VFD question

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SteveHGraham
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Re: VFD question

Post by SteveHGraham » Wed May 15, 2019 9:08 am

Well this is interesting. The German Tiger tank had disc brakes, years before they appeared commonly on passenger cars.
Every hard-fried egg began life sunny-side up.

hanermo
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Re: VFD question

Post by hanermo » Wed May 15, 2019 10:36 am

Cheapish chicom inverters to 220V ac are available on the chinese bulk sites like aliexpress.
To 16 kW, peak, at least.
Maybe use one to feed the vfd, 220v, and a cheap 3 phase industrial motor, used.
The dc inverter, vfd inverter, and 3-phase motor of == 20-30 hp industrial, continuous output, should each cost less than 1000$.

The inverters wont like/last at 100% duty (16 kW) but you are not using that.
Program the inverters for lower amps than max, and they should last.
Double-insulate the 220V parts via plastic boxes of choice, ventilate with large D fans, like PC/rack stuff, cheap.
220V stuff has dirt cheap household magnetic breakers.
Put in 2 in series, like modern ac code, 15 ms + 30 ms breakers on ground fault. 20€ each, +/-.

The electrics will die from condensation over time, 5-8+ years like most-all boat stuff.

10 kWh of power from lead-acid == 2 kWh of usable power at 10 kW load.
So if you have theoretical (very large) 10 kW of power for one hour, in practice it is 2 kWh, or == 12 minutes at 10 kW load. Lead.
Any higher load kills the battery lifetime, fast.

Modern lion batteries will be much better, and cost about the same in usable capacity in kWh.
But much harder to manage, need bms to charge.
And will last 4x longer.

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liveaboard
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Re: VFD question

Post by liveaboard » Thu May 16, 2019 8:00 am

hanermo wrote:
Wed May 15, 2019 10:36 am
Modern lion batteries will be much better, and cost about the same in usable capacity in kWh.
But much harder to manage, need bms to charge.
Lion batteries? sounds powerful!

Lithium-Ion of course.

An interesting point about $ / usable capacity.
My early rough calculation is that I'll need 5kw for 45 - 60 minutes.
That's how long the journey takes me at the moment.

What is "BMS" ?

whateg0
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Re: VFD question

Post by whateg0 » Thu May 16, 2019 8:53 am

liveaboard wrote:
Thu May 16, 2019 8:00 am
What is "BMS" ?
I think he's talking about the balancing circuitry needed to charge multiple cells, maybe.

Dave

rrnut-2
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Re: VFD question

Post by rrnut-2 » Thu May 16, 2019 2:40 pm

What everybody is missing with standard VFDs is this. 220VAC 3phase rectifies to about 500Vdc on the dc bus. That means that you will have to have that many batteries for the drive to work. 220vdc on the bus? ya, the unit will fault out on "low bus voltage". That's a lot of batteries for a boat. I installed a system of 24 VFDs on an exhaust blower system, and the master dc power supply put out 720vdc from 480vac 3 phase to run the system. That's what 480vac 3phase will rectify to on the dc bus.

Jim B

whateg0
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Re: VFD question

Post by whateg0 » Thu May 16, 2019 3:18 pm

I think the suggestion was made to use a DC-AC inverter to get to 220VAC 1ph, then use the VFD from there.

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liveaboard
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Re: VFD question

Post by liveaboard » Thu May 16, 2019 4:49 pm

The original question was whether there is such a thing as a low volt DC to high volt AC 3 phase VFD; later in the thread, someone suggested 2 inverters, one feeding the other.
38 or 48V is doable, after that batteries are impracticable.
Of course the idea had occurred to me; if anyone does it and it works, let us know. I think something bad would happen. In the past, when I fed an inverter with an inverter, they argued and fought with each other.
I've found that there are 8HP electric forklift motors, so I'll be looking out for one of those.
Now I found out that a shiny new electronic control for a 400A motor only costs around $300. So I guess that's the way to go.

mikechoochoo
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Re: VFD question

Post by mikechoochoo » Fri May 17, 2019 7:48 pm

Yes a forklift motor with an electronic control circuit is the way to go. Here in the States, forklifts that don't have swapable batteries are often scrapped when the batteries wear out because the new batteries are more than half of the cost of a whole new forklift. Good Luck'
Mike. N.

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