Millpwr Users - Need Help

[pofo]

I have a 3 axis Millpwr minus the controller. I'm converting it to use a DSPMC. Each motor assembly has a power supply card (combined with a small PIC controller) and Servo Dynamics amplifier.

The power supply takes AC in, and converts to DC. I'd like to know if the AC coming into the motor assembly is straight 120VAC from the wall or if it is stepped down.

I'd appreciate if a Millpwr owner can measure this for me. Each motor assembly has the AC daisy chained from the control console to the motors. The last motor unit has an extra connector with a cap on it with 3 pins. This is a convenient point to measure it.

The reason I question that it is straight AC is that 120 VAC converted to DC would be 170VDC. The motors are only rated for 140VDC max. The amplifier is rated for 170VDC..

[Larken]

How old is the machine ?
Maybe its an SCR drive that runs off the AC directly. There is no big DC powersupply.
SCR drives chop the phases of the AC directly. As the AC crosses the zero crossing point the SCR turns off.

SCR drives are tough, but not as smooth and precise and a PWM drive.

Good luck with that DSPMC. Ethernet with cnc can be a real pain. Just look at the Grex. If the Grex had been USB, i bet it would have been a success.

Larry K

[mike_Kilroy]

all servodynamic drives i know of are pwm not scr. many people cheat and use wall socket 120vac to make the 160vdc bus to run 90v, 120v, and 140vdc max terminal rated motors. they can spark a tad more but if you do not run them at their max torque ratings at speeds along its speed-torque curve, the sparking is less. so less from not 100% load plus a tad more for 140v motor on upto 160vdc pwm spikes = normal operation you get a way with just fine. now try this with 48v rated motors and they likely will not last long.

much more important is grounding and isolation if using wall socket 120vac to the drive. we do this on occasion with servodynamic drives but you gotta know what it means when comparing grounds. if one side of the dc bus is gorunded and you supply wall socket 120v you will gry the drives instantly. know what is grounded and what isn't well and you might be fine. if in doubt, stick an isolation xfmr in series with the wall socket to separate grounds in the 120v from the dc bus and the control input wiring (which might end up at 120v above ground if not or simply burn out).

[pofo]

Thanks Mike. I'll be sure to check that I don't ground the DC output of the supply. Since I'm using the system as-is, without modification, things should be right as the Millpwr is a well-engineered product. I just need to make sure the AC is isolated going to the motor units.

Larry, Thanks. I don't understand your Ethernet comment.

[Larken]

The best way to get 170Vdc without a transformer, is to use both lives from 220Vac and use a half bridge rectifier. The common center (neutral) is the ground and just use the Pos from the rectifier. This way the neg is grounded. Using 120V from the wall makes neither ground.
But you should add a big resistor (10 ohm in series before the Main cap) that prevents inrush blowing the rectifier or cap. Use a relay to shunt out the resistor when the voltage reaches 80%.

A lot of guys run my Viper 200 drives directly off the mains, but your motor will run hotter if you run a 140 volt motor at 170 volts.

Larry, Thanks. I don't understand your Ethernet comment.

The main problem with Grex was the device hanging when communication errors happened. How many times when you loose communication with your internet router do you have to reset it (alot !). Windows is very poor at recovering from errors.
Cnc creates a lot of noise and ethernet is not optically isolated (not that i know)

Larry

[gta/spec]

My understanding is that 120vac is input into the Millpwr console, then distributed to the individual servos via daisy chain. If you look in your servo amp housing, I believe that you will find a bridge rectifier and a filter cap.

The installation manual refers to the round connection on the motor housing as AC power in.

[Larken]

What year is the mill. ?

Were the servodynamics origionally on the mill, or a retrofit ?

[pofo]

GTA,

Yes, it is as you describe. What I'm wondering is if there is a step-down transformer in the console. From what Mike says, perhaps not.

Larry, this is a Bridgeport series 1 (year unknown) with a Millpwr retrofit. Acu-rite used Servo Dynamics amplifiers in the motor assembly along with a custom power supply (simple rectifier)/control card. The SD amps are part of the Acu rite Millpwr retrofit system. This is a $15,000 retrofit package sold today.

Still awaiting a response from any Millpwr users. Thanks.

[Larken]

Looks like its direct 120vac

Product Manuals :: Acu-Rite

[pofo]

Thanks Larry. I have been to the Acu-rite site many times looking for documentation (many months ago). At that time, they only had the user manual. I never noticed an installation manual. That's a big help. Thanks for finding that.

[gta/spec]

I dont believe that there is a transformer in the Millpwr console. It would need to be pretty sizable to deliver the current required to drive the servos. Even in a torroidal design.

There may be a decent line filter, but that would be it.

[sachurch]

pofo,

I'd like to help you, but my millpwr 2axis doesn't boot up. I was told to polish the connectors of the BMDC board, but don't know where that is! If you or someone knows, please let me know. I have the "older" millpwr with the big computer box. Any manuals, schematics, etc would be greatly appreciated.

Thanks!
Scott