Thanks Miles! I see another of the charts I have labels the X axis "LBIN" which I should have noticed...
--- In electricboats@yahoogroups.com, "Myles Twete" <matwete@...> wrote:
>
> Almost..the X-axis is Torque in units of Inch-Pounds. With permanent magnet
> motors, the torque and current are essentially proportional (note the line
> relationship) and so you can confirm this. Also you can calculate Kt and Kb
> from that line.
>
>
>
> Kt = dT/dI ~ 200 in-lb / 180 amps = 1.11 in-lb/amp
>
> Convert that to N-m/amp and you then also have Kb in units of volts/rad/sec.
>
>
>
> -mt
>
>
>
> From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
> On Behalf Of F Neil Simms
> Sent: Friday, May 20, 2011 6:47 AM
> To: electricboats@yahoogroups.com
> Subject: Re: [Electric Boats] High efficiency at low rpm AND low power
>
>
>
>
>
> Can you guys confirm I'm reading the performance charts on the bigger motors
> properly?
>
> I am interpreting them to indicate that, even if I run them at as high a
> motor rpm as possible (ie, with reduction that allows that), at low
> power/current levels the efficiency will be very low.
>
> Here's the chart for a Mars ME0708:
>
> http://www.cloudelectric.com/v/vspfiles/assets/images/me0708data.pdf
>
> The plot for efficiency starts at 10% and doesn't approach 90% until halfway
> across the chart.
>
> And I'm assuming the X-axis on the chart is amps (why don't they label it)?
>
> I knew I should have become an electrical engineer rather than a software
> geek :)...
>
> --- In electricboats@yahoogroups.com
> <mailto:electricboats%40yahoogroups.com> , "Eric" <ewdysar@> wrote:
> >
> > John,
> >
> > Good info. However, Neil want's to be able to run at 8.5kts with the same
> motor, batteries and prop as well as long distance. Like you, I can give
> advice on how to achieve either one of those goals, but not both with the
> same system.
> >
> > Fair winds,
> > Eric
> > Marina del Rey, CA
> >
>
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