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Mcgyver
11-29-2016, 08:32 AM
Currently in the shop I have 240V 3P and 600V 3P that I make - diy rotary converter -> 3P transformer. Almost all machines are 3P, 50/50 600V and 240V. RPC is 10 hp and largest motor is on the lathe , 7.5hp. Distribution is all in hard conduit, separate obviously for 120/1P, 240/1P, 240/3P and 600/3P (yes it looks like surfaces of silver spaghetti in places ).

This set up has served me very well however spotting a cache of new VFD's I can get on the cheap has got me thinking.....removing the RCP and going with VFD's. it does hold several advantages, biggest of which is silence. It would also be nice to just go to the machine and use it vs the gymnastics to get to the other side of the shop to turn on the rpc, and it would nice to have soft start/stop on the surface grinder.

Then there is speed. I'm not a fan of VFD's as speed controllers in traditional sense - to replicate the existing speed range. However, running the vfd over 100% of line frequency gives the potential for increased high speeds. Obviously this only makes sense where the rest of system is up to task, but assume it is...added top end would be an advantage.

So, thats the background....assume all reasons vs cost make it a no-brainer. So remove the RPC. Its easy to change over distribution of 240 3P to 240 single.....Where I'm unsure is the 600V stuff. What what do I do about bringing 600V 1P to the VFD's for the 600V machines? Use the same transformer but only use 2 of the 3 coils? Do the VFD';s work the same way - ie can I run 600 1P into the VFD same as you would for a 240 vfd?

thanks for your ideas

J Tiers
11-29-2016, 10:00 AM
Most designed-for-1P input VFDs are 120V and 240V. There is plenty of 1P in 120V and 240V, because there are so many things that use it. Not much 1P 600V, I don't know of any common devices that need it.

I don't know if I have seen any designed-for-1P 600V class VFDs. While it may be possible to use a1P input, when you get to that class of VFD, there are often design features that make 1P input impractical. Most are straight-up designed for 3P input, with input phase loss detection, etc. You will need to read the manual and see if the VFDs will accept 1P to begin with.

If it is at least possible, then the question is what derating to use. And that may or may not be easily answered. If the VFDs have minimal bus capacitance, just enough for 3P input, then there may not be a practical derating for 1P input. Again, the manual MAY have something to say, but for 600V VFDs, it is not something that comes up much.

It's going to come down to the particular VFDs in question.

I HAVE in fact used 1P input for 480V class VFDs, but almost every application was a lab setup to test controls, etc, and not for actual high power usage.

As for the transformer, it wil work OK for 1P input on 2 wires. Generally the power will be reduced to 1/3 to 1/2 the total power rating, because you are not using all the windings, and the current allowable through what you are using is limited to a bit over the normal current (you do not have the heating input from the unused windings). It depends on how the thing is made and wired-up as to what you get. For instance, if it had a wye input, and you wired input from neutral to a phase wire, you would have 1/3 of normal capacity, plus some allowable overload.

EDIT: I should mention that it is possible to use a VFD through a transformer.... with the transformer on the output. The V/Hz issues are the same for the transformer as for the motor. There can be issues with the low end of the speed range, and use of vector control is not advisable.

enginuity
11-29-2016, 10:08 AM
I don't have any direct experience with running 575 V VFD's off single phase 575V in. My understanding though is many of the 575V VFDs will not run on a single or 2 legs, but I'm sure this has a lot to do with the individual VFD and the firmware on it. Most higher voltage VFDs might be designed assuming 3 phase input? I would really want to physically try the specific brand you are looking at. You might get an alarm.

By going to 2 wire single phase and cutting out the RPC, are you going to have to resize your supply lines after the RPC? It seems like a lot of work if your setup is working well now. I get the noise, RPCs can be noisy. You really need a phase perfect ;). Too bad they are pricey.

flylo
11-29-2016, 11:34 AM
I have a NIB 575V VFD I somehow bought & have no use for it & will find it & post it for free if someone can use it.

