Fully automatic d/c switching


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I’ve followed the recent thread on “semi-automatic switching for d/c systems”; some of you might be interested in the solution I’ve come out with. I’ve done quite a lot of reading on this; US w/workers tend to opt for an infra-red manual switch, but I wanted something truly automatic, which led me to: (a) vibration sensors mounted on each machine; (b) using mechanical l/v switches built into blast gates, or; (c) current sensing.

On (c), I got as far as reading about Hall effect sensors but my knowledge of electronics is not good enough to design such a circuit, and I never found a ready-made circuit diagram. The answer I found came from Maplin, who sell something called a “master/slave power controller module” (http://www.maplin.co.uk/, product code N74AU). This switches on the “slave” (the d/c in this case) when the “master” machine draws current. The master can be up to 4kw, and the slave can draw up to 10A according to the spec (it can cope with 3-phase as well as single, it says).

I fitted a second ring main in my workshop with distinctive sockets (metal clad, versus white plastic for my first, existing ring) which is solely for the machines to be d/c connected. Wiring the live conductor of this second ring through the master side of the controller module means that any time a machine on this ring draws current, the slave d/c (which is powered from a socket on the first ring) comes on. For extra versatility, the d/c power is controlled by a 3-way switch so that it’s either off, on for the automatic master/ slave circuit, or a “manual override” on position so that I can hoover up loose dust at the end of the day.

I would just mention that I stumbled across this site thanks to a passing reference in the Google uk d-i-y discussion group. It's absolutely fantastic to find a UK group that has a critical mass of knowledgeable contributors; I've spent years reading the likes of The WWA Info Exchange (fantastically enthusiastic contributors, but v. galling to see such HUGE shops and such CHEAP tools) and Taunton's "Knots".

John Forbes
OLD":25cxkqfv said:
Does this device switch the d/c off when M/C current falls to zero.

Yes. There's a 1/2 second delay before the slave circuit comes on to avoid too much current pull, and as far as I can tell the slave circuit shuts off as soon as the master current ceases to draw any current (in other words, when the saw/planer/whatever is switched off)

I like this device and at £11.99 looks very good value and made for the job.
The nvr on the d/c will have to be removed as on my previous now out of date proposal.
I intend to use this its a 'better solution' in my opinion and fully automatic only safety consideration is to isolate the d/c when working on it .
Interested to see others observations.
As an update I just tried to buy one from Maplin but they are now discontinued due to poor sales. The Maplin telephone sales girl was incredibly helpful and gave me a list of stores that still carried stock. :D :D but sadly none were close to me.

I tried ringing one store and offered to pay P&P if they would post it to me. 'No - not company policy' was the reply :evil: :evil: :evil: :evil: :evil:

Has anyone tracked down any alternatives?
Roger Sinden":33hw3xvg said:
I tried ringing one store and offered to pay P&P if they would post it to me. 'No - not company policy' was the reply :evil: :evil: :evil: :evil: :evil:

Has anyone tracked down any alternatives?


How about telling us where the stores are. You never know a helpful forum member may live next door.

I am in Cambridge but stuck in work today.
I'll try and get missus to pop in and get a couple (I fancy using one myself!)

I'll let you know...
Hi Houtslager

Yup...0208 881 3288 is the telephone number. They have two left so if you could get them both that would be fantastic. That way i can 'bank' one in case someone else needs one.

Amilford - still interested in one from cambridge (but if they only have one and i can get one via Houtslager then go fot it :D )

I accidentally deleted my Inbox recently and so have lost the emails relating o this.

I believe that one of you was successful in getting a couple and so I'd like to give you some money for mine :oops: :oops:

Thought I'd bring this up again as I managed to get it working, but with one problem......

The blade brake on my machine causes this device to chatter for some reason. I'm not sure what method is applied electrically to stall the blade but it obviously upsets this device for 10 seconds or so until the blade break does it's job. I guess the chattering might not be unsafe per-se but it will probably shorten the life of the device (which might degrade in an unsafe manner I guess)

Any ideas or suggestions anybody? :(


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