Hi there
I have a customer that has acquired a 3ph Icecream Batch freezer - Carpigiani LB502

So far they have installed a 10hp Rotary Phase converter to generate 3ph from the 1ph service.

The customer wants to make sure the batch freezer is getting the right quality of hydro to make sure it works consistently. I have done a few tests and am looking for a bit of input regarding voltages. And I have included the numbers off the rating plate on the back of the machine.

The machine has 3 main components:
1. the controls (must not be connected to the generated leg)
2. 3 hp beater motor 8.4FLA
3. 3 hp compressor with water cooling 9.8FLA 78LRA

The phase converter is a Phase-a-matic PAM-1200HD with 10hp idler motor, with a disconnect switch of the generated leg back to the phase converter once the system is running (to prevent startup sequence to kick in).

The utility input is 250v split phase (125v + 125v).
The batch freezer is rated at 25a 3ph 208/230v 60hz 3 wire - max fuse size 30a.
Manufacturer suggests voltage between 215 and 218 as the best operating range.

Currently here are the voltages (line 3 is the generated leg):

No load
line 1-2: 250v
line 1-3: 237v
line 2-3: 238v

Beater motor load only:
line 1-2: 248v
line 1-3: 231v
line 2-3: 223v

Beater motor and compressor:
line 1-2: 246v
line 1-3: 225v
line 2-3: 221v

When the batch freezer is started up and running to produce ice cream the beater motor turns on first then 3 seconds later the compressor kicks in. The whole process takes about 8 minutes. After that the compressor turns off (and could/should kick back in to keep the temperature steady) with the beater still turning to dispense the icecream.


The batch freezer makes icecream just fine except that the controls that automatically sense and control the consistency of the icecream do not work as intended. If left unattended the machine will continue to freeze the icecream until the beater freezes stuck instead of cycling the compressor at a preset consistency of icecream. Therefore the operator must manually keep an eye on the progress.

I am thinking the high input voltage and difference of voltages between lines have something to do with the controls not working as intended. The machine worked perfectly in a utility 3ph environment prior to moving it to this location.

Not having too much experience with RPC as such - how do I reduce and balance the voltages over all.

1. Possibly I could reduce the 1ph input using 1 buck transformer to reduce to 215-220v BEFORE the phase converter. This would reduce the voltage of the generated leg as well!? as low as 200v under load possibly???

2. Is there a way to reduce the voltages (bucking) of the 2 utility lines only, AFTER the phase converter, leaving the generated leg as is so that the voltages are all closer to the 220-230v range?
Would this make the phases or anything go out of sync?

3. If a buck transformer were to be helpful does a 12kVA unit suffice?

4. A 3 phase buck transformer setup of all 3 lines AFTER the phase converter would reduce the voltages of each line from what I understand... defeating goal to balance voltages?

Let me know what any of you think and what my best coarse of action could be (or if I have left out any info that you might need let me know)

thanks

Fred

I think the voltages look pretty good for a rotary phase converter. How well are the amperages balanced?

You might try rolling the phases around. I imagine the controls are single phase, picked off of 2 phases and if it is 1-2, that might be the problem.

Hi have not checked the amperage yet...

The controls are off of 1 and 2. They are not supposed to be off the artificial leg. These machines are run off of phase converters quite often according to the manufacturer help line.

Looking at the wiring diagram the line to the beater motor that is monitored for the ice cream consistency (load of the motor) is the artificial leg... that might be the reason it doesnt reliably read the icecream consistancy. The voltage drops when the compressor kicks in changing the load I guess.

Here is a link to the wiring diagram that I took a pic of

https://picasaweb.google.com/114928007554591248284/April32015?authkey=Gv1sRgCN6f-7aOivjVZg

click on the pic and then to the right click on full details.

I was thinking of getting a VFD just for the beater. Though I dont have much experience with them. Can they be set up to have a steady 60hz 220v from my input voltage? --NOT variable as the usual use for them?

If the controller is isolated from the load by relays, I suppose you could just run a separate cord to it straight from the single phase circuit ... at least to test the theory.

