90 amps through a
bank of 3 parallel wired batteries means each battery
is receiving a 90 amp current draw. Wouldn't each
battery be contributing 30 amps current (3 x 30 amps = 90
amps)? Now, if I take the same 3 batteries and wire them
in series, I've increased the voltage 3x, so I'd
still only draw 30 amps through the series for the same
wattage. Actual battery voltage is irrelevant at this
point. Please clarify if my math or understanding of
electricity is in error here.<br><br>Now, I don't think this
is what you were referring to in your reply, but I
see how running a motor to the left of the typical
knee in it's efficiency curve would waste power -this
is typical of any of the DC motors I'm familiar
with. For example, the LEMCO motor at 24 volts is only
50% efficient @ 2.5 kW output, but that eficiency
peaks at 88% at 4 kW output. But again, this phenomena
occurs irrregardless of voltage irregardless of voltage.
One assumes one would size and select a motor to
spend the majority of its running time near near peak
efficiency, no matter the voltage or type of motor they go
with.

I checked out the web site for the LEMCO motor,
and sent off an email to Wilde EVolutions, and about
a half hour later, Roderick Wilde called me. He was
very nice and is sending out literature and a write up
on an installation of the LEMCO motor in a boat. Now
that's what I call service. I also gave him the address
for this site, maybe he will join in.<br><br>Bill in
Utah

Chris.response to you is on message 217 but it doesn't show up on home page ??? Don't know why.

www.evparts.com

The reason the motors work so well at lower RPM
is larger diameter. The smaller the diameter/number
of polls the higher the rpm and lower torque at low
rpm. Conversly...the larger the diameter and number of
polls the more torque at lower rpm. The key is to ask
your prop what kind of torque and rpm it wants to
see...and even before that ask your boat what size prop it
wants. For launches and displacement hull vessels the
bigger the better. Get the biggest prop you can fit into
the aperture then determine what torque and rpm the
prop requires and select the motor from that. Just to
establish a point of reference the Solomon motor has 72
polls and is 12" in diameter and therefore develops
almost a ft.lb. of torque per amp up to 1000 rpm with
the same 3 phase efficiency as an AC motor. As I seem
to be the "smart alec" in the room..guess what rpm
big props like...oh..about 1000. Also do you know
what Advanced DC sells the most of...brushed DC
motors..litle wonder they have found some deficiency in every
other motor technology. The narrow band of operation
they mention about Brushless DC magnet motors has been
accomodated by increasing the number of polls allowing full
variability with efficiency through the
range..additionally...the higher the voltage the greater the range of
extreme efficiency. And...check the survivability MTBF in
the salt water environment...but you can always carry
a pocket full of those brushes with you. But who
wants to be at sea changing them ? However for smaller
KW vessels that are in fresh water they work pretty
nice. An actually...Brimbelow Engineering in the UK has
the best kit in the 2kw and less range. It comes with
built in transmission and thrust bearings ....it's a
drop in replacement. Brimbelowengineering.co.uk. Don't
know how to do that fancy link stuff...My final
comment is that I hate motors that have to have
commutation...whether with brushes of contacts...and they don't
regen...for you sailboaters...REGEN is a new buzz word that
you won't be able to live without...

Chris..forgive me my friend..but read what you
wrote...1st. Higher voltage motors are more efficient. 2nd 12V
X 30 amps=360 W and 36V X 10 amps = 360W which is
right..on a small motor that is at 1kw or at the most 2 kw
it's not 30 amps but rather close to 90 amps at 12
volts for the 1 KW and 180 amps for 2kw. Now using 36V
we find that the 1kw motor comes down to 1/3 of that
amperage because of the inverse proportions of the
equation (A x V = W) therefore it is 30 amps for the same
1kw and on the 2kw motor it comes down to 60 amps.
These amperages are easier on batteries because they do
not like heavy amp draws. Deep Cycle batteries can
"handle" it but they don't like it and it reduces their
service life. They also allow you to go to a deeper
discharge level...say 80% instead of 50%.<br>3rd...you are
absolutely correct..the lower amperage does use much smaller
wires, is less prone to skin effect (lost energy
radiated from wires) and less costly connectors and
charging systems. <br> Ok...so you have answered your own
question...now lets look at a 4Kw or 7.5Kw system. at 36 Vdc for
4kw(6hp) the amperage is 111 amps...7.5Kw (10hp) its 222
amps ! at these amperages the depth of discharge can
only be 50% or you risk doing damage to the battery.
But if we consider going to 120/144 vdc...carrying
the same battery weight but wired in series, 4kw is
only 32/38 amps. 10kw is 58/64 amps. I can get a
deeper discharge of the same lead acid and the
motor/controller efficiency is better also. Those mosfets and
Igbts are much cheaper and more efficient the lower the
amperage is. Hope this makes sense.

