Are electric horses really bigger?

Understand. Graph is have some problems for P1 and P2 are not Synchronization in this graph. Thank you. I think we should make less testing result in one graph show.

 

Caroute, that graph is a complete mess. I guess only your engineer knows how to read it.

For example: you say that the overload condition is I=57.25A, P1=2699.9W.
But the curves I (magenta) and P1 (yellow) never arrive to those values.
By looking at the relevant lines, they extend to (approximately):
- Imax=50A
- P1max=2400W.
So where do you read those values in the graph?

Sorry, I disagree.
You have to show the correct data, not less data.

 

Thanks for your intersting. We also have Excell Data. I get them from excell fill. The fraph stop in max P2. When max P2, the I=50.14A V=48.03V, P1 is 2408W. P1 please look left ruler, P2 look right ruler.
Due to there is too many results in one graph, and P1 and P2 not Synchronization. It make a little complicated. Sorry for make confusing.

 

P1 please look left ruler, P2 look right ruler. P1 and P2 not Synchronization. Sorry make the confusing. There are too many resulting in one graph.

 

There is no confusion. What there is, is wrong data and calculations. Technical specifications and sales pitches are two very different things.

 

I've been digging around on this subject for months and my understanding is, it's torque that turns propellers. Who cares what the horsepower rating of the engine is.

I've taken two engines with close horsepower ratings to compare.

The Perkins M92B Diesel (86 Horsepower) and the Curtis 1239-8501 electric motor (82 Horsepower)

The Perkins develops 227ft lb of torque at 1200rpm and the Curtis 94ft lb at 5000rpm

If we're running both through a transmission to turn the prop at 800rpm then my rough calculation after deducting 10% loss for the transmission is a total torque at the prop of 306 ft lb for the Perkins and 528 ft lb for the Curtis.

Is this where the proponents of electric drive get their idea from that an electric motor can produce 50% more power than the equivalent Diesel?

Or have I got this totally wrong?

Please would you provide your thoughts / input on this?

Regards

Dave

 

NO.

POWER (the rate of doing WORK) is dependent on TORQUE and RPM.
TORQUE and RPM are the MEASURED quantities of engine output.
POWER is CALCULATED from torque and RPM, by the following equation:
HP = Torque x RPM ÷ 5252

 

"my rough calculation after deducting 10% loss for the transmission"

That is a very high loss , 2% or 3% might be closer on a modern marine unit.

If you have a home brew chain or belt setup 10% might be correct.

 

Yes. Agreed. 10pc might be high. But it's the same deduction for both. The point I'm trying to clarify is...it looks like I could swing a larger prop at the same 800rpm because the electric motor, although lower in torque at it's output shaft, runs at a much higher rpm and can be geared down more than the diesel to obtain a higher output torque. This must be true? Or not? Is this where the electric boys get their "more powerful" from?

 

Dave
You are using the numbers incorrectly here
The Perkins while rated at 86 hp, it is not rated at the rpm that you have used in your calculations
The Perkins at 227 lbft of torque at 1200 rpm is actually producing about 52 hp

 

Maximum torque at 1200 rpm out a gearbox for either the motor or the engine will be obtained using a gearbox with ratio selected so that the motor or engine operate at the speed for maximum power (not torque). Redo your calculations with the Perkins engine operating at the speed it produces the maximum 86 HP and the gearbox ratio which results in 1200 rpm at the prop shaft.

 

The Curtis 1239-8501 is an electric motor controller, not an electric motor. http://www.electriccarpartscompany....-550A-Maximum-br-SV-PWM-Controller_p_495.html

94 ft lb torque at 5000 rpm is 89.5 HP, not 82 HP.

What motor did you use in your comparison?

Maximum torque and maximum power for a given motor or engine usually do not occur at the same engine/motor speed.

 

94 foot lb torque at 5000 rpm (89.5 HP) into a 90% efficient gearbox results in 352 ft lb torque at 1200 rpm output speed, not 528 ft lb torque.

In comparison 86 hp into into a 90% efficient gearbox results in 339 ft lb torque at 1200 rpm output speed, not 306 ft lb torque.

The difference in output torque at 1200 rpm is proportional to the difference in input power.

http://www.calculatoredge.com/new/horsepower.htm#hp

 

Hi Barry,

I just used the specs from the manufacturers website.

https://www.perkins.com/en_GB/products/new/perkins/marine-power-systems/pleasure/1000003196.html

M92B MARINE PROPULSION ENGINE

4 cylinder
4.4 litre
64 kW at 2400 rpm
Peak torque 308 Nm at 1200 rpm


And from this website for the Curtis motor

http://www.evwest.com/catalog/produ...ucts_id=383&osCsid=2ouirfujonvul0g2ffcgooo6i2

Motor Type: AC Induction Brushless
Weight: 95 lbs (43.1 Kg)
Max Voltage Input: 165V
Terminal Stud Size: 5/16 Inch
Integrated Sensors: Encoder and Temperature
Rated Torque: 94 Lb Ft
Rated Power: 82 HP
Max RPM: 10,000

Not knowing much about it I had to start somewhere

 

Hi David,

I used this motor for the comparison:
http://www.evwest.com/catalog/produ...ucts_id=383&osCsid=2ouirfujonvul0g2ffcgooo6i2
And the torque / performance graph is on the same page.

I got the perkins info from here:
https://www.perkins.com/en_GB/products/new/perkins/marine-power-systems/pleasure/1000003196.html

Regards

Dave