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Max Range: Theory and Reality

mdkaiser
Fri, 03 Jun 2016 09:28:32 GMT

Hi! Very interesting project; I've enjoyed the videos very much and the addition of writeup is amazing. Thank you for sharing all this great information. I have 2 questions (please correct any assumptions, I'm not experienced with electro motors, batteries or boats): 1: Based on the 125 Ah@48 V you should have 6 kWh (only half of this can be used due to the nature of lead batteries, correct?). So for practical purposes lets say you have 3 kWh of propulsion energy. The power|speed|range graph shows that at 2.7 kt you'd spend 600 W, allowing you to motor for 5 hours = 13.5 nm. In the last section you estimate that you can get 6 nm at 2 kt speed. Any idea where that rather substantial difference comes from? I know the power|speed|range graph is for a 'high-end motor/controller', but does that really make such a difference? 2: On YouTube someone recommended using 18650 Li-Ion batteries soldered together instead of lead-batteries - I believe it was linked to a 'DIY Tesla-Powerwall' Video. On your to-do list you mention getting an old battery from an electronic car. Any rea son not to go the 18650 battery route? They seem incredibly cheap and easy to maintain for the cost. Again thanks for making great videos and sharing your experiences with other people interested in the topic! :) Oh, last question: How come you're not utilizing wind energy? Simply because solar is enough?

umacrew
Sat, 18 Jun 2016 17:55:42 GMT

Hey, great questions. 1. The graph and our predictions are all theoretical. We are working to finalize our charging system now and will be doing some test in the coming weeks, to get some real world numbers. Also, the 50% discharge is relative BS. You can discharge a deepcycle lead acid 100% and still charge it back up, it just reduces the life span significantly. But, for us, Even if we had to replace our batteries every year, that's still only $400 a year. WAY cheaper than diesel fuel. So we feel like its still a win. 2. We've thought about using the 18650's. But, 1. The labor to put them together is intensive to say the least. 2. they are actually no cheaper than normal Lithiums, unless you can find then "used" which is vary difficult without the right connections. There is a company that sells used Tesla batteries from their cars. We're looking into using them. They're about 3kw and 50V so 2 would work for us just nicely. 3. So far solar has really been more than enough. We sized our battery bank to be recharged from 100% discharge in one sunny day. So far, tha t has been the case. Wind is also a relatively low wattage charging source. Also, noisy. We are however designing and will soon be testing regeneration from the prop, which in theory will be a great, reliable power source while sailing. Hope that helps answer you questions.

derekrichey
Fri, 24 Mar 2017 22:53:28 GMT

Following this aspect of your project, very interesting. The gas outboard on my Precision 23 crapped out several months ago and I haven't replaced it in part because I tried using the smallest Minn-Kota motor and it got us in and out of the marina just fine as long as the wind was light or favorable. If the wind was too strong, we could sail out and in. This has also made us better sailors I feel. I definitely have to think much further ahead with electric, at least this small, not having the torque/power that the 9.9 Johnson did. But it's so quiet, it has really got me thinking about the possibilities. If necessary in a pinch, have you researched the efficiency of keeping your battery bank charged with a gennie so as to keep motoring if you had too for whatever reason? Thanks: Derek jgrmdr@gmail.com