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Blown band saw circuit.

Help asked for please.

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Marischal Ellis23/08/2020 15:19:56
73 forum posts
27 photos

I jammed my ultimate pride and joy, a De Walt 3501 Band saw of 30 + years. Instantly cut-out with a pop and doesn't work now. I use it so much and is so convenient to me. How stupid of me.

I did a long think through; the trip switch was not working (open or closed?) and bought a new one. I also bought a new neon warning light (white Light) which had never worked. (Possibly a running light). The start capacitor which I commenced the checking with was AOK . Re-assembled switch box but nothing happened. I pressed the trip switch and kept it pressed (open or closed?) to try it and motor started up, so that was OK. The contact switches as a set of four are now no longer available via De Walt and were about £40 + or so, years ago

Having fiddled with things, and my mind, I now think that the contacts are bad (jammed open or shut?) but what do I replace them with, as the capacitor is required and 'modern' motors appear to have built-in capacitors which I think cut-out on functioning?

Current Off/On button switches (load is 16 amps) would seem possible but I don't know how a capacitor would be wired in as they appear to rely on cutting off instantly after firing up, so running as I did would not last too long. More correctly it is probably the magnetic coil that is damaged so no control over instant time.

My question is : What can I ,replace my broken contacts and/or switches with. I can add a elect box housing or what ever is need, to house new 'bits'. I have drawn the circuit as I see it and can see why it presently works by keeping my finger on the trip switch.

Your help and advice would be most welcome as it is not my subject. As I grow older there are lots and more of 'not my subject' but that is another story for another day. A way of switching and a means of including a start capacitor would seem to be the way forward if that is correct.

sawcircuit.jpg

Diagram of circuit.

clogs23/08/2020 15:46:13
588 forum posts
12 photos

shame after all those years.....

their machine wiring was always a bit weird.......

there's plenty of contactors out there.....and also many varied size and style of boxes...none of which is expensive....

I can't help u with the wiring but I'd be inclined to bin the lot and go with the Brit idea....no volt stop start switch etc....

even if it ment replacing the motor.....but that should not be nec......

and I'm sure somebody who's a wizz with wiring will be along shortly.....

My Bridgeport's wiring was a messy affair, will just bin the lot and replace all contactors......

not so cheap but it'll last my lifetime...and it will be reliable...

Les Jones 123/08/2020 17:35:43
2225 forum posts
153 photos

It sounds like either the coil on the coil on the contactor is open circuit or the maintainer contact is not holding the coil in after the start button has been pressed. The stop button will be a normally close push button and if that was open circuit it would also prevent the the coil from holding the contactor in. I assume the rectangular thing with 8 connections is the combined contactor and start and stop buttons. you have not shown which connections go to the coil or the layout of the contact sets. I have tried to find a picture of your contactor assembly but failed. Some pictures of the contactor may help in understanding the contact and coil connections. I think a standard NVR switch can be made to work.

Les.

Ed Duffner23/08/2020 17:57:43
827 forum posts
94 photos

What is the large rectangular block between the capacitor and the Warning Light" ? Is it a connector or 4-pole switch?

Ed.

Pete Rimmer23/08/2020 18:06:56
940 forum posts
57 photos

I don't think that the capacitor is designed to be switched out of the circuit, not by looking at that circuit diagram anyway. Two leads come out of the motor and go to only one switch terminal (one with the cap in series). This suggests that the cap and start winding are always live with the run winding.

What's not apparent is how the contacts are connected by switching.

Les Jones 123/08/2020 18:14:00
2225 forum posts
153 photos

There is probably a centrifugal switch inside the motor that disconnects the start winding when the motor is up to speed. Probably an NVR switch such as this can be used. (There are also many advertised on ebay.)

Les.

Phil Whitley23/08/2020 18:38:53
avatar
1324 forum posts
147 photos

If the motor runs when you press the contactor in, there is nothing wrong with the motor, capacitor, or the centrifugal switch. Something in the starter circuit is the fault, like the start button, or as above, the coil in the contactor is open circuit, or the stop button, which should be normally closed, is not! can you post up some pics of the controls and switches etc. If you had to press the new trip switch in and hold it to get the motor to run, the new trip switch is faulty, once pressed in, it should close the circuit and lock in with a click.

Phil

Ed Duffner23/08/2020 18:48:05
827 forum posts
94 photos

Assuming it is a multi pole switch, I think only the 3 right-most contact pairs would be normally open and the far left pair is possibly just isolated connection posts (or there would be a direct short L-N if they were closed).

A centrifugal switch could switch between the capacitor or the solid wire to complete the neutral side of the circuit. Not sure if it would be a start or run capacitor.

Ed.

Marischal Ellis23/08/2020 21:55:34
73 forum posts
27 photos

All

What a wonderful collection of thoughts and ideas. I am tied-up tomorrow but will sort out answers for everyone later in the day. Mean while a big thank you to you all.

