is it possible to jog a reversing starter.I have a forward/off/reverse position switch and a jog button is being requested.there are 2 no. nc. aux contacts unused on the reversing starter.feeling braindead . can only figure that i need a second jog button; 1 for forward and one for reverse.
reversing motor cotrol
- Thread starter hogknob
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- Status
- Location
- Massachusetts
I would use two jog buttons clearly labeled forward jog and reverse jog.
I'm thinking it would be better to have a single jog push button and a two-position run/jog switch. With two jog buttons, the operator could push both jog buttons at same time.
- Location
- Massachusetts
Either way would work fine but two buttons may be more convenient if they have to jog both ways a lot.
As far as both buttons at once, I assumed it went without saying you would wire it so that one locks out the other.
I got to see and repair the results of an overide signal from a fire panel burn up dozen or so coils of bypass contactors because someone did not wire it properly. They did not cut power to one contactor before energizing the other.
Perhaps.
Reversing starters come wired that way. There may be a mechanical interlock, too. Been awhile since I've had my hands on one, or my nose in a catalog... but electrically speaking, adding two jog push buttons and pushing both at the same time makes it a crap shoot as to which direction locks out the other first. If I had to provide two jog push buttons, I'd likely use a momentary rocker and wire it so it would only jog when the forward/off/reverse switch was in the off position... and ensure there's also a full-stop/e-stop too, to prevent an inadvertent jog...!!!
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
he could but both coils cannot come on. Reversing contactors have both electrical and mechanical interlocks that prevent both coils from being on at the same time.
- Location
- Massachusetts
I see that as operator error but your idea of rocker type switch makes sense.
I seem to recall at least once seeing reversing contactors which did not have a mechanical interlock. Don't recall the details, unfortunately...
Even with mechanical, I'm still thinking there is nothing which gives priority to one direction over the other, so pushing both jogs would still be a crap shoot... and could be a safety issue, not knowing which way the motor's going to turn. I'd rather eliminate the possibility from the design.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If the Forward-Off-Reverse switch was a multipole toggle or drum type switch which actually did the reversing of the appropriate phase leads, then you would have to set the main switch to the correct position before being able to jog. Hence a single button plus a Run/Jog switch would be more appropriate.
As long as all of the switching is done within the starter based on only two control input wires, you would have the freedom to wire it with two buttons or one button and a switch.
novemberaudi
Member
- Location
- boston
there is a diagram at www.industrial-electronics.com/motor_control/3i_Jogging-Control-Circuits.html
The two diagrams use all push buttons.
Am I the only one that sees there is a jumper missing in Figure #2 on the left side of the Jo/Run selector switch.
Anyway here is a very good site to learn about this very starter.
http://www.exman.com/index.html
Now that you mention it, I do :happyyes:
It's a poorly drawn diagram, so I didn't bother to evaluate it when I first looked at it.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
If you have a Fwd-Off-Rev SELECTOR switch, the direction selection is made by the selector switch, why would one need a Jog button? Flip switch to Fwd or Rev, flip it back to Off, motor "jogs" and you never took your hand off the switch. Is that so difficult that one needs a different button?
If however there is a Fwd-Rev selector switch (no Off), and THEN there is a Start-Stop 3 wire control circuit with momentary push buttons, a Jog button makes sense. You select the direction FIRST, then hit the Jog button. The difference between Jog and Start is that the Jog button bypasses the seal-in contact that goes around the Start button, so the contactor drops out as soon as the Jog button is released. Done all the time like that on machines that need a Jog function to set up belt tracking etc. where leaving it in Run for even a few extra seconds can cause damage.
By the way, the QUICKEST way to jam up a Reversing Contactor's mechanical OR electrical interlocks is to tempt fate by ASSuming they will always prevent simultaneous closing. They should both be BACKUP plans, the first line of defense is to not allow the control circuit to get there in the first place. Doing so purposely is just asking for it.
Re: Reversing contactors without mechanical interlocks. I just came off of a disaster of a project where the interlocks between two large contactors (bypass of a VFD) were electrical only. The engineer who designed it that way wanted to save $$ by using simpler contactors. He defended his decision, even though we were there to replace a 250HP VFD that had blown up because the electrical interlocks on the contactors had failed. He forgot the basic law; Murphy Rules! This was at a turd farm, vents in the pump station were not working so H2S gas built up in the room, mixed with condensation when the power was off, formed Sulfuric Acid on all warm surfaces which caused the contacts to corrode and they failed to stop the control circuit from energizing the VFD contactor when the Bypass contactor had welded shut. They went through 4 VFDs before they called us in to check it out. That's right, 4 VFDs for "smoke testing"! Bless their hearts...
If however there is a Fwd-Rev selector switch (no Off), and THEN there is a Start-Stop 3 wire control circuit with momentary push buttons, a Jog button makes sense. You select the direction FIRST, then hit the Jog button. The difference between Jog and Start is that the Jog button bypasses the seal-in contact that goes around the Start button, so the contactor drops out as soon as the Jog button is released. Done all the time like that on machines that need a Jog function to set up belt tracking etc. where leaving it in Run for even a few extra seconds can cause damage.
By the way, the QUICKEST way to jam up a Reversing Contactor's mechanical OR electrical interlocks is to tempt fate by ASSuming they will always prevent simultaneous closing. They should both be BACKUP plans, the first line of defense is to not allow the control circuit to get there in the first place. Doing so purposely is just asking for it.
Re: Reversing contactors without mechanical interlocks. I just came off of a disaster of a project where the interlocks between two large contactors (bypass of a VFD) were electrical only. The engineer who designed it that way wanted to save $$ by using simpler contactors. He defended his decision, even though we were there to replace a 250HP VFD that had blown up because the electrical interlocks on the contactors had failed. He forgot the basic law; Murphy Rules! This was at a turd farm, vents in the pump station were not working so H2S gas built up in the room, mixed with condensation when the power was off, formed Sulfuric Acid on all warm surfaces which caused the contacts to corrode and they failed to stop the control circuit from energizing the VFD contactor when the Bypass contactor had welded shut. They went through 4 VFDs before they called us in to check it out. That's right, 4 VFDs for "smoke testing"! Bless their hearts...
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I think it's because in Diagram 1 they used a Form C contact symbol, but in Diagram 2 they were trying to relate that to separate contacts and actually just put the feed from the left onto the wrong terminal. All Jog needed to do there is interrupt that flow to the Seal-in circuits.
Perhaps for safety reasons if jog is required to be a time limited function?
Press the jog button and you get maybe a half second of operation before it is disabled no matter how long the operator leans on that button.
It's a function I've seen used.
ptonsparky
Tom
- Occupation
- EC - retired
You would think some one working with a highly corrosive area would monitor the contacts.
They fail often enough normally.
They fail often enough normally.
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