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Offline Hood

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Re: Power Supply Unit
« Reply #80 on: January 16, 2011, 11:15:12 AM »
Diag looks ok to me but maybe best wait for the  electrical guys to comment, oh would go for the 5 amp fuse myself.

Have 2 of these caps, if you want them PM me your address and I will send them off ASAP.
As seen in the pic they are  15,000uF and 80v +-20% so should be fine for you, hopefully there are no restrictions sending capacitors by airmail.
Hood
« Last Edit: January 16, 2011, 11:18:03 AM by Hood »

Offline kolias

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Re: Power Supply Unit
« Reply #81 on: January 16, 2011, 11:40:31 AM »
Thank you Hood very much for your help, its appreciated a lot

I feel more confident when I get comments on my diagram and I hope the electrical guys can also give me some comments to confirm all is ok. I will go with the 5A fuse. Ultimetly ff course I’m the responsible person but will be nice to have an ok

I sent you my address by PM and again much appreciated. Dont either if there are restrictions sending caps by airmail but honestly I dont believe so.
Nicolas

Offline stirling

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Re: Power Supply Unit
« Reply #82 on: January 16, 2011, 12:11:46 PM »
Kolias - Don't know if anyones raised this yet but it looks as though you have a double primary and double secondary transformer there. Wiring is not complicated but you need to be aware of how they need to be configured. Generally speaking it looks like you'll need your primaries in parallel (for 120Vac) and your secondaries in series (for 24Vac). Also you'll need to establish the phases of the windings or that fuse might well come in handy (hopefully there'll be some marking or whatever). To cover my *rse Please check it out - don't take this as instruction - just a cautionary heads up.

Ian
Re: Power Supply Unit
« Reply #83 on: January 16, 2011, 12:12:58 PM »
Your schematic looks fine.  Personally, I would connect the DC and AC grounds together at a single point.  Better to have them tied together at one point intentionally, than to have a connection occur later on it's own, and create all kinds of flaky problems.  It will save you some grief down the road.

When you get around to wiring up E-Stops, limits, etc. always use shielded cables, and connect the shield to that same ground point ONLY at the electronics box, NEVER at the far end, and NEVER at both ends of the cable.

BTW - It would also be wise to wire in a relay for E-Stop, that cuts the AC power to the transformer.  There are many ways to wire an E-stop, but the most direct, and certain is best.  You NEVER want to depend on the software working properly for your E-stop to work, and it's best not to depend on the BOB either.  The simpler the better when safety is concerned, as it reduces the number of potential failure modes.

Regards,
Ray L.
Regards,
Ray L.

Offline stirling

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Re: Power Supply Unit
« Reply #84 on: January 16, 2011, 01:06:07 PM »
If the fuse on the DC blows while the machien is moving, the back EMF frpm the motors can blow the stepper drivers.
Ray - This just caught my eye whilst browsing. I wonder if this is why this fuse arrangement has been taken out of geckodrives's current version of their "step motor basics guide". I have the older version on file and saw that the DC quick blow fuses (between PS and drive) had disappeared on the latest version. Surely Mariss didn't make a mistake - oh no is nothing dependable any more :)

Ian
« Last Edit: January 16, 2011, 01:14:03 PM by stirling »
Re: Power Supply Unit
« Reply #85 on: January 16, 2011, 01:17:03 PM »
If the fuse on the DC blows while the machien is moving, the back EMF frpm the motors can blow the stepper drivers.
Ray - This just caught my eye whilst browsing. I wonder if this is why this fuse arrangement has been taken out of geckodrives's current version of their "step motor basics guide". I have the older version on file and saw that the DC quick blow fuses (between PS and drive) had disappeared on the latest version. Surely Mariss didn't make a mistake - oh no is nothing dependable any more :)

Ian

I'm surprised it was ever in there.   Mariss has recommended against fusing the DC side for many years.

Regards,
Ray L.
Regards,
Ray L.

Offline stirling

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Re: Power Supply Unit
« Reply #86 on: January 16, 2011, 01:45:01 PM »

Offline kolias

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Re: Power Supply Unit
« Reply #87 on: January 16, 2011, 01:52:30 PM »
Now I like all these answers and thanks all for your time........

Ian, the transformer was suggested to me by ger21 who was kind to send me a link where to buy it and I know that I may have trouble wiring it up but when I get it I will post a picture of it along with all the wiring hanging out from it and I will ask what else? more questions. Thanks Ian for pointing out this critical point.

Ray that was a question which always was puzzling me but I was not sure if I could connect the ground from the AC along with the ground (black) from the DC. Now that you confirm this point, I will do as you say – much easier anyway. I always use shielded cables and I do connect the shield as you mentioned. For the motors I use 22 gauge cable with 5 wires on it and for the limits / Estop I use 18 gauge with BLK / RED on it. That’s what I did with my 1st CNC and seems it worked just fine. I would have liked to go heavier on the motors cable but my local store had only 22 gauge available with 5 wires

Regarding the relay for the Estop I did pursue this subject on my 1st CNC machine with a Swedish guy from the CNCZone forum who was extremely helpful. I did buy 2 relays and was ready to install them based on his schematic but then I got tied up with other work and never installed the relays. I still have the relays and left space in my new control station for them and later I will install them. I know that is not wise to depend on software for the Estop and thanks for pointing out this item

Nicolas
Re: Power Supply Unit
« Reply #88 on: January 16, 2011, 02:53:02 PM »
A Bit Of The Logic Behind Grounding And Shielding....

