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480V 3 phase moter with VFD
2

480V 3 phase moter with VFD

480V 3 phase moter with VFD

(OP)
I have a 480V 3 phase fan motor (<5HP) that i want to keep running for 14 seconds once the power it cut off. is it possible to connect a string of batteries to the DC bus of the VFD that will keep the DC bus energized in the event of a power outage? the DC bus would also have to keep the batteries charged.


RE: 480V 3 phase moter with VFD

It should be possible. At least with some VFDs.

There are a few things to consider:

1. Most VFDs are constantly monitoring invoming Three-phase supply. You need to deactivate that function. Not Always possible.
2. Not all VFDs derive their auxiliary Power from the DC link. Most do. Needs to be checked.
3. The trickle charging may need some extra care. A resistor may not be the solution - or it is.
4. You need to connect the battery via a low-ohm link to the DC bus when the grid fails. Simplest way is to use a heavy diode.

It could work. If you are in a position to chose VFD, the odds are in your favour.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V 3 phase moter with VFD

(OP)
I need about 2 BHP per motor with a total of 2 motors so 2000 joules are not even close.


RE: 480V 3 phase moter with VFD

So back to Gunnar's answer!

FYI, I got about 200 minutes from my 35KwH worth of Lithium batts in my electric car outputing about 10hp load. So sounds like you want about 4hp=3000w *14sec = 42Kws or 12wh worth of batteries. So double it for safety. Made up of 200pc of 3.2v, 10ah Lithium cells..... Sounds like around $ 6,000.00 battery pack plus another $ 1000 charger with individual balancing PCBs for each cell... Good news it should last 10+ years!

I agree with Gunnar you must consider a separate sophisticated charger for your batts if you do not want to service them every few months.

www.KilroyWasHere<dot>com

RE: 480V 3 phase moter with VFD

The first big problem I see here, in case you missed it, is that to run a 480V motor your VFD DC bus will have to be somewhere around 650VDC; not easy with batteries because they need to be an a long series string to get there. That's why Mike's example looks so extreme. So let's say you used 12VDC automotive batteries instead. That still means 650/12 = 55 batteries in series just to get to the voltage level you need. Then you have to look at the possibility of voltage drop under use, so you have to over shoot a bit, then deal with possible over voltage effects.

Doing this with batteries alone is not likely a great solution, you might be better off using something designed to do this already, such as a UPS system. The difference is, they will have a DC boost converter inside that can deal with getting to the necessary DC bus level without having to add so many batteries in series, so then all you need to worry about is the amp-hours necessary to survive your 14 seconds, which will be much more reasonable. You could, if you are so inclined, construct your own DC boost converter from scratch I suppose, but I'm of a mind to not try to re-invent something that someone else already mass produces. It never works out well for me. The UPS will have the DC boost converter, the trickle charger and the batteries already. Done.

"Will work for (the memory of) salami"

RE: 480V 3 phase moter with VFD

(OP)
Battery's in series is not an issue for me. VD is not an issue. just need to find a VFD that will do this with no power on primary AC Bus. perhaps i'm posting the the wrong place. really need a VFD expert.


RE: 480V 3 phase moter with VFD

Trust me - we have VFD experts here. A couple of them have already answered your question. Not me, of course.

RE: 480V 3 phase moter with VFD

perhaps i'm posting the the wrong place. really need a VFD expert.

That's funny!

What part of like 400 years of top notch experience here does NOT make a vfd expert?

And what part of having vfd DESIGNERS answering you here does NOT make a vfd expert?

If you don't like he answers, don't blame US!

www.KilroyWasHere<dot>com

RE: 480V 3 phase moter with VFD

Well if you are OK with that aspect, then are you looking for brand name suggestions? That becomes difficult because of forum policies against promotion, and because I work for a manufacturer, suggesting products made by my company could be construed as a violation of that policy. But how about this. If you were to begin a search of available suppliers by starting with an alphabetical list of two-letter acronyms, your search would be very very short before you came to find one that could meet those criteria. On most of our small products like this, the electronics are indeed powered off of the DC bus, we provide DC bus terminal blocks and allow you the option of defeating the AC line loss protection functions. So they are therefore suitable for being powered by a battery backup source. Just follow the other suggestions made by Skogsgura.

