Electromagnetic switch

**Bob Willson** · 28th February 2014, 05:51 PM

I have a H&F bandsaw. model number BS300

The switch that is on the machine was underwater during the floods and has never been that great since, as it hums when power is applied to the saw regardless of whether the saw is actually turned on or not.

I decided to get another switch for the saw and I ordered one on ebay from China. The switch on the saw is a KEDU KJD12 switch

I ordered a similarly spec'd switch, a JUCHE JCZ3B that is only 1/4 the price.

I got the switch, but it doesn't seem to behave properly. The KJD12 has a label on the side saying to use inputs 1 and 3 for the 230V input and then output goes through 2 and 4. The pins are clearly labeled 1, 2, 3 and 4 on the rear of the switch. It only has 4 pins.

The JCZ3B says to use pins 1 and 3 for the inputs and pins 2 and 4 for the outputs. There is a diagram on the side of the switch explaining this.

This is where the problem starts. The rear of the switch has 5 pins. they are labelled 13, 14, 23, 24 and A1 respectively. I connected the inputs to pins 13 and 23 and connected the outputs to 14 and 24 leaving A1 unconnected.

The saw starts but fails to hold the switch in the on position, so unless I physically hold the switch on, the saw stops. Not an acceptable state of affairs.

Can anybody tell me what I am doing wrong? Is it that I should not have got a momentary switch? Should I have got one of these instead?switch back.jpg Switch sides.jpg

Thanks

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**RustyArc** · 28th February 2014, 07:06 PM

You need to connect A1 to 24 so that the coil is energised and holds the switch on.

**Bob Willson** · 28th February 2014, 08:21 PM

Wonderful

Thanks for that RustyArc. I would never have managed to guess that by myself.

**Bob Willson** · 1st March 2014, 03:56 PM

The switch is all set up as per the instructions, but it still hums as loudly if not louder than the old one. Can anybody point me in the right direction for looking at causes of switch hum please?

Thanks

**snowyskiesau** · 1st March 2014, 04:12 PM

The only thing that can hum in a switch of that design is the relay coil.
Hum could be from overvoltage - unlikely as the coil should be designed for use at the rated voltage. Wrong frequency could do it but again, if it's meant to be rated for 50Hz, unlikely.
A faulty switch would be my guess.

I have some similar NVR switches and there's no audible hum from them.

**A Duke** · 1st March 2014, 05:15 PM

Dirt between the magnetic faces of the coil cores will do it or if they are not seating properly. A broken shading ring will cause a terrific chatter but is not likely.
Regards

**Bob Willson** · 1st March 2014, 06:55 PM

Thanks Hugh and Geoff.

As I said, the previous switch also hummed so I think that the fault is more likely to be external to the switch.

The hum didn't start until I shorted the A1 pin to pin 24, but without that connection the switch doesn't work properly.

Is it possible that a faulty capacitor could cause it to happen, because these are the same caps that went under water?

**RustyArc** · 1st March 2014, 08:54 PM

Without A1 connected, do you still get the hum if you hold the switch on manually?

**BobL** · 1st March 2014, 10:29 PM

Have you had this or any other machine that have been underwater megger tested?
If not I would not use the machine without getting it checked out.
The hum could easily be due to a light coating of gunk inside the motor.
Pity you are not closer or I could have come around with my new IRT.

FWIW I have fitted the same switch to a metal cutting bandsaw and also to a small WW bandsaw without a problem.

**Bob Willson** · 2nd March 2014, 12:15 AM

Originally Posted by BobL

Have you had this or any other machine that have been underwater megger tested?
The hum could easily be due to a light coating of gunk inside the motor.
Pity you are not closer or I could have come around with my new IRT..

I did take the motor apart and clean it out 2 years ago. I also put new bearings in most of the motors but I cannot remember if I did so on this one as well.

No, I didn't get the motor meggered. But I have been using it for a while now.

Maybe I will take it apart again.

**BobL** · 2nd March 2014, 12:39 AM

Originally Posted by Bob Willson

I did take the motor apart and clean it out 2 years ago. I also put new bearings in most of the motors but I cannot remember if I did so on this one as well.
No, I didn't get the motor meggered. But I have been using it for a while now.
Maybe I will take it apart again.

Did you try Rusty arc suggestion.

**Bob Willson** · 2nd March 2014, 10:31 AM

Originally Posted by BobL

Did you try Rusty arc suggestion.

It is now quite difficult to do this, as I soldered a link between the two posts.

I was also looking at the paperwork that came with the switch and noticed something connected to the A1 terminal, but I do not know what it is. I haven't seen this symbol before.

**RustyArc** · 2nd March 2014, 11:20 AM

The symbol represents the solenoid coil. If you look at the old switch, it has a very similar diagram, although in that case the coil symbol is more explicit.

The new switch has the coil on a separate pin (A1) so that it can be wired into equipment that has specific switching behaviour (machine stays on provided part x reaches a certain RPM or safety switch y is closed etc.).

**BobL** · 2nd March 2014, 12:02 PM

Originally Posted by Bob Willson

It is now quite difficult to do this, as I soldered a link between the two posts.

I was also looking at the paperwork that came with the switch and noticed something connected to the A1 terminal, but I do not know what it is. I haven't seen this symbol before.

That's the solenoid.

These switches are best connected with 6.3mm spade connectors. The small (A1) is a special size but I found the 4.8 mm ones available at altronics fit it nice and snuggly.
http://www.altronics.com.au/index.as...item&id=H1991A

**RichardL** · 30th March 2015, 07:00 AM

Hi all

I have just bougth a Kedu KJD 12 and installed it on a home-made linisher. It also has quite a loud buzz when energised but otherwise works OK (switches on and off and the motor runs the right direction). I wasn't quite sure which way around to connect it but if I had done it incorrectly, it wouldn't work at all...right?

Thanks
Richard

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