resistor on non resistor relay which one?

Submitted: Tuesday, Nov 04, 2014 at 23:10
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I am a little confused as the suitability of which relay to use for the job described below.......in fact I have always purchased a "relay" in the past and not seen the types as described above before...change over relay or normal relay ...yes that is straightforward....

These switches fit perfectly into the Land Criser 200 series dash blanks just like an OEM

Please see the diagram below DIAGRAM 1



My understanding is that a relay can at times send a spike of current or voltage in reverse when the coil is disengaged in the relay.........wouldn't perhaps matter in a mechanical switch but these switches have an electronic switch circuit and can be damaged if this happens

My question is two fold...what type of relay to use?......

Secondly is a 3 amp blade fuse in line between the switch and pin # 86 going to protect the switch circuit?

Thanks in advance


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Reply By: TomH - Tuesday, Nov 04, 2014 at 23:35

Tuesday, Nov 04, 2014 at 23:35
The diode in the bottom circuit stops reverse current as it can only flow one way through it
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Reply By: Member - Allan L2 - Wednesday, Nov 05, 2014 at 06:38

Wednesday, Nov 05, 2014 at 06:38
I agree with Toms reply and I believe diode equipped relays should be used in all applications on late model vehicles e.g. any vehicle that utilises Electronic Engine Management.
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Reply By: HKB Electronics - Wednesday, Nov 05, 2014 at 09:14

Wednesday, Nov 05, 2014 at 09:14
The fuse is to protect your vehicle as the switch is not protected, ie currents in excess of 3 amps could cause the switch to over heat and stat a fire. I would suggest you use a fuse rated at around 1A - 1.5A, it will generally take at least 3 amps current flow to blow a 1.5A fuse.

If the switch has been designed properly and is intended for use with inductive loads, ie relays it should have internal spike suppression to protect its switching stage, if it hasn't then it is very poorly designed or not intended for the use it is going to be put to?

Not being familiar with the switch is it possible the switch is designed to either source or sink, ie when on switches 12V positive when off switches earth, this would explain why the diode is required, if the diode wasn't installed the relay would operate when the switch is off and the high beams are off?

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Follow Up By: HKB Electronics - Wednesday, Nov 05, 2014 at 11:23

Wednesday, Nov 05, 2014 at 11:23
On doing a bit of research it would seem it is just a mechanical switch, the diode in the negative switched circuit will be to prevent the "on" LED be illuminated by the positive from the light globes.

It is always a good idea to use suppressed relays if your not sure the device that is operating then won't be damaged by the back EMF.

The car electronics themselves have to be able to withstand spikes from starter motors, wiper motors, blower motors and all sorts of solenoids so they are pretty much bullet proof, add on accessories may not be so well designed.

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Follow Up By: HKB Electronics - Wednesday, Nov 05, 2014 at 11:36

Wednesday, Nov 05, 2014 at 11:36
Should have elaborated a bit more, if you change the cars electrics, ie for example a module directly turns a head light bulb on and you add a relay to the circuit then a spike suppressed relay should be used as the modules output stage may not have been designed to handle the back emf of a relay coil. Adding a totally new circuit to the car that incorporates a relay will not affect the cars electronics as they are designed to handle spikes on the power supply.

If your not sure then it is simply much safer to always use suppressed relays.

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Follow Up By: Member - bungarra (WA) - Wednesday, Nov 05, 2014 at 11:52

Wednesday, Nov 05, 2014 at 11:52
Thanks for your assistance

I spent ages composing a rely to Alan with the intent of then posting to your response only to find that whilst doing so you had added further info that has helped me immensely....perhaps didn't need to make such a long post to Allen

I guess I have it sorted now in the bottom of my reply to Allen and you have added to what I think I have right....if not then I guess I will be corrected

Thanks Graeme

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Follow Up By: HKB Electronics - Wednesday, Nov 05, 2014 at 12:05

Wednesday, Nov 05, 2014 at 12:05
One other point to be aware of, not all relays are designed for continuous operation, in the case of driving lights I would suggest you ensure the relay is rated for continuous operation.

