Electrical problem

[sawkerf]

I have a 2004 PRT Alpha, and for a couple of years now, I've had issues with my router contacts working sporadically. Recently, I replaced both contactors and they worked for a few days then suddenly not at all. Then, after a period of time they will work for a little while and then quit again. The odd thing is, even when they are "not" working, I can hear and see them move and the router still will not come on. How can this be? I've talked to tech support a few times to no avail and I'm just kind of frustrated that I spent the money on new parts and it still won't work. My gut tells me it's probably something simple, but for a guy who is not real handy with a voltage meter, it is a big challenge to figure out. Do any of you guys have experience with this issue? On another note, I just finished upgrading my Z axis and it was very well worth the money!

[richards]

If you have a volt meter, troubleshooting a contractor is fairly simple. You said that you could see the contactor operating properly. That means that the voltage to the coil is working as expected. I'm assuming that you're running A.C. voltage through the contactor's contacts to the router. On the input side of the contactor, you should be able to measure 120VAC (assuming that you're using a standard 120VAC router). One contact will be connected to the "hot" or phase side (usually a black wire, but sometimes a red wire if U.S. 240VAC is being split into two 120VAC lines) and the neutral, which should be a white wire. (In most areas, electrical code forbids running a neutral line through a relay or contactor in order to minimize the possibility of shock, so look around the control box to find where the white neutral wire enters the control box.) That voltage should always be present when your control box is turned on. (The exception would be if another contractor, switch or relay is wired in series with the contactor that is controlling that voltage.)

If you have voltage on the input side of the contactor, then turn off the control box and set the dial on the volt meter to continuity. Disconnect anything except the router that is attached to the output side of the contactor. Check the output side of the contactor with one lead of the meter on the black wire and one lead on the white neutral wire. You should have continuity between the black wire and the white wire. If the continuity test fails, then you have a break in the wires leading to or from the router, or perhaps a faulty switch on the router.

If the continuity test is successful, then turn on the power to the control box, activate the contactor and then check voltage between the black and white leads on the output side of the contactor. If there is no voltage, then either the contactor is wired incorrectly or the contacts are not making contact properly.

Good luck. If you still have problems, post some photos.

[shilala]

Have you ever changed out the brushes in your router?
Mind ya, I'm not familiar with your machine. But my router plugs into a socketed cord on top of the machine. It's very easy to unplug the router and see if you have power at that socket when the contactor is closed.

It'd be very easy for me to imagine a break in the cord that leads to the router, as well. Especially on a machine that old and on wiring that moves constantly.
It's also a very easy fix to replace that wiring.

When you say "contactors aren't working at all", do you mean they won't pull, or that they aren't supplying power out to your router?

[sawkerf]

I will try to post a pic of the contactors sometime soon. As for the router, it is perfectly fine, absolutely no problem with it whatsoever. It works fine when plugged into a regular receptacle. The power cord coming from the contactor to the router plug is also fine. The odd thing is, the contactors will sometimes pull but do not supply power. Sometimes they don't pull at all. Other times they work just fine, then suddenly stop working. I'm perplexed.

[sawkerf]

Here is a pic of the new contactors

[bcondon]

Hey Kip,

Tell me what you mean by "PULL". The contactor is engaging, hence the
coil is engaged...

I have to say that this contactor is very busy!

So I have a couple of thoughts...
1. the contactor's contactor surfaces are already worn (which seems impossible to me)
2. Some contactors have thermal cutouts in them that have to be sized for the loads... They will not make contact when they are hot because too much load has been placed across them -or- there is a high resistance
path that makes these cutouts hot.

These would randomly cutout which is what you are reporting. There is so much going on with this contactor that there may be cutouts in the upper right piece of the contactor...

Just some thoughts...

Bob Condon

[sawkerf]

Well by "Pull" I mean "engage". No way they're worn, They have less than ten hours of actual use on them. It seems logical to me that the problem is not the contactors themselves, but rather some other issue related to their proper connectivity. I just lack the proper diagnostic skills needed to figure this out. Any suggestions are much appreciated.

[bcondon]

do you know the make and model of the controller?
Does it have OVERLOAD RELAYS in them?

The overload relay is a bimetalic strip that acts like a resettable fuse.

When it gets too hot, then the relay opens and shuts the load (aka. router)
off.

The reason for high heat is the relay is improperly sized (too small for the load) or the tool is pulling to much current.

Where the controller is new, they may have just thrown in a default-sized
relay which may be under-sized...The tripping of these relays would be somewhat random which you are seeing

Just a thought...

