480V 3 phase moter with VFD 2

[mrcheese]

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.

 

[Skogsgurra]

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

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[mikekilroy]

After Skogsgurra's step 1&2 are verified, you have another possible option: by a standby DC bus power backup device made for just this use:

http://www.wiki-kollmorgen.eu/wiki/tiki-index.php?page=KCM Capacitor Module

I unit stores 2000 watt-sec (joules). so that gives 2000/14sec= 142watts or .2hp power for those 14 sec. How much power do you really need?

http://www.KilroyWasHere<dot>com

 

[mrcheese]

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

 

[mikekilroy]

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.

http://www.KilroyWasHere<dot>com

 

[jraef]

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"

 

[mrcheese]

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.

 

[dpc]

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

 

[mikekilroy]

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!

http://www.KilroyWasHere<dot>com

 

[jraef]

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"

 

[ScottyUK]

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.

 

[Skogsgurra]

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

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[LionelHutz]

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.

 

[mrcheese]

ScottyUK (Electrical) thanks

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

 

[jraef]

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"

 

[Skogsgurra]

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!

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Marke]

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

 

[Skogsgurra]

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.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[mrcheese]

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

 

[ScottyUK]

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.