"Will work for (the memory of) salami"

RE: 480V 3 phase moter with VFD

Has anyone ever done trials running an active front end drive running off a UPS? In theory it should make life easy for the UPS, if it has a true sinusoidal output, as the crest factor should be near unity. Such an arrangement would handle all the battery interfacing problems.

RE: 480V 3 phase moter with VFD

Sorry mrcheese, if we delivered a solution without first telling you in-depth how a frequency inverter works, how an induction motor works and what electricity in general is about. It was very inconsiderate of us and I can very well understand that you feel disappointed by the lack of expertise.

If you need better support, I will be happy to provide that. Just contact me, place an order and I will visit you and tell you everything that has been said in this thread. The cost will be in the 5 - 20 kUSD bracket, depending on where in the world you are, and I understand that you want a bill in that range - which must mean that you get EXPERT ADVICE - instead of receiving cheap advice here.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V 3 phase moter with VFD

Forget just connecting a battery bank onto the DC bus terminals and having everything work happily.

Bonitron Inc. makes ride-through solutions you can add to a standard VFD by using the DC bus connections. I don't know of any others offhand, but there must be others around that also specialize in this type of solution.

RE: 480V 3 phase moter with VFD

(OP)
ScottyUK (Electrical) thanks

LionelHutz (Electrical) have also looked at the Bonitron. it would work for my purpose but very pricey


RE: 480V 3 phase moter with VFD

Quote (skogsgura)

The cost will be in the 5 - 20 kUSD bracket, depending on where in the world you are.
It would be worth every cent of that...

By the way Gunnar, I recently dropped your name and contact info to a customer of mine here in California who is having motor bearing damage issues from VFDs (not mine). He is buying what I told him, but his bosses want corroboration that does not come from a vendor with something to sell (a reasonable position), so I suggested you. I hope they call and hire you, I wouldn't mind getting together again, plus the job site is up in the wine country north of San Francisco.

"Will work for (the memory of) salami"

RE: 480V 3 phase moter with VFD

Jeff.

I just tried to make a point. We try real hard to help people here. And we have done so for many years. And I think that we, taken together, have a lot of knowledge and experience that has been tested and proven over quite a long time of continuous activity in the Eng-Tips. Unbeatable, I dare say. It is then sad to hear that someone needs to talk to an expert instead.

Free is obviously not worth much. But if you pay just about anyone, that says he is an expert, a lot of money - it seems to outweigh decades of experience and joint effort.

I like the thought to go west and do something useful. No probs. Also, I was contacted by people in the oil sands north of the border a few days ago. So travel costs could be split.

There's one other reason also, I need to brush up on my Skunk Distance Estimation skills. And I know of no better place than the Bay Area to do that! smile

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V 3 phase moter with VFD

The energy to keep the fans running needs to come from somewhere.
One way is to use batteries for the energy storage, but another approach would be to increase the inertia of the fans. - a mechanical solution may be cheaper.

Mark Empson
Advanced Motor Control Ltd

RE: 480V 3 phase moter with VFD

Yes! Brilliant!

That is exactly how the good old rotating UPSes worked. Just a large fly-wheel connected to the shaft. You can even use belt-and-pulley to double the speed of the fly-wheel and get four times the energy from it.

It takes a REAL drive expert, like Mark, to come up with such an out-of-box solution.

I herewith withdraw my offer. smile

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V 3 phase moter with VFD

(OP)
there is not enough inertia to get the CFM I need.(@14 seconds i only have about 25% of the CFM i need) that was my first and most obvious path. next i tried to see if i could increase the rotating mass of the fans... for various reason this did not work. then i thought i could add more fans again this was a no go. Also crossed of the list was. UPS, standard, fly wheel and compressed air were all looked at.

Guess i just need to call around. thanks for the help


RE: 480V 3 phase moter with VFD

What were the reasons why the UPS options were taken off the list? Most UPS designs are designed to handle rectfier loads like a VFD, and they would take away all your battery interfacing problems. 14 seconds support time wouldn't need a particularly big battery.

