VFD question

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liveaboard
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VFD question

Post by liveaboard » Sun May 12, 2019 12:21 pm

This isn't really a machinist question, but I know some people here use variable frequency drives and have experience of them.

I have a 100 year old, 12 ton steel boat I use for work in Amsterdam [Netherlands].
Powered by a 1965 Mercedes OM636 diesel of around 35HP

Amsterdam has announced it is banning all fuel powered vessels from the city canals in 2025.

An electric boat conversion from a company that sells boat things would cost tens of thousands; that's not going to happen.
It seems to me that a 5 or 10HP 3-phase motor on a VFD would power the boat just fine.
Would it?

I would need about 5hp for an hour for passage through the inner city. This would equal about 400AH at 12v, or the total capacity of 2x 200ah batteries. In reality that would require 4x 200ah lead acid batteries, which is probably cheaper than going for hi output drive batteries. The weight is not an issue in this application.
But; I need short hard higher power for maneuvering and stopping. At least 10hp, 20 would be better. Max about 20 seconds.

I would keep the diesel in there for use outside the city, where life is faster and distances are longer.

5 or 10 HP 3-phase motors are regular things, and available cheap new or used.

At the moment, I don't find any such thing as a 24V DC to AC 3-phase VFD.
There are single phase AC to 3 phase VFD, there are DC to single phase AC inverters for solar power etc, there are welding inverters, and these are all affordable.

Electric drive systems are popular for all sorts of things.

I'm wondering why I don't find such a product as a low volt DC input VFD for this sort of application.
Am I missing something? is there a fundamental reason it wouldn't work?

rrnut-2
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Re: VFD question

Post by rrnut-2 » Sun May 12, 2019 12:44 pm

Go here and check out this website and click under the marine tab. They also have 3 phase systems there as well on their website.

https://www.electricmotorsport.com/marine

Jim B

Russ Hanscom
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Re: VFD question

Post by Russ Hanscom » Sun May 12, 2019 12:54 pm

Also remember that electrical HP and engine HP are not quite the same animal. An engine rated at X hp rarely delivers that except under optimal conditions, so a 10 HP electric may be more than ample.

No engineering reason that your goal cannot be met except that the power conversion you desire is not very common.

Have you considered a DC motor for the driver? DC controllers are common.

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Re: VFD question

Post by Glenn Brooks » Sun May 12, 2019 1:16 pm

Also wondering about a hydraulic power unit as secondary power, rather than DC or 3 Phase direct. You might be able to build an electric hydraulic unit with off the shelf components.

How do you plan to decouple the existing Mercedes motor and reverse gear and hook up the alt power plant?

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Re: VFD question

Post by John Hasler » Sun May 12, 2019 2:08 pm

I second the DC motor idea. An industrial motor rating of 10 hp means 10 hp continuously 24 hours a day, usually at something like 40 C ambient. For 20 seconds such a DC motor can easily deliver four times its rating without exceeding any limits.

Your best deals on such motors will be ones rated 240 V or higher. You can drive one by stringing 12 V batteries in series, but first study up handling DC at those voltages and currents. It's much more dangerous than AC, and not just because of shock hazard.

It might also be possible to drive a VFD designed for 120 or 240 VAC input with DC since they rectify the input anyway. Talk to VFD manufacturers about that.

rrnut-2
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Re: VFD question

Post by rrnut-2 » Sun May 12, 2019 4:34 pm

Just realize that the EU might have something to say about high voltages. The usual safety limit is 50V and less. That website that I listed does have 3 phase motors and controllers that run off batteries. None of this is cheap, but the reliability is there. We use these systems for the diesels that we build.

Jim B

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Re: VFD question

Post by liveaboard » Sun May 12, 2019 6:32 pm

Thanks for all the replies; you've given me some things to consider.
rrnut-2 wrote:
Sun May 12, 2019 12:44 pm
Go here and check out this website and click under the marine tab. They also have 3 phase systems there as well on their website.
https://www.electricmotorsport.com/marine
Jim B
Thanks, they look ok; batteries are not included. also no charger included. $$$
If the price difference is high enough, I would consider importing from the US, but it's a big hassle.

Glenn Brooks wrote:
Sun May 12, 2019 1:16 pm
Also wondering about a hydraulic power unit as secondary power, rather than DC or 3 Phase direct. You might be able to build an electric hydraulic unit with off the shelf components.
How do you plan to decouple the existing Mercedes motor and reverse gear and hook up the alt power plant?
Glenn
I see no sense in turning torque to hydraulic power and then back again.
I had a neighbor who built hydraulic accumulator systems for bigger canal boats to maneuver, the idea was to use smaller cleaner diesels.
It was massively expensive and no one would pay for it. The system was basically hydraulic pump, large pressure tanks [200 bar, 3000 psi] under the cabin floor, and hydraulic motor to give an extra squirt on the prop. lots of expensive controls. It was a government contract.

