Or once the boat gets up to speed everything will reach an equilibrium which depends on the entire boat and the throttle setting
Put in a PWM controller and mark the throttle settings for given current draws.
Or go to wrecker (this is extremely complex) and get a cruise control and run it from output shaft rpms – it will move your throttle a little bit every now and then or a lot if you run aground …
Yours,
Andrew Gilchrist
fastelectrics.com
Australia
0419 429 201
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of Arby bernt
Sent: Friday, 2 November 2012 12:29 PM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] the device name???..
Dear Michael,
Every controller does this already. It's called open loop. When you set a throttle value, it provides a PWM signal to the motor. In the case of a PMAC motor, there is a field established on the stator according to the amount current being provided by the controller. In fact, nearly every electronic device operates from current, MOSFET's being one exception. MOSFETs are voltage controlled devices.
Closed loop is a control scheme that measures the speed of the rotor and adjusts the current accordingly. I prefer using closed loop on our motors because the motor speed will remain constant during the ever changing load and source conditions. Many diesel engines use closed loop as well. A diesel truck "pullls" up a grade without changing the throttle position, for example.
You might take some time to study Ohm's Law. It describes the relationship between current, voltage, and resistance. Any two of the three determine the third.
A control scheme that might come close to your idea would then change the resistance of the stator to control the current, assuming the voltage remains the same. This is not practical now, but was used in early electric cars. A massive rotating contactor would change the winding connections to the motor. Lots of sparking, contacts blasted away with every shift, and reliability decreased quickly with time. Later systems used battery switching through sequenced contactors with similar results.
Modulating the current using PWM has proven both reliable and efficient. Since current in an inductor rises relatively slowly over time, short pulses with a low duty cycle will only allow small currents to flow. As the duty cycle of the PWM increases, the current flow increases with time, and more current flows. Eventually, at 100% duty cycle, each pulse will last as long as the commutation allows, and the current flow will be regulated by the current limit of the controller, not the PWM.
A long answer to a short question.
Be Well,
Arby
Advanced Marine Electric Propulsion
From: Michael Mccomb <mccomb.michael@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Thursday, November 1, 2012 5:41 PM
Subject: [Electric Boats] the device name???..
I'd like to be able to control a PMAC motor by amperage rather than voltage. Surely there is a device that does this function but I do not know what it would be called.
As one would move the controller/actuator one would be increasing the number of amps that would be supplied to the motor. The "controller" would feed a voltage to the motor, detect the amperage being consumed and then adjust the voltage continuously until the called for amperage was attained.
So let's say that one moves the controller of such a device up from zero amps and so as to be set for 20 amps. The device would detect that setting raise the voltage supplied to the motor as it monitored the amperage being drawn. Of course the amperage would go way up when the voltage was first applied but then quickly come back down to below the selected 20 amps that was called for and therefore the voltage would increase some more with the same resulting cycling reoccurring until a steady state of some unknown voltage BUT 20 smps was attained.
I know that I could build the thing but surely it already exists. Can someone tell me the name of such a device?
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