Simple delay timer - UK Vintage Radio Repair and Restoration Discussion Forum

Ed_Dinning · 1st Aug 2022, 4:20 pm

Hi Folks, some information please as I'm having a senior moment

It used to be possible to buy contactor/ relay delay timers that were 2 terminal devices and were wired in series with the contactor coil.
They offered a delay (sometimes adjustable) of a few seconds and were often used for motor starting duties.

I believe they used a PUT or SCS device as well as a CR timing circuit.
As far as I know SCR's were not used in this application.

Anyone got the circuit details?

Thanks, Ed

Refugee · 1st Aug 2022, 7:29 pm

I may have one but have not seen it for a few years.
If I see it while this thread is still open I will see if I can get a photo of the inside.

Alistair D · 1st Aug 2022, 8:15 pm

In the past there have a few threads about soft start circuits for large transformers on this board.

This is the only one I have found so far.

https://www.vintage-radio.net/forum/...d.php?t=119636

It might give you a few ideas.

A few months back I stripped a not long out of warranty microwave oven that had a small PCB that combined input filter and a similar circuit to the above soft start arrangement. It may be possible scavenge more from faulty microwaves.

Al

Ed_Dinning · 2nd Aug 2022, 9:12 am

Hi Folks, thanks for that.
A little more detail: contactor coils is a 24V/ 200mA unit and should operate after about 2 secs and remain held in, so relatively low current

Ed

Electrical · 2nd Aug 2022, 3:34 pm

Hello Ed
Have a look at the attached data sheet for the MTE TK3 and TK4 multi function timers.
This timer can operate on both AC and DC and can drive an external load up to 200mA.
RS used to stock them but they may be hard to find now.
Sorry for the rather poor scan, but I am sure it is readable.
Regards Stan.

McMurdo · 2nd Aug 2022, 4:27 pm

I've seen PTC thermistors packaged as 'on-delay' timers for solenoid valves in the pottery industry. Providing the mass of a contactor armature is big enough to avoid chattering, I'd imagine one of these would work. In fact one brand of american furnace control uses a relay in series with a ptc thermistor. The relay is an open-frame type and has a lead weight riveted to the moving contact so it doesn't chatter as it comes in.

Getting a suitable PTC these days may be another matter.....

Maybe a din-rail timer, you can get them for around £20. I've never seen an electronic 2-terminal device commercially, may be before my time!

Ed_Dinning · 2nd Aug 2022, 4:33 pm

Hi Folks, thanks for the information, but this was a small simple device that was in a small box, about 20mm cross section and 45mm long wit only 2 leads.

I believe Albright DC contactors supplied them, but have drawn a blank there.

Ed

1st Aug 2022, 4:20 pm	#1
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Simple delay timer Hi Folks, some information please as I'm having a senior moment It used to be possible to buy contactor/ relay delay timers that were 2 terminal devices and were wired in series with the contactor coil. They offered a delay (sometimes adjustable) of a few seconds and were often used for motor starting duties. I believe they used a PUT or SCS device as well as a CR timing circuit. As far as I know SCR's were not used in this application. Anyone got the circuit details? Thanks, Ed

1st Aug 2022, 7:29 pm	#2
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Simple delay timer I may have one but have not seen it for a few years. If I see it while this thread is still open I will see if I can get a photo of the inside.

1st Aug 2022, 8:15 pm	#3
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: Simple delay timer In the past there have a few threads about soft start circuits for large transformers on this board. This is the only one I have found so far. https://www.vintage-radio.net/forum/...d.php?t=119636 It might give you a few ideas. A few months back I stripped a not long out of warranty microwave oven that had a small PCB that combined input filter and a similar circuit to the above soft start arrangement. It may be possible scavenge more from faulty microwaves. Al __________________ I won't tell you how I discovered that.

2nd Aug 2022, 9:12 am	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Simple delay timer Hi Folks, thanks for that. A little more detail: contactor coils is a 24V/ 200mA unit and should operate after about 2 secs and remain held in, so relatively low current Ed

2nd Aug 2022, 4:27 pm	#6
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,271	Re: Simple delay timer I've seen PTC thermistors packaged as 'on-delay' timers for solenoid valves in the pottery industry. Providing the mass of a contactor armature is big enough to avoid chattering, I'd imagine one of these would work. In fact one brand of american furnace control uses a relay in series with a ptc thermistor. The relay is an open-frame type and has a lead weight riveted to the moving contact so it doesn't chatter as it comes in. Getting a suitable PTC these days may be another matter..... Maybe a din-rail timer, you can get them for around £20. I've never seen an electronic 2-terminal device commercially, may be before my time! __________________ Kevin

2nd Aug 2022, 4:33 pm	#7
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Simple delay timer Hi Folks, thanks for the information, but this was a small simple device that was in a small box, about 20mm cross section and 45mm long wit only 2 leads. I believe Albright DC contactors supplied them, but have drawn a blank there. Ed