RE: 480V 3 phase moter with VFD

mrcheesy, what is your budget?

$ 1?
$ 10?
$ 100?
$ 1,000?
$ 10,000

This will really effect the answers you get. Sorta important info you have not yet given.

www.KilroyWasHere<dot>com

RE: 480V 3 phase moter with VFD

Unless I'm seriously mistaken, a flywheel should work very well for you, cheesy.

I did an Excel exercise: http://gke.org/pub/files/Flywheel%20mrcheese%20eng...

You say that you had checked the energy storage possibilties in flywheels. How much energy do you really need? From what speed to what speed is the fan allowed to drop in those 14 seconds?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V 3 phase moter with VFD

(OP)
ScottyUK the UPS option was remove because of cost. A 480V 3/P UPS that is large enough to start the motors is about 26K. had about 3 manufactures price this for me


mikekilroy: great point! I am looking at a price point of between 1k-and 2k each for the first 500 units.


Skogsgurra: Fly wheels are great! and designed to do this very thing. I spec them all the time for the data center projects i do. Unfortunately, the low load requirement of this project does not allow for efficient sizing if a fly wheel. the rotating mass and the vacuum chamber does not allow for manufactures to build these things to match the load requirement so it would have to be very over-sized and/or custom. again i contacted 3 manufactures price this for me and we are looking well above the ups cost.

the other option i am looking at is DC motors feed by battery bank and charger. this might be the ticket but still waiting in charger pricing. because the the torque requirements i need a motor that will be 540VDC. I can get the batteries that i need for about $400 per string to get me to the 550VDC. the issue here is the charger. The charger would have to carry the motors in normal operation while charging the batteries. there is no charger i found that will do this. battery chargers are not designed to run motors! have calls into several manufacture on this as well

the reason i came to the VFD is that the 480V motors are already on a VFD. If i could simply connect batteries to the DC bus then i could solve this problem for about $500 per unit.

The VFD solution has 2 issues

1. all the VFD's that i have looked at require 480V input to run the controls for the unit ( i have a work around that uses and inverter to power the controls via the batteries but again this is pricy and fairly complex)
2. the DC bus on a VFD is not designed to charge batteries. yes they would charge but there is no way to prevent over charging with out addition components connected between the DC bus and the batteries.

I have also looked at capacitors and in fact there are many VFD's that have that ride through function by way of capacitors, unfortunately this is GREAT for 2 seconds but could not be able to run 14.

there are about 100 way to skin this cat if cost was no option or i wanted to have an overly complex solution. ALL good engineering solutions are simple! I know there is a solution i just have to find it.


RE: 480V 3 phase moter with VFD

IF you used 220V fan motors off a 480 V VFD with the output set back to 220V, you could get away with round 250 V DC batteries coupled back into the DC bus via a decent rectifier. Probably much easier to charge and less batteries etc.
The drive would adjust the output modulation to enable it to run on the higher DC bus voltage while on mains supply.

Mark Empson
Advanced Motor Control Ltd

RE: 480V 3 phase moter with VFD

I think that you overspec things quite a lot.

It is only high-speed flywheels that need to run in vacuum. You havent said anything about the speed from which you need to cover a power outage and down to which speed the fan is allowed to reduce its speed.

I assumed, very arbitrarily, 3450 and 2700 RPM for those limits and also that the fan would be fully loaded across that speed range, which it will not be.

Under that assumption, you need a two feet diameter disk that is less than an inch thick, coupled to the fan shaft. Compared to your battery arrangement, that you actually did consider, such a disk is neither big nor expensive. Life is next to infinite, if you align and couple it well and the extra losses (windage, mostly) will be very small if you compare it to the battery solution.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V 3 phase moter with VFD

ScottyUK the UPS option was remove because of cost. A 480V 3/P UPS that is large enough to start the motors is about 26K. had about 3 manufactures price this for me

I don't think you asked the right question. The UPS salesman would have been looking at the start up currents of the motor and going from there, and then specifying a UPS which is way, way to large for what you require.

