[Scooby Doo]

I was wondering if the amps of the G540 would be sufficient enough for a machine that is 72 x72 using 495 oz steppers (2 on X and one on Y). I have larger explaination of the machine in the JGRO forum.
Any and all help is appreciated

Thanks,
Scooby

[CoAMarcus]

If you could post the specs of the motors that would help out. You can't tell a whole lot from oz/in. and table size. I would need to know specifically the voltage, current, and inductance of the motors on your table.

Marcus

[sawmiller]

hey marcus,
i clicked on the lil gecko spot up above, doesnt go to the website like i think it should.thought you might want to know


if i get the G540 i plan on using it with keling's 425 oz/in motors
KL23H286-20-8B
4.17 v
2.8 a
6.8 inductance.
at least untill i get the cash for some 201's

now i realize that with that inductance it wont be the best, but
will it drive them better than a set of chopper drives from pminmo
at 38 volts ?
dan

[CoAMarcus]

Dan,

The G540 will run that motor just fine even with the high inductance. Because our drives are pulse width modulated they will run much quieter than a chopper drive, so the answer would be yes.

Marcus Freimanis

[Crevice Reamer]

To get the fastest rapids with the 425s, you would need an 83 volt power supply. I can get 350 IPM on my SX3 with 72 volts and G203Vs.

However, the 50 volts able to be used with the G540 is WAY better than the 24-36V available for the other cheap drives.

CR.

[Scooby Doo]

Thanks for the advice, I will probably go with the larger power supply. I am making one change to the lineal motion, that I believe will help the motors. I am going to be using a rack and spur gears for the the X and Y. My theory on this is that there will be less power needed from the steppers if they are not having to pull/push from 72" away. Is this a valid theory or am I all wet?
Thanks again and any
Scoob

[Scooby Doo]

I meant to end that reply with "Thanks and any further advice that you have to give will be welcomed"

[ViperTX]

Dan,

The G540 will run that motor just fine even with the high inductance. Because our drives are pulse width modulated they will run much quieter than a chopper drive, so the answer would be yes.

Marcus Freimanis

Okay Marcus....now, I'm totally confused. In the Cheap Drives thread, you stated that the inductance had to be below 3mH. So, what did I miss? I'm getting ready to order the Keling (sp?) 4 axis kit for use on an X3.

Paul

[CoAMarcus]

Paul,

The 3mH recommended inductance is to get the best performance out of your motors. The G540 will run those but not as efficiently as a higher power drive would because of the high inductance.

Marcus

[Crevice Reamer]

I'm getting ready to order the Keling (sp?) 4 axis kit for use on an X3.

Paul

Hi Paul.

The X3 needs a N34 motor for the Z. Currently available N34s pull about 6 amps. Until some lower amp/volts N34s are available, the G540 may not be the best choice.

CR.

[devincox]

what about these:
http://stepper3.com/shop/stepper3-12...hase-p-88.html

STEPPER3 1200 OZ-IN 4 WIRE 3A/PHASE
NEMA 34

[Crevice Reamer]

That would be a huge amount of money wasted on very poor performance. The 22 mH inductance would rule these out even for the G203V, let alone the G540.

CR.

[Crevice Reamer]

So far, it looks like the larger Geckos will be best for the X3. If you still want plug & play with 4 LARGE Geckos, try this:

http://www.pmdx.com/PMDX-132/

CR.

[devincox]

How about this one:
KL34H280-45-8A (Single Shaft) Specification Price: 89 ( in stock)
Rated Current: 6.3A, Rated Voltage: 2.3V 2.2mH (in Bipolar Parallel)
Rated Current: 3.2A, Rated Voltage: 4.5V 8.8mH (in Bipolar Series)

Just trying to find some steppers around 600oz-in.

[Crevice Reamer]

How about this one:
KL34H280-45-8A (Single Shaft) Specification Price: 89 ( in stock)
Rated Current: 6.3A, Rated Voltage: 2.3V 2.2mH (in Bipolar Parallel)
Rated Current: 3.2A, Rated Voltage: 4.5V 8.8mH (in Bipolar Series)

Just trying to find some steppers around 600oz-in.

Amperage = Torque. At 6.3A this motor is 640 Oz. The G540 can only output 3.5A That 45% less amperage will turn the 640 oz into a 352A motor. That kind of defeats the purpose.

Voltage = Speed. 8.8 MH = a best speed voltage of 95 volts. Running this motor in series at 48V may give you miserable rapid speed.

I'm beginning to think there ARE no N34 motors that will be happy with the G540. You may have to use larger drives for a larger mill.

CR.

