Hi, sorry, I was off line a few days with a computer disease.
Ken, Thanks for sharing all those Minkota experiences!
Kirk, Motor efficiency...
I haven't actually done definitive efficiency tests on the Hubcap motors owing to all the other things I'm doing and not having made a brake to put a specific load on the motor. I arrive at "about 95%" based on experience and the several major improvements I made while developing the motors. First is polypropylene-epoxy composite housings (non-magnetic/non-conducting so no drag). Second is low loss iron powder coil cores. (Lower RPMs <2000 that keep those iron losses trivial.) At that point I figure I probably had the typical 92% or so of many motors of this sort. Third is nanocrystalline ilmenite (TiFeO3) in sodium silicate ("water glass") coil coatings. Paramagnetic/ferromagnetic nanocrystalline materials in a glassy substrate can redirect magnetic fields, so the flux that would have gone into empty air is redirected into the cores. After I painted that on, the no-load currents dropped 25-40% at various RPMs. (Rutile [TiO2 mineral] also helped, but it wasn't as good as ilmenite.)
So now I have a 5KW motor doing 1000 no-load RPM using just 70-90 watts - a couple of amps at 36 volts. (The earlier prototypes with metal casing parts and laminated iron coil cores used maybe 300-450 watts - 10 or 15 amps.)
& Motor Making Reading...
For 500 watts, I don't know. My Electric Hubcap motors are 5000. On the other hand, the idea is scalable. You can get all the stuff - supermagnets, iron powder coil cores, etc, in various sizes.
To read about making my Electric Hubcap motors and controllers:
http://www.TurquoiseEnergy.com/hybridize/hybridize.html
(I had to delete the earlier motor stuff because Shaw Cable only gives 20MB of web space.)
The latest developments are in my newsletters (now moved off the Shaw site for the same reason. I've improved a mold and I'm putting together another motor now. So far, even 4 years into the development, every motor is a little better than the last one...
http://www.saers.com/recorder/craig/TurquoiseEnergyNews/
Cheers,
Craig
an MK 36lb thrust is about 400w, a 55lb unit about 600w.
just tried a kipawa 314 on my 36lb thrust MK, its definitely nicer-faster.
thinking upping to the 55lb thrust MK I have and getting a kipawa 358,
it might or not perform any better than the 36lb thrust honestly, I'd be
adding another 65-70lb 12v battery for longer runtime.
50% more power, so it might spin up a little faster, but a bit more weight.
these are "endura" units, they're cheep... really cheep..
they use resistor coils and the switches DO get hot on high speed.
same speed control switch in all of em too, darnit. MK's tech told me,
I was asking if a 55lb switch would solve the heat-up problem.
I've put in two BIG roller-lever cam actuated microswitches,
in high speed they parallel share the voltage-current to feed the motor.
it solved the problem of the stock switch heating up robbing power.
the speed control switch is in the dashboard, not stock housing,
so I had some room to do that kinda stuff. rope and pulley steering etc.
PWM electronic speed controllers are lots better, but lots spendier too.
I might go to electronic speed control, just ignore the 2 smaller wires,
they just feed the resistor coils that live in the motor casing anyway.
the 36lb with stock prop, first I'd boiled the blades for an extra 1/8" twist-pitch,
carefully measuring-marking as I went.. it improved speed a good little bit.
cant tweek em too much, rpm's will fall, current draw will go up lots.
I think the kipawa 3 blade prop is much better on it.
(wish I'd just gone straight to the kipawa)
between the BIG micro-switches sharing the current to feed the motor,
and the kipawa 314 on the MK 36, its moving pretty good at speed 5.
before I'd got the kipawa prop,
tried an MK "weedless wedge", for me it was disappointing.
having more blade surface area and diameter, less pitch,
it'd probably move a heavier boat better than the stock MK "speed prop",
less prop slip, but.. no legs for running! it was cheep thru amazon-dot-com anyway.
(for a heavier slower boat the weedless wedge probably a good idea)
the boat is 12ft, 12v throughout, if I could find and afford 15v worth of lipo4 for it, I'd take that small risk of 20-25% over-voltage, but it probably wouldnt do even 10% more speed.
(also seen 16v "racing" batteries, gel-mat type, hmmm....)
the boat fully loaded might be 530 lbs total with 2 aboard, a shorter "planless" rendering of a henley slipper launch seen at duckworks. had I known more I'd gone 19-21 ft length, I'm sure it'd cruised faster-easier for the longer waterline. something light, narrow, and long,
oughtta scoot pretty decent on 5-600 watts worth of trolling motor + kipawa prop.
"decent" being a solid 5 to 6 mph. big frieghter canoe category pretty much.
you'd said 500 watts so theres what I know now, hope its a good read.
500 watts is right in the trolling motor ballpark, about 45lbs thrust.
(MK = Minn-Kota)
--- On Mon, 5/14/12, Kirk McLoren <kirkmcloren@yahoo.com> wrote:
From: Kirk McLoren <kirkmcloren@yahoo.com>
Subject: Re: [Electric Boats] Re: File - Welcome- Electric Hubcap
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Date: Monday, May 14, 2012, 3:08 PM
interested in how you measured 95% efficiency.I am interested in building a 500 watt pancake.Any suggestions re what to read?... How beautiful it is to do nothing, then rest afterwardsFrom: Craig Carmichael <craig@saers.com>
To: electricboats@yahoogroups.com
Sent: Sunday, May 13, 2012 7:00 PM
Subject: [Electric Boats] Re: File - Welcome- Electric Hubcap
Hi,
I just joined. I've been developing the "Electric Hubcap "
36V/130A/5KW BLDC pancake motor. (Among other things.)
Here are short snips from an early version (converted Honda 7.5 HP), Nov. 2010.
Launch from wharf: http://www.youtube.com/watch?v=yUfqSSnEh5c
From Onboard: http://www.youtube.com/user/TurquoiseEnergy
Inside motor: http://www.youtube.com/watch?v=X1MkdixNLcc
The motors are now much improved... enclosed in a tough
polypropylene-epoxy case and have perhaps 95% peak efficiency. I'm
re-doing the Honda with the latest motor. (It should be quiet - the
shaft was pressing down on the gears in the first version.)
For a speedboat, the Honda's RPM is too low because of a built in
2.8 to 1 speed reduction at the bottom of the leg to the prop. The
motor gets to its top RPM (~2000) without pushing very hard. So I'm
also planning an "electric outboard from scratch" that would have 1
to 1 or thereabouts. I was going to use a chain drive, but have
realized a toothed belt (as in car engine timing belt) would be
quieter and could let the leg be made narrower.
Regards,
Craig
Victoria BC Canada
http://www.TurquoiseEnergy.com/
=====
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