M&M Metals http://www.mmmetals.com/pages/custom_aluminum_and_copper_heat_sink/custom_copper_and_aluminum_heat_sink_fabrication.htm
provides heat sinks of all kinds which is what I will be using for my Kelly controller.
--- In electricboats@yahoogroups.com, David Goldsmith <suntreader@...> wrote:
>
> Just to keep things clear, there are two 'Daves' in this discussion, Dave
> Cover with the electric Porsche; and Dave Goldsmith with the sailboat build
> underway.
>
> I certainly get the impact and concern over heat and you're numbers are all
> what I was expecting, the personal experience was what I was hoping for, and
> those that have shared have made me rethink how I'll mount the controller.
> It'll be on an alloy plate, and I was looking for a surplus heat sink that
> would either mount on the plate or as a cover over the whole electronics
> board. Forced air cooling with some fans seems to be the way to go. If I
> install everything in the same box I can build a plenum into the back of the
> box and run the air out that way and into the cabin. I just don't want to
> heat things up down there too much or make too much noise. The intended use
> is going to be minimal, just where its really needed and at low amps, but
> the possibility is always there to need the full 100 amps for the full
> capacity of the batteries so I'd rather build things such that full capacity
> is available without worrying about over heating. I'll take some pictures of
> the installation and unit for some input from the group before I install
> anything.
>
> The claimed efficiency of the Kelly controller is very high. The controller
> and electronics are going to be delivered today, so I'll try and work on it
> this evening and get some pictures posted.
>
> FLA cells are my choice because of cost, AGMs are simply too expensive and
> it seems a lot of users have had good experiences with cart batteries. They
> won't be ideal but they should get me going for a couple of years before
> lithium become less expensive. As for being 100 year old tech, doesn't that
> just mean its more reliable and robust;) Aren't sailboats basically the same
> as they were a century ago too;)
>
> Thanks everyone for your experience and knowledge, its making my system a
> much better one than if I had just winged it.
>
> David
>
> On Tue, Oct 19, 2010 at 12:31 PM, James Lambden <james@...> wrote:
>
> >
> >
> > Dave,
> >
> > A small PMAC electric motor is 85 to 90 percent efficient.
> >
> > Now lets drive 5 KW through that motor. That means that 500 to 750 watts
> > is being dissipated as heat inside the motor.
> >
> > Imagine running a hair dryer on the low setting inside a small aluminum
> > enclosure with very little air circulation. Its going to get hot quick.
> >
> > Most small electric motors used for sailboat conversions do not have
> > adequate cooling fans to dissipate that heat on a continuous basis so we
> > need to do everything we can to get rid of the heat.
> >
> > Controllers, especially inefficient ones, also create enormous amounts of
> > heat so should be mounted in a different heat space as the motor and on a
> > heat sink.
> >
> > The introduction of forced air cooling helps cool things down but even
> > better is the removal of heat from the engine space. This can be done by
> > enclosing the electric drive in a sealed area and then drawing the heat away
> > from the motor.
> >
> > The Sevcon Gen 4 controller has a temperature sensitive output that will
> > turn on a fan at a certain motor temperature - we choose 70 degrees C
> > winding temperature.
> >
> > Another advantage of the Gen 4 controller, is it creates very little heat.
> > It is rated at 180 amps continuous so this application is a walk in the
> > park for it. But we still mount the controller to a large heat sink,
> > offset from the wall with spacers.
> >
> > Current at rpms is a function of the gear ratio chosen. It is vitally
> > important that a motor does not have excessive AC current going to it. You
> > can have low DC current and think everything is fine, but when you measure
> > the AC current it can be right of the map. We like to choose a gear ratio
> > that balances the DC and AC currents. 100 amps DC from the batteries -
> > 100 amps AC to the motor.
> >
> > I don't like to exceed 100 amps continuous on any 48 volt air cooled
> > system. We are developing a water cooled system that will be capable of
> > 200 amps but we will be using two battery packs and two stators and the most
> > any one battery pack will see is 100 amps. The only place we will see 200
> > amps is the battery cable between the battery bus and the controller.
> >
> > On Kapowai, we have two battery packs, a string of 4 D's and a string of 8
> > D's. Each battery pack sees approximately half of the load or 50 amps
> > continuous. This way we avoid heat issues in the batteries, the wires, the
> > fuses and the connections.
> >
> > Boats are far different from cars because the motors are used continuously.
> > Cars, golf carts, motorcycles all have intermittent loads on the motors.
> > They accelerate then coast, go up a hill, then down, stop and wait at a
> > red light or golf tee. These applications always have time to cool down
> > and can consequently be used for short burst of power at high current
> > levels. Boat applications running continuously do not have the
> > opportunity to cool down and the heat builds up so must be managed.
> >
> > We don't have any heat problem at all with Kapowai, largely due to the low
> > currents throughout the system. Twin batteries and double stators! Low
> > currents mean low heat.
> >
> > We like to run the motor at no more than 1900 rpm, mostly because at these
> > low rpms the system is very quiet and noise is another pollution we don't
> > like. We could make more power by running faster, but we don't need it.