Mcgyver
12-04-2016, 08:41 PM
I thought I'd bump this....

Jerry, I somehow missed your response. so you think its theoretically possible. afaik the power bus works the same....ie a some sort bus the VFD draws from then sends out as 3P. I'll try and get particulars on the VFD's.

I don't want to put transformers after the VFD as then I'd need lots of transformers vs one on the input side (I think there are 4 600V machines).

Yes, a phase perfect would be perfect :). I'm not very worried about the wiring, I think its overbuilt and doing as I like i'd still be transmitting power at 600V over the wires.

lakeside53
12-04-2016, 09:06 PM
This was already answered above. It depend on whether you can find a 600v class vfd that will allow single phase input and deliver the correct output power.. If you choose a Hitachi, then you can derate a 3 phase VFD by following their guidelines of doubling the FLA. Other manf - -depends... you need to get the model numbers and research.

Don't assume Hitachi guidelines for other manfs. I have a really nice pair of ABB 480v ACH550. These are rated 7.5hp 3 phase, and 1.5hp when on single phase.

Replacing rpc with vdf... that alone has issues. A general rule is should not just use them as a "phase converter" and connect to the existing machine inputs, but to connect them directly to the motor and convert your controls to LV.

Mcgyver
12-04-2016, 09:27 PM
It depend on whether you can find a 600v class vfd that will allow single phase input .

I figured there was little chance of finding that specified as the VFD makers likely never imagined someone wanting to input 600 single phase....who'd ever have 600V single phase (except for crazy homeshop types)? whereas 1P is common for 240V.

Are all VFD's used as phase converters specifically designed for 1P input? I thought it was more the case the way power bus works is that its ok with 1P input so long as you over rate the VFD's size whether it it is specifically declared that is good for 1P input. ie, that common practice was grab one sufficiently oversize and it will work. I could be wrong, I'm not long on VFD experience.....just was thinking if that's how it is for 240.....would it be the same for 600V.

That downrating on Hitachi perhaps throws the idea into a tailspin. wow, I thought common practice was bumping them up 50%

Let me try to get my hands on specifics.

lakeside53
12-04-2016, 10:00 PM
Here's the hitachi app note that also explains the problem. No.. Bumping 50% isn't a good rule of thumb idea. Then there are my ABB drives... at 7.5/1.5.

No, not all are designed for or allow single phase operation. You need to overcome the "loss of phase detect". Some easy, some not so.

http://www.hitachi-america.us/supportingdocs/forbus/inverters/Support/AN032404-1_Rev_A_Sizing_for_Single-Phase.pdf

JRouche
12-04-2016, 10:55 PM
Sorry, no help here Mac. Do not read:

""So remove the RPC. Its easy to change over distribution of 240 3P to 240 single.....Where I'm unsure is the 600V stuff. What what do I do about bringing 600V 1P to the VFD's for the 600V machines? Use the same transformer but only use 2 of the 3 coils? Do the VFD';s work the same way - ie can I run 600 1P into the VFD same as you would for a 240 vfd?""

NO!!! The rating for the 600 volt box might be very low with current. You have to examine the wattage rating for the VFD. It might be very low, considering a 240 unit. Magic mystery smoke left the house :)

An old adage with us techs. There is never a short in the circuit you are troubleshooting. They are all Opens. JR

J Tiers
12-05-2016, 12:11 AM
Warning: Too much information........

1) Power supply in a VFD: Basically they rectify the 3 phase (or 1 phase if so rated) and use a capacitor to filter out the AC component, so that the "bus" voltage is a high voltage DC. With a 575V AC input, the DC bus inside the VFD will be around 815VDC. That sort of voltage ain't playing around, it needs good insulation on the wiring.

The first thing affecting the rating is the rectifiers. 3 phase gives a good DC when rectified, even if unfiltered. The voltage out of the rectifiers never goes below about 86% of the peak voltage (peak is 815V for your 575VAC). BUT, the rectifiers have a current limit. With 3 phase, the current is spread over 6 rectifiers, and the peak currents are relatively low, because the peaks of the AC come at 3x the line frequency.

