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Discussion Starter · #1 ·
What are my options for powering this motor apart from the absurdly expensive tesla model S battery pack? Could I possibly run a custom pack of something along the lines of LG chem modules? I've seen that the operating voltage varies from 275-400 for this motor.
 

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Yep, pretty much any battery will do it, As long as you have the right voltage and the battery is capable of supplying enough current at peak demand (C rating)
If you really wanted, You could even use lead acid batteries, But they would be very heavy and bulky. The great thing about the tesla battery modules is they are very energy dense.

This is the battery im going to be using to power my tesla motor, 24 of these modules in series to get me upto 400v at full charge
 

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Why?

Nobody says you have to source 900Amps. If you did...you'd need a Tesla pack 🤦‍♂️

300A may be enough for his application.
Because if you go WOT with an LDU you are going to draw right at 900 amps. You may not need it but if you have selected an LDU then you should have the battery to support it, otherwise you could hurt things.
 

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Discussion Starter · #10 ·
Be very aware of the thermal capabilities of the LDU, they are pretty terrible. You'll derate to less than 50kW after ten minutes, some people say 35kW is all they are good for steady-state. Is that enough to push your boat at the speed you require?
This is regardless of a custom cooling setup? I will be taking cold water in off of the lake and running it through heat exchangers. The cooling loop will also have a decent amount of fluid and should take longer to heat soak compared to a standard Tesla.
 

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This is regardless of a custom cooling setup?
For the most part yes, although any temp reduction of the water going in compared to the car will be a direct offset- so a small improvement to be had. The issue is not the cooling, it is getting the heat from the copper to the coolant and that is not something you can solve easily. The biggest problem of any induction motor is cooling the rotor, there is a pic on Reddit of a Tesla rotor that has reached over 400degC as it is purple color in the middle.

You can move the inverter to a separate coolant loop which will help a little- OEM the motor pre-heats the inverter coolant so it isn't a particularly good design for high power.

The later Y/Plaid magnet motors would be a better shot as they have a much better coolant system, however they aren't as easy to implement as the LDU since there isn't a drop-in inverter option yet. There will be one coming though, somebody will hack it for sure.
 

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Discussion Starter · #13 ·
For the most part yes, although any temp reduction of the water going in compared to the car will be a direct offset- so a small improvement to be had. The issue is not the cooling, it is getting the heat from the copper to the coolant and that is not something you can solve easily. The biggest problem of any induction motor is cooling the rotor, there is a pic on Reddit of a Tesla rotor that has reached over 400degC as it is purple color in the middle.

You can move the inverter to a separate coolant loop which will help a little- OEM the motor pre-heats the inverter coolant so it isn't a particularly good design for high power.

The later Y/Plaid magnet motors would be a better shot as they have a much better coolant system, however they aren't as easy to implement as the LDU since there isn't a drop-in inverter option yet. There will be one coming though, somebody will hack it for sure.
So say I undervolt it as a start so I am not running the full 400 volts since it is rated down to 275 I believe, that should help initially with cooling, correct? Also, most of this motors life will not be spent at WoT. Cruising Around 2500-3000rpm is where it will be sustained.
 

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Discussion Starter · #15 · (Edited)
No boat that'll carry the weight can get pushed more than about 6-10 knots for about 3 hours using a 100kW Tesla pack.

Electric sucks for a power boat unless it's a dragster.
Where are you getting those numbers? I have personally seen a boat that uses a 40kw pack move up to 30knots for a range of 80+ miles. Propellers, propeller layout, inboard or outboard, overall vessel weight, and the number of motors all play a MASSIVE role in range. There is also a boat that can move up to 40 knots on a 120kw pack for 100 miles. Both are full size vessels that certainly have some weight.
 

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Do you have some equivalent ICE fuel burn data? That will give a good indication of your electric load. Is it a planing or displacement hull?

Under-volt and load are not related, lowering the volts just lowers your maximum available rpm. What causes most of the heating is the required torque output and hence the phase current. Choosing a prop that cruises with the motor spinning at 7500~8000rpm (800rpm prop if you are using the Tesla transaxle) will put the motor at its most useful rpm for steady-state power, however the peak power will be quite a bit down due to the low rpm. You don't really want to spin faster than that for very long as it will be less efficient and create more heat.

Electric is really good for boats under the right conditions and expectations, however it needs a bit of planning ahead of time to avoid underpowered/overheating. Personally I wouldn't use a LDU for a boat, they aren't very efficient and don't make much steady-state power for their weight
 

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^^ You have seen a boat with a range of 80 miles. Yes. You have seen same boat with a top speed of 30kt. OK. You have not seen that boat run for 2 hours and 40 minutes at 30kt on 20hp carrying 500# of battery.
 

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It is driving a boat propeller. Certainly lower current draw than street use since at no point will this motor be near stall condition.
The concern isn't really a stall condition. Motor current isn't the issue in battery selection, battery current is. The inverter converts battery voltage and current to lower voltage and higher current to the motor. Battery current is simply the power needed from the battery divided by the battery voltage. So determine your peak power requirement, and your energy requirement (based on range or operating time and power), and choose the battery size based on that.
 

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Discussion Starter · #19 ·
Do you have some equivalent ICE fuel burn data? That will give a good indication of your electric load. Is it a planing or displacement hull?

Under-volt and load are not related, lowering the volts just lowers your maximum available rpm. What causes most of the heating is the required torque output and hence the phase current. Choosing a prop that cruises with the motor spinning at 7500~8000rpm (800rpm prop if you are using the Tesla transaxle) will put the motor at its most useful rpm for steady-state power, however the peak power will be quite a bit down due to the low rpm. You don't really want to spin faster than that for very long as it will be less efficient and create more heat.

Electric is really good for boats under the right conditions and expectations, however it needs a bit of planning ahead of time to avoid underpowered/overheating. Personally I wouldn't use a LDU for a boat, they aren't very efficient and don't make much steady-state power for their weight
This is a planing hull. Center Console planing hull to be exact. Boat weighs about 3,000 lbs. If the LDU has cooling issues and other problems etc for my application, is there another option you would recommend? I need high HP on tap if I want to get up and go, but mostly will be cruising. I would like to achieve a cruising speed of 25-30mph. And I do have ICE data, for my application they're burning about 1.5GPM at cruise and down under 1 when running. Also, a prop that cruises at 7500rpm? I'm not sure if that exists? That would be screaming for any ICE outboard. Most of these props that we use are designed to cruise at 2500-3000 max and I intend to run the motor at the same RPM for cruising. Also, if most of my heating is caused by the required torque, will my required torque not be lower since I am not driving a tire on a road but rather a propeller through water?
 

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Discussion Starter · #20 ·
^^ You have seen a boat with a range of 80 miles. Yes. You have seen same boat with a top speed of 30kt. OK. You have not seen that boat run for 2 hours and 40 minutes at 30kt on 20hp carrying 500# of battery.
Most certainly not, I can agree with that :). The intention is not to carry high speed all of the time. This is not a race boat. The intention is if I want to go fast for a bit, I can. Mostly cruising is the goal.
 
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