Timer board

[JohnW2]

Ok thanks @JohnW2 to be fair I have enough 4004 for my needs so im gonna get a few 4007 as there less than a couple a quid, scanning the net 4007 appears to be quite commonly mentioned for maglocks ( though I respect what you say about unnecessary in most cases) ... I can at least add them to increase my range of Electronic bits I have for Fire alarm repairs and the like.

Fair enough, but for any of the sort of applications we're talking about you're never going to need a higher PIV than 400V. Even if the back EMF were very high, that's in the forward-conducting direction, so the PIV is irrelevant and, when used for this sort of purpose, the highest 'reverse voltage' it would encounter would be that of the supply - 12V/24V/whatever.

Out of interest I called them "IN4xxx" ( as it was hard to read off the diode) as did you, or was you patronising me but Winston called them "1N4xxx" as do the Ebay listings, so what are they

He must be having a very atypical day, since winston is correct again As BS3036 says, the first character of that ("JEDEC") semiconductor naming system is a number, one less than the number of wires/connections - hence 1 for a diode, 2 for a bipolar transistor/FET and 3 for a dual-gate FET. The second character is always an "N". You must have come across transistors with 2Nxxx or 2Nxxxx numbers, haven't you?

Kind Regards, John

 

[bernardgreen]

How does each contact know whether it is the 'one that does the dirty work' or 'the one which stays clean'?

When the relay contacts are adjusted one pip ( contact ) can be set a bit ahead of it's partner if necessary to ensure.

Been a long time since I worked with telecom relays so very rusty.

 

[JohnW2]

When the relay contacts are adjusted one pip ( contact ) can be set a bit ahead of it's partner if necessary to ensure.

Yes, that could be done - but it's not "how they come", or how they were intended to be used, is it?

Kind Regards, John

 

[JohnW2]

.... As BS3036 says, the first character of that ("JEDEC") semiconductor naming system is a number, one less than the number of wires/connections - hence 1 for a diode, 2 for a bipolar transistor/FET and 3 for a dual-gate FET. The second character is always an "N". You must have come across transistors with 2Nxxx or 2Nxxxx numbers, haven't you?

@333rocky333 ... I should perhaps have clarified (for 'your education') ... the reason why that first number is 'one less' than the number of wires/connections is that it refers to the number of junctions between two types of semiconductor material - e.g. between 'N' and 'P' silicon/germanium. Hence a diode has '1 junction' (e.g. between N and P) whereas an NPN or PNP transistor has '2 junctions'.

It amazes me how something so small can do what it does, so therefore a final query, does the diode get hot and is its lifespan limited.

I could also have added ... a diode is not doing all that much, or anything particularly complicated - it is merely acting as a one-way valve, just as would, say, a hinged flap over the outside of a hole in a box. That would enable things to easily come out of the box (pushing the flap open) but would prevent things going into the box. It achieves that simply by having a single semiconductor 'junction'.

As for size and heat, individual semiconductor junctions are incredibly small and, individually, generate very little heat. A modern computer CPU chip contains well in excess of 1 billion semiconductor junctions, somewhat overshadowing the one junction in your 1N400x If a diode were 'perfect' (zero forward resistance) there would be no heat generated at all - it's only because of a very small forward resistance that some heat is dissipated when forward current flows. When 'reversed biased' (as would be virtually always the case in your application), no current flows through the diode/junction and hence no heat would be generated.

There endeth the lesson

Kind Regards, John

 

[SUNRAY]

When the relay contacts are adjusted one pip ( contact ) can be set a bit ahead of it's partner if necessary to ensure.

Been a long time since I worked with telecom relays so very rusty.

In that case I think you've just failed your relay adjusting course.

 

[bernardgreen]

I failed. The skills of the engineers who designed relay circuitry always amazed me,

Quoting LINK

Delay Slug Relays

A time delay can be produced on a telephone-type d.c. relay by placing one or more shorted turns around the magnetic circuit (usually the core) so as to produce a counter-m.m.f. which ******* the build-up of the operating flux, and upon de-energization provides an m.m.f. to ****** the collapse of the flux. This shorted turn. or turns. is called a slug. Usually it consists of a copper collar on the core of the relay. In some designs, a copper sleeve is used over the full length of the core, and the coil is wound on the sleeve.

The principle of operation of the slug is as follows: When the relay coil is energized, the flux build-up passes through the slug and by self-inductance produces an m.m.f that opposes the coil m.m.f. This opposing m.m.f. delays the build-up of the magnetic field in the air gap to a strength that will cause the armature to close. The time delay on drop-out occurs in the opposite manner. When the relay coil is de-energized, the field starts to collapse, thus inducing a current in the slug that provides an m.m.f. oriented so as to sustain the magnetic field and thus delay the drop-out.