With single phase, only 4 rectifiers are involved, the peaks occur only at 2x the line frequency, AND the output voltage does go to zero between peaks. The result is that there is more time between peaks, the peak current is higher, and it is spread over fewer rectifiers. So they are stressed more.

Then also, that capacitor to filter the DC: With 3 phase, because it is decent DC with NO filtering, the capacitor can be small, and need not carry much AC current, the variation in voltage is at most 14% of peak. It's a cushy job for the capacitor, which can be a "98 lb weakling".

With single phase, all is different. The rectifier output is lousy DC, it goes to zero between peaks, meaning that the capacitor must be much larger to "hold up" voltage between peaks. That means it has also a lot more AC current flowing in it, which it must handle without overheating. This all takes a much larger and differently rated capacitor.

There is normally also some device or method to charge up the capacitor slowly when power is applied. This avoids the very high current surge oof initial charging, which might damage rectifiers or capacitor.

2) Output of a VFD: The IGBTs (semiconductor devices) In the VFD are controlled so as to produce a series of pulses that add up to 3 phase output. The motor inductance then smooths out the pulsing to give a current in the motor that is quite close to a sine wave, usually. The VFD varies the frequency and effective voltage of the output by adjusting the pulse timing.

All it asks for is a good DC bus voltage. The single or 3 phase issue with input is irrelevant to the output circuit , SO LONG AS THERE IS GOOD DC FOR IT TO USE.

3) Using single phase:

Because single phase is so much more stressful, a VFD optimized for 3 phase input will generally have some sort of detection to check that it really has 3 phase. If it did not, the rectifiers or capacitor could fail, damaging the unit and requiring replacement.

That protection can just check for voltage on all inputs, in which case you can fool it by hooking the unused phase to one of the others. Or, it may check to see that all the phases are in correct relation to each other, 120 degrees apart. That is far more difficult to fool. but easy for the control computer in the VFD to check.

So, what can go wrong with single phase?

The rectifiers can be damaged by the higher peak currents of single phase. The builders of VFDs trim them down to minimum cost, because it is a very competitive market, especially in the US. So they don't typically use any larger rectifier than they have to. Bad news for trying to use full power at single phase.... but if the VFD supplies only some lower power, the rectifiers may only see normal currents just like three phase. How much lower the "lower power" must be is something the design engineers can specify.

Then also, the capacitor must handle more AC current, and must be larger to "hold up voltage". Again, the designers try to use the minimum, for cost and size reasons, so what is good for 3 phase may be unable to deal with full power at single phase. The designers can specify how much lower the output must be to avoid trouble with the capacitor.

If you exceed the allowable power, the capacitor may overheat and leak, or even explode, spewing gunk everywhere and most likely ruining the drive.

A damaged rectifier is pretty much a death sentence, because a VFD in the smaller sizes typically uses a "semiconductor module" including rectifiers, IGBTs, and other protective diodes all in one package. More expensive to replace that than to get a new drive, and likely it is not the only item to go bad. A bad capacitor due to over-power at single phase is like;y to have taken other parts with it. Again not feasible to repair unless you can do it yourself and have access to parts.

Here is a yaskawa drive module (everything inside the black plastic case attached to the heatsink). The capacitors are on the PWB to the left partly out of the picture. You can see a couple of places where capacitors could be, but are not. I am not sure if the missing parts are used for a single phase input unit, or for a 3 phase unit of larger power :

http://img.photobucket.com/albums/0803/jstanley/yaskawa%20module%20w_text%2024486350979_fec0f9a945 _c_zpsud9h2fdn.jpg (http://smg.photobucket.com/user/jstanley/media/yaskawa%20module%20w_text%2024486350979_fec0f9a945 _c_zpsud9h2fdn.jpg.html)

