“i will test the system up to the point just below failure”
To test an electric motor to close to failure will most likely damage the polymers used in the motor or destroy commutators.
With electric always keep the motor as cool as possible. It will not harm its materials, it wont help its performance and it will help ensure a reliability and a long service life – in brushless the coils and magnets & their bonding benefit from cool running. In brushed motors water cooling on the brush hoods can help avoid brush damage and may help the commutator (use a small bilge pump running under volted).
When measuring motor temp avoid using case temps unless the case is in direct contact with the coils and be conservative. The coils themselves are a better indicator of heating – use an infrared thermometer for that. If brushed the brush/commutator interface will be the hottest part of the motor and the first to fail (unless you overvolt into catstrophic iron losses)
The best way to keep a motor cool is to run it at the highest recommended voltage within its highest efficiency amp range – rpms of 85-93% of peak rpm for the voltage under load are generally correct for permanent mag neodymium motors.
Gearing gearing may be useful to run as a close as possible to peak efficiency rpm given the prop you have. The most efficient way to run is always full throttle at say 85-92% of peak rpms (given the voltage underload). First the speed controls are more efficient – about 3% in brushed but up to 50% in brushless. Gearing by varying prop speed and keeping the motor rpm constant allows the amp draw to be increased or reduced – we are looking for reduction, so optimal gearing and a shorter gear for cruising at low amps and high throttle settings
Electrics are a simple technology unlike internal combustion which can be radically affected by a range of environmental factors. Once the operating range of electric is known, and temp measurements checked and ok, the motor will run consistently in that range given similar throttle and air temps. Once these are established the bearings are an important failure point which should also be monitored as wear there will increase temps and reduce motor effiency
From:
Sent: Thursday, 8 September 2011 10:56 PM
To:
Subject: Re: [Electric Boats] Cooling motors
thanks Capt. Mike, i think that no matter what i end up with in the end i will have to test the motors abilities to the point of heat related shutdown or at least, if i can read the temps via perhaps the controller, i will test the system up to the point just below failure... i completely agree that KISS is the way to go and an additional fan or two seems pretty much a no-brainer....
i am more and more wanting to take a shot at doing this all myself with two or three of the ME0913 motors... looks fairly straight forward.... pulleys, drive belts, bearings, shaft, frame to support it all.... when i think of possibly three motors i have to wonder about a double sided drive belt, i have no idea of the appropriate terminology but a sort of... M configuration for the three motors with the powered shaft directly below the M... motors in parallel??? or i perhaps not but I must learn more as i am out of my depth at the moment.... do you know, does a motor such as a ME0913 require an individual controller due to some sort of frequency feedback that the motor must supply?
From: Mike <biankablog@verizon.net>
To:
Sent: Thursday, September 8, 2011 7:18 AM
Subject: Re: [Electric Boats] Cooling motors
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As for water cooling I think it adds another layer of complexity (especially on a boat) not only with I assume having some type of pump to circulate the coolant but, to me also some concerns about corrosion and dissimilar metals especially in a salt water environment possibly requiring sacrificial zincs etc... Anyway it's just some issues that I think needs to be considered when installing them on a boat. Capt. Mike
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