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Follow Up By: olcoolone - Wednesday, Nov 05, 2014 at 18:29

Wednesday, Nov 05, 2014 at 18:29
QUOTE "The car electronics themselves have to be able to withstand spikes from starter motors, wiper motors, blower motors and all sorts of solenoids so they are pretty much bullet proof, add on accessories may not be so well designed."

Lee I am sure you understand it very well but to elaborate a bit more.

To a certain point, starter motor and any other motor will emit back EMF, EMF that effects electronics is more to do with a On/Off situation as in a relay or solenoid and specifically the de-energising phase .....stored energy has to go somewhere.

Starter motor solenoids in nearly every case are either direct driven from an ignition switch or a starter relay that controls the solenoid..... the starter relay can be driven from a ECU/ECM/BCM.

The vehicles battery is a good spike suppressor.

Where EMF back feed comes in to play is most relays in modern vehicles are direct switched from an ECU/ECM/BCM on the negative side and the energy flows from the positive (proton and nucleas) to the negative (electron) , this energy can spike the output of the ECU/ECM/BCM when the coil de-energises.

All ECU/ECM/BCM have protection circuits built in to stop EMF and works very well but over time these circuits can and have been now to fail due to constant EMF attacks.

Hence why all modern vehicles use suppressing relays.

Again it is only a real concern when the solenoid or relay coil is directly driven from a ECU/ECM/BCM

And one to many spikes may be the last.

Years ago we would only carry 6 relays and now we carry something like 26 different types in stock.

Replacing relays can cause heaps of issues if the wrong one is used.
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Reply By: Allan B (Member, SunCoast) - Wednesday, Nov 05, 2014 at 09:52

Wednesday, Nov 05, 2014 at 09:52
Hi Bungarra,

I see confusion arising here.

I cannot see where your reference to a "Resistor Relay" came from.
There are such things as suppression resistors used with relays but I do not see one here.

The text in your wiring diagram makes reference to a "fused relay" and a fuse is shown in series with the relay contacts (30 & 87) The fuse is not part of the relay.

A diode is shown in Diagram 2. This is a 'blocking diode' required to prevent reverse positive current from the headlight filaments. It is not a 'quenching' or suppression diode.

Relays containing a suppression diode, or having a diode wired across the coil terminals, are a good idea in modern cars but your wiring diagram above does not specifically call for them.

When using a diode suppressed relay, care must be taken in regards to polarity applied to the relay coil. The manufactured relays incorporating diode suppression require that the positive be connected to terminal 86 and the earth or negative to terminal 85. The same convention should be followed if wiring a diode across a standard relay. See diagrams below. If wiring a diode across a relay, it should be connected with the 'striped end' connected to the positive, terminal 86.


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Follow Up By: Member - bungarra (WA) - Wednesday, Nov 05, 2014 at 11:45

Wednesday, Nov 05, 2014 at 11:45
Hi Allan...yes confusion is happening a little...by way of explanation

1) You are correct about the diagram having no mention of resistor or non resistor relays being required........Probably should have been a separate post to avoid confusion
I asked because I had not seen the option of these before on the shelf and would like to know the difference please......

* Under what circumstances would you use one or the other type?

2) As for diodes I understand the need in certain circumstances and how these work but I am surprised there is not an option to purchase a relay with one in built...or is there?.......other than soldering / crimping one inline appropriately?

3) Are these diodes only needed if negatively switching the relay on a headlight circuit because of the filaments?