For all practical purposes, ALL electrical conductors have resistance.  When current is passed through those conductors, that resistance causes voltage drop.  The greater the current, or resistance, the greater the voltage drop.  If the current is pure, constant DC, this voltage drop will be constant.  But, if we're operating in the real world, this is almost never the case.  The voltage drop will add "noise" to the signal, and the shape of that noise will be more or less the same as the shape of the current.  So, where, in an ideal world, you night have a 35V DC supply driving a constant 35V into your load (motor or electronics), you will instead have a noisier, lower voltage, signal present at the load.  So, what happens if you run a wire from the power supply, to your motor drivers, and from there on to your electronics?  The motor drivers will introduce a lot of noise into BOTH the power and ground wiring.  This noise will then be passed along to the electronics, possibly leading to the electronics misbehaving, because the noise may "look" like a signal to the electronics.  If, however, you run one set of wires from the supply to the motor drivers, and a completely separate set from the supply to the electronics, the electronics will not "see" the noise introduced by the motors and drivers, making the electronics operate more reliably.  The whole point here is to provide a dedicated path from the power supply to each "load", so noise introduced in one part of the system does not get into other parts of the system.

Similarly, you want to ideally have one, and only one, path the power, and ground can take.  Electricity will always take the path of least resistance.  If you provide more than one path, SOME of the current will go down each path, creating the possibility for current to take a path that will introduce noise into places you don't want it.  This is part of the reason you generally don't want to ground the shield on both ends of a shielded cable, as it creates the possibility for current to flow through the shield, rather than through the ground conductor, and that current can induce noise, through inductive coupling, into the signals carried on all of the conductors in the cable.  Make the current go where you WANT it to go, don't let it find just its own way.

There are two generally "safe" ways to make ground connections.  One is to bring all the ground wires to a single point, and tie them all together there.  The other is to create a VERY low-resistance ground bus, using terminal strips, heavy ground cables, or a ground plate.  The E-box for my big mill is a 24"x24"x12" steel box.  In it, I've mounted a 24"x24"x1/4" aluminum plate, to which ALL the electronics are mounted.  This box contains the entire PC (all removed from its case, and all the bits re-mounted to the door of the enclosure), the servo power supply (dual 72V@20A supplies), a giant E-Stop contactor to cut the AC to the power transformer, rectiifers and filter caps, all the servo drives, the VFD for the 3HP spindle motor, three breakout boards, relays for coolant, pwoer drawbar, etc, a Modbus controller, four fans, and some other odds and ends.  Everything is open, and in rather close physical proximity, but from the very first time I powered it up, it has worked absolutely rock-solid reliably, with no glitches or flakiness whatsoever, despite having the VFD inches away from the PC, which is inches from the servo drives, etc..

The AC line (220V, plus neutral, plus AC ground) comes into one side of the box, through a fuse, then goes directly to a terminal strip.  From the terminal strip, I branch off separate wires to power the VFD and servo power supply transformer.  The AC ground connection is tied, through a heavy conductor, to the 1/4" plate to which most of the electronics are mounted.  There are additional heavy conductors from the terminal strip to the enclosure itself - one to the main enclosure, one to the door, where the PC electronics are mounted.  ALL DC ground connections are to the 1/4" plate.  The separate ground connections for all the high-current AC devices ensures there can be no AC ground currents flowing through the 1/4" plate.  The 1/4" plate itself acts as a very low resistance ground conductor.  Since the currents drawn by all the electronics are relatively small, there is no real possibility of ground currents through the plate causing any measurable voltage drops, or noise injection, into any of the electronics.

All I/O cabling is shielded, with the shields connected ONLY at the BOB, or whatever device they connect to.  Where appropriate (limits, E-Stop, etc.), I try to use higher voltage I/Os (limit switches, etc), and ALWAYS provide good, stiff pull-up resistors (100-300 ohms) on logic-level inputs, to make it much more difficult for noise to false-trigger an input signal.   If you follow a similar, simple layout, you will rarely have problems with noise, ground loops, and other such problems.

Regards,
Ray L.
Regards,
Ray L.

Offline kolias

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Re: Power Supply Unit
« Reply #89 on: January 16, 2011, 04:12:03 PM »
Thank you for taking the time Ray to educate me, very interesting.

One thing I noticed: you are saying that you use 1/4" aluminum plate which you mount your electronics plus you use this 1/4" aluminum plate to connect your grounds. I thought that aluminum is not a good conductor and I was planning to use a steel flat bar 1/8” thick to mount all the grounding wires.

Is it better to use an aluminum bar because of its low resistance?
Nicolas