In my last posting I had given a breif
discription of the electric outboards I build. The
description was pretty lousy to say the least! Therefor, I
have posted a diagram of the motor, in the photo
section, for you to view.

william:<br><br>what part of the country are you
in? I may know of a boat in Chesapeake Bay region you
might be interested in. you can e-mail me directly at
reata.bill.swanson@... if interested<br><br>bill

First off, I would like to say Hello to everyone
here! I am certainly impressed with what I have read in
your postings! I live Columbia Maryland (it's in
between Wash. D.C. and Baltimore)<br>I have built two
different electric outboards in the past, The first was an
old golf cart motor (24V) using everything that came
off of the Cart (controllers and all). <br><br>The
second was (36V) but I pushed 48Volts into using a
Curtis PM Controller. It was fairly
fast.<br><br>Basically what we do is remove the powerhead off an old 5
to 8 HP Gas powered outboard motor. We then take two
aluminum plates and mount one to the <br>lower unit and
the other to the face of the Elec. motor. Then using
four spacers (about 2 inch tall, one on each corner)
to allow room for the shafts to clear one another. I
couple the shafts of the motor to the lower unit using a
LoveJoy connector. <br>No pulleys or belts (direct
drive).<br><br>The boat is a 14' aluminum flat bottom jon boat used
for fishing in the local lakes (no gas engines
allowed. <br><br>I would like everyone to know that I
don't know a thing about Electrical parts including
(current draw, amps, killowatts, jigawatts or willowalots
:) Nor do I have test equipt. So everything I build
is on a "pure luck" senerio!<br><br>With all that
junk being said, I would like to ask a few questions?
But I will do that in the next posting. I just wanted
to introduce myself for now..<br><br>Thanks for
listening!

Good observation Chris, the battery people look
at Watt/ KG that is to say how many watts can a
given battery package produce per unit of weight. It
makes no difference in the batteries to a point. There
is some advantage in motor design the motor can be
made smaller. It used to be an advantage with
controlers. Now however the semi conductor maufacturer are
making power MosFets that are capable of seveal hundred
amps and actualy. High current low voltage
semiconductors are more redily available than the higher voltage
ones. I am still looking at costs but from what Iv'e
been able to tell 3 ZHp and below 24-36 Volts systems
are the most economical above that there is some cost
saving to 48 and 72 Volt systems.

What is the main reason why those motors work so
well at low rpm? Also, I note that some very small
brushless PM motors spin at high rpms to yield good power.
Is this because power output is a function of the
magnitude of magnetic flux change, and higher speeds yield
greater rates of change to allow more power for the same
sized magnet? By the way, what is the best kind of
motor if I need about 7K rpm and about 7 hp using 60v?

I'll grant that higher voltage systems are more
efficient, but I don't understand how having the same number
of batteries in a parallel system versus a series
system results in a higher amperage draw from the
individual batteries. If I'm pulling 30 amps from 3 12 volt
batteries in parallel, I have 360 watts, with 10 amps drawn
from each battery. If I pull 10 amps from 3 12 volt
batteries in series, I still have 360 watts with 10 amps
through the series. I think the effect on the batteries
discharge curve would be the same. I think where the real
advantage of higher system voltage comes in is the lower
resistive losses through wiring and components. You can
keep these losses low with a low voltage system by
using larger wiring, high amperage controllers, motors
with low winding resistance, etc.<br><br>Chris Krumm

You will find that the RPM's these PM motors work
best at are something less than 1500. This is the real
reason why they are so good at pushing props when used
in a direct drive mode. It is also why they are so
good at producing energy in the regeneration
mode...low RPM hydroelectric power generation. Combine this
with higher voltages which are easier on batteries
because of lower current requirements and you have the
perfect (at least with the technologies) system.....

I have been following this line of dialogue
because like most members I am very interested in the
types of motors available to us. In that context, there
is an informative "motor" site at
<a href= target=new></a> That site well summarizes the difficulty in
comparing electric with fossil fueled motors via one
statement: "It is not accurate to refer to a "10 hp motor"
or a "15 hp motor", because horsepower will vary
with volts and amps, and peak horsepower will be much
higher than the continuous rating. It is also confusing
to compare electric motors to gas engines, since
electric motors are given a continuous rating under load,
and gas engines are rated at their peak horsepower
unloaded." The site also states that PM motors are efficient
only at a narrow range of speeds (This may be an
advantage of the Solomon wheel which I believe helps
maintain a constant motor speed: is that right?) Does
anyone have a more detailed understanding (for example
some speed v efficiency data) of this alleged PM motor
characteristic?