[CNCfun&games]

That call was with Bruce, the developer of the "CNC Brain", one of the smartest people I have run into in a while. It concerned the G540 and his CNC Brain device. This may turn out like the traffic collision between the Hersey's Chocolate truck and the Planter's Peanuts truck. Good ideas are afoot.:-)

Mariss

O Happy Day!!!!

The only thing that would please me more is if it were ported to LINUX!
You could also help Bruce with his Electronic packaging... yours is the best!!!

W Smith

[Mariss Freimanis]

Short Version: Never switch the DC side of your power supply! Hard-wire the power supply DC side to the G540. Switch the AC side of your supply for your On/Off switch! You will damage the G540 if you don't!

Long Version (no exclamation marks):

OK, I got a second G540 returned for repairs today. I unsnapped the cover, unplugged the main board and found the short-circuit sense 0.04 Ohm 2W resistor on it was burned open. This was identical to the first returned G540.

I replaced the resistor with a new one, plugged the main board back onto the drives and everything worked perfectly. No other damage. Just like with the first returned one.

I put the failed resistor under a microscope and saw damage consistent with being caused by a large impulse current. It didn't die from overheating, it died from a very large (>100A) current pulse vaporizing a small portion of the resistive element leaving most of the resistor intact. Underwattage (overheating) would have discolored the entire resistor and charred the board. It was just like the resistor from the first returned G540.

What caused this?

Only two possible reasons: Reversed power supply polarity or a power on/off switch on the DC side of the power supply.

1) The 0.04 Ohm resistor is designed to vaporize if you reverse power supply polarity. It throws itself on that grenade and sacrifices itself to protect everything else in the G540. Mind the '+' and '-' wires from your supply when you first hook it up and you will never have this problem.

2) On/Off switch on the DC side of the power supply. You have a 50VDC power supply and you have done a good job wiring from your DC supply, to an On/Off switch, to the G540. Your wiring resistance is 0.1 Ohm or less.

The G540 has four G250 drives in it. Each drive has a 150uF supply bypass capacitor totaling 600uF for all 4 drives. You throw the power switch from Off to On.

Those 600uF of capacitance present a dead short to ground at the instant you close the switch. The instant the switch closes, 500 Amps of current flows (50VDC / 0.1 Ohm) to charge those capacitors. Those 500 Amps flow thru the 0.04 Ohm, 2W resistor. It sees an instantaneous pulse dissipation of 10,000 Watts (50VDC squared times 0.04 Ohms). The resistor element vaporizes because the poor resistor, rated at 2W, gets hit with 5,000 times more power than it's rated for.

Your switch doesn't fare so well either. Its contacts may weld closed after the first try. Even if not, the contacts are now severely pitted and cratered. The switch will fail after a few dozen cycles of this abuse.

Hard-wire the DC from your power supply to the G540. Put your On/Off switch on the AC side of your power supply. Everything will then live a long and prosperous life and you will be happy.:-)

Mariss

[Crevice Reamer]

Thanks Mariss, for another fascinating, well written report from inside Gecko!

But the G540 WILL survive an accidental motor disconnect, as long as power is off when reconnected--RIGHT?

CR.

[Mariss Freimanis]

Disconnecting the power supply causes no stress to the G540.

Let me expand on this subject a little:

Most electronic devices have no problem with DC being switched on or off to them. They contain voltage regulators which are current limited (a 7805 5VDC regulator has a 1.5A current limit). This current limiting prevents large currents from flowing during power up.

Motor drives are different. There are no voltage regulators for the main DC supply bus in a motor drive. Heat dissipation in the regulator at motor power levels makes them completely impractical. Motor drives also have large DC power supply bus bypass capacitors.

When a DC On/Off switch turned on, the drive input voltage rises from 0VDC to supply VDC in less than a microsecond and the inrush current is enormous. Secondly, a motor drive has oscillators and analog circuits that must start up and stabilize before the power transistors are energized. These events happen at distinct input voltage levels as the power supply voltage comes up. A microsecond is not enough time for stabilization before the supply voltage is high enough to energize the power transistors.

If the On/Off switch is on the AC side, the DC voltage rises from 0VDC to supply VDC in about 1millisecond or more. This is 1,000 times longer than 1 microsecond so inrush currents are 1,000 times smaller (0.5A versus 500A) and the internal circuits have all the time in the world (1/1,000 of a second) to stabilize before the power transistors become active.

On/Off switching the DC side is brutal, On/Off switching the AC side is being kind to motor drives.

Mariss

[Crevice Reamer]

But the G540 WILL survive an accidental motor disconnect, as long as power is off when reconnected--RIGHT?
CR.

I would NEVER put a switch on the DC side. MY question was about a MOTOR cable that accidently came loose.

Will the G540 survive THAT?

CR.