4) if (3) is yes then is a diode needed with LED's

--------------------------------------------------------------------------------

Fused relays are available but my understanding is that these fuses sitting externally on the relay housing are protecting the input to pin #30...and thus the relay........unless the relay and power source are immediately adjacent to each other I would use an "unfused relay" and protect the wire at the source of the power going to pin # 30

Back to DIAGRAM 1

Ignore the fact the diagram shows a headlight source ...as the + source can be either the headlight switch ....such as for fitting spotlights or a direct power source for other non lighting accessories as in my case ........
Actually in my case one switch will activate spotlights via the high beam switch circuit and the other switches activating relays (+ switched) powered direct from a fused 12v + source for accessories

Are you able to help me in the following query as well please?

a) As the vehicle in question is a Land Cruiser 200 series with a + switched high beam circuit is there a need for a diode post relay to protect the switch for spotlight circuit...using HID lights?

b) The other relay circuits will feed direct (fused appropriately) to a relay and then to the switches....therefore no diodes required?

c) I feel the bottom paragraph on the supplied wiring diagram is misleading / confusing as the FUSED RELAY they insist must be used infers it is switch protection (3amp required) but in fact the diagram only shows fuse required between + and pin # 30.........no switch protection in that circuit!...is the load circuit

----------------------------------------------------------------------------
So unless advised otherwise (and if I had no access to advice on this forum) my intent would be

* on the accessory relays AND the spotlight relay to fuse the power source to the relay pin #30 appropriately for the load and install no diodes or switch protection ( Diagram 1 )...because it is all + switching
* the ambiguity ( to me at least) in the bottom paragraph indicates that switch protection is not required on a + switched circuit

Appreciate your time and trouble

Thanks

Graeme

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Follow Up By: Allan B (Member, SunCoast) - Wednesday, Nov 05, 2014 at 12:35

Wednesday, Nov 05, 2014 at 12:35
Hi Graeme,

Glad I saw your followup to HKB before I replied. Saves me a lot of typing! lol

As Leigh (HKB) has said, the OEM car electronics are pretty much bulletproof, so suppressed relays are not really necessary for their protection. Some aftermarket accessories may benefit from suppressed relays. So it can be prudent to use only suppressed relays, but be careful about their polarity. Some relays are suppressed with 'Bilateral Transient Diodes' which are not polarity conscious.
Yes, relays are readily available with fitted suppression diodes.

Switches that control relay coils would normally be capable of handling a relay 'back EMF spike' so a suppressed relay is not essential here either. In truth, there are no suppressed relays installed in my vehicle (I think).

Long ago, before cheap silicon diodes were available, relays were sometimes 'suppressed' by connecting a resistor of a couple of hundred ohms across the coil. Less effective than a diode. Besides, I haven't seen one for many years.

If suppression is required, or desirable, it matters not whether the relay coil is positively or negatively switched, the diode is still required.

Relays incorporating a fuse on the input to pin 30 only protect the relay itself and the circuit downstream of the relay. They do not protect the wiring supplying the relay from fault to earth.

As for your ........"c) I feel the bottom paragraph on the supplied wiring diagram is misleading / confusing as the FUSED RELAY they insist must be used infers it is switch protection (3amp required) but in fact the diagram only shows fuse required between + and pin # 30.........no switch protection in that circuit!...is the load circuit"
Yes, it confuses me also. The fuse as shown is in the relay load circuit and provides no protection for the switch controlling the relay.
Leigh, can you throw light on this?

And I would endorse your final paragraph re your intent.

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Follow Up By: HKB Electronics - Wednesday, Nov 05, 2014 at 13:16

Wednesday, Nov 05, 2014 at 13:16
The description is a bit ambiguous to say the least, I don't believe they are referring to the fuse shown in the diagram?

I would suggest they are indicating a 3 amp fuse should be fitted in line with the switch to protect it from excess current but then they don't show one on the circuit diagram, probably due to the relay coil limiting the current. As as most sources of power under the dash are going to be fused with a higher rated fuse it might be a good idea to fit one should a short circuit develop in the wiring before the relay coil.

Interestingly and contrary to the description the switch itself does not appear to be electronic, I have "very" similar ie identical switches in my own car, probably supplied by the same supplier and they are a mechanical type?