Hi -<br>I've been reading the entries in this
forum over the past few weeks, and thought I'd join in.
I've designed and built two PV/battery electric
inboard boats with high school students, and have helped
out on two additional original designs. My first
project was a tortured ply proa with PV array taking up
the deck area. My current project is a 20'LOA x 4'-4"
BOA strip planked launch. All boats run on 24V with
two group 24 deep cycle batteries for an annual
competition, but the launch will be converted to 36 or 48 v
using 6V TrojanT-105 batteries for extended use. Now
for comments and questions:<br><br>1) There's been a
bunch of back and forth regarding cog belt vs. gear
drive efficiency. A mech engineer friend of mine feels
a properly adjusted (i.e., min backlash) spur gear
and cog belt reduction drive would be pretty
comparable in efficiency (~ 93-96%). Gear drive
disadvantages are typically noiser, need for very accurate
backlash adjustment, and greater complexity if you want to
change ratios. Cog belt is quiet, simple to tension,
easy to reconfigure pulleys. What say
others?<br><br>2) There's also been some discussion of regenerative
controllers. I haven't looked at the Ewheel patent, but
regenerative braking via mosfet PWM controllers has been
around for years, and many of them designed for EV's
have the capability (Curtis, 4QD, etc.). My question
is how useful is this on a boat. Regenerative
braking depends on using inertia of a "relatively" heavy
vehicle with a limited (virtually none) slip between
rotating drive wheel and road surface. How much regen
would you typically get using the momentum of an
electric boat to spin its own prop with power
off?<br><br>3) How does regenerative braking through the PWM
controller actually work? Is there a DC-DC conversion in the
controller that boosts the motor (now generator) voltage
during braking to get voltage above level of batteries
to effectively charge the batteries?<br><br>4) I'm
interested in developing a larger electric proa for day
cruising, and am intrigued with hybrid drive systems. A
series drive with a small diesel or gas generator would
be simplest, but I know it's really most efficient
to just drive the prop directly with the IC engine,
'cuz when your cruising, you'd assume you'd select and
operate your engine/motor (IC or electric) at pretty
close to optimum efficiency. <br><br>I'm curious about
setting up a parallel system. Either IC or electric motor
could be primary drive optimized for energy efficiency,
with other system kicking in for peak power
(emergencies, maneuvering). If I were running a diesel, and
wanted to add the power of an electric motor, would I
have to have a means of insuring matched motor RPM's?
I.e., would I need to go the trouble of having a servo
loop that measured diesel RPM and used that to control
RPM of electric motor? Also, would I need to have the
diesel typically run at lower RPM's so that it wouldn't
exceed it's max rated RPM's if power of electric motor
were added to it (I'm assuming prop shaft RPM's have
to increase to get increased thrust out of a fixed
pitch prop)? What about using a controllable pitch prop
as an option to maintain constant prop shaft RPM's
and allow additional torque input of a second motor?
<br><br>Sorry for the dump, but I'm guessing people on this
forum are the one's to ask.<br><br>Chris

Am I missing something! Where do you get the idea
that gears are not efficient. They have a lot less
friction than belts. Look at a 200 hp ob motor. You can
spin the lower unit with your small finger with not
resistence. Even the cog belt has some friction.

Good to see more members, more input and more
sources - there's also more questions!<br>As i wish to
retro-fit an o/board, my existing bevel gears must stay.
What options are there? A belt down a tube? Is there a
hydro-efficiency factor with a bigger leg?<br>I have an allergic
reaction to cutting a hole in the hull for a shaft and i
stay where it is warm enough to leave batteries
outside living space.<br>I hear the permanant magnet DC
argument well, but wouldn't a PWM, variable frequency
inverter driving an inductance (brushless) motor be pretty
good?

It sound like a fun project. I am finishing up mine this spring. Check out the photo I posted. I hope to have some more later. They might give you some ideas.

Thats a very good design, Particularlyy with the
high effency Permenate Magnet (servo) motor and the
Kortz Nozzle. The only objection I have to it's design
is that he is using a low effency gear drive just
like they use on Engine driven outboards.

I also found this electric outboard<br>Looks interesting.<br><br><br><a href= target=new></a>