3.5 knots may be possible…
Yours,
Andrew Gilchrist
fastelectrics.com
Australia
0419 429 201
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of Orest Iwaszko
Sent: Tuesday, 16 April 2013 4:19 PM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Illusive gear ratio THE RESULTS ON PAPER
yes at 1750 rpm at 100 % throttle with no load
220 volts ac goes to controller which outputs up to 180dc volts to the 3 hp motor
torque 108 lb. in.
rated 14 amps
ty Orest
On 2013-04-15, at 10:39 PM, Andrew Gilchrist wrote:
Since the motor should spin at 1750 at 100% full power
Max power is at 50% of rpm - do you mean 1750 at 100% throttle.
What is the kv and voltage of the motor?
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of Orest Iwaszko
Sent: Tuesday, 16 April 2013 2:49 PM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Illusive gear ratio THE RESULTS ON PAPER
Here are the results for my 180 volt 3 Hp system .
I'm trying to determine the correct pulley size for the shaft . This is the challenge right now
Since the motor should spin at 1750 at 100% full power but with the present (2.5 inch on the motor and 9 inch on the shaft ) it bogs down at 1100 rpm / 65% power setting. Here the controller ( the weak link ) starts warming up anything over 65 really heats up the controller in 15 min to plastic smelling levels. The dc motor remains cool .
I did tests and here are the results
power motor amp dc shaft Hp developed HP developed boat ( I DIDNT DEVOTE ENERGY TO BOAT SPEED BECAUSE IT WAS THE MOST UNRELIABLE MEASUREMENT OF THE LOT )
level rpm draw voltage rpm at motor at shaft speed IM CONFIDENT THAT 60% POWER WAS AROUND 2.3 -2.5 AND TOP SPEED OVER 3 MPH )
amps X volts
750
10 120 2.3 18 30 .05
20 310 4.6 38 77 .23 In my case my pulley ratio is 2.5 : 9 or 3.6 : 1
30 490 7.0 56 122 .52 So Hp at motor x 3.6 = Hp at the shaft ?
40 650 9.8 74 162 .96
50 790 12.5 92 197 1.53
60 910 15.1 108 225 2.17 2.5
70 1005 17.1 120 251 2.73
80 1180 18.1 128 270 3.08
90 1100 18.6 128 275 3.17 3.3
100 1100 18.8 128 275 3.2
The question is how much larger should the shaft pulley be and what benefits can I expect with an optimized pulley.
On 2013-04-15, at 11:06 AM, Orest Iwaszko wrote:
My 3 dc hp 1650 rpm motor is boging out at 1100 rpm . Everything works great up to the 65% power setting where things overheat.
I have tested and graphed power setting %, motor rpm , shaft rpm, amp draw , dc voltage , and boat speed . things absolutely flatten out at 1100 rpm.
Im hoping a larger gear ratio ( Its 2.5' pulley at motor and 9" on the shaft ) should be increased to maybe 13.5 ???
I have a feeling some of you may know how to calculate this .
Orest port alberni
On 2013-04-09, at 2:24 PM, Jon Olson, GED wrote:
Eric,
Thank you for the rational & detailed response. I look forward to your posts.
Jonny Olson
From: Eric <ewdysar@yahoo.com>
To: electricboats@yahoogroups.com
Sent: Tuesday, April 9, 2013 9:30 AM
Subject: [Electric Boats] Re: does anyone have current real world performance figures please
Hi Eric,
I think that you missed my point on efficiencies. The question becomes "If I make this system more complicated by "optimizing" components for partial throttle, how much energy will I save?" Followewd by " Is it worth it?"
Let's look at what was suggested. I installed a 5.5kW drive in my 5.1 ton boat. Perhaps installing two 2.5kW drives would increase efficiency at low speeds because the motor will be operating at a more efficient power level.
So, my boat uses about 500W (about 10% power) to cruise at 3kts (50% hull speed). My ME0913 motor operates at about 70% efficiency at such low power ratings, so the shaft output should be around 350W, if the manufacturer's motor performance charts are correct. So we now know that my boat takes about 350W of shaft power to motor at 3kts. Now, let's use a smaller motor and see how much power we can save. I don't have specs for another PMAC motor tha maxes out at 2.5kW but I can see that my motor at 10% power is 70% efficient and at 20% power it is 80% efficient. To get the same 350W of shaft power, the smaller motor should use about 440W, a savings of 60W.
So if your typical cruising throttle settings are 10% power, installing two smaller motors could give you an efficiency increase of a little more than 10%, at the price of more complexity and potential losses. My range at 3kts is currently 38.1nm, if the power requirement dropped to 440W, my 3kt range would increase to 43.5nm.
Since I have installed my system, I find that I rarely motor at less than 20% power (1000W or 20A) and usually aim for 30A, 30% power or 1250-1500W. So for my usage, the motor efficiency is already at 82%. If I installed two smaller motors and only ran one, my cruising speed motor efficiency would jump to 84%. Applying the same math process, my present 1500W cruise might drop to 1470W, saving 30W or 2%.
My motoring range today at 1500W is around 18nm. If I could drop the power requirement to 1470W at the same speed, my range would increase to 18.4nm.
So, for me the increase in cruising range of 0.4nm is not worth the additional cost and complexity of having two smaller parallel drives. But everyone would have to do their own math and make their own decision about how their system works and how they actually use their boat.
Fair winds,
Eric
Marina del Rey, CA
--- In mailto:electricboats%40yahoogroups.com, "cire" <cirejay@...> wrote:
>
> Eric,
>
> I'm onboard with your point about unnecessary complication, however I think you confuse the efficiency of a hull at 50% hull speed with the efficiency of an electric more at low power.
>
> I admit to not being up on the absolute latest in electric motors but have observed in the past that they seem to operate most efficiently at 75% power or so and least at 25% or below.
>
> What I am saying is that I see the point that Dan is making; the question that you ask about it being worth the complications and loss of efficiency created by two drives is a good one.
>
> BTW, as to the use of one large battery bank, I have a 32' sailboat – Allied Seawind II – with a single 630amphr battery bank and when I explain the Peukert effect as part of my reason for a large single bank to my sailor friends, their eyes roll back into their heads:-).
>
> eric SV Meander
>
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