I would make the electric motor reversible, and couple it to the output shaft with a belt. the existing gearbox turns in neutral with little loss, and when the diesel is engaged the electric motor can just spin free too.
I think.
My boat has a big bearing block on the front of the prop shaft so side loading is no problem, and there's room in there for things.

John Hasler wrote:
Sun May 12, 2019 2:08 pm
I second the DC motor idea.
Your best deals on such motors will be ones rated 240 V or higher. You can drive one by stringing 12 V batteries in series,
Twenty 12V batteries? Too much battery for this project. 10kwh, which would equate to 600-800 ah capacity at 12v, is all I think I need.
What?
Twenty 40ah batteries?? Please, no!
rrnut-2 wrote:
Sun May 12, 2019 4:34 pm
Just realize that the EU might have something to say about high voltages. The usual safety limit is 50V and less. That website that I listed does have 3 phase motors and controllers that run off batteries. None of this is cheap, but the reliability is there. We use these systems for the diesels that we build.
Jim B
As far as I know, I can do whatever I want in my boat. Things are surprisingly lax; this changes above a certain length [19 meters I believe] or for boats that are capable of high speed [planing hulls].
I will look at that site some more.

What I really need is CHEAP. I probably can't escape the battery cost; but I wonder if a junk forklift or golf cart would provide the other parts, charger and all?
Really I need to do the whole job at 1000- 3000 euros.

Next time I'm there I'll get some numbers; hull speed / prop speed, and measure the prop, try to figure out the pitch.
Then I can work out the power requirements , torque and shaft speed more reliably.

Russ Hanscom
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Re: VFD question

Post by Russ Hanscom » Sun May 12, 2019 7:24 pm

Might be a plan; buy a junk forklift and salvage the motor, controls, and battery.

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SteveHGraham
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Re: VFD question

Post by SteveHGraham » Sun May 12, 2019 7:38 pm

Assuming the Dutch have not gone insane, a conversion industry will spring up on its own, and you will have easy access to good answers to your problems.
Every hard-fried egg began life sunny-side up.

John Hasler
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Re: VFD question

Post by John Hasler » Sun May 12, 2019 8:55 pm

liveaboard writes:
I would make the electric motor reversible, and couple it to the output shaft with a belt.
the existing gearbox turns in neutral with little loss, and when the diesel is engaged the
electric motor can just spin free too.

If you use a DC motor the diesel can drive it to charge your batteries.

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SteveM
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Re: VFD question

Post by SteveM » Sun May 12, 2019 9:13 pm

Keep a 2000 watt Honda inverter generator on board.

If you need to run it, nobody will ever hear it.

Steve

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Re: VFD question

Post by liveaboard » Mon May 13, 2019 4:16 am

SteveHGraham wrote:
Sun May 12, 2019 7:38 pm
Assuming the Dutch have not gone insane, a conversion industry will spring up on its own,
There are plenty of firms selling electric propulsion; mostly they fit systems into new boats with high budgets.
A new 50HP diesel drive train for a new boat would run $10,000 or more; double that, and you have an 'eco' electric boat.
The customer is paying $60,000 for the boat, so the option is viable if the use is mostly in the city [where speed and distances are limited]. So cool you know. Their tech guys charge $80 per hour, it's all top quality, and I can't pay for that.

Old boats like mine sell for $6,000 or not at all. There are few left, as the maintenance and mooring tax is very high compared to the sale value.
You would think that the rarity and historic blah blah would start to add value; but so far, these are just considered old scrap crap.

The city is taxing them to death, intentionally. They like shiny new things, not old greasy iron.

Individuals like me who use a thing like this for occasional work are being rubbed out. The high tax has gotten rid of most that were kept for private use, and what are left are used as semi-legal party boats; they host bachelor parties and that sort of thing, sail through the residential areas with screaming drunks and monster sound systems. Not popular with the public.
So instead of enforcing existing laws, they're making new ones; just ban it is the easiest to police.

I used to sail through town with my dog standing at the prow; tourists would be taking our picture, ignoring the tour guide telling them about whatever historic building was above.
They thought here's a typical Dutch guy with his typical Dutch dog; Ha! I'm actually American and the dog was brought from India.
P0002813.JPG
I'm sure I'm not the only one thinking of retrofitting a heavy old boat, but there will be few of us willing to sink more money into something like this.
I no longer live there, so that makes it harder to do anything clever.
I'm rebuilding the 1965 diesel motor in my workshop in Portugal. I'll ship it back and drop it into the boat in the fall.
P0002809.JPG
P0002808.JPG
Originally it had a sail and leeboards. It would have been used for small transport jobs on inland waters, the shallow draft suitable for getting up into farmland drainage canals. It was built with thin plate, maybe 3mm. That's why so few are still floating today.
I bought it in 1983.
There used to be a very ugly square cabin on it, and we lived in there for 7 years.

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