Here is a closeup of a module from Fuji, used in several VFD types, showing how all the major semiconductor parts are in one unit.

http://img.photobucket.com/albums/0803/jstanley/Fujimodule2.jpg (http://smg.photobucket.com/user/jstanley/media/Fujimodule2.jpg.html)

Mcgyver
12-05-2016, 08:06 AM
Jerry, thanks for the detailed explanation...that was pretty much my understand of what happened on the input circuit. I also understand that DC input is often possible, but as you point out the resulting 800V is nothing to trifle with. If it just shuts down based on not seeing the separate 3 phases, its over before it begins. I've also likely been over estimating how robust these things are.



Here's the hitachi app note that also explains the problem. No.. Bumping 50% isn't a good rule of thumb idea. Then there are my ABB drives... at 7.5/1.5

That article sort of confirmed what I was thinking, anyone could handle it if the rating was accounted for . I was thinking 50%, but that's saying its 73% which is a bit higher. Still, it is very different than the ABB which is 500%. On phase detection, you're right and it may scupper the idea.....I don't have a good answer to that one.

Might be back to making my own Phase-perfect. Said mostly tongue in cheek.....but how hard can it be?

lakeside53
12-05-2016, 11:31 AM
Might be back to making my own Phase-perfect. Said mostly tongue in cheek.....but how hard can it be?


There's significant robust hardware in a PP, but it's all in the software... Interestingly I haven't seen any "copies or clones" and they been around for a long time.


PP = Blue box - original model in my shop. Current model is the PT-330.

http://i238.photobucket.com/albums/ff150/lakeside53/Phase%20Perfect/DSCN2011Medium.jpg (http://s238.photobucket.com/user/lakeside53/media/Phase%20Perfect/DSCN2011Medium.jpg.html)

Inside front

http://i238.photobucket.com/albums/ff150/lakeside53/Phase%20Perfect/DSCN2003Medium.jpg (http://s238.photobucket.com/user/lakeside53/media/Phase%20Perfect/DSCN2003Medium.jpg.html)

Looking down from the top. Most of the high power stuff is in the back
http://i238.photobucket.com/albums/ff150/lakeside53/Phase%20Perfect/DSCN2004Medium.jpg (http://s238.photobucket.com/user/lakeside53/media/Phase%20Perfect/DSCN2004Medium.jpg.html)

http://i238.photobucket.com/albums/ff150/lakeside53/Phase%20Perfect/DSCN2005Medium.jpg (http://s238.photobucket.com/user/lakeside53/media/Phase%20Perfect/DSCN2005Medium.jpg.html)

lakeside53
12-05-2016, 11:39 AM
That article sort of confirmed what I was thinking, anyone could handle it if the rating was accounted for . I was thinking 50%, but that's saying its 73% which is a bit higher. Still, it is very different than the ABB which is 500%.

The article actually says double (100%) the current. VFD don't really care about HP.. just current.

From the article:

The rule of thumb Hitachi recommends is to start with the 3-phase motor’s nameplate full
load amperage (FLA) rating and double it. Then select an inverter with this doubled
continuous current rating. This will give adequate margin in the input rectifier bridge and
bus capacitors to provide reliable performance. NOTE: Fusing or Circuit Breakers should
be sized to match the INVERTER input current rating, NOT the motor current rating!

J Tiers
12-05-2016, 01:01 PM
If you do not bother with the bidirectional business, you can do it significantly more simply. That takes only one conversion instead of two. It would not be a huge disadvantage, as only one line of reverse power would be involved. The other two are connected through in any case, and will return power on that phase.

You can see the connections in Lakeside's picture, two come in to the contactor, and are tapped off for unit power. Those two go right out again, with a third added that comes from the filter that is behind the panel.

You still need a good filter system on the output (and input). But filters are obtainable for just this purpose, and can be designed.

A slightly simpler still version could be made by taking advantage of the US 230V neutral.