If they are mechanical then they will most likely not last long switching unsuppressed inductive loads, though in this application it probably won't be a big issue as the switch won't be used that often.

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Follow Up By: olcoolone - Thursday, Nov 06, 2014 at 08:29

Thursday, Nov 06, 2014 at 08:29
On Board Airs wiring diagram is a bit miss leading and seeing it has been written for a beginner to understand it, it leaves a lot of guess work for the installer.

The one place I could see a 3 amp fuse being used is pin 86 to safe guard the wiring from the positive feed off the headlights and to stop the headlights blowing a fuse if something went wrong with the additional wiring and relay added. A 3 amp fuse is an overkill for the application but 3 amp fuses are more communally available then lower rated fuses especially in blade types.

As said above regarding the additional diode, all I can see that it's good for is for stopping feed back to the light in the switch to stop the light illuminating or keeping the relay energised or latched when switched off.
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Follow Up By: Allan B (Member, SunCoast) - Thursday, Nov 06, 2014 at 09:30

Thursday, Nov 06, 2014 at 09:30
I cannot see any shortcoming in the wiring diagram, although a 3A fuse in the takeoff from the high beam in Diagram 1 would be a good idea. Maybe also in the 'ignition' supply in Diagram 2.

The diode shown in Diagram 2 (Negative headlight switching) is there to prevent the relay from energising when the ignition is off. Otherwise current would be sourced from the positive via the headlight filaments, through the relay and to negative via the ignition loads. This is sometimes called a 'sneak circuit'.

The light in the switch is supplied from the dash lights via the Red/Yellow wire as per the note in the diagram panel.

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Follow Up By: HKB Electronics - Thursday, Nov 06, 2014 at 09:43

Thursday, Nov 06, 2014 at 09:43
The plot gets more involved, I don't know about the specific swicth but many of these switches have a back light and a "on" led, the diode would also prevent the on lamp illuminating but I must admit I didn't think about the positive feedback to the source circuit.

The diode may also have an added benefit, the negative switched diagram has a fundamental design flaw that may or may not become apparent depending on the characteristics of the relay and where the positive potential is sourced for the switch.

The problem presents itself as the driving lights will not turn off when the head lights are dipped unless the driving light switch is turned off.

The problem is caused by voltage drop in the head light circuit, some vehicles may have a 1V to 2V or higher voltage drop between the battery positive terminal and the globe.

If the positive for the driving light switch is sourced from a point that has little voltage drop and the relay is sensitive enough the 2V across the relay can be enough to hold the relay operated. The diode in the circuit may actual help in this regard by introducing another drop in the circuit thus reducing the voltage available to keep the relay held in. Additional diodes may be required.

Another solution to the problem is to pick up the 12V for the switch at the head light bulb but this then means running another wire from the dash to the lights though.

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Follow Up By: Allan B (Member, SunCoast) - Thursday, Nov 06, 2014 at 10:13

Thursday, Nov 06, 2014 at 10:13
Point taken Leigh although it would need to be an unusually sensitive relay to hold-in to as low as 2 volts.
I just went and tested the four relays in my workshop. They all dropped out at 4 volts.
If there was a 4v drop in the headlight supply it would be producing only about 20% light output in fact. The real answer to your proposition would be to fix the headlight volt-drop.
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Follow Up By: HKB Electronics - Thursday, Nov 06, 2014 at 10:53

Thursday, Nov 06, 2014 at 10:53
Allan,

I'll see you and raise you two, I just tested a couple of spare Narva compact type relays, one dropped out at 3.5V the other 2.2V, the problem can compound overtime as the relays get dirty and sticky due to contamination on the pole face which is often caused by adhesive from the coil migrating to the pole face. This is can be even more puzzling as it worked ok when it was first installed.

