Wanted: Latching Manual-Reset Relay

Have you got a constant supply available? If so, you could use a double-pole relay in self-latching configuration, with an NC pushbutton to reset.

Thank you for responding JohnDG.

This application is a fault protection device for a gasoline engine driven alternator. On detection of a fault condition, it is to shut down the engine via a kill switch circuit. The alternator driven by the engine is the power source for the circuit and the engine is not an electric start; once this circuit activates it grounds out the electronic ignition.

Once the kill circuit is closed, electrical power drops off untill there is not eneough to maintain relay coil current and the engine still has enough RPM to restart.

It is not an option to have a battery in the system.

The relay I am using requires 145 mA coil current and the 5 VDC coil drops out at ~ 1.85 VDC.

Thanks again,

blueice

Best I can suggest is finding a magnetic latching (bistable) relay that you can "modify" with a manual reset button. I've had a quick look, and haven't yet found one that isn't a sealed unit.

They must be out there somewhere!

Old, old, automobile voltage regulators used a relay/coil which was used to detect over-current. It was virtually a regular relay wound with large (8 ga.) wire with very few turns. When current got to a level that actuated the relay, it pulled in.

Is it possible to use this concept to modify a latching relay with a manually operated latch?

Better to open the supply to the circuit feeding power to the electronic ignition, surely?

It would be better practice to have the circuit wired failsafe, i.e., an opening contact shuts everything down. That way, if a wire falls off a terminal inadvertently, the thing will stop. If wired as described here and a wire falls off, the circuit cannot stop the generator as the stop relay cannot be energised and the electronic ignition cannot be grounded.

A good point PWSlack.

Again, it is the nature of the electronic ignition module that causes a problem.

It is a self contained, potted unit. A connection is provided for the kill switch and nothing else other than ground and the high tension wire to the spark plug.

Reversing the logic is not of much help as the kill circuit must be open to start the generator.

This protection device is to be wired in parallel with a kill switch so that manual control is available for shut down.

If I could locate a switch that would serve as both the reset function and the kill switch then I would have an ideal solution. I haven't been able to locate anything like that.

blueice

"It is not an option to have a battery in the system."

Not even a lithium cell or two driving a MOSFET? Might be worth thinking about.

Wire the coil of an ordinary relay in such a way that one of its normally-open contacts is connected in parallel with whatever initially energises the coil. Once turned on, the relay stays on until power is removed from the circuit, which becomes the manual function.

Thanks PWSlack.

It's the falling voltage that is the real problem. I tried adding a capacitor in parallel with the relay coil and was able to achieve a seven second delay before coil dropout occurred but a 1.8 Farad capacitor is too expensive.

Part of the reasoning behind a manual reset was to indicate to the operator the cause of the shut down. The other part is to mechanically maintain the kill circuit regardless of voltage level.

blueice

Sounds like the engine ignition system is a magneto rather than Kettering. What faults are you trying to detect? Perhaps engine overheating? Can Use disc type manual reset thermostat available through Granger, used in heating and cooling applications brand name Klixon, or MARS. Detecting loss of lube oil pressure? manual reset lube oil pressure switches also available, would have to manually defeat for starting. Are you detecting ground fault in electrical supply? A Ground fault circuit breaker can accomplish this.

Also check GEMS controls for possible source.

Hope this is help for you, regards CEKM

Yes, these are a magneto ignition.

I have done the design work up to this point as defined by management. Software and circut design are complete except for this last piece, which could be a relay or a sort of remote trip backwards circuit breaker.

I really appreciate all the help that has been offered, but I could put my job on the line if I describe in too much detail.

I believe the problem needs to be appraoched from a new direction as it seems this last critical piece of the design does not exist.

Now I just have to convince some one else that their idea will not work and that may be just as improbable. In the mean time, I'll have to suggest an alternate approach. As always, cost is a major issue.

