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Need help with 72v motor for sailboat

TommyR

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Nov 16, 2019
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I recently purchased a sailboat which the seller had removed the diesel engine and purchased an electric motor. It isn't installed as of yet. I called the manufacturer of the motor to learn more about it. It came with everything to hook it up. They said it could be wired ro 48v-96v battery bank. They recommended 72v. My question is do I need to separate battery banks? One for the motor and one for the house (12v or 24v not sure yet), or is there a way to separate the loads and downgrade voltage for the house side. I'm not going to use the motor unless necessary as it is a sailboat. I did purchase 10kw genset as a backup power source. Ideally want to run on solar but extended motoring could drain the batteries. Please help me figure this out. Thank you.
 
Sounds like fun.
Take lots of pics.
Depending on the house loads, the bank could have a converter connected to feed stuff.
I'd prefer to have separate banks though.
What kind of motor? What controller?
 
You could probably use a few of these or similar to convert down to 12v. The bigger problem may be the proper charge controllers and inverters for 72v. I'm currently running 36v and sometimes finding compatible devices is a challenge, but I haven't gotten too deep into it yet.
 
Sounds like fun.
Take lots of pics.
Depending on the house loads, the bank could have a converter connected to feed stuff.
I'd prefer to have separate banks though.
What kind of motor? What controller?
It is HPEV's ac35 motor kit. I have a background in electrical but not a lot of experience with batteries and dc voltage. They told me I needed at least 200 amp hours, so I figured I would research udon three Tesla batteries in series. Didn't know if I could wire two systems feed by one power source. And on top of that, how to tie in the genset and solar components. In the planning and learning stage right now so any layman advise would be greatly appreciated.
 
Look at the byd batteries will has linked for us.
LithiumCobalt-Ion batteries are lighter for sure, but in a boat scenario, I wouldn't want something flammable...
Stick with LIFEPO4 or SLA
Weight isnt an issue on a boat usually...
 
I just liked at the diy dollar blueprint section and had a question. I would like to think of myself as a creative thinker but sometimes that gets me in trouble. I so the diagram for a 24v solar setup and was thinking is it possible to convert the voltage up to 72v with a the same size battery bank stated before. Instead of 72v 250ah, it would be 24v 750ah. I realize you advise against Tesla in this application but the numbers are more what I'm trying to work out.
 
That motor is rated for up to 96v at 650 amps for full power. That's 62kw!!! I haven't looked for a data sheet to see what the draw/rpm #'s look like at 72v, but lets assume you only need half the rated rpm; you'll probably be in the 20kw+ range drawing ~300ah @72v. That would be 833 amps at 24v, making any kind of buck-boost device (24v-72v) impractical, if not impossible.

If you plan on using your electric drive for anything more than docking I'd be designing a 72v 900ah+ battery bank for that kind of draw.

What size is the boat, what is it's hull speed and what is your goal max speed? On a smaller, efficient sailboat, it's likely you only need 20% of the motor's rated power to reach close to hull speed, and if that's the case you may be able to get away with only a 200ah bank.
 
It's 46'. This what I have as far as a graph showing power consumption at 72v. I would mainly be using it for docking and travel to and from a marina. I purchased a 10kw genset ro create short of a hybrid setup for extended use. ie. Bad weather, no wind, etc. Really need to know more about power distribution and what components I need to look at using ro incorporate the genset plus solar to operate thre motor and house.
 

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To match the speed of the original diesel chugging along at 1500rpm (assuming you are using the same prop) you'll be drawing about 400ah @72v according to that chart. If you are using a 200ah battery it will have to be capable of a 2C continuous discharge rate, and you'll get about 15-20 minutes of useable runtime at that speed. 400a @72v is almost 30kw, so if you want your 10kw genny to extend your range you'll probably have to keep it below 500rpm. Re-propping may be a way to drastically change the above #s to better make use of the electric motors low rpm torque, but I'm not sure. Solar will be a nice way to keep the house battery charged up while on the hook, but don't expect it to help much with runtime or bulk charging. I don't think there's enough room for enough panels for that.
 
What type of charge controller do you think would work best for this type of application.
 
That would depend on how many watts of panels you can fit. Then it depends who makes one in that size capable of being adjusted to work with a 72v battery. That second part may be tricky and off the top of my head the only one I can think of is the Midnite Classic, which is probably overkill for the amount of solar you are likely to be able to fit on the boat (physically).
 
Ok thanks for your time. Not sure how much solar I'll have. Mainly the solar will be for the house usage anyway. Still have a lot of homework to do.
 
Sounds like a reason the previous owner sold was he got part way into the project and realized the numbers didn't add up. You are going to need more panels and batteries than is practical.
 
If I have to get two battery banks I will, but going to do more research first.
 
Sounds like a reason the previous owner sold was he got part way into the project and realized the numbers didn't add up. You are going to need more panels and batteries than is practical.


With a project this size, the cheapest thing to do may be buy a crashed Tesla for $20k ;)
 
I don't think I need that much power. Just enough to motor in and out of marinas. I don't have ro get up to hull speed.
 
I don't think I need that much power. Just enough to motor in and out of marinas. I don't have ro get up to hull speed.
Yeah, hull speed, and battery capable of it, would need a HUGE solar array... maybe at your dock? But if you rent a dock, you will simply need a charger. Several choices out there to plug in a Tesla bank.
 
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