I would just try moving the CT to a non-generated leg.

A VFD might be more trouble than it's worth. You would have to find a place to mount it, re-route the power conductors, connect the controls and program the vfd. Then, it's bad to quickly switch the power off and on to a vfd so it adds another complexity to turning off the machine and turning it back on.

You would have to warranty the vfd for a period of time and, if it failed, provide a replacement while the manufacturer decided whether they would pay for the new one - which they probably wouldn't. I love the way vfds handle a motor but I hate dealing with a vfd failure.

Personally, Fredweet,
I'd not go with a VSD on any sort of an agitator/beater drive motor and especially with something that has the viscosity of ice-cream.
Reason I say that, is because you need to be able to get this product moving for a start, this is where you need the initial "oomph" from a DOL starter, to get the drive unit turning in the first place.

This is only my thoughts on this, I could be way wrong too, I've worked with milk vat agitators in 22,000L refrigerated vats before and getting the blades of the agitator to turn first off with a VSD on it, was just about impossible.
What you need to think about is the amount of force required to get that beater turning.

Hope that this of some help.

I tried rolling the phases around with no luck yet. However the 24v transformer running off of 1 line of 120v has helped. Though the controls are not reading the ice cream consistency very well yet. So I am going to suggest to the customer to invest in a VFD to get a more balanced 3phase for the beater motor alone.

The icecream mixture at the start is very fluid and it is only up to 14 liters of mixture. Near the end it gets a bit more firm but not more firm than soft serve icecream. So I don't see the motor needing to have too much more oomph to get going.


any input would be great as I don't have too much experience with VFD sizing.

The beater motor is a leeson 3phase 3hp motor with the following details

2.24KW

1760RPM

208-230V

9-8.8 FLA

10-9.8 SFA

86.5 NEMA nom Eff



What would be the minimum VFD that would be sufficient.

The input voltage is 240v 1phase



Thanks again...

The single phase current is 1.7 times the three phase current, so the vfd should be either rated for single phase to three phase conversion or double the H.P. rating. (Make sure the vfd will run on single phase)

I like the Leeson VFD and they are the cheapest. However, I had warranty issues with Leeson. Put enough profit in so you can cover a new vfd if there is a problem.

Ok thanks for that info.
Would a 3hp 2.2kW VFD run a 3hp motor?
If the output of a VFD is 11A @ 220v the output is 2420W (Or rounded to 2.2kW) A leeson model is available to convert from 1ph to 3ph with an output of 2.2kW.

However is a 5hp 4.0kW a better choice?

Fred

Fred...

The general answer is no... if the current coming in is single phase.

The reason is that the incoming AC is rectified into DC and stored in a series of capacitors. (An electron 'tank', if you will.)

The variable frequency alternating current wave form is created out of this DC potential by using the magic of solid state electronics -- which can switch at speeds into the gigahertz.

Such a high speed is not used for VFD logic, though. Megahertz speed is plenty fast enough to generate a sequence of DC pulses -- that when stacked -- create a synthetic wave form -- which is easy to craft between 10 Hertz up to 400 Hertz.

In all VFDs -- they are strictly designed for 3-phase power input -- they have to be de-rated for 1-phase power -- because the rectification side of the system will be starved of power... you're actually trying to get the same output -- power wise -- out of 1/3 of the wave cycles.

This means for actual devices that 2/3 of the rectifier is actually sitting idle.

Then you have to throw in the extreme ripple that a single input phase places in the rectifier.

So a 2.5 hp VFD unit (3-phase inputs) requires that you bump up to a 10 hp VFD unit -- to power the same motor.

(There are no intermediate range units to hand, so you have to jump all the way to 10 hp.)

Even a 5 hp VFD will be starved of current -- and afflicted with nasty ripple -- that makes the rest of the device 'suffer.'

Fortunately, the pricing of a 10 hp VFD is NOT 4 times that of a 2.5 hp VFD. I've seen units (eBay)(Red Chinese) that are only 60% more expensive at 10 hp than they are at 2.5 hp. (side by side -- same manufacturer, etc.)

