Thanks again John:-)
A small difference in peak efficiency compared to optimal motor conditions I can accept of course (I am not looking for hitting the 94% spot;-). And also a narrower high efficiency "window" is ok, but then as you say the gear reduction has to be correct. And if the motor supplier has not provided enough data (e.i. an efficiency map or similar) it is rather impossible to find the right gear reduction:-/ Or I have to do bench-tests as I did with my 17kW motor (not easy to perform with my simple equipment I have in my basement!)
By the way, my 17kW motor does not seem to have any high efficiency window at low power at all - or I did not find it because it is extremely narrow;-) I tested it for several rpm and torque combinations (approx 200rpm to 3000rpm at 1kW to 4kW).
This motor (Perm) and its curves (12-72V) looks interesting since the motor has both high efficiency at low power (e.i. 36V, 1650rpm, 4HP) AND high peak power at the double rpm (72V, 3200rpm, 25HK) which is exactly what I am looking for. But the peak efficiency is really narrow (for all voltages). With this motor it is crucial to find the perfect gear reduction! Waiting for price on this one...
The Gori propeller looks nice, but I am not sure if it would be a good choice on my boat (not a sail boat). I think I rather go for a very large, fixed propeller if I need to change the one I have.
Regards
Bendik
On Thursday, August 11, 2016 6:39 PM, 66b6dcd5b59507e7d751ea81382ea1f6 <no_reply@yahoogroups.com> wrote:
Hi Bendik,
Re efficiency. In the case of my D135 motor http://lynchmotors.co.uk/pdfs/lmc-lem-200.pdf then it can run up to 84V but of course it can run at any voltage up to that and efficiency with more voltage has a bigger spread of efficiency in terms of amps as you suggest, so there are still ratings for 12V, 24V, 36V etc where the right combination of volts and amps can achieve the same peak efficiencies but in a narrower band. So for me and as most sailing boats run at a constant speed it's fine to run a lower voltage. The difference between my 24V direct drive system say compared to 48V geared is say 3% in peak efficiency but then again the 48V needs to have a reduction gear to get the same shaft speed so losses there - which all makes it much the same in terms of efficiency, if not peak and continuous power.
I'm originally a marine engineer Bendik but I may add steam to trade so I'm no electrical or electronics engineer. But yes I've learnt some stuff with DC brushed in the last 5 years and as you suggest have limited knowledge when it comes to other motor types and field weakening etc., where the rpm/volt is not contant at higher speeds.
Yes, to your 400 shaft RPM @ 4.5 Knots prop. I'm 800 at that boat speed.
John R.
Re efficiency. In the case of my D135 motor http://lynchmotors.co.uk/pdfs/lmc-lem-200.pdf then it can run up to 84V but of course it can run at any voltage up to that and efficiency with more voltage has a bigger spread of efficiency in terms of amps as you suggest, so there are still ratings for 12V, 24V, 36V etc where the right combination of volts and amps can achieve the same peak efficiencies but in a narrower band. So for me and as most sailing boats run at a constant speed it's fine to run a lower voltage. The difference between my 24V direct drive system say compared to 48V geared is say 3% in peak efficiency but then again the 48V needs to have a reduction gear to get the same shaft speed so losses there - which all makes it much the same in terms of efficiency, if not peak and continuous power.
I'm originally a marine engineer Bendik but I may add steam to trade so I'm no electrical or electronics engineer. But yes I've learnt some stuff with DC brushed in the last 5 years and as you suggest have limited knowledge when it comes to other motor types and field weakening etc., where the rpm/volt is not contant at higher speeds.
Yes, to your 400 shaft RPM @ 4.5 Knots prop. I'm 800 at that boat speed.
John R.
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Posted by: Bendik Vignes <bendik.vignes@yahoo.com>
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