Pickup delays up to 120 milliseconds and drop-out delays up to 500 milliseconds can be achieved by the use of slugs. The delay time will vary due to mechanical wear over life and ambient temperature and this type is not intended for high-accuracy applications. Slugged relays are not generally an off-the-shelf item and are available only on a special-order basis from most manufacturers of telephone-type relays.

 

[SUNRAY]

Wearing my 'controls hat' I've designed many a relay logic system - interlocks between boilers, air supply fan, flue extract fan, boiler circulating pump, water valves, water flow stitch, air flow switch, thermostats (mulpiple with big boilers) - is just the first thing that comes to mind. And far too often this is on the hoof when changes are made to the equipment being controlled.

 

[plugwash]

Sorry...yes put the diode across the coil as in the diagram.
When the relay contacts open the solenoid connection to the relay goes several hundred volts positive forward biasing the diode

The voltage only spikes to the extent needed to keep the current flowing.

A modern computer CPU chip contains well in excess of 1 billion semiconductor junctions

Sure, but the currents flowing through those junctions are tiny.

Diodes handling continuous high forward currents very often do need heat sinking. Indeed high-power applications are often moving away from diodes. Relay protection diodes though only conduct briefly so heat is unlikely to be a concern.

If a diode were 'perfect' (zero forward resistance) there would be no heat generated at all - it's only because of a very small forward resistance that some heat is dissipated when forward current flows.

It isn't really meaningful to talk about diodes in terms of resistance.

In the forward direction, diodes are usually characterized in terms of forward voltage drop, usually somewhere around 0.7V-1V for a regular silicon diode (less for a germanium or silicon Schottky diode) this does vary with current but not nearly as much as the voltage across a resistor does. Generally in the diodes normal operating range forward voltage is roughly proportional to the logarithm of current.

 

[JohnW2]

Sure, but the currents flowing through those junctions are tiny.

Sure, but "tiny multiplied by billions" can be quite significant, hence the need for pretty hefty heatsinking/cooling of CPUs in PCs etc.

Diodes handling continuous high forward currents very often do need heat sinking. Indeed high-power applications are often moving away from diodes. Relay protection diodes though only conduct briefly so heat is unlikely to be a concern.

Indeed

It isn't really meaningful to talk about diodes in terms of resistance. ... In the forward direction, diodes are usually characterized in terms of forward voltage drop, usually somewhere around 0.7V-1V for a regular silicon diode (less for a germanium or silicon Schottky diode) this does vary with current but not nearly as much as the voltage across a resistor does. Generally in the diodes normal operating range forward voltage is roughly proportional to the logarithm of current.

Whilst everything you say is true, I think you're rather quibbling in relation to the 'simplified' explanation I provided for Rocky

It is the resistance presented by the junction which, when multiplied by the current flowing through it (squared), represents the amount of power (hence heat) dissipated in that junction.

The point you correctly make is that the effective resistance of a semiconductor junction is a varying (current-dependent) quantity, rather than the fixed resistance of a passive component, such as 'a resistor'. As a result, and as you imply, the amount of power dissipated rises much less rapidly as one increases current in the case of a semiconductor junction that would be the case with, say, a resistor. In fact, if one ignores the (relatively small) increase in forward voltage drop as current through a junction increases, then the power dissipated in a junction would be proportional to the current, rather than proportional to the current squared in the case of a resistor.

Kind Regards, John

 

[aptsys]

If you are stocking up get 1N4007 which has the highest PIV and can be used in many instances where a 1N4001 or 1N4004 is used.

Correction

when the contact opens the back EMF from the inductor is of the opposite polarity (Hence the reason the the diode is fitted reverse biased) I've corrected your drawing such that the diode fitted across the contact can pass the back EMF current.
View attachment 233198

The drawing is incorrect. In this instance the switch is pointless as the diode is always forward biased. The original diagram was right for back EMF protection.

The voltage only spikes to the extent needed to keep the current flowing.

Indeed, so with the diode in place, the back EMF will not exceed much over one volt.

 

[winston1]

winston1 said: ↑
If you are stocking up get 1N4007 which has the highest PIV and can be used in many instances where a 1N4001 or 1N4004 is used.]

Correction

[/QUOTE]
Can you give examples where a 1N4007 could not be used in place of a 1N4001, or 1N4004?

 

[JohnW2]

Can you give examples where a 1N4007 could not be used in place of a 1N4001, or 1N4004?

I must say that I was wondering that, too. As I said before, the operating characteristics for the entire range appear to be identical other than for the PIVs.

 

[aptsys]

I must say that I was wondering that, too. As I said before, the operating characteristics for the entire range appear to be identical other than for the PIVs.

Where you care about the parasitic capacitance. The capacitance is usually quite different for a 1N4001 than a 1N4007, so you'll find a it starts to pass more and more high frequency content with no rectifying action.

 

[aptsys]

First datasheet on google shows only with a test frequency of 1 MHz, but you get the idea.

 

[BS3036]

That seems to be showing the capacitance for the 1N4007 to be lower than for the 1N4001.