Circuit Opening Relay: How does it work?

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,887
Aside from understanding the title, I'm having trouble getting this relay to open up by itself. Honestly I don't see how it's going to do that.

Below is a drawing of the pinouts and as best as I can tell how the relay is wired. I can clearly identify the route of the Capacitor and the Resistor to the pins, but I can't be sure about the coils. I see two wires twisted about at every terminal. Is there four coils in there? And I've tested the pins with 12 volts. The pins, I've numbered them for reference (actual pin count may differ). When I strike pins 1 & 4 with 12 VDC the relay energizes and kicks in like it should. When I apply 12 VDC positive to pin 2 and negative to pin 6 the relay energizes. In both cases I've left the relay energized for one minute. That's GOT to be long enough for it to open the circuit. But in neither case does the relay ever open. I've even jumpered pins 1&2 and 4&6. With those pins jumpered the relay still clicks in and never opens. When I jumper pins 1&4 and 2&6 the relay does nothing.

This thread is being opened because another thread was asking about relays and I happened to mention I have a delay opening relay. I've never figured out how it works. It comes off of a 1987 Toyota Celica (wife wrecked it). The cost to replace is at AutoZone about $45.00. Just wondering how to make this work and what to expect of it. I'm actually waiting on parts for another project. Meanwhile I'm just tinkering about with silly stuff.

[edit] When I energize 2&6 the relay closes softly. But when I energize 1&4 the relay clicks in with more force. And I've tried to energize the relay by various combinations of 1&6 and 2&4. No matter what - - - .

Circuit Opening Relay.gif
 

AlbertHall

Joined Jun 4, 2014
10,226
Looking at the location of the capacitor, I would expect its function to be that if you energise 2 & 6 and then remove the voltage, the relay would stay closed for a little while and then open. A delayed release. Energising 1 & 4 should give quick close and release.
 

Reloadron

Joined Jan 15, 2015
5,601
Either coil will close the relay contacts. My read on these relays is they are used as part of the starting system on a Toyata. They are used in the fuel pump control. You may want to take a look here where they mention:
When the engine is cranked, current flows from terminal ST of the ignition switch to the starter relay coil and also current flows to terminal STA of ECM (STA signal). When the STA signal and NE signal are input to the TCM, Tr is turned ON, current flows to coil of the circuit opening relay, the relay switches ON, power is supplied to the fuel pump and the fuel pump operates. While the NE signals is generated (engine running), the ECM keeps Tr ON (circuit opening relay ON) and the fuel pump also keeps operating.
This would run along with what Albert mentions:
Looking at the location of the capacitor, I would expect its function to be that if you energise 2 & 6 and then remove the voltage, the relay would stay closed for a little while and then open. A delayed release. Energising 1 & 4 should give quick close and release.
During transfer from start to run the relay needs to remain closed for a short time, thus a delayed release on one of the coils.

Ron
 

Alec_t

Joined Sep 17, 2013
11,501
If relay contacts 2 and 3 never open they are presumably welded closed. Either that or perhaps magnetic bias is latching the relay and a reverse polarity pulse is needed to unlatch it.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,887
Hey all: Here's what I've observed: Powering pin 2 (positive) and pin 6, the relay turns on immediately but softly. The contacts are functional (not welded). When I let it sit for 5 minutes, the relay remains on for that period of time. When I disconnect the relay it falls out almost immediately. And by "Immediately" I mean just about as soon as you disconnect. I can not perceive any lag in the relay falling out.

When I energize pins 1 & 4 (1 positive) the relay closes immediately and with full force. Upon disconnect the relay falls out.

When I energize pins 1 & 2 (positive) and 4 & 6 the relay operates just as when either of the two above combinations are tried. When I energize pins 1 & 4 (positive) and 2 & 6 the relay does nothing. Magnetic energy is canceling itself out and the relay does not function.

The ONLY thing I haven't tried is reversing the polarity on pins 2 & 6. Reason being is that the capacitor involved is electrolytic. It's positive lead is connected to the resistor, which is connected to pin 2 (as in the drawing). I don't want to try reversing the polarity for fear I may blow out the cap. The resistor is difficult to see, but it appears to be Yellow, Violet, Black, Silver. I'm interpreting that as 47Ω. The cap is housed in a lot of plastic and I can not get a read on the value. The ONLY thing that confuses me further is that every terminal where a coil is tied in has two wires twisted together and soldered to that lead. Two wires on pin 1, two wires on pin 2, two wires on pin 4 and two wires on pin 6. Resistance measurements between pins 1 & 2 - infinite. 1 & 4 is 23.4Ω. 2 & 6 is 114Ω. 2 & 4 and 6 & 4 are also infinite.

Contacts ( pins 2 & 3 ) are functional.

It's been my experience that when you turn the key on (before you start) the fuel pump will run for a few seconds, building up pressure in the fuel rail so that when you start the engine there's fuel. As soon as the engine starts up the fuel pump has to kick back on to maintain the engine running. I've seen schematics in OTHER cars where the fuel pump was powered chiefly through an oil pressure sensor. In other words, if oil pressure fell below a certain point the fuel pump shuts off.

Nothing I've tried has resulted in the relay shutting off after any period of time. Hence the reason for asking why. Or why not.
 

AlbertHall

Joined Jun 4, 2014
10,226
To make any estimate of the expected time delay requires the value of the capacitor. If you can't read the value, can you estimate its dimensions?
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,887
can you estimate its dimensions?
2 cm tall, 1 cm diameter.

Since automotive electrical energy can go as high as 14.5 volts, I would guess it's voltage is going to likely be the next higher than 16 volts. I suppose I COULD de-solder the one lead, being that it's lap soldered to the terminal. Let me give that a try as well.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,887
Capacitance meter says it's 183 µF. I don't have a lot of faith in my meter, I've seen it read a 22 µF cap at 27 µF. Don't know if that's normal or not. I have this cap totally isolated and tested with standard length test leads. Maybe a shorter lead will give more reliable results, but I bought this meter at Lowe's Home Improvement (like Home Depot) (big box store).
 

Reloadron

Joined Jan 15, 2015
5,601
Capacitance meter says it's 183 µF. I don't have a lot of faith in my meter, I've seen it read a 22 µF cap at 27 µF. Don't know if that's normal or not. I have this cap totally isolated and tested with standard length test leads. Maybe a shorter lead will give more reliable results, but I bought this meter at Lowe's Home Improvement (like Home Depot) (big box store).
Actually Tony that is not unusual. Capacitors, unlike resistors, have a real wide tolerance and numbers like +/- 20% or greater are not unusual.

Also, relay coils wound using a pair rather than single lead is not unusual. This effectively increases the cross sectional area of the coil turns. That allows us more current for our amp turns of the coil which needs to create the magnetic field.

Ron
 
Last edited:
Top