J & S grinder – electrics

[gerry maddenParticipant @gerrymadden53711]

 

I’m close to completing my refurbishment of my J & S 540 and now setting about installing the electric controls.

These were an ugly oily chaotic mess when I got the machine but surprisingly though they all functioned …albeit with a broken earth connection! I have dismantled and cleaned it all and reverse-engineered a wiring diagram which I show below. Despite care I may have made mistakes so please let me know if you see any mistakes / blunders.

The hardware is shown below. I have rebuilt it all with temporary wiring (and connections, no sheathing etc) just to get an idea of wire length and routing really. But feel free to comment on this also, bearing in mind that it’s a work in progress.

As regards the transformer, I will probably remove this as I don’t intend to use the tungsten lamp that the grinder came equipped with.

One puzzle for me though is that the heavier power motor seems to be connected to the (physically) smaller of the two contactors, ie. the right-hand one. The motor plate rating on this is 3A but the Danfoss contactor unit plate states only 2A.  Does this make sense ?

The larger of the two contactors (MEM) has a smaller rating, 1~2A, and feeds a motor with a plate rating of 1.6A.

In terms of input and output cables, only the input had any form of protection originally. This was in the form of a flexible metal conduit. The feed cables to the motors had no protection. The only things these cables can rub against in the machine are themselves or some rubber hydraulic hoses. I therefore I plan to wrap all three cables in that helical plastic sheathing. Is this suitable protection considering it may need to stay safe for another 50 years?

And finally, to check that the contactors latch correctly when energised by the switches, would it be permissible / sensible / safe to put briefly a domestic 240V feed on the individual input lines? (I’d put an appropriate resistive load on the output lines of course.)

Gerry

[Dave SParticipant @daves59043]

Is this a 4 push button grinder? If so I can check the actual wiring and ratings on mine.

Dave

[Martin CargillParticipant @martincargill50290]

Your contactors have 415 volt coils, so you can’t test them on a 240 volt supply. If you are doing a rebuild why not replace the contactors with new ones? You could drop the control voltage to 24 volts DC this would provide a safer circuit as there would only be 24 volts at the push buttons (you would need to add a 24 volt power supply into the circuit)

 

Martin

[gerry maddenParticipant @gerrymadden53711]

Dave S – no it doesn’t have 4 buttons. It has two switches, both which have push up for on, and push down for off.  So I would imagine it’s the same as yours, electrically. My switches are normally closed at one end and normally open at the other.

Martin – I did think about new contactors as other people seem to do this. But then I thought, well they have been good enough for 50 years of service, they should be ok for a few more :). I’ll give it some thought though. To get the 24V supply, I guess I’d use the transformer that’s currently there?

Gerry

[Chris CrewParticipant @chriscrew66644]

The smaller NVR contactor is not original and must have replaced a contactor of the same Crabtree type which is the other one in the picture. As regards the transformer, if you are scrapping it I would be happy to buy it as the one on my machine failed several years ago and I had to replace the low-volt lamp with a 240v bulb plugged directly into the mains which is obviously not a safe practice.

[noel shelleyParticipant @noelshelley55608]

Bear in mind that the ” rating ” of the MEM contactor is the heaters for the overload current . The reddy brown knob is to set the Full load current as stated on the motor spec plate. The Danfoss unit will have something similar and need setting. Keep the transformer and use 24v lighting be it filament or LED, if it needs DC then a simple bridge rectifier is all you need – KBPC 100Volt and as many amps as you need, I think that is it, small square block, 2 AC in and 2 DC  spade terminals look for the squiggle (ac) and + dc. and a screw hole in the middle. If it flickers put a 1000 uf capacitor across the + and – . Good luck. Noel.

[John HinkleyParticipant @johnhinkley26699]

Gerry,

I have a copy of the manual (pdf) for the “mid period model” which appears to be visually similar to the one in your first picture.  On page 7 there is a wiring diagram which I have reproduced below:

I have not appended the legend, which is on the same page, to save space.  Although not brilliant quality, it’s clearer in the pdf version, which is downloadable from VintageMachinery.org.

Apologies if you already have the manual.  Can’t  think why you wouldn’t have, but it’s not clear from your enquiry whether you have it or not.

Regards,

John

 

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