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7.5hp Phase Perfect for Speedio?

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
The factory "Chip-to-Chip" toolchange spec. is 1.3 seconds. That spec is exact as far as we can measure. That being said, the 9.5 KVA rating goes out the window when you go from 16K rpm to zero, change tools and back up to 16K rpm (worst case)in that time span. I'm not sure what size digital phase converter would handle that but I think that the power draw ends up being several times the nameplate KVA rating on the machine.


Yes, that's exactly the sort of issue. How much actual energy is involved would depend on the mass of the spindle & drive system, workpiece, rpm and decel time.

PP units are pretty good, and naturally can handle more than the nominal "use-with" published motor / power rating. There is a considerable "designed overload capability" baked into them to handle starting motors, etc. They are quite a nice solution, actually. But any design has limits.

The acceleration energy draw in the CNC would likely come substantially out of the internal bus, and not be directly seen on the line. At least the peak will be "blunted", so that there is a longer, lower, current demand from the line.

The decel may be different. That energy will go to the bus, but then the input circuit will start dumping it out on the line to keep the voltage down. The CNC manufacturer knows what the max energy would be, and will have designed the power system to deal with it.

I feel relatively certain that there is a published maximum spec for that from the CNC maker, if you dig for it. The PP probably has a spec for it's return energy capability as well, so those can be compared. You would need to account for the fact that the PP handles only one line of the three, so the power through the PP is only around 1/3 of the net.

If these numbers can be found, it should be possible to determine exactly what PP unit will work with a given CNC.

Maybe thesjg can get those with issues in touch with the right folks at PP to sort out the needs.
 

thesjg

Plastic
Joined
Nov 4, 2021
Location
Sturgis
The factory "Chip-to-Chip" toolchange spec. is 1.3 seconds. That spec is exact as far as we can measure. That being said, the 9.5 KVA rating goes out the window when you go from 16K rpm to zero, change tools and back up to 16K rpm (worst case)in that time span. I'm not sure what size digital phase converter would handle that but I think that the power draw ends up being several times the nameplate KVA rating on the machine.

The PT010/PTE010 are capable of delivering in the ballpark of 60kVA for that chip-to-chip window, but not of dealing with that much regen, I'm still pinning down the spec. for the latter.
 

SomeoneSomewhere

Hot Rolled
Joined
Dec 24, 2019
If the CNC drive has an exposed DC bus, more capacitance or an external braking resistor could help. But there's probably only so much you can do.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
The PT010/PTE010 are capable of delivering in the ballpark of 60kVA for that chip-to-chip window, but not of dealing with that much regen, I'm still pinning down the spec. for the latter.

It's best to look at the total delivered energy, and not the kVA (a rate measurement).

The see what the boost in bus voltage would be to absorb that energy at the level of bus capacitance in place. It's a voltage squared function, so the energy storage is larger than one might think off-hand.

Finally, the removed energy by the regen circuit has to be taken into account.

A possible way is to take the regen rate back to the bus, subtract the amount the regen-to-line can handle (account for any delays in switching modes), and then use the difference and duration to get the energy, using that to work out the voltage rise.

There could be more factors in any given machine.
 

johansen

Stainless
Joined
Aug 16, 2014
Location
bainbridge island
one experiment iI did was to solder up an assembly of about 9000uf of 400 volt rated capacitors, and connect it to a rectifier connected from the wild leg of a 20hp rotary converter and the neutral of the 120/240 side.

When the spindle stopped from 16K rpm the capacitors would be charged up to 350-360 volts, corresponding to an increase from 208 volts, to a peak of about 250 volts ac. this was not enough capacitance to safely absorb the energy, but it did have on the order of 95% effectiveness at preventing the spindle from tripping on overvoltage. -however you would need 40 watts worth of bleeder capacitors and keep your tool changes to be more than 10 seconds apart.

anyhow that's hardly 200 joules of energy absorbed in the difference between 250 and 360 volts dc at the capacitor.


the resistor i wired up through a SSR triggered by a string of zener diodes, presuming it turns on for 150 ms corresponds to 700-1000 joules of energy dissipated.

anyhow it would certainly be possible to add a lot of capacitance to a Phase perfect but you would be looking at several hundred dollars.

i'm seeing a few stragglers on ebay but nothing reliably cheaper. here's a link to a 4700uf 400v rated cap, 60$ for 10 of them.

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