Flood Coolant Set Up Questions

[TomS]

In the never ending task of trying to get the most out of my CNC mill I decided to set up Mach3 to control my flood coolant pump. I've configured Mach3 and my PMDX-126 BoB so that the KM1 relay is operated by Pin 1. This all seems to work fine. When I press the "Flood" button or enter a M8 command in Mach3 Pin 1 becomes active and sends a 5VDC signal to my SSR. I confirmed that I'm getting 3.95VDC at the SSR and the red indicator light does come on. The problem I'm having is the pump is not starting. I must have a mental block because I'm not understanding what's going on with the AC side of the circuit. Whether the SSR is activated, or not, I'm reading 120VAC across the SSR AC terminals. When I check continuity across these terminals I get nothing when the SSR is activated.

Here is a schematic of my wiring. Like I said I'm just not seeing what I'm doing wrong.

 

[Boswell]

First, I think that a motor will look like an inductor in the circuit and so if the SSR is OPEN and so no current is flowing you would expect to see 120VAC across the terminals. If it was closed and conductin then you would see 0VAC across the terminals and you would see 120VAC across the motor as all the voltage is dropped across the load. So, I think (not an expert here) your SSR is not closing. Could be the Triac (or whatever it has inside) is fried or you are not getting a good trigger for some reason. You might try a resistive load instead of the motor like a lamp to see if you get a different result. You can try to short across the terminals of the SSR to verify that the pump is working properly (remove power, install short, re-apply power).

 

[JimDawson]

First, I think that a motor will look like an inductor in the circuit and so if the SSR is OPEN and so no current is flowing you would expect to see 120VAC across the terminals. If it was closed and conductin then you would see 0VAC across the terminals and you would see 120VAC across the motor as all the voltage is dropped across the load. So, I think (not an expert here) your SSR is not closing. Could be the Triac (or whatever it has inside) is fried or you are not getting a good trigger for some reason. You might try a resistive load instead of the motor like a lamp to see if you get a different result. You can try to short across the terminals of the SSR to verify that the pump is working properly (remove power, install short, re-apply power).

I agree

 

[spumco]

On the PMDX-126, the K1 relay is rated at 30A at 120/240VAC. K2 is rated at 10A. Good schematic on page 26 of the manual when using K1.

You might try just using K1 as the only relay and leaving the SSR out. You already have 120 or 240 powering the PMDX, so I'm guessing it's not a big wiring job to just use it directly and 30A should be fine for a pump motor (I hope!).

PS - don't forget to fuse it upstream of the relay.

 

[TomS]

First, I think that a motor will look like an inductor in the circuit and so if the SSR is OPEN and so no current is flowing you would expect to see 120VAC across the terminals. If it was closed and conductin then you would see 0VAC across the terminals and you would see 120VAC across the motor as all the voltage is dropped across the load. So, I think (not an expert here) your SSR is not closing. Could be the Triac (or whatever it has inside) is fried or you are not getting a good trigger for some reason. You might try a resistive load instead of the motor like a lamp to see if you get a different result. You can try to short across the terminals of the SSR to verify that the pump is working properly (remove power, install short, re-apply power).

It's a new SSR. I guess that's guarantee it's good. I'll do the lamp test and see what happens. Then I'll do the short across the terminals test.

Thanks

 

[TomS]

On the PMDX-126, the K1 relay is rated at 30A at 120/240VAC. K2 is rated at 10A. Good schematic on page 26 of the manual when using K1.

You might try just using K1 as the only relay and leaving the SSR out. You already have 120 or 240 powering the PMDX, so I'm guessing it's not a big wiring job to just use it directly and 30A should be fine for a pump motor (I hope!).

PS - don't forget to fuse it upstream of the relay.

I didn't realize K1 was rated at 30A until you mentioned it above. Must have read the manual a dozen times today and didn't see the relay amperage ratings but looking at a picture of the BoB on the PMDX website it's clearly labeled 30A. Like I said I had a mental block.

I'll look at the pump but I'm sure it doesn't pull anywhere near 30 amps. It's on a 20A circuit and hasn't tripped the breaker yet. The wiring change is easy. Just route the AC wiring to K1 instead of to the SSR. Actually this makes for a cleaner installation.

I have a few things to try. Thanks guys.

 

[jbolt]

Mine is wired like yours except I use the relay on the pmdx-126 to switch a 12vdc power supply for the SSR. The cheap SSR's don't seem to work well below 5-6 volts.

 

[Robert LaLonde]

I used analog very low current draw 5V relays. Why do you have so much less than 5V? All of my machines have solif 49.-5.1VDC on the logic circuits of the BOB. Its pretty solid with a mediocre to decent 1A 5V regulated PS. I've even left my old RS meter hooked to a laptop logging voltage levels while doing testing. I do have a PMDX BOB, but its still in the box it came in. Anyway, then for heavier loads I use the 5V low current relay to activate a heavier relay or a contacter for motors, solenoids valves, etc.

 

[TomS]

I used analog very low current draw 5V relays. Why do you have so much less than 5V? All of my machines have solif 49.-5.1VDC on the logic circuits of the BOB. Its pretty solid with a mediocre to decent 1A 5V regulated PS. I've even left my old RS meter hooked to a laptop logging voltage levels while doing testing. I do have a PMDX BOB, but its still in the box it came in. Anyway, then for heavier loads I use the 5V low current relay to activate a heavier relay or a contacter for motors, solenoids valves, etc.

I haven't investigated why I'm getting 3.95vdc. I'm out of town for a couple of days. Could be my power supply but don't know for sure.

As I recall I had a similar problem when I first converted my machine. IIRC I upped the power supply to 12 or 15vdc and that solved the problem. I'll check it out when I get home on Thursday.

 

[TomS]

Mine is wired like yours except I use the relay on the pmdx-126 to switch a 12vdc power supply for the SSR. The cheap SSR's don't seem to work well below 5-6 volts.

I think you hit on something. I had a similar problem when I first started my conversion. Installed a 12 or 15vdc power supply and that cured it. Thanks for the reminder.