Electric Conversion log for Kahleesea - Page 2 - SailNet Community
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post #11 of 282 Old 10-29-2018
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Re: Electric Conversion log for Kahleesea

Sailing Uma did a 3-way chat comparing electric setups with them, Sailing Saoirse and Learning the Lines. It was all over my head when they started talking about which motor and battery set up they went with


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Re: Electric Conversion log for Kahleesea

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Sailing Uma did a 3-way chat comparing electric setups with them, Sailing Saoirse and Learning the Lines. It was all over my head when they started talking about which motor and battery set up they went with
It's actually much easier since these days as there are more boats that have been converted than ten years ago when I made the leap. There are also a number of EP distributors who have been around for a while. They can provide you with a system that is basically "turn key" spec for your boat. More expensive than building your own but, somebody has done all the design calculations and component specs.

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Re: Electric Conversion log for Kahleesea

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It's actually much easier since these days as there are more boats that have been converted than ten years ago when I made the leap. There are also a number of EP distributors who have been around for a while. They can provide you with a system that is basically "turn key" spec for your boat. More expensive than building your own but, somebody has done all the design calculations and component specs.
I'm homebrewing it, mainly because I want to fundamentally understand how it works.

Also, kits are intended to be diesel replacements, which pretty much ignores the prop physics, leading to inefficient designs.

An electric install really needs to be thought out end to end.
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Re: Electric Conversion log for Kahleesea

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I'm homebrewing it, mainly because I want to fundamentally understand how it works.

Also, kits are intended to be diesel replacements, which pretty much ignores the prop physics, leading to inefficient designs.

An electric install really needs to be thought out end to end.
I kept my three bladed prop from the diesel as it works well with my system. Might consider changing it at some point to see if I can make it more efficient. But, I'm in a "if it ain't broke don't fix it mode" right now. I upgraded to a new controller last year and discovered my system now goes into regen at 4 knots while the old controller did not regen until six knots was obtained. Good luck putting together your system just allow some extra boat bucks for contingencies.

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Re: Electric Conversion log for Kahleesea

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I kept my three bladed prop from the diesel as it works well with my system. Might consider changing it at some point to see if I can make it more efficient. But, I'm in a "if it ain't broke don't fix it mode" right now. I upgraded to a new controller last year and discovered my system now goes into regen at 4 knots while the old controller did not regen until six knots was obtained. Good luck putting together your system just allow some extra boat bucks for contingencies.
What controller are you using now? That's one of the bigger decisions for my conversion, and I'm waffling between three different brands.

Are you using a DC or AC motor?

Physics says for the best efficiency in a water environment you want a large-diameter two-blade prop with a big pitch that doesn't generate any cavitation at all. 600 rpm is my working number for this. Thing is, I don't know if I have enough clearance for a big two-blade prop. When I pull the boat this year, I'll take exact measurements. With a slower rotation speed, you can get closer to the hull without damaging it. If I'm short space, I'll go with a three or four blade prop.

Here's a math-heavy instructional from MIT about props, if you're interested in getting into the nuts and bolts of it.

http://web.mit.edu/13.012/www/handou...rs_reading.pdf
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post #16 of 282 Old 11-01-2018
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Re: Electric Conversion log for Kahleesea

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I'm open to suggestions as to motors, batteries, etc. I'm leaning towards a motenergy 1114 with a 5:1 gear reducer
I don't know Captain Canuck, 5:1 gear ratio seems to low to me based upon what I've seen out there. The drive sheaves between the motor & prop shaft would be huge. I think Baldor or Browning has a program you could play with to calculate sheave diameter.

I've got a Motenergy 10 KW ME 1115 & connected it to a Browning 1.8:1 gear box. It seems to be working for me. The motor spins fast enough to keep it cool. Seems most of the folks out there are running 2:1, a couple at 3:1 & a few are doing or experimenting with direct drive.
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Re: Electric Conversion log for Kahleesea

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What controller are you using now? That's one of the bigger decisions for my conversion, and I'm waffling between three different brands.

