Retrofitting knee mill

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24 May 2019 21:11 #134850 by PCW
Replied by PCW on topic Retrofitting knee mill
No problem with 7I92 in any setup , but 5I25/6I25 + 7I77 in separate cabinets
is more susceptible to ground loop issues

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24 May 2019 22:43 #134852 by BigJohnT
Replied by BigJohnT on topic Retrofitting knee mill

OT-CNC wrote: Nice clean box JT. I wish mine was roomy. The old ones were smaller and I had to hang the 7i77 off the end in a separate enclosure. I assume your drives don't emit that annoying high pitch whine? Where did you mount the vfd?


The VFD is in the other cabinet on other side, there were 3 cabinets total and I removed the back one, completely gutted the left one and removed all but the drives and DC power supply from the right cabinet. Wine not that I can hear lol oh you said whine.

JT

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24 May 2019 22:44 #134853 by BigJohnT
Replied by BigJohnT on topic Retrofitting knee mill

PCW wrote: No problem with 7I92 in any setup , but 5I25/6I25 + 7I77 in separate cabinets
is more susceptible to ground loop issues


And I can verify that is a fact!

JT

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24 May 2019 22:51 #134854 by rodw
Replied by rodw on topic Retrofitting knee mill

bevins wrote:

PCW wrote: A 7I77 + 7I92M is a good choice if the PC is in a separate cabinet than the control/power electronics


Whats the problem with the 7i92M and 7i77 in same control cabinet as the PC?


Nothing. Just that Ethernet is good for 100 metres and you don't need that in your situation. PCI/PCIe may have been a cheaper choice.

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24 May 2019 22:57 #134855 by BigJohnT
Replied by BigJohnT on topic Retrofitting knee mill
$9 cheaper in fact, but having the 7i92 next to the 7i77 is a plus.

JT

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24 May 2019 23:58 #134861 by tommylight
Replied by tommylight on topic Retrofitting knee mill
7i92m can be plugged directly to the 7i77, so no 25 pin cable required.
That is what I use I several retrofits.

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25 May 2019 22:08 #134935 by austin136
Replied by austin136 on topic Retrofitting knee mill
I see the 7i77 has a sourcing and a sinking output version witch do I need. I really don’t understand the difference.

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25 May 2019 22:17 - 25 May 2019 22:18 #134937 by PCW
Replied by PCW on topic Retrofitting knee mill
Sourcing current path (7I77)

+24V --> 7I77 field power+ --> 7I77 output --> load --> field power -

Sinking current path (7I77D)

+24V --> load --> 7I77D output --> 7I77 field power common --> field power -

Notice that for sourcing drives the load common is negative and for sinking drives,
the load common is positive. Polarity is important because the relay will have flyback
diodes installed. This means that if you are driving existing relay arrays
is best the get the 7I77 type that matches the original wiring, unless you want to rewire
every relay.
Last edit: 25 May 2019 22:18 by PCW.

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28 May 2019 04:16 #135114 by austin136
Replied by austin136 on topic Retrofitting knee mill
Wiring is kinda a mess right now but it doesn’t even look like the relays are hooked up right now. Looks like previous owner bypassed them.
I’m assuming that sinking would be standard right?

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28 May 2019 11:22 #135155 by Todd Zuercher
sourcing

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