> > With respect to sweet spots, the motor and controller run efficiently at
> > all speeds. We only use what we need and motorsail all the time.
> >
> > With respect to flooded cells: this is technology that hasn't advanced
> > much in 100 years. Though many people would argue with me, I don't think
> > that flooded cells belong on a boat in any situation. They are dangerous,
> > vent explosive gases and lose there capacity in a straight line until they
> > are done. Flooded cells especially should not be used on an electric boat
> > because of the extended run times at high current levels.
> >
> > AGM batteries are the best way to go for now and Lithium is very close to
> > taking over once supply issues are resolved.
> >
> > thanks for your interest.
> >
> > Good luck on getting an e-boat soon.
> >
> > James
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > On Oct 19, 2010, at 5:58 AM, dave cover wrote:
> >
> >
> >
> > Jim
> >
> > Excellent writeup. It's very helpful to see real numbers showing whats
> > going on. It looks like you've put a lot of effort into this.
> >
> > First, a little introduction. I've been watching this list for a while
> > but do not have a boat of my own yet. I'm still in the planning stage.
> > I live in New England and hope to start out by sailing in Long Island
> > Sound. I commend you guys for the work you've done and look forward to
> > "joining the fleet." I learn something new with everything I read
> > here.
> >
> > I own and drive and electric car, so I have a slightly different slant
> > on electric propulsion. There's a link to my car at the bottom of this
> > email. While many of the parts, concepts and terms are the same,
> > moving a boat through water is a lot different than rolling a car on
> > pavement. Driving a car, it's not unusual to pull 700 amps from my
> > pack taking off from a stop. Cruising the hills where I live I will
> > draw between 75 to 300 amps on a regular basis. Not what you guys see
> > sailing. I'm not here to tell anyone how to sail, I'm the newbie.
> >
> > Ok, enough of the introduction.
> >
> > You bring up a very good point that I haven't seen mentioned before,
> > heat. Heat is usually an indicator of inefficiency or problems with
> > electric drives. But even when it's a product of working hard, you
> > need to manage it. Your comments on forced air cooling are very
> > important and I hope more people keep this in mind when repowering
> > with electric. With a motor, heat can be most damaging when you try
> > and push a lot of current through a motor at low RPMs. Cars often see
> > this when starting from a dead stop, and I imagine a boat would almost
> > never have this. So cooling over a long cruise is probably more the
> > issue. Your comments on heat are spot on.
> >
> > But heat can also rear it's ugly head in other ways. With your main
> > wiring (from pack to controller and controller to motor) you should be
> > aware of heat issues. If you have a loose battery connection it can
> > heat up enough to melt a battery post right off. It doesn't hurt to
> > feel (safely, don't get shocked) around after running electric to see
> > if any wires or connections are warming up. If you find a hot spot,
> > you need to address it. This applies to all the components in your
> > electric drive. I even have liquid cooling for my controller.
> > Controllers are probably more prone to heat failures than motors. If
> > any of you are running Curtis controllers, or any controllers that are
> > designed to dissipate heat through the case, be very careful how you
> > mount it. Mounting your controller on a vertical aluminum plate and
> > adding a simple 12v fan can save you hundreds or thousands of dollars.
> >
> > Also, batteries can generate heat during charge and discharge. If
> > you're in the tropics and running hard, you should provide some
> > cooling to the pack. Most good chargers will have a way to monitor
> > pack temperature and adjust the charge to compensate. I have flooded
> > NiCad cells in my pack and I ventilate them during every charge. I
> > usually charge right after a drive, so they are a little warm to start
> > with. No sense in letting them overheat. This is mainly for the
> > hydrogen, but also to cool them. Don't forget, anyone with flooded
> > batteries must control the hydrogen! Floodies have great capacity but
> > require more care. Not sure if it's worth it in a boat. I'd avoid
> > them.
> >
> > Jim, you also put a lot of effort into understanding the efficiency of
> > the propeller, but I didn't see much mentioned about the efficiency of
> > the motor. Electric motors have an RPM sweet spot for efficiency and
> > this should be incorporated in the calculations. While you will vary
> > the speed for maneuvering around the harbor, you should design your
> > drive to use the most efficient RPM range for long cruises. In normal
> > driving my motor runs from 0 to 4000 RPMs, but it likes to be around
> > 2500 to 3000. So I plan my driving accordingly. I won't always shift
> > into a higher gear as you might with a gas powered car. I know,
> > sailing is different, but your should be aware of your motor speed and
> > use it most efficiently. The biggest mistake is to run your motor too
> > slow with too much current. This generates heat and heat is a problem.
> >
> > Anyway, the ElectricBoats list has been great and I'm learning a lot.
> > Didn't mean to run off at the mouth like this. As I said in the
> > beginning, I know a lot about electric cars, but very little about
> > electric boats. I don't know when I'll have my own to sail, but I'm
> > working on it. If anyone in Connecticut want's some help with their
> > electric drive, I'd love to lend a hand.
> >
> > Dave Cover, learning all the time
> > --
> > http://www.evalbum.com/2149
> >
> >
> >
> >
>
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