M

Marischal Ellis25/08/2020 19:38:24
73 forum posts
27 photos

saw contols1.jpg

sawcontrols2.jpg

Here is a couple of shots of the controls.With the 'electro' coil 'thing' pressed in, I get ohms across each two terminals on all four 'contactors', but when with not pressed in I get nothing. However, if I press the trip button I get ohms at contactor 4. that serving the capacitor. Not much the wiser I am afraid. Look forward to your thoughts. I am happy to start again and fit modern kit as long as I understand he wiring and so on.

Les Jones 125/08/2020 20:54:57
2225 forum posts
153 photos

This is my interpretation of the wiring.

band saw.jpg

Contacts 3 to 7 and 4 to 8 must be working as the motor runs while the start button is held in, (The start button just pushes the solenoid in,)
The fault must be the coil is open circuit or contact set 2 to 6 not closing. With the mains cable unplugged first measure the resistance between 1 1 and 5. You should get a reading of a few hundred ohms. Then connect your meter to 2 and 6, You should get a very high (Probably over range reading.) Then push the solenoid armature in. The reading should drop to close to zero ohms. Report the result of these tests.

Les.

Les Jones 126/08/2020 08:37:54
2225 forum posts
153 photos

If the fault is the contact set 2 to 6 then it should be possible to get it to work by a small change to the way it is wired.

Les.

Marischal Ellis26/08/2020 11:12:38
73 forum posts
27 photos

Morning

I've done my homework, but not sure of my results, so, whilst hoping for 10/10 I will probably only get 4/10 on a good day. I am beginning to know a little more so learning. Thank you everyone so far as it takes a bit to pick some of it up. Here are my results this morning.

contact 1- 5 ....thing.

contacts 2-6 ...nothing.

contacts 2-6 with solenoid press in ...nothing.

I have unplugged as always, but is that safety as well as something to do with possible continuity?

Best wishes all,

M

Les Jones 126/08/2020 17:42:13
2225 forum posts
153 photos

I assume that when you say "nothing" you mean infinite resistance. If not what do you mean ?

What was the resistance reading between 1 and 5 ? (I don't understand what you mean by "thing".)

Les.

Edited By Les Jones 1 on 26/08/2020 17:43:33

Marischal Ellis26/08/2020 18:22:03
73 forum posts
27 photos

Les

Thank you for answering and I'm sorry for being misleading. By nothing I meant no reading. Nothing came up on my meter. My reading stayed at 1 which is nothing to me. I hope this is a bit clearer and thank you.

Yours

M

Phil Whitley26/08/2020 20:45:21
avatar
1324 forum posts
147 photos

what do you mean by "the trip button" If you mean the overload trip, that should lock in when you press it, and stay locked in till the circiit overloads and trips, if it does not lock in when you push it in (try hard push) the the overload trip is faulty, and that is why it is not working. Try holding the o/l button in and pressing the start button to see if it runs. The overload trip should have continuity through it all the time. the button is to reset it after it has tripped.Please show the start and stop buttons on the diagram! If you have nothing between 2 and 6 when the contactor is held in, that is the fault, 2 and 6 are the circuit that hold the contactor "in" once the start button is released

Phil

Marischal Ellis26/08/2020 21:17:51
73 forum posts
27 photos

Hi Phil

I am tied up tomorrow morning but will look and consider what I am being told so thank you for your respect. Probably mid afternoon. Trip is the overload button, which I think doesn't stay (is new). Stop start switches are mechanical action. But will check it all again, so thank for the moment.

Yours M

Les Jones 127/08/2020 14:58:16
2225 forum posts
153 photos

I am even more confused. Are you using an analogue or a digital meter and if it is digital is it auto ranging on the resistance setting ? I don't understand the 1 reading. (You don't say if this is 1 ohm, 1 K ohm or 1 Meg ohm.) Normally on a resistance range with the test probes not conneted to anything or each other the meter would display something like ol to indicate the resistance between the probes is higher than the meter is capable of reading. If the probes are shorted together it would read 0.00. (If it is set to al low resistance range it can give a small reading of probably les than 1 ohm which will be the resistance of the test leads.) Does your meter behave this way ?

Note to Phil. This type of NVR switch does not have a normal start an stop button. The start button just manually pushes the solenoid to the closed position and the stop button just forces the solenoid to the open position.

Les.

Edited By Les Jones 1 on 27/08/2020 15:00:05

Phil Whitley27/08/2020 18:10:18
avatar
1324 forum posts
147 photos

Thanks for that Les, that sounds very piss poor to me, but makes sense when you read the diagram!

Les Jones 127/08/2020 18:54:20
2225 forum posts
153 photos

Hi Phil, Many of these NVR switches do not even have a separate maintainer contact. If It turns out that the only fault is the maintainer contact (2 to 6) then I am going to suggest linking 1 to 4. I think it is unlikely that the 2 to 6 contact AND the coil have both failed.

Les.

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