Conversion from electromechanical to SSR for 3-phase motor 1

[kingkiller]

Hi, everybody. Figured I'd come over here for some advice on how to proceed with a project I'm working.

First, I'll start by explaining the situation.
I run a music rehearsal facility in Brooklyn, NY called King Killer Studios. We have a garage on the ground floor, but all of our rehearsal rooms are on the second, and we have a funicular lift that is used for hauling equipment (amps, drums, etc.) up to the 2nd level.

The lift is pretty basic: a 3-phase motor couples to a winch system, which either pulls or releases a rope attached to a platform, depending on the direction it's running. There is a 3-button controller (UP [normally open], DOWN [normally open], and STOP [normally closed]) connected to the contactor points of the current relay, as well as two auto-stop switches at the bottom and top of the lift platform, also connected to the contactor points.

Recently, we have had issues with the relay, which I suspect are the result of various archs over time damaging the contacts. It's a VERY old system, and the wiring is an absolute rat's nest and needs to be cleaned up no matter what I decide to do. The biggest issue is that occasionally, the "auto stop" switches (both normally closed, like the STOP button) have been failing at the top, leading the platter to slam against the top platform, which in turn makes the chain slip and eventually break. When that happens, well...I'm sure you can figure that out. With no tension keeping the winch in place, the platter flies down the lift riser (about 35 feet), and slams into the bottom. If someone were standing there, it would be bad news, obviously.

SO:

The "auto stop" switches are brand new. I tested them for continuity before installing, and again after the latest incident, and they have a 0% failure rate. The motor was recently respun, and is working fine. I have also tested the controller box, and each of the momentary switches seems to be working correctly (however, the few times that this has happened, pressing the STOP button did nothing), which leads me to believe the electromechanical relay is worn out and beginning to fail more often, which I can't have.

I've decided to replace it, and I've purchased a 3-phase reversing relay from Mouser (the Crydom D53RV25C). However, I have a few questions.

1) The motor is pretty old, and I'm unsure how many HP it is. The main fuse/cutoff box says it is RATED for 7.5 HP, but I do not think the motor is that big. We have 3 legs of 120V/20A coming into the box, on which the motor runs solidly, which is why I purchased the 25C instead of the 50C; it is rated for up to 25A PER PHASE, which is already higher than the motor is running on. Should I have gotten the larger one (rated at 50A/phase), and why?

2) I am confused about the contactor connections. There are two terminals, one for forward, and one for reverse, and one common terminal for both, which makes sense. However, it seems as though the contactor itself needs to be powered separately, with a range of 4-32V. Will I be able to retrofit my existing switchbox and auto stop switches, or will I need to revamp the entire contactor/control system? If I can use what I currently have, how would I go about it? There is very little data on this specific SSR, and I'm unsure whether or not it supplies the control voltage, though it seems as though it does not.

3) VARISTORS. The SSR I purchased has only 2 legs that get reversed depending on the direction they are told to spin. One datasheet I read recommended attaching MOVs (or VARISTORS) between each "active" phase and it's reverse counterpart, both outside and within the SSR, for a total of 4 (see picture below). For this circuit, what would be the recommended value of this MOV?

4) Will this SSR require a heatsink for this application?

5) Here's the big question: should I just get a new electromechanical relay and rewire the whole system, essentially as is, but get rid of the mess of wires? The wiring will be redone one way or another, but I'm starting to wonder if I should just keep the system as is to keep my costs down.

Please let me know how I should proceed. Time is also of the essence, because I have a large clientele all getting impatient with each passing day that the lift is not working!

Here are some more pics of this whole mess:

 

[jraef]

1) If this is a passenger elevator or one that people CAN ride on, there are specific rules and regulations as to the control and protection of the motors on them. It's not something you should mess with, your liability is enormous.

2) Simple SSRs like that are not really designed to be used for motors (despite what they say), they do not provide the necessary motor overload protection, and that circuit as shown is just down right illegal in the US.

3) The failure mode of an SSR is to fail SHORTED, so that would mean you CANNOT turn it off, which comes to the previous point about rules and regs on elevators. If you use it on an elevator, you must ALSO provide the contactor anyway for isolation if there is a shorted SCR (which that unit will not detect), which makes it basically pointless.