These days one has to be a little wary of correcting voltage drops in headlight circuits, the standard operating voltage for a headlight globe is 13.2V or there about, as little as 5% increase in voltage can cause a significant reduction in globe life especially with the high equivalent wattage types. So if the charging system is running at around 14.4V a 1V to 2V drop can actually be desirable.

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Follow Up By: Allan B (Member, SunCoast) - Thursday, Nov 06, 2014 at 11:58

Thursday, Nov 06, 2014 at 11:58
Leigh,

2.2V dropout??? You win!

I just looked up specs for Tyco relays. Tyco is a major US manufacturer.
Their specs for a nominal 12v type 002 coil is 'pull-in = 6.5v, drop-out = 1.0v'. So I stand well and truly corrected on the drop-out voltage!

Re the effects of voltage on globes: If the lamp is operated at 5% above rating then the life can be expected to be reduced to 60% whilst the lumens will increase to 120%.
Even more alarming at 9% above rating where the life will be 40% with the lumens at 130%.

In the 'old days', spotlighting for roos, we used to use a 6v lamp run at 8v to get a brighter light. This increase is off my Lamp Characteristic Chart but is was a bright light even if the lamp light was short. Sometimes we pushed our luck even further and moved up tp 10v. The light would singe the roos pelt although the lamp often failed as soon as it was connected to 10v.
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Follow Up By: HKB Electronics - Thursday, Nov 06, 2014 at 12:24

Thursday, Nov 06, 2014 at 12:24
What are roo pelts worth these days, one bulb one roo might be economical:)

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Follow Up By: Allan B (Member, SunCoast) - Thursday, Nov 06, 2014 at 12:36

Thursday, Nov 06, 2014 at 12:36
Dunno. I gave up shooting the poor things many years ago.
Mind you, the spotlights of today would put my old home-made spotty literally 'in the shade'!
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Follow Up By: olcoolone - Friday, Nov 07, 2014 at 16:36

Friday, Nov 07, 2014 at 16:36
Still think the earth feeding back to the relay through the filament globe in the switch will be the issue causing the relay to stay on when de-energised...... the globe will act like a resistor supplying enough voltage to the coil.

If the light in the switch was LED you would not have a problem.... but you would need two different switches, on negative switch and one positive switch for the different headlight polarities.
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Follow Up By: Allan B (Member, SunCoast) - Friday, Nov 07, 2014 at 18:49

Friday, Nov 07, 2014 at 18:49
The lamp in the switch has no connection to the circuitry associated with the switch contacts. The lamp connections are red/yellow (+ve) and black (-ve).

Although hard to read, the text in the panel for the red/yellow wire states..........
"Connect this wire to your cars dash light circuit. It is to supply12v+ when you turn your dash lights on. This is optional and has no effect on the switch operation. The cigarette lighter lamp is a good place to get your dash light power from.

When connected in accordance with the wiring diagram, that lamp is isolated from the switch contacts and can have no effect on the circuit operation. It merely illuminates the switch in company with the dash lights.
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Reply By: Bob Y. - Qld - Wednesday, Nov 05, 2014 at 12:09

Wednesday, Nov 05, 2014 at 12:09
Bungarra,

Part of your original question was "....... changeover or normal relay".

The photo below shows relays used in a heavy duty headlight upgrade. As I understand it, the relay on the right, a P2512X, is a changeover relay(changing between high and low beam) and the other 2 relays are normal, ie they are used to power either high or low with, one hopes, heaps of volts 'n amps, so the lights are really bright. :-)



Hope that helps somewhat?

Bob

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Can't remember most of it.

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Reply By: Member - bungarra (WA) - Thursday, Nov 06, 2014 at 10:58

Thursday, Nov 06, 2014 at 10:58
Appreciate the input from you men its been interesting reading....just goes to show that "apples aren't always apples" when electronics get involved

gets a little tricky when DIY people like me know more than some and a lot less than many others!.....the input and experience has been much appreciated

However I am still not sure if I have missed a point in one of the questions to my original post here............that is

where would you use a "resistor relay" as against a "non resistor relay" ?

