On 2/28/2012 11:29 AM, Chris Hudson wrote:
Chris
motors vary a lot depending on the design
the safe way to approach an electric is low loading first -
1/2 voltage is your easiest option
then you have a good base line to work from - and estimate whether your current motor gearing prop setup will enable you to run full throttle at 100% volts
Andrew
Thanks Eric. I know the power required to reach my target speed and the prop RPM needed to get there. I'll keep my current prop for now. With this data shouldn't I be able to calculate my gear ratio?
--- On Mon, 2/27/12, Eric <ewdysar@yahoo.com> wrote:
From: Eric <ewdysar@yahoo.com>
Subject: [Electric Boats] Re: PMAC gear reduction
To: electricboats@yahoogroups.com
Date: Monday, February 27, 2012, 5:14 PM
Hi Christopher,
Your optimum gear ratio will depend on a number of factors. What kind of boat (how much load)? What kind of controller (target RPM)? What performance (target speed)? What prop specs (max diameter, pitch, etc.)?
For an auxilary sailboat in the 27'-32' range, you can use a lot of the specific info that has been posted in this list by other people using 48V ME0913 systems (including me) like Electric Yacht, Propulsion Marine and others.
In my boat, the max motor RPM is 1900 and the max amps are 106, well within the continuous rating for the motor. My controller is a Sevcon Gen4, my prop is 13x15.5 and I use a 2.55:1 reduction. You can see a photo of the prop in this group. http://groups.yahoo.com/group/electricboats/photos/album/1967401930/pic/1689340396/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc With a less aggressive prop, I would need to move to a lower gear ratio (higher prop speed) to hit the same balance. Likewise, if I changed to a lower gear ratio while using this prop, the motor be turning slower and it would pull more amps to hit the same prop RPM (boat speed). If I switched to a higher gear ratio, I would run out of motor RPM at a lower boat speed and my max amps would be correspondingly lower too. As it is, I'm getting the amps that I want at the speed that I want, so it's good enough for me.
For other types of boats, you need to describe more of what you're trying to do.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "ChristopherH" <clh5_98@...> wrote:
>
> Hi Andrew, thanks for the reply. To clarify, I'm looking at the ME-0913 motor. The mfg website states 92% efficiency between 24-96V. They give the torque constant at .15 N/Amp. I don't think that gives me the data I need. I plan to run a 48VDC system, how can I figure out what gear ratio I need for a PMAC motor such as this?
> Thanks,
> Chris
>
> --- In electricboats@yahoogroups.com, Andrew Gilchrist <andrew@> wrote:
> >
> > Chris dont complicate it
> >
> > get the manufacturers spec sheet
> >
> > Find out the amps at max efficincy - this will be at a particualr
> > amperage the three are locked together at a given voltage on the same motor.
> >
> > For the voltage to be used, the recommended or a little more voltage is
> > usually the preferrable range
> >
> > Then gear to ensure the motor is running at the maximum efficeincy
> > amps/rpm. That way you will have least heating for the power generated.
> >
> > Nontheless the motor life may benefit from a cooling jacket.
> >
> > Andrew Gilchrist
> >
> >
> >
> > On 2/27/2012 2:31 AM, ChristopherH wrote:
> > >
> > > I understand how to calculate gear reduction for PM DC motors based on
> > > the manufacturer stated motor RPM/V X System Volts/desired max prop
> > > speed. I'd like to understand how to calculate gear reduction when
> > > using a PM AC motor.
> > >
> > > Thanks,
> > > Chris
> > >
-- AJ Gilchrist Fastelectrics 0419 429 201
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