Help Identifying Relay

[KeepItSimpleStupid]

Hey, I know what a thermofax machine is. It is ancient.

The contacts are rated AC only and HP rated, So you have one NO contact and one NC contact and likely a 12 V coil. Let me look.

 

[KeepItSimpleStupid]

Are only 3&6 (contacts) and( 5&4) coil being used?

The coil resistance would be useful.

 

[Les Jones]

Hi Mike,
Can you answer Max's question about the shading ring. ( Or take a very close up picture showing the armature end of the coil so the end of the core is visible. This is where the shading ring would be located.) and can you answer my question about the coil resistance. (Between terminals 4 and 5) If I understand your description correctly the motor should start when paper is fed into the machine. (Probably by the edge of the paper operating a micro switch.) If this is so then tape up the ends of the wires that went to terminals 3 and 6 on the relay. Re connect the wires that went to terminals 4 and 5 (The coil) but also attach an extra wire to each so they can be brought out of the machine and connected to your meter. Assemble the machine so it can be operated. Go through all the steps to operate the machine and as you insert the paper note the voltage on the ends of the wires that you connected to the relay coil before the paper is inserted and just after it is fully inserted. I suggest you start with the meter set to AC and then set to DC. The voltage you measure when the paper is fully inserted should be the relay coil voltage rating.

Les.

 

[JMW]

Napco Industries
333 Bayview Avenue
Amityville, NY 11701
USA

• Phone: 631-842-9400
  Fax: 631-842-9137 Website:

 

[Rave0035]

I'm back. Things to report.

I was able to hook it up as Les suggested and YES we have 120vac across the coil. Coil resistance, if it matters, is about 700 ohms, and it does appear to have the copper ring at the top.

Mike

 

[KeepItSimpleStupid]

12 mA 12 V coil doesn;t seem unreasonable = i.e. 12 V / 700 ohms ; This correlates to your voltage measurement.

My other question was equally important: Were all of the terminals used? Any tied toegther?

In my searching, I ran into something I had never seen before where one contact such as the NO was rated at a higher capacity than the NC contact.
If the NC contacts are not used, then you could use as SPST relay, for instance.

 

[Rave0035]

Sorry KISS - nothing else is used. Just the NO and coil.

Is there really nothing else special about a "motor starting" relay like this? Any SPST with the correct coil and voltage capacity would suffice?
Mike

 

[Les Jones]

Hi Mike,
I think any relay with the correct rating contact and a 120 volt AC coil should be OK provided it will physically fit. I'm not convinced that this relay is starting the motor directly but what it actually does is not important. I think KISS may have misread your message #25 with his comment about a 12 volt coil. The coil resistance now is not important now you have measured the voltage across the coil. (Other than it shows that it is not open circuit. If it had been open circuit we would not be sure that the 120 V AC you measured was a reliable indication of the coil voltage) It was initially important when we had no information about the coil voltage. We were all trying to get some answers that would give us some clues as to the likely voltage range that the coil fell into. Max's question about the shading ring was to find out if it was an AC or DC coil. It gets frustration when trying to help someone when they do not answer questions.

Les.

 

[Tony Stewart]

.Hard to tell if there was damage to the parts on the PCB like the transistors of plastic cap, which if faulty can cause Relay to fail from arcing during back EMF when contacts are opened. With contact bounce or chatter, it gets worse.

THe circuit ought to detect zero crossing then drive the diode bridge to the motor for a start and back EMF clamp function during a stop. Even still the surge current will last many cycles at 8x the average rating,

so as long as the relay contacts dont bounce, you'll have a good relay.

I might consider a ZCS SSR SPST on the hot line. rated for 10A

 

[KeepItSimpleStupid]

Rave:
Great. That means we don't have to look for something funky.

Relays and switches are not simply two contacts that come together with some force, unfortunately. We stuff as arc suppression, wiping of the contacts, relays where the contacts are literally "pulled apart", ability to cool for a short time. We have relays that cannot be switched when the circuit is live.

So, these relays belong in a family called "Definate purpose contactors". Tungsten lighting and motor starting are two such sub-categories. They have "high inrush currents"

This makes it a LOT easier. A 12 VDC coil and an SPST NO contact, HP rated,
AC Only - 250V 18a
1hp 125v / 2hp 250v

 

[KeepItSimpleStupid]

Would this https://www.alliedelec.com/schneider-electric-magnecraft-725axxbc3ml-12d/70185403/ work for you?

It should be available with screw-terminal finger protected contacts too.

 

[Rave0035]

KISS - I think it will! Physically it will fit fine and I can easily mount that. Actually these terminals will work fine and I can shrink wrap the female ends.

We'll try another relay and then I guess we'll find out chicken or the egg on this... thanks again all! I'll report back once I've got this installed.
Mike

 

[Les Jones]

I don't understand why relays with 12 volt DC coils are being discussed when Mike has measured the voltage across the coil as 120 volts AC and also confirmed that the original relay has a shading ring on the end of the coil.

Les.

 

[KeepItSimpleStupid]

I don't understand why relays with 12 volt DC coils are being discussed when Mike has measured the voltage across the coil as 120 volts AC and also confirmed that the original relay has a shading ring on the end of the coil.

Les.

Somewhere in this thread there was a DC voltage measured. I believe across the coil.
700 ohms /120 V is 171 mA. This is WAY OUT OF LINE for a 120 VAC relay that small.

Les: I would re-read this https://www.electro-tech-online.com/threads/help-identifying-relay.145115/#post-1227135 post!

 

[MaxHeadRoom78]

Of course it is pointless measuring the DC resistance of a AC relay coil to obtain current, the actual current depends on the Inductive Reactance when the relay is fully energised and the armature is seated.
Max.

 

[KeepItSimpleStupid]

Who said it wasn't. R is still dominant for a small AC relay. DC was, in fact, measured across the coil. Read the post I told Les to read.

 

[Les Jones]

Hi KISS,
Message #14 that you link to is meaningless (Without a schematic.) as the 14 volts is measured from one side of the coil (Terminal 4) and one side of the normally open contacts. (Terminal 6) Also I agree with Max that the inductance of the coil of an AC relay will effect the current. (We could ask Mike to measure the current.) I think the current for a 700 ohm coil on 12 volts DC (17 mA) would be too low on a relay of that size. The relay you link to in message #31 has a coil power rating of 1.9 watts. (76 mA at 12 volts.) The fact that the coil has a shading ring also suggests that it is an AC coil.

Les.

 

[KeepItSimpleStupid]

OK 4 & 6 aren't the coil. So why can't the OP measure the voltage where the coil is supposed to be or is?

The relay you link to in message #31 has a coil power rating of 1.9 watts.

for DC voltages and 2.5W for AC voltages.

 

[KeepItSimpleStupid]

In any event, everyone is confused:

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

 

[Rave0035]

Sorry to cause so much confusion. I'll be honest - life has been crazy and this has been more rushed than I'd like with this project, so I hope I haven't misstated anything as we've gone. I can confirm with 100% confidence that the coil voltage is 120vac. I've tried again to read the voltage across the NO contacts but no dice (possibly a DC voltage that I should be referencing to a different point in the circuit?).

I haven't pulled the trigger on the relay yet, but will do so soon.

KISS - got a comparable relay available from Digikey? I like to give them my business whenever possible

I so appreciate the help, everyone. Learning a lot as we go, and not possible without your help.

Mike