You're right that it would be nice to put the resistors in the pod where they are cooled by the water. The problem is that you would THEN have to add relays to switch the leads, or at least run extra wires down the tube.
If you did a "full out", "med", and "slow" speed, you could then just have two resistors in the pod. The motor would have a neg. terminal, and the pos. terminal would go to the two resistors in series, with taps running up to the control handle. This would just give you two additional wires up to the conrol head. Is there space in the pod for two resistors?
I saw the web page for Kipawa props - but don't see any specs for them... Is there a page anywhere that has specs for the Kipawa props?
From: Carel Ruysink <c.ruysink@hetnet.nl>
To: electricboats@yahoogroups.com
Sent: Tuesday, June 18, 2013 9:03 AM
Subject: Re: [Electric Boats] Re: Minnkotas - resister vs pulse width modulation
I hasve uploaded to the FILES maps an exploded view, parts list and wiring diagram of my Minn Kota Maxxum 55T (jpg 297, 298 and 299). As you can see all the controls are in the handle only one thick red and one thick black wire go trough the shaft to the motor (part 43).
This is also what I learned when I shortened the shaf to be more fitting with my canoe.
It is wise with a resistor controller to have the resistors under water in the pod but I doubt if that is the case (no special construction for a cheap version I would think).
I now switched my Minn Kota prop (2 blade 11x3 weedless wedge) for a Kipawa 358 (3 blade 10x4,5) with an increase of speed from 10% by the same amp consumption.
One day I will try a Torqueedo 2 blade ultra light prop 8x8 or even a clipped 3 blade Torqueedo travel 12x 10 to a diameter the Minn Kota still can handle.
And of course some experiments with modelairplane props but I have slight doubts if they have enough surface for our slow turning motors
----- Original Message -----From: EricSent: Monday, June 17, 2013 7:28 PMSubject: [Electric Boats] Re: Minnkotas - resister vs pulse width modulationHi John,
If full speed is only 3kts, then I agree, all motoring will be at full throttle. But an well engineered electric drive will deliver more speed with less energy than a trolling motor.
Using my Torqeedo 801 on my inflatable dinghy, I rarely use full throttle, half throttle seems to deliver about 3.5kts from 400W. On my 5 ton ketch, 500W gives me 3kts and 1000W drives the boat at 4kts. In practice, more than 90% of my motoring is at 1500-2500W or 4.3-5kts. That's still less than 1/2 power for my drive. I'm guessing that I could throw more energy into a trolling motor and take longer to get anywhere.
And efficiency is important, even for the smallest drive systems. Every wasted watt is a weight and cost penalty in batteries that you need to carry that don't increase your speed or range.
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