This works out because most of the expense is in the logical part of the VFD. The actual power flow part of the device is actually pretty simple, and scales cheaply.

Undersizing a VFD for single phase service use leads to short life, and poor performance. It's sort of like running a gasoline engine with two dead cylinders out of six.

With a high torque need at start-up, this is only amplified.

A local motor house supplied a Leeson drive for one of their customers that was rated for single phase input at the rated h.p. output. I specifically asked why it wasn't rated double like the others and that was the answer that I got. You need to check the ratings for yourself.

I have a customer with a VFD that has been converting single phase to three phase for years. It was rated at double the motor rating because the input rectifiers have to handle the input current at 1.7 times the motor load. In fact, I've installed at least a half dozen sized that way - sized by Leeson.

If it's going to be a hard start, get a vector drive. Apparently, they have better torque.

I have two drives that I am responsible for that are hard starting.

One unloads grain from a silo and, when the material freezes, it has to be broken free. I installed a switch to reverse the motor so they could plug it back and forth. The drive will look after the motor and itself.

The other pressures hydraulic lines to test oil wells. When it has to start from a stall to bump the pressure up, it can shut down on an overload fault and has to be manually reset after a few minutes.

There are settings on the drive to allow a higher overload for starting torque. I can't say how a drive compares to a motor across the line because I haven't had an opportunity to make the comparison. If you use a drive, your results aren't guaranteed.

I was put off drives when Leeson refused to warranty a drive because the input rectifiers where blown. I don't give a rat's ass about their excuses, so I supplied the replacement drive and installed it at my own cost. My warranty is good even if Leeson sucks. Still, Leeson drives, at least here, are about 25% cheaper. My deal with the motor house, now, is that they sell the drive direct and supply the warranty.

I did have another manufacturer warranty a couple 50 h.p. drives that were manufactured with the wrong rectifiers, but even then they didn't cover labour or temporary replacement parts.

Make sure you have enough profit that it is worth the risk. If it doesn't work, you are going to own a drive.

"Vector drive" is sales lingo for a motor that has been specifically designed to tolerate the spiky nature of VFD waveforms.

Cute, no?

Vector drive units don't have better torque -- per se -- they have their wiring -- especially the tap wires -- insulated to a wholly different, higher, standard than the normal NEMA stuff.

Once the windings have wrapped into the magnetic circuit/ taken a couple of laps around the silicon steel -- the magnetic field effects will have shaved off the highest spikes in the AC waveform.

From that point onward, even traditional winding insulation techniques will do fine.

The superior torque sales pitch is due to the fact that the VFD -- itself -- will adjust its frequency towards an idealized pull-in frequency during spool up.

This is to be contrasted with the common induction motor -- that starts out at zero rpms -- and 'sees' a rotating magnetic field racing away faster than the rotor could possibly catch up to. So, during spool up, it -- the rotor -- gets heated up -- and slips very, very, badly... particularly during high torque start-ups. (Traction motors, etc.)

The VFD slows the frequency down -- during the spool-up -- so that the speed of the revolving magnetic field is not so absurdly faster than the rotor.

A vector drive motor can tolerate this condition, too.

Slowing the spinning field down -- dropping the apparent frequency -- increases the delivered torque. (Inverse square law applies)

A VFD is brainy enough to spool up its waveform in tempo with the motor. Such pull-in/ spool up dynamics are adjustable in the field -- see the documentation provided with them.

Vector drive motors and mated VFD have almost entirely replaced DC traction motors. (!!!)

BART, most subways, the major railroads, etc. have all swapped out their DC systems for Vector 3-phase drive systems.

In the case of BART, it takes in 1000 VDC off of the third rail and uses it to power its 3 phase vector drive traction motors. The original power system (DC) was never changed.

It was in this fashion that both old style DC and new style AC could run side by side.

Otis Elevator has done the same thing for their product line. DC is out, vector drive is in.