The UPS doesn't need to be able to handle the start up currents of the motor. Let the bypass line of the UPS do that function. You're going to have UPS input voltage available when you start up, so use that. The UPS would only need to be 4 or 5 kVA, and a line interactive model would probably suit your needs, and a 4kVA model could probably be picked up for less than $2K. Now unfortunately I don't think there are many (any) three phase UPSs made at that size.

Can you source a single phase input / three phase output VFD, and perhaps use 220V fans as Marke suggested, and run the input via a UPS?

RE: 480V 3 phase moter with VFD

sibeen beat me to it - the UPS only needs to handle the VFD input rectifier, not support a DOL start from a pair of motors. A 10kVA UPS with a small battery should be way less than $26k. I agree that very small 3-phase types are hard to come by, but 10kVA types are easy to find.

RE: 480V 3 phase moter with VFD

mrcheese, we're all working here from limited information, so a follow up question.

Why are you using a VFD int his application?

Ga,

Sibeen stated:

and then specifying a UPS which is way, way to large for what you require.

Oh, for an edit button...which is way, way too large for what you require.

RE: 480V 3 phase moter with VFD

OK, I'll put a rough price to it: 3000 GBP without any serious looking around.

You need a new UPS salesman.



RE: 480V 3 phase moter with VFD

Yes, a better UPS specialist. But, hey - aren't we that, too?

Sorry, didn't really mean to be mean.

I did some work in a spread-sheat, which can be found at http://gke.org/presentationer/files/EngTips%20flyw...

I think it is correct. But would appreciate if someone checked the results against known-good data.


Re: starting an induction motor from a VFD. You can start fom zero RPM with even less than rated current. So, I see no reason to make the UPS very large. Then again, some UPSes arent ready to see a VFD input rectifier and its not-so-nive current waveform. So, then you may need a PFC/AFE in the VFD. Which can be a problem to run from an UPS.

I think that you should look very seriously into the flywheel solution.

But, first of all: Please give us (and the specialist you are going to consult with) complete data. The green cells in the spreadsheet say what those data are.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V 3 phase moter with VFD

There is one thing that I cannot understand. You say that "had about 3 manufactures price this for me"

What does "about 3 manufacturers" mean? Is it 2.7 - 3.3 or are the margins wider? 2 manufacturers? or 4? 5, perhaps? And all these manufacturers didn't care to understand your needs? Are you sure you talked to the right people? Or any people at all?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V 3 phase moter with VFD

More than 20-25 battery in a string is not recommanded and equalization circuit increase cost. I think you may use 20 battery (240V) and a buck/boost DC-DC converter to 480Vdc connected to VFD DC bus. Same converter, configured in buck topology may be used as battery charger, feed from VFD bus. Regarding power of converter, for 14s working time (no time to warm up), need to check firstly current requested, not power of converter. If there are not such converter on market, I think may be made or may request to a specialized company and maybe don't overpass 1-1.5k$.

RE: 480V 3 phase moter with VFD

More than 500 motors? You can't run the VFDs from a common backup system or run multiple motors from a single large VFD with a dedicated backup system?

RE: 480V 3 phase moter with VFD

There are issues with attaching a long series string of batteries to the DC bus.

I once worked at a place that had a 'battery room' of large cells series connected for
emergency back up. The emergency reared its head one day and the battery bank was
called up quickly to pick up the load. Unfortunately one cell in the string was in bad shape
and it became the load for the whole system exploding violently.

The take away is that some kind of monitoring or other assurance is needed to verify the
cells are all good and post an alert if there is a bad one.

Now if you can tolerate a failure and the batteries are located in a place where they can fail
safely then just rely on quarterly maintenance checks.

Also 650 volts of battery can be quite dangerous from an electrical hazard point of view making a home
brew setup a bit of a worry for future maintenance. Make sure the bank is fused with a fuse that will
interrupt 650 VDC at short circuit current levels. DC is harder to interrupt than AC.

Personally I would make the company buy a solution for the above reasons so I could sleep easier.

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