Cooked Circuit Board

[RichE]

Looks like I'll be harassing you all for a while more.

PRTAlpha was connecting intermittently when we bought it. When I say intermittently, I mean connect for a second or two then comm error. Now it will not connect at all. See the pics at the end for the probable reason.

I'd like to know if it is was for sure something we did when we wired it in. The auction we bought it from gave us a 30 day guarantee, but I don't want to try and hold them to my screw-up.

I had a neighbor electrician come over before we hooked it up and told me it was good to go, but he was just basing that, as I was, on wire color codes. I now have schematics so I'm not so sure it was right. The setup I have doesn't quite match up to schematic (10216), as in wire ID's and terminal numbers are mixed up and the previous owner has an additional 220 wire.

HOWEVER, in the end power goes to the places it is supposed to go. The one exception is the white (neutral/ground) wire on the 220 circuit. It goes into Contactor #1 at terminal 5L3, jumps to contactor 2 where nothing comes out the other side. My schematic shows nothing regarding a 4th 220 line. The green ground wire to the main chasis ground is hooked to earth ground.

We'll be back in touch with Shopbot on Monday, probably sending the control box in to be tested. Until then I'd like to try and figure out what went wrong.

Any ideas? BTW, I have 5.5 volts on the 5 volt circuit so the power supply is still working and I never saw or smelled the "magic smoke" from the circuit card burning up.

Large burn on 5 volt trace


smaller burn on same trace

[RichE]

Thought I'd follow up on the wire mystery. We are probably the 3rd owner of this machine and it was originally equipped to run 3 phase and the last owner converted it to single phase, hence the extra 220 wire that doesn't go anywhere.

We just sent the control box out to Durham for testing. Hope there is nothing seriously wrong with it.

[gene]

I have a 48x96 prt alpha that the spindle is 3 phase but i only have single phase in my shop. NO converter . in my control box there is a place to hook up a extra wire for 3 phase but nothing has ever been hooked to it.

[Brady Watson]

Alpha boxes are pretty bulletproof. You have to do something seriously wrong to fry anything in the box. They are fairly well protected. There are ZERO connections to line voltage on the board itself. All high AC voltage goes through the switch and contactors. All voltage on the board itself is low DC voltage (5v-24vdc). I'm curious to hear what SB has to say about what they suspect torched the traces on the board. Please post a follow-up when you find out.

-B

[dana_swift]

Brady- what follows is just conjecture..

I suspect the trace is a ground trace. So it connects to one pin of each of (most of) the terminal blocks.

Now imagine something like the zzero plate, or its aligator clip comes into contact with an un-fused power source, possibly an external source (120v? or lightening or a battery), perhaps the 5v or some other Bot supply. Where can that power go? The "weak link" will be the trace on the PCB the wires each have far greater cross sectional area.

The writeup says they were "hooking it up", so my guess is some wires that the PCB uses for ground got connected to 5 or 24.

But this is all predicated on that being a ground, or 5, or 24v trace. But it makes the most sense until someone knowing exactly what that trace does provides that information.

Just a musing from somebody who has seen more than his fair share of charred PCBs. If that happened to me, I would just run a jumper wire around the bad trace, check everything and go back to work. After some words usually only found in a George Carlin routine..

D

[RichE]

If that happened to me, I would just run a jumper wire around the bad trace, check everything and go back to work

Just a musing from somebody who ha After some words usually only found in a George Carlin routine..

D

Trust me, there was plenty of the Carlin spirit alive in my shop when this all went down. We did consider jumping the scorched spots but being the noobs that we are we decided to send it it before we ruined anything else. I suspected it was the ground trace as well since it goes to multiple terminal blocks. I have 5 volts on it at the burnt spots, which means it is the 5 volt trace or something shorted and is now sending power all the way through to the ground which is what fried it? Pure speculation. I'll let the sb techs handle it from here.

As for something coming into contact with the circuit...possibly from the previous owner. I'm pretty anal with my wiring since I was an aircraft electrician in a previous life. I even re-wrapped some of the wiring in the box and cleaned up the "ugly" wire splices from the VFD and limit switches.

I'll make sure to post when I hear from them. They should receive the box tomorrow.

[RichE]

Ok, here is my follow-up. It took my box a month to get from Utah to NC. It seems the post office lost it. The collective reply to that has been "how the @#$% did they lose a 50 pound box". After many sleepless nights it did arrive tho.

The box works! Scott said the board got hot but didn't do any damage. So we sent it out prematurely after assuming the worst when we saw the board.

While the box was on its wild ride across the country I decided to install a sub panel in my shop. I had an uh oh moment when I opened my main breaker panel and see that I have no neutral bus. Grounds and neutral wires all go to the same bus. I am calling out an electrician because I'm over my head a little now. I'm curious what some of you have to say about my options tho so I opened a new thread here
http://www.talkshopbot.com/forum/sho...421#post132421

[Brady Watson]

From the web:

>>... He said it is ok to have ground wires and and nuetral wires on the same bus bar in both subpanels and a main panel...<<

You need to find another electrician. One that understands the proper bonding and grounding of panels, sub-panels, and circuits.

>>...Whats the theory behind separating the nuetral and ground wires in a subpanel but not in a main panel that contains the service disconnect?<<

First, you have to understand that the neutral is a current-carrying conductor, whereas the ground wire is not. As such, the neutral wires are insulated, the same as any other current-carrying conductor. The misunderstanding comes from the fact that the neutral wire is intentionally grounded at the main service panel only. The reason for this action is to allow ground-faults (or "short circuits" to ground) a return path back to the source of power, the utility transformer. Having the ground wires bonded to the neutral makes it possible for the circuit breaker to trip out easily under such conditions.

IF one were to connect the current-carrying neutral wire to the ground wires "downstream" then it's possible for some of that current to follow what is called a parallel path -- over the bare grounding wires -- instead of the insulated neutral wires -- as it finds its way back to the source.

Keep in mind that the metal outside frames of your utilization equipment --> appliances, furnaces, water heaters, etc. are connected to that bare ground wire, and you absolutely do not want those metal frames to be carrying any of that current in their normal course of operation. Such stray currents can have potential differences between them and a grounded surface, such as a concrete floor, or the frame of a different appliance connected to another circuit. Potential difference = Voltage.

And Voltage can = shock

Source: http://www.electricalknowledge.com/f...hives/1098.asp


-B

[RichE]

So after everything we've been through it was a $2 problem. One of my outlets in my shop was internally shorted. Replaced the outlet and we connect just fine. I haven't powered the spindle yet but ghost cuts are working great.