Whoops caution re low power applications say under 10hp
On 3/6/2012 11:42 AM, Andrew Gilchrist wrote:
Asynchronous motors are not a great option for marine use
They are most common in apps when AC is available and speed is constant. The controllers achieve varying speed by varying the frequency of the supply .
Efficiency is generally 85-96%. Low power induction motors are inherently less efficient that high power versions with the 90% level arriving around 10hp/7.5kw.
http://www.icrepq.com/icrepq-08/352-mantilla.pdf is a good reference showing the efficiency rating can also varying significantly 72 <-> 84% for the same motor (2hp in this case) depending on the test method used. High power motors show less variation in efficiency due to testing procedures.
As batteries and solar are DC these motors require inverters which commonly vary in efficiency from 98-84%. Depending on the components chosen and the power level (higher being better) the efficiency could range between 71 and 92%.
Torque is the most problematic element of electric systems. It is not abundant, it depends on amp draw (which means high torque = high losses and high heat is the motor is not well matched to the task. Asynchronous motors have idiosyncratic torque curves depending on whether they are single or polyphase and where the are single or double squirrel cage. Other motor types have more consistent torque characteristics. It is important to match the type of asychronous motor to the working load to be dealt with; any asynchronous motor will not do.
In any electric power system - if cable weight is an issue the power system is very poorly specified.
On 3/6/2012 1:21 AM, marcdrachten wrote:Low cost: industrial high voltage (110v/220v) asynchronous motors are far cheaper compared to DC engines with same power ratings. For controllers the same applies (at least what I can find so far)
Power: HV motors come in a wide power range starting below 1kW. You can use an inverter to get power from batteries starting at 12v batterie supply and everything up as you like. The inverter can also double as a charger.
Weight and cost is not much of an issue indeed, but 24v @ 100 amps requires a bigger cable compared to 110v @ 22 amps or 220v @ 11 amps, making installation easier. If I'm not mistaken, length of cables could also be longer offering more flexibility. But I'm not entirely sure about that.
My assumption is that durability is far higher since all off the shelf industrial grade parts can be used.
The only disadvantage is that these motors are slightly less efficient, but doesn't price, durability and flexibility compensate for this?
-- AJ Gilchrist Fastelectrics 0419 429 201
-- AJ Gilchrist Fastelectrics 0419 429 201
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