[Ken Sully]

Kip,
I have a PRS so I do not have a Schematic for a PRT.
Do you have one? Also do you have something to check voltage with? A simple 2 wire tester you could check an electrical outlet with should work.
Let me know and I will try and help

[bcondon]

These contactors have built in heaters which are essentially
fuses or bimetalic strips so when they get too hot (undersized or device
pulling too much power).

You need to select the appropriate heater and order the controller with that heater.

I think the heaters are tripping which is causing your randomness

THX

Bob Condon

[sawkerf]

The contactors were bought from Shopbot so there should be no question of wether they are the "correct" ones, although I guess anything is possible. Overheating can't be the problem unless they are overheating with no load since they are not working most of the time. Only once have they stopped working while running a file and it was less than 1 minute into the file. All the other times they have quit working has been just a failure to start at all. For instance, I could run a few files with no problems then just randomly when I start the next file it fails to start the router, even though can hear the contacts cycle. Although most days they don't work at all. Did I get defective brand new contacts? I guess that's possible too.

[richards]

Sometimes it's best to hire an expert. An electrician with a meter should be able to find the problem in about 15 minutes, so the cost would be minimal.

[bcondon]

There are actually 3 sets of controllers in your picture.

I would get a schematic from Shopbot before making the call to
the electrician.

I believe you have a defective contactor or defective heater.

The problem is in the power side of the circuit which could be that
the coil is not closing the power circuits even though you hear the
coil engage, or could be the heater.
Good luck

[MogulTx]

When he said the contactors were very active- it sounded like that should have defined the area to look for the problem... I have had large contactors fail and they can "chatter" or "stutter" as they rapidly engage and dis-engage. That is never appropriate activity for a contactor. You want a positive, non-ambiguous contact. Could be an electro-magnetic coil that is failed/failing... "Heaters" etc... depending on the type of contactor. Often happens from electrical overload, age, lightning strike or other surge, contaminants, etc.

Can also be an issue of poor heat sink to the contactor, or a manufacturing fault. Wiring error?

[gerryv]

Let's see; the fact that you changed the contactors implies that you were having this or a similar problem before changing them. But, the problem persists,. This would suggest that the problem is not likely with the contactors themselves.

That leaves incorrect wiring of both the original and new ones as one possibility - only likely if you or a previous owner did something with any associated wiring just before the problem started. If yes, that's a strong candidate.

Next, you mentioned testing the router on it's own works fine so if you take that out of the equation what's left and easiest to verify with it and the contactors out of the equation?

You indicated "The power cord coming from the contactor to the router plug is also fine." Just wondering how you know this for sure? The reason I ask this is the router works fine when plugged into the wall receptacle but not when plugged into the system so what's different? The first thing that comes to mind is the power cord between the contractor and router plug, which has several components.

The two easiest check/test possibilities that come to mind are:
1. The blades of the router's plug are making good contact in the wall receptacle but are not making good contact with the "pinching components" of the other cord. This is a pretty common problem in everyday life with plugs and receptacles.
2. There is a partially failed wire inside the power cord coming from the contractor. More of a PITA to check out than #1 but not uncommon.
Each might play havoc with your incoming voltage. I'd be tempted to check #1 first and then number 2 and, at worst, eliminate these as possibilities.

Next I'd ask if you might have a light gauge and long extension cord in the mix and finally if you know that your line voltage is not low?

[Brady Watson]

There are usually 2 major culprits when it comes to the contactors. 1) The electromagnetic coil in the contactor itself gets tired and fails to work properly or 2) The 24v power supply isn't putting out full voltage or D) Each of them have degraded enough to cause a failure.

Check the output of the 24v power supply & then your wiring connections from 24v to the contactor. You could have inadvertently forgotten to tighten up the lug!

There is a small possibility, if you are running an older Alpha tool, that the ice cube relays on the control board need to be replaced.

-B

[sawkerf]

After years of this being a mystery, I accidentally fixed it yesterday! I had electrician at the shop yesterday, wiring up a new office for me. I asked him to take a look at my contacts to see if he could figure out what was causing them to work intermittently. After about 90 seconds, he opened up the disconnect switch that the control box is wired through. Turns out that one of the two screw-in fuses was loose. He tightened it up and we are good as new. I'm not exactly sure how this fixed it but I'm very glad to have it fixed!

[Brady Watson]

Thanks for posting the solution & glad you got it sorted! These things can be very frustrating when you just want it to work...

-B