Your contactors are failing because they are old. They don't last forever, they need periodic maintenance and replacement. Bulldog has not existed as a separate company since right after WWII when they were bought by GE. That particular A-B contactor was made obsolete in 1978, so right there is probably at least 40 years old, more likely as old as the Bulldog disconnect switch. Your entire system is well past it's prime and in fact if you were inspected, you would not be allowed to reconnect it. Hire a qualified elevator technician or an electrician that is certified to work on elevators and have them modernize your controls.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[kingkiller]

1) If this is a passenger elevator or one that people CAN ride on, there are specific rules and regulations as to the control and protection of the motors on them. It's not something you should mess with, your liability is enormous.

2) Simple SSRs like that are not really designed to be used for motors (despite what they say), they do not provide the necessary motor overload protection, and that circuit as shown is just down right illegal in the US.

3) The failure mode of an SSR is to fail SHORTED, so that would mean you CANNOT turn it off, which comes to the previous point about rules and regs on elevators. If you use it on an elevator, you must ALSO provide the contactor anyway for isolation if there is a shorted SCR (which that unit will not detect), which makes it basically pointless.

Your contactors are failing because they are old. They don't last forever, they need periodic maintenance and replacement. Bulldog has not existed as a separate company since right after WWII when they were bought by GE. That particular A-B contactor was made obsolete in 1978, so right there is probably at least 40 years old, more likely as old as the Bulldog disconnect switch. Your entire system is well past it's prime and in fact if you were inspected, you would not be allowed to reconnect it. Hire a qualified elevator technician or an electrician that is certified to work on elevators and have them modernize your controls.

Thanks so much for the response!

For starters, it is NOT a passenger lift at all, and there are numerous signs posted as well as language in the lease that strictly forbids riding on the equipment lift. It is grounds for lease termination and forfeiture of deposit, and everyone abides.

Thank you for the note about the SSR. I will return it to Mouser.

I'm sure you are absolutely correct that the current configuration is illegal. There's no possible way it would ever pass an electrical inspection using current code (which, if you're familiar with NYC building and electric codes, are unflinchingly rigid). However, we have passed every electrical and building inspection we have had, mainly because this contraption is filed as "existing to remain," which essentially means that as long as the unit functions and no major structural work is done to or around it, that it is grandfathered into whatever code existed when it was first built, and any changes made to it can only be to continue its functionality, which is not to say that you can not modernize it (for example, if there is a better solution for the relay, contactors, controls, etc., it's fine to upgrade them in the name of safety). Strictly speaking, this is not an elevator, it is a funicular lift; I have contacted elevator companies to service it, and they refuse because it is not really what they do.

Luckily, I do have an electric motor company that has serviced the motor in the past, and they are going to come by on Wednesday morning to have a look and figure out our options for modernizing the system. I primarily asked all these questions because I LOVE to know how things work (and to get things right the first time), and I also wanted to be armed with knowledge about what kinds of questions I should be asking these guys when they do come, because I want to make sure that the job isn't just done thoroughly and correctly, but with the safety of my membership first in mind.

 

[flexoprinting]

Hello King

I'm just a Tech, guy's like Jeff are the God's, your system is a very simple design and it looks like you can get by with replacing the control box, pulling some new wire, replace the contactors with a model that has auxiliary contacts for the braking system (I assume it has a brake, if not it Should) add proper overload protection and mount your limit switches on a better bracket. Not sure a license contractor will do the work due to liability issues, their call though.

Chuck

 

[melspuds]

Kingkiller,
I believe New York City has a code that requires only a licensed elevator tech is the only one that can work on elevators of all types and including your type of lift. For years Bulldog was made in NYC and to keep the company going, the city said that all disconnects must be Bulldog. I found out the hard way. I was one designers of the Times Square traveling message signs that were new 1970 and had to replace a bunch of Square D disconnects.
Good luck,
Dave

 

[waross]

Back in its day those Allen-Bradley starters were considered one of the best motor starters on the market. It may be the mechanical interlock which is failing and jamming and holding the contactor in or partially in. But that information comes under the heading of interesting but of no present use.
I would consider looking at the current Allen Bradley reversing starter of the same size.
The most important issue however is codes and liability. Probably the best way to cover your assets is to hire a qualified and licenced technician.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bohdand]

I won't comment on the code or liability issues. From a strictly technical perspective, the simplest and most reliable solution is to just replace the reversing contactor and the raise/lower/stop station with new devices with the same ratings, or slightly better. Electromechnical relays are very reliable and reasonably priced. Since you already have AB, you should be able to order a very similar replacement.