Are you using a DC or AC motor?

Physics says for the best efficiency in a water environment you want a large-diameter two-blade prop with a big pitch that doesn't generate any cavitation at all. 600 rpm is my working number for this. Thing is, I don't know if I have enough clearance for a big two-blade prop. When I pull the boat this year, I'll take exact measurements. With a slower rotation speed, you can get closer to the hull without damaging it. If I'm short space, I'll go with a three or four blade prop.

Here's a math-heavy instructional from MIT about props, if you're interested in getting into the nuts and bolts of it.

http://web.mit.edu/13.012/www/handou...rs_reading.pdf
My system uses a LEMCO brushed DC motor operating at 48 volts. The new controller is a Sigma. Had a nice surprise that it starts regen at 4 knots. Previous Navitas unit needed 6 knots of boat speed for regen to begin.

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post #18 of 282 Old 11-01-2018 Thread Starter
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Re: Electric Conversion log for Kahleesea

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I don't know Captain Canuck, 5:1 gear ratio seems to low to me based upon what I've seen out there. The drive sheaves between the motor & prop shaft would be huge. I think Baldor or Browning has a program you could play with to calculate sheave diameter.

I've got a Motenergy 10 KW ME 1115 & connected it to a Browning 1.8:1 gear box. It seems to be working for me. The motor spins fast enough to keep it cool. Seems most of the folks out there are running 2:1, a couple at 3:1 & a few are doing or experimenting with direct drive.
The actual ratio I go to will depend largely on how big a prop I can place. I'm aiming for 600rpm, which is generally where cavitation starts and efficiency starts to go down. I'll need x amount of thrust, which means a y sized prop. Once I know my maximum prop size, I can do the math backwards and find out what speed the prop will have to spin at. I may end up with a less-efficient 3 or 4 blade prop. Once she's out of the water I'll be able to take an accurate measurement.

Direct drive would probably work with a water cooled motor. Not so certain an air cooled motor wouldn't run too hot and burn itself out. Maybe if it was wound for lower speed it would be OK, but low speed motors tend to be very heavy.
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Re: Electric Conversion log for Kahleesea

Don't forget that Volt batteries need their liquid cooling hooked up to safely do anything close to their rated output. That widened bit at the bottom of the long edge of the packs contains the cooling-plate inflow and outflow. They're designed for Dexcool 50/50 mix and it's PROBABLY okay to forgo the whole communications bus that allows reading of the temperature in each cell-pack and just meter the temp of the coolant prior to a heat exchanger. As long as it stays between about 40 and 90F (Gee, ocean temps -- how convenient) you won't need to run the raw water circulator, just the coolant circulator.
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Re: Electric Conversion log for Kahleesea

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Don't forget that Volt batteries need their liquid cooling hooked up to safely do anything close to their rated output. That widened bit at the bottom of the long edge of the packs contains the cooling-plate inflow and outflow. They're designed for Dexcool 50/50 mix and it's PROBABLY okay to forgo the whole communications bus that allows reading of the temperature in each cell-pack and just meter the temp of the coolant prior to a heat exchanger. As long as it stays between about 40 and 90F (Gee, ocean temps -- how convenient) you won't need to run the raw water circulator, just the coolant circulator.
That's an excellent point. I won't be using an entire Volt pack, I'm planning to start with 4 subsections (48V each) wired in parallel. That should give me ~10KwH. If I run it at a .2C drain rate, I doubt that heat buildup will be a problem, but I'll be closely monitoring everything.

Part of this process is going to be figuring out the limits of the system. If I have to add more subsections to keep the overall drain rate low enough to avoid thermal issues, I will.

There are still a lot of variables that I'm not sure of, and this is definitely one of them. If it turns out Volt batteries aren't going to work out, I can always try another type. I had thought about using Tesla subsections, but they come in 24 V pieces and the form factor is tough to work with at 12x24x3.
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