Thanks to everyone who replied!

blueice

I have thought more about this problem, if temperature fault is to be detected, on water cooled engine, an automotive electric fan switch is inexpensive and available, find a Volkswagen Rabbit or Jetta in a junkyard, also for an oil failure switch an automotive oil pressure idiot light switch also available in your local junkyard. for an oil pressure failure switch with a delay, a common refrigeration compressor oil failure switch will work, Ranco makes them, they need 120 or 230 volts to operate the delay timer (A bimetal switch operated by a heater), with a manual reset button. also available from Danfos (Danish) with solid state digital delay timer, can likely find these in local junkyard or from refrigeration wholesaler (New), or used from a refrigeration and air conditioning service organization. If fault to be detected is a ground fault in the electrical load, a three pole GFCI circuit breaker will provide a contact that can be used for the ignition kill, or connect the normally closed contacts of a 120 volt relay to the load side of the GFCI, and use the NC contacts to ground the magneto upon ground detection and CB opening.

A small amount of power can be taken from the magneto ground wire without seriously degrading the ignition performance, alternately mounting another coil near the flywheel to generate a small amount of power from the flywheel magnets can supply a small amount of power for control application. Flywheel alternators are readily available from some small engine manufacturers, this is common practice for battery charging and "Oil Guard" protection function on small Honda engines.

This is a problem that can be solved inexpensively, you can contact me directly if you care to. Cell phone is 860 334 1738. I am on a research ship operating in the vicinity of the Hawaiian Islands and am occasionally in cell phone range, leave a message.

Regards CEKM

Instead of Google search you give some details like:

1. Is it a PCB mounted or Panel mounted?

2. In a base or soldered on PCB; Fitted on Chassis or panel w/o a base?

3. Is it a compact Equipment or open place sufficient to accept a larger or different format of relay?

from above + more info you can select another much cheaper & better relay.

Normally off-shelf components can be used as replacement for specific ones provided you have space & voltage range.

Instead of for example you may get 2/3 pole contacts [use as you need].

In such case Vendors like RS Components, Farnell are from lot of vendors who have lot of collection of such parts.

I was told that this design had to satisfy strict requirements imposed by my manager.

In discussion with him, I told him that the problem would be holding the relay contacts in a closed position after the fault had been detected and the generator RPM and Voltage output were decreasing.

There are three states to this design.

1. Engine stopped and ready to be started.

2. Running under normal conditions.

3. Fault detected and engine shut shutdown via magneto kill circuit.

At first glance, the solution seems to be one that can be solved by the use of relay logic. That is not true as there is no power available in state 1.

There is no auxiliary source of power available in state 3 to hold the relay contacts in the closed postion until the engine has completely stopped (no electric start). As output voltage falls, the relay "hold in" voltage falls below the required level, the relay contacts open and the engine still retains enough RPM to effect a restart.

It seems to be as simple as a set of N.C. contacts on an "arming" relay wired in parallel with the "kill relay" contacts so that when voltage falls off, the contacts close maintaining the "kill" circuit untill the engine completely stops its rotation.

That part of the circuit would then have to be maually reset by the operator so that the generator could be restarted.

One of the design paramaters that I have had to work with was it must be an automatic function that was transparent to the operator.

I believe that the operator needs to be made aware of why the engine shut down.

Another requirement was to use the magneto kill circuit as it could be added to any portable unit as an easy field retrofit.

I thought about a triac circuit instead of the relay. It's been several years since I've worked with these so I'd have to study that subject. I believe keeping a triac in conduction would be the same problem as with a mechanical relay.

Given these design restraints, I don't see a way to get this done in a cost effective manner and I believe it needs to be rethought in how it is applied. The job is not impossible, just this particular approach.

Thanks for all replies. I appreciate your help.

blueice

I am currently facing a similar problem in the design of a regulator for an AC generator.

I'm wanting to kill the excitation in the advent of an over-voltage condition and ensure when the operator arrives it will be obvious what the fault was.

The nearest thing that I have found so far is a "remote tripping circuit breaker" that is made by Schurter of Germany and bears the part number of TA45R22R.

Digikey, Mouser and Newark all handle Schurter breakers but do not appear to stock that particular model.

It's not that many years since latching manual resettable relays were quite common and if my memory serves me correctly they were made by IMO and IZUMI_DENKI.

Hope that helps - Down-under Kiwi

Thanks, Guest.

Yes, it may help. Off to do more digging!

This is guest #2 I have used a tale-tell relay/switch system on similar situations maybe one of these types of relays will work for your app.

Just guest #2 again. I just realized that i gave you the nick name of the device that i used. the real name is a murphey Tattletale safety switch. Just google the name and you will find oodles of info. Good luck.