Another VFD question

[tiptop]

Hey All,
I am looking for a sensorless vector VFD, single phase in three phase out to run a 220V three phase 5 hp motor that requires 13 amps at start. I have found Three phase in and three phase out but not what I want. Am I missing something or is this not available?

Thanks in advance, Jay

[lazlo]

You won't find a single-phase inverter much higher than 1 HP -- not enough power: 110V (minimum) @ 15A = 1600 Watts. By the time you account for power losses and the RMS loss, you're barely above a KWatt.

A 5 HP motor needs a 230V, 15A circuit:

[MTNGUN]

If you got the money, they got the VFD.

http://dealerselectric.com/item.asp?PID=645

I think it is just a derated 3ph in/ 3ph out VFD.

[TexasTurnado]

Hey All,
I am looking for a sensorless vector VFD, single phase in three phase out to run a 220V three phase 5 hp motor that requires 13 amps at start. I have found Three phase in and three phase out but not what I want. Am I missing something or is this not available?

Thanks in advance, Jay

Here is the highest rated single to 3-phase converter I have seen:

http://cgi.ebay.com/30-HP-PHASE-CONV...QQcmdZViewItem

Of, course they also offer lower powered ones. Here is the 5 HP model:

http://cgi.ebay.com/5-HP-PHASE-CONVE...QQcmdZViewItem

Whether these are designed for this service, or just derated 3-phase units, I have no idea.

The only first hand experience I have had is with a 5HP Hitachi L200-037NFU, which, indeed will run a 3HP motor on my mill from single phase power with no problems. If you dig into the Hitachi site far enough, they recommend derating the 3-phase units to 1/2 of their 3-phase rating for single phase use at full motor nameplate power.

Electrically, this goes back to the peak and average power considerations of the rectifier diodes used and the fact the rectified waveform from single phase has higher ripple components than that of a 3-phase system. A higher powered 3-phase vfd will have larger filter capacitors to help remove the larger ripple of the single phase waveform, which keeps the following electronics happy.

As a side note, has anyone tried running a 460 volt unit (all I have seen are 3-phase rated) from single phase 230 volt lines using a 2:1 step-up transformer to get single phase 460 volts? There seems to be many more surplus 460 v vfd's , and thus lower priced units, available on the market. Only one step-up transformer with high enough KVA rating for the largest load would be needed for a shop full of 460 v vfds for the HSM.

[lazlo]

Sorry Jay, I may have misunderstood your question -- I thought you were asking if there was a single phase, 120V VFD that goes up to 5 HP.

On a 50A breaker you can get up to 10 HP on a 230V line, but most VFD's in the 5 HP and up range are three phase, because they're intended for industrial use, where there's always 3-phase power.

[barts]

Hey All,
I am looking for a sensorless vector VFD, single phase in three phase out to run a 220V three phase 5 hp motor that requires 13 amps at start. I have found Three phase in and three phase out but not what I want. Am I missing something or is this not available?

Thanks in advance, Jay

I have an AC-Tech drive that's 220 single phase in, 3 phase out and runs my 5 hp lathe just fine; it's a SF250Y. It's not a sensorless unit, but they claim full torque down to 10% speed (6 hz). It certainly works very nicely on my 15" lathe. They're about $475 or so IIRC. I bought mine from Wolfautomation...

http://www.wolfautomation.com/assets/15/scf_data.pdf

- Bart

[rdfeil]

Jay,
Most but not all 3 phase VFD's will work on single phase input power. You have to derate the unit and most manufacturers will have that information available. A good rule of thumb is 2 to 1 so in your case you would use a 10 Hp drive. Now in actuality I would use a 7.5 Hp unit unless you plan on loading the machine very hard most of the time. The only other thing you need to do is disable the phase loss protection in the programming of the drive. This is easy to do just another programming parameter. Ask the suppliers for the proper information.


Texas,

Short answer to your question is YES. I have done it many times. A lot of machines have 480 only motors, two speed motors are normally only single voltage. Step up transformers can be much cheaper than a new motor. A 480 volt three phase VFD run on 480 single phase still has to be derated but they work great. Again, ask the supplier and they will point you to the right drive.

Robin

[Bruce Griffing]

VFD's work by converting the input (either single or three phase) to DC. The DC is then used to generate the three phase output. The problem with high HP single phase input is in the rectifier and capacitor section of the VFD. This is the section that makes DC from the single phase input. A larger capacitor and beefier rectifier is needed to keep the DC voltage up between cycles with single phase input. With some VFDs it is possible to get full HP rating by adding a extra capacitor to the DC section. I would talk directly to someone a large supplier to see if you can get a sensorless vector unit with an added capacitor to handle 5hp.

[lazlo]

It's not a sensorless unit, but they claim full torque down to 10% speed (6 hz).

All VFD's are constant torque. The problem is that Power = RPM * Torque, so on a VFD, your power drops off in proportion to the speed reduction.

Sensorless Vector units can boost the power at low RPM by tweaking the V and Hz vectors.

VFD's work by converting the input (either single or three phase) to DC. The DC is then used to generate the three phase output. The problem with high HP single phase input is in the rectifier and capacitor section of the VFD.

Right, but the problem is that a VFD designed for 3-phase input has a 3-phase bridge rectifier to convert the line power to DC, with the input load distributed across 6 SCR's.



A single-phase bridge rectifier has 4 SCR/Diodes, so you're only using 4 of the 6 input SCR's. So the input filters on a VFD designed for three phase input are 4/6th smaller than you need.

So you de-rate a 3 phase VFD by 4/6 (33.3%) to get the single-phase rating.

[Bruce Griffing]

Lazlo-
I think you have abbreviated the design. Here is a schematic from Wiki:



If you beef up the DC section - usually the rectifier is already good enough - you can use single phase rather than three phase.