In the past I have only seen "relays" on the shelf and was a little confused as to what to use under what circumstances when I had the option of purchasing either/or

Can one of you explain examples put simply for me?

Thanks

Graeme
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Follow Up By: HKB Electronics - Thursday, Nov 06, 2014 at 11:27

Thursday, Nov 06, 2014 at 11:27
High Graeme,

By "Resistor Relay" I'm assuming you mean a relay that contains a resistor suppressor unit. If the relay is going to be connected to any electronic equipment in the car, in fact any existing car circuit then it is safest to use a relay with an inbuilt protection unit, the protection unit is generally shown as a box, a resistor symbol or diode symbol across the coil.

As Alan pointed out if if diode suppressed then you need to be carefully of the polarity applied to the coil.

For other applications, for example you wish to add a work light to the rear of the vehicle and switch this via a relay turned on and off by a new switch you are installing then an ordinary relay will suffice for this application.

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Follow Up By: Allan B (Member, SunCoast) - Thursday, Nov 06, 2014 at 12:12

Thursday, Nov 06, 2014 at 12:12
Once again I stand corrected!

I thought relays with inbuilt shunt resistors had passed on with the advent of silicon diodes............. but no, I see they are still frequently listed. I have probably used some without realising.

Whilst shunt resistors are less effective than diodes they have the distinct advantage of not being polarity sensitive. A boon for the DIYer as if a diode protected relay is wrongly connected in reverse, something will be damaged.

As 'Bilateral Transient Diodes' are now almost as cheap as regular diodes, I would expect relay manufacturers to change to them and so eliminate the risk of improper polarity connection.
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Follow Up By: HKB Electronics - Thursday, Nov 06, 2014 at 12:50

Thursday, Nov 06, 2014 at 12:50
If it costs a cent more forget it, we have share holders who want ever increasing dividends!

One would think relays would be a thing of past by now and yet it is still one of the cheapest and most robust ways to switch large currents with little insertion loss and still found in a great many electronic appliances.

It will be interesting to see what happens as can bus systems become more prevalent in cars, presently a lot of the peripheral equipment ie relays is done using latched outputs, the ECU sets the output and it remains latched till the ECU turns it of. This is effective but expensive as it requires extra components. Some circuits are now using PWM to operate the solenoids, this allows the ECU to "modulate" the solenoids.

With CAN bus one would expect it is only a matter of time before the designers decide to cheap out and remove the latch circuitry altogether, the relay would be operated by a series of pulses rather than a direct current similar to the transmission setup, in such a system one would expect that they would use the back EMF of the coil to keep the relay operated during the absent pulse ie slow release relays going back to the good old days of telephony. This would negate the need for suppression, in fact suppression would have an adverse affect on the circuits operation, that is of course if the good old relay continues to live on and it certainly doesn't look like dying yet!

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Follow Up By: Allan B (Member, SunCoast) - Thursday, Nov 06, 2014 at 12:53

Thursday, Nov 06, 2014 at 12:53
I knew that dampening a relay coil would slow its opening to the detriment of contact life but I had not realised just how much that effect could be until I researched. The table below tells it all.
An unsuppressed relay may produce a transient voltage of 750. Whilst the plain diode really squashes the transient to 0.7 it slows the drop-out time to 9.8mS. The diode/zener device does a fair job bringing that transient down to 25 yet still providing a drop-out time of 1.9ms.
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Follow Up By: HKB Electronics - Thursday, Nov 06, 2014 at 13:08

Thursday, Nov 06, 2014 at 13:08
Yes, if you maintain the current flow you increase the release "lag" are for the good old days before transistors!

There's lots of ways to manipulate the operate times and release times of a relay, copper slugs, armature residual plates, C/R timing networks etc

You can have operate and release times of several seconds to minutes if you like:)

And then there are thermal relays!

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