All you need is a synchronized 60Hz modulation, good (but high) current limits, and a rugged set of IGBTs, with the ancillary parts. I have thought about it. Have not looked up their patents and patent expiration, because I really do not want to go into business making them, I don't see the market for a cheaper version. But it would not be difficult for "one skilled in the art" to do.

Added trimmings would be adjusting modulation to maintain rms voltage, etc. But one COULD just rectify and let it rip as is, That would do as well as any RPC and most VFDs.

I might do one for myself sometime.

Jon Heron
12-05-2016, 05:43 PM
I think the most cost effective and reliable solution for you is to build a sound proof box over your RPC.
If you desire VFD control for certain motors you can then purchase standard 3 phase units too.
Cheers,
Jon

Mcgyver
12-05-2016, 06:13 PM
I think the most cost effective and reliable solution for you is to build a sound proof box over your RPC.
If you desire VFD control for certain motors you can then purchase standard 3 phase units too.
Cheers,
Jon

that is true statement.....except its not just noise, its convenience....but I could rig some sort remote IR thingy to start it. The drone it creates its really annoying and I think the garage acts like a soundbox. The RPC running is quite noticeable in the kitchen next door, so I'd have to figure out or copy a design to vibration isolate the rpc from the floor. I wouldn't that that would be insurmountable - springs maybe?

There are some other VFD advantages that appeal: I've always wanted a soft start and stop on the surface grinder, and also thought some machines like lathes could be overdriven for high rpm's (assume for the moment the mechanical bits are capable).

I've a stupidly big transformer, can't remember the rating, so am conditioned to think 3P transformers = BIG. Maybe the solution is 240V VFD -> small 3P transformer at the machine. Doesn't seem like a common thing though, small 3P transformer. Biggest motor is 7.5hp that would have to be driven by 600V (yes thought of swapping out motors for 240V......huge pita, and two are balanced on grinders).

Jerry, I say go for it.....and do an article and/or post the drawings :D

lakeside53
12-05-2016, 06:32 PM
But remember... you loose a bunch of feedback when driving a motor via vfd though a transformer. And don't assume you can on all vfd... although some have done it it is unusual.

J Tiers
12-05-2016, 06:55 PM
that is true statement.....except its not just noise, its convenience....but I could rig some sort remote IR thingy to start it. The drone it creates its really annoying and I think the garage acts like a soundbox. The RPC running is quite noticeable in the kitchen next door, so I'd have to figure out or copy a design to vibration isolate the rpc from the floor. I wouldn't that that would be insurmountable - springs maybe?
...

Rubber feet for the floor issue.

For the drone, depends on frequency. If low frequencies. moving elsewhere is best. But higher frequencies can be usefully reduced with even a bit of sound absorbing material in front of the unit, and on any wall it may be close to.

Listen, and decide if it must be cut in half, or if it would take more. Cutting in half is between 6 and 10 dB reduction, and can be done without much issue using simple covers and absorbers.. Cutting by significantly more than that may be best done by moving the unit, possibly combined with absorbers.

lakeside53
12-05-2016, 06:57 PM
Oh yes... rubber... never bolt your rpc down hard if you want the bearings to last. If you have, slide a thick rubber mat under the rpc - HUGE difference.

garyhlucas
12-05-2016, 08:43 PM
I installed a 15 hp verticle pump next to the shipping department in a plant and people were really pissed about the noise. I got a 30 gallon cardboard drum and a sheet of sound deadening foam from McMaster Carr. I cut a hole on the bottom of the drum the size of the cooling fan intake. I surrounrd the hole with the foam on the inside, and covered the entire insides with the foam. The plant made steel tubing. I got two pieces and poked them through the sides about 4" from the bottom. Then set the drum over the motor resting on those crossed tubes sitting on top of the fan guard. Everyone was blown away by how quiet it was! The customer congratulated me for solving the problem without a single complaint. I was worried about the motor overheating. It actually ran noticeably COOLER with the cover on! It ran for 15 years that way before they replaced the whole unit