Help Identifying Relay

Hi all - I've got a beefy old relay that I need to replace, and the coil voltage has been scratched off of the casing. I can post photos later.

I believe it's a motor starting relay. Here's what we DO know:

Mfg: RBM Controls
AC Only - 250V 18a
1hp 125v / 2hp 250v
Model Number: 129990-1540B
Other Number: JZJ? IZJ?

Lug layout:
6-----] [-----3
1-----]\[-----2
5---- O -----4

It's very similar **broken link removed**, but a little different (my unit has JZJ or something in place of the 7823, and has more lugs).

Can anybody help?
Mike

THe part may be obsolete. WHat powers the coil? 24V ac transformer?
What is the load 240V or 120V motor?
How many wires are connected? Does it look like DPST?

It appears to be a NO and a NC contact plus coil.
You can use a P&B PRD series with the correct coil once you know the coil voltage, if replacing an original, you should be able to measure the coil source voltage .
Max.

Whoa sorry... fell off the face of the earth.

Lugs 5 and 6 have 120vac across them in normal operation. The relay is damaged, so I can't tell what 3 and 4 show when engaged, but they somehow interface with the motor control circuit (wires are buried in this machine). The motor is a small electro-craft DC servo motor that can't be more than 1hp, but no ratings are viable on the casing.

I know I'm not much help... but any assistance in finding a replacement?
Mike

Is it just for running one direction or does the motor reverse?
Max.

Just one direction.
Mike

You can use a P&B PRD style relay or pick up a contactor off ebay and just use two of the 3ph contacts.
You need to verify the coil voltage and AC or DC.
Max.

I would be carefull to do that since you have no idea if it is AC or dc motor.

analog1 said:

I would be carefull to do that since you have no idea if it is AC or dc motor.

Click to expand...

I used many of these Electrocraft motors most are DC brushed, if it were BLDC it would have a controller of some kind.
Max.

Max - are you suggesting getting something as a temporary workaround so I can read the coil voltage? I wish this unit wasn't beyond the pale.

A few photos might help someone:







The motor says "DC Servo Motor, Part # 138000, Serial # 13080, Electro-craft corp Hopkins MN".

Mike

The voltage on the conductors that go to 4 & 5 in the OP has to be known in order to obtain one with the correct operating coil voltage.
What is the reason for replacing it in the first place?
Max.

The relay was being very noisy - lots of chirping and some arcing in the relay at motor startup. I'm assuming dirty contacts of some sort, but the relay came apart while trying to remove it and now has a dead short somewhere... which is why I can't easily find the coil voltage.

Mike

Is it not possible to either trace the source of the coil supply or measure it by powering up?
Also detect if AC/DC.
Max.

OK I've got some strange readings I hope all can help me sort this out.

The relay is damaged so I can't use it to test full operation. It came apart when I removed it from the unit and can't get it back together correctly. It's got a dead short if the relay engages.
I hooked things up, and the unit shows 120VAC across lugs 5 and 6. One side of lug 5 is the hot side of the AC plug, and the other side seems to go to the Power Transformer. Lug 6 is a neutral AC line.
I hooked up the coil side of the relay without anything connected across the switch lugs, and show 14VDC across lugs 4 and 6 in normal operation, but I'm not sure if this is the "engaging" voltage. I'm assuming this DC voltage is possible based on the side of lug 5 going to the PT and likely DC PS from there? It's nearly impossible to trace the circuit, but it looks like that's a distinct possibility.

SO, we must have an AC voltage across 3 and 6, correct? I'm assuming that because lug 6 is a neutral AC line.

That would also explain the AC voltage ratings on the casing. I just wish I could fully verify that 14vdc is the voltage the relay engages at.

Thoughts?
Mike

I think you need to get someone with some electrical knowledge to actually look at the relay. They should be able to identify the contacts and coil. From the way you show the markings next to the terminals in post #1 I do not think the coil is connected between terminals 4 and 6 If you can post some good quality photographs showing views from all 6 sides of the relay it might be possible to help more. I do not think this relay will directly control the servo motor with built in tacho generator shown in your photograph. The type and model of the machine that this is in might also help. Someone might even have a schematic of the machine. What is the resistance between terminals 4 and 5 of the relay with no wires connected to those terminals ?

Les.

Hi Les - typo. 14vdc between terminals 4 and 5, not 4 and 6. 4 and 5 are definitely across the coil.

The other two connections are on the NO contacts 3 and 6. 6 is a neutral AC line, 3 is a mystery.

Mike

There is one clue if it is an AC coil is the presence of a copper shading ring, this is a heavy single turn of copper close to the coil around the coil stator.
Max.

Hi Mike,
Do any wires go to terminals 1 and 2 ? What function does the relay perform ? With not even knowing what type of machine it is part of we don't even know the questions to ask to decide if it would be safe to see if the machine performs any of its functions if you connected the wires together that go to terminals 3 and 6 It might be a 12 volt DC coil and the voltage is a little on the high side. Or it could be a 24 volt (or higher.) coil and the real fault was a fault in the drive circuit with the voltage being too low of totally unsmoothed DC due to a failed capacitor or some other fault. This may have been a progressive fault initially causing the relay to chatter. I think we may have reached the limit on the advice we can give with the limited information you are prepared to give.

Les.

Thanks Les - here's everything I've got. I appreciate all the help with this.
What it's from? An obscure transparency-making copy machine from the early 70's. I've posted about it here before - it's called a Thermofax, made by 3M. I've looked in multiple sources for a schematic, including this site and 3M directly, with no luck. I don't have the specific model number either, but it was from a run of 15 amp machines (most of the current pulled from the high-intensity heat lamp).
What function does the relay perform? My speculation is that it is a motor-starting relay, but I just don't know. It engages when the motor turns on to run the transparency through the rollers, which is tripped by a switch triggered by the paper entering the machine.
Is the motor AC or DC? It is almost definitely a DC motor, and the unit includes a power supply and smoothing capacitors. The smoothing capacitors have been replaced and the machine functioned normally for several weeks after replacement.
What kind of resistance measurements do you get across the lugs? 1 and 2 show about 22ohm. 3 and 6 are open.
Can you bench test any of the components? Sort of. I don't have a variable power supply, but I do have a 3a 13.7vdc supply. I tried running this across the coil of the relay and it does click over after a few moments of receiving voltage directly from the PS. When engaged, however, the resistance across the NO and NC lugs don't change - I attribute this to the dead short in the relay since I mucked it up.
I thought you said it was chattering and arcing. Why doesn't the relay work anymore? I pulled a screw out of the cover that I should not have when removing the part from the machine, and that bungled things. I don't have high hopes for it ever going back together correctly. Honestly, I had hoped to just read the specs from the side of the housing and get a new one. No such luck...
Can you post more photos? Yes!









What if I ran a variable resistor between the connections on 3 and 6 and slowly increased the voltage to see what I see? Too dangerous?

Mike

If you have a neutral connected to one side of the coil, which you appear to have, then it most likely is a 120vac coil.
The DC motor shows a control board which for which the relay may switch on the AC supply to it to run the motor?
If this is the case then there are several suitable 120v SPDT relays out there that would fit the bill. As it looks as though only the N.O. pair are used.
Max.