Electrical/electronic advise needed

[daveo]

Hi All
I need your thoughts
I have been using a Delta 650 Q3 now for some time, when I first got it I fast found out (from our members) that when you switch it on there is a time delay of about 2 seconds before the motor starts running, and this is the norm.
Now recently I have been experiencing a fault, in that some times when you flick the switch the motor attempts to run instantly, but only momentary and then stops, thus meaning that I then have to switch it off and then back on and usually it works fine. This problem has got worse over the past couple of weeks, so I stripped the machine and took the circuit board (and motor) to the local repair shop for him to investigate, his initial findings were that there was no failing components on the board. We then switch the motor on and off several times (in his workshop) until the fault showed itself. The conclusion was that he believed the fault was with the motor, in that one or more of the segments were failing or failed and when the motor stopped or came to rest on the segment, that this is when the problem would happen, so I thanked him brought it home.
Later as I thought that really logic does not prevail here ( and I may well be totally wrong) but
If there should be a time delay of 2 seconds before the board starts to feed the motor with power, and if on occasions the motor tries to start instantly, then this means that at times the motor is getting power to it at a time when it should not (if that makes sense) and if this being so how can it be the motor that is at fault.
I have asked the question to Delta, but still no reply, so if anyone has half an idea I would be grateful, xmas is not getting any further away and really need to get this sorted as orders are already increasing

Regards

Dave

[Kragax]

I know what he is talking about and it is possible. Sometimes the insulation between the commutator bars will smear on the copper if the bars are worn. We used to cut it back with a hack saw blade and it ran for a long time after. Also if it is a capacitor start motor the cap my be getting weak and acting up.

[daveo]

I know what he is talking about and it is possible. Sometimes the insulation between the commutator bars will smear on the copper if the bars are worn. We used to cut it back with a hack saw blade and it ran for a long time after. Also if it is a capacitor start motor the cap my be getting weak and acting up

Wow thanks for that, the commutator bit I am lost with, the capacitor bit I half understand, but yet I still cant see how the motor would receive momentary power instantly when there is a time delay on the circuit??
there is no capacitor on the motor itself unless there is any chance that there is something electronic inside the motor and infact the motor gets power on start up and the timer delay is inside the motor

Dave

[Kragax]

The commutator is at the end of the main shaft. Its made of small copper bars that the brushes ride on. If the motor stops where the insulation ( used to be mica) is smeared on the copper maybe it delays the start up. The capactor may be inside the motor housing itself.
Just a semi educated guess.

[EIEIO]

How long is "momentary"? If it's "short", that sounds like a capacitor discharging into a DC motor. A big power supply filter capacitor can hold enough energy to make the motor spin (usually for less than a second), then as the cap is discharged the motor stops. Do you have a schematic for the control board? If you can figure out the voltage, you can remove the motor and put a DC supply to it (a 1 amp wall wart supply would work if it's the right voltage), and switch it on and off until you get it to stick. If it sticks then the motor dead spot makes sense - verify by turning it 1/4 turn and try to power it again (it should spin). But a dead spot would not explain the instant start of the motor that you reported, so I doubt that's the problem.

If it will not stick, the control board is suspect. Hard to diagnose w/o a schematic, but usually you start by verifying that the power supply output looks good. There can be high voltages (multiples of 120V) in a switching power supply so watch what you touch.

If you don't feel the need for fancy or proper, and you can determine the right DC voltage for motor full speed operation (measure it when the motor starts correctly), you could replace the controller with a fixed DC supply. This would not give you variable speed control, but if you don't use variable speed, so what?   

[daveo]

Hi Ray
thanks for coming in on this one
firstly "momentary" is like a tenth of a second,
on switch on if this happens then the arm twitchs and then nothing happens, so I switch off the machine and then back on and it usually runs.
Now since my last post I can confirm that there is no other electronic parts on the machine (no capacitor on or in the motor), so the motor is fully reliant on the PCB. That said we know that on switch the built in time delay(approx 2 seconds) delays the start of the motor, thats how its supposed to work.
Therefore when at switch on and I get this momentary twitch of the arm, it suggests to me that the motor is getting a supply at the time it should not,
of which of course means that the supply has to be coming from the board itself, as you say a charge from a cap. But trying to convince the man in the shop this, is like trying to push rope.
the variable speed is important I use it all the time
I am trying to track down a shcematic of the board but delta seem to hold these things close to the chest, I will keep trying but in the mean time here is a picture of the board if that helps at all

Dave

[EIEIO]

dave  - just a few thoughts while you're looking for the schematic.
The green cylinder looks like it might be a reed relay and might be your 2 sec delay control - letting the power supply stabilize before trying to control the motor.
The 5W18KJ rectangle is a 5 watt power resistor. They are ceramic because they get hot and are places where failures can occur.
It looks like a PIC processor that controls speed by switching a DC source on and off (Pulse Width Modulation or PWM). The PIC can do some checking before trying to start and might sense an off voltage and shut down. You could put a meter on contacts and look for voltages when it's good and when it's not good.
Which wires go to the motor? Which to the AC supply (I see you're in GB so the 230VAC makes sense)? To the left of the trandformer is a rectifier (AC to DC). I'd guess that feeds the logic part of the board.

Can you tell if it is a Permanent Magnet motor?   

[daveo]

Ray

on checking the net it appears that the green cylinder is in fact a reed relay, I did question this at the shop as it appeared to be some what melted at one end, and was told it was OK, and after seeing pictures of the same component it seems to be how they are (PIC1)
As for the wiring (PIC2)
the Blue and Brown are the incoming supply
The Blacks (top centre) come off the board through a glass fuse holder, up to the on/off switch and back to the board.
The other connections (PIC3) the bottom plug in goes to the speed control dial
and the top brown one goes to the back of the motