Digital Phase Shifters?

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ErichKeane

Making scrap at ludicrous speed.
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So, I was browsing the internet the other day, and found this: https://www.amazon.com/gp/product/B07F243HLG/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

It claimed 3 phase output from 1 phase without all the VFD business. I personally am a huge proponent of VFDs, I've owned 5 of them (typically the chinesium ones) and liked them for what they are.

However, one of mine is(spoilers, was) on my surface grinder. The surface grinder has 3 different motors, two that power up together, and 1 that does not. The two that power up together are Spindle + hydro pump, then a coolant pump powered up later.

It also has a pretty complicated electric panel of its own (including an outgoing 220v 1 phase plug for the coolant pump AND a 110v 1phase plug for something else), so I opted originally to wire the (greatly oversized) VFD in 'after' the switch and leave it always-on. I ended up programming it to recover-on-fault, so that when I pressed the power button (which is on the 'wrong' side of the VFD, wired exactly as they tell you not to!) I would have to hold it to allow the VFD to 'fault' and recover and turn the 2 main motors on.

After that, everything seemingly worked acceptably. However, I did discover 1 annoying issue, the spindle motor didn't 'recover' well under resistence. I would take what should be a perfectly reasonable cut, and the spindle would slow/stop! I presumed that this was because the VFD didn't properly respond quickly enough to the increased amp load due to the other motor.

Thus, I opted to see if this "Digital Phase Shifter" would be any better.

I got it in the mail yesterday, and it seems to function alright! It starts up perfectly on the first press of the power button, and the spindle spins at the correct RPM still.
I did a somewhat 'heavy' test cut, and it slowed a little but didn't stop! I consider it a success.

Now, these things seem pretty expensive (more so than the VFD!), but for someone who doesn't want to deal with a VFD and already has an electrical panel/wire-up they'd like to still use, these are perhaps just the ticket! They are very simply: 220v 1 phase (2 wires) IN, 220v 3 phase (3 wires) out!
 
I wonder if that is the solid state version of a Phase-A-Matic. Be interesting to put a scope on the output.
 
I would not expect that to produce sinusoidal voltage, so do not connect it to anything digital, like the mains of a 230V 3P CNC. The voltage spikes would damage the power supplies and computers. It looks like a solid state phase converter. Expect to only get 2/3 of the nameplate HP of a connected motor.

At $200, I'd buy a basic VFD from Automation Direct. More features and more information available.
 
JimDawson said:
I wonder if that is the solid state version of a Phase-A-Matic. Be interesting to put a scope on the output.
Click to expand...

I didn't put a voltmeter on it, however others have claimed that it gives power on all 3 legs all the time. My understanding is that is not the case for the phase-a-matic (which IIRC is a static phase converter?).

macardoso said:
I would not expect that to produce sinusoidal voltage, so do not connect it to anything digital, like the mains of a 230V 3P CNC. The voltage spikes would damage the power supplies and computers. It looks like a solid state phase converter. Expect to only get 2/3 of the nameplate HP of a connected motor.

At $200, I'd buy a basic VFD from Automation Direct. More features and more information available.
Click to expand...

Others in the reviews show it puts power out on all 3 legs, which is unlike a static phase converter, right? I would agree about getting a VFD instead, except this case (wanting the 'switch' between the VFD and motors) is explicitly listed as a 'do not do' for VFDs.
 
Seems to be just a static converter with what appears to be two start and 4 run capacitors. The 3rd leg can only be measured when the motor is running "Only DPS check the voltage is the output voltage 2 phase and the output voltage 3 phase when the only motors movable". A true digital output would show voltage on the 3rd leg. There are some types of 3 phase variable speed drives that do not convert the incoming power to DC and then use PWM, they use the incoming 3 phase power and use chopper circuits for each leg. These require additional noise filtering and are only suitable for 3 phase input. Phase Perfect is the only single phase converter that I am aware of that generates just the 3rd leg from single phase input that is pretty much sinusoidal, and can drive any types of loads up to its rated specs.

Surface grinders do not do well with static converters, others that have used them in this application have noted irregular surface finish issues when using them. I would recommend an RPC in this application. In some cases with surface grinders the main drive motor is run off of a VFD, the ancillary drives are sometime DC and/or run off of a transformer that uses 2 legs of the incoming 3 phase power.
 
mksj said:
Seems to be just a static converter with what appears to be two start and 4 run capacitors. The 3rd leg can only be measured when the motor is running "Only DPS check the voltage is the output voltage 2 phase and the output voltage 3 phase when the only motors movable". A true digital output would show voltage on the 3rd leg. There are some types of 3 phase variable speed drives that do not convert the incoming power to DC and then use PWM, they use the incoming 3 phase power and use chopper circuits for each leg. These require additional noise filtering and are only suitable for 3 phase input. Phase Perfect is the only single phase converter that I am aware of that generates just the 3rd leg from single phase input that is pretty much sinusoidal, and can drive any types of loads up to its rated specs.

Surface grinders do not do well with static converters, others that have used them in this application have noted irregular surface finish issues when using them. I would recommend an RPC in this application. In some cases with surface grinders the main drive motor is run off of a VFD, the ancillary drives are sometime DC and/or run off of a transformer that uses 2 legs of the incoming 3 phase power.
Click to expand...

Well shoot, I thought the power on the 3rd leg meant it wasn't a static converter. This is disappointing, as the VFD was doing so poorly.

I would have loved to do a RPC but they are seemingly silly-expensive. For a case like this (~3hp total for motors), would a RPC powered by a 5HP motor be sufficient? I DO have a 5 HP 3 phase motor (out of a converted sawstop) that I could use, then I would possibly be able to just purchase the electronics...
 
I made my own RPC out of a 5 hp 3 PH motor, a static converter, and a bank of oil filled capacitors to balance the voltage on the 3rd leg, it works well enough although some motors are a little slow to start or plug reverse; I use it on my B&S Micromaster, it works fine with no issues.
 
Nothing digital about it as far as I can see- it looks like a static phase converter with (probably) the start relay replaced by a solid state switch in the base. Maybe a little digital timer or current sensor circuit- I don't see any provision for dropout time adjustment
So you still would get only 2/3 power from any given motor. Kind of an expensive solution vs a true VFD
Also, those caps don't look like the long-lived oil-filled types we've come to expect, so it may not last
-Mark
 
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markba633csi said:
Nothing digital about it as far as I can see- it looks like a static phase converter with (probably) the start relay replaced by a solid state switch in the base.
So you still would get only 2/3 power from any given motor. Kind of an expensive solution vs a true VFD
-Mark
Click to expand...
Yep, seemingly so. I guess I should have asked before purchasing it :/ Oh well, perhaps useful in the future for a future project (same as the VFD I removed). Looks like I'm going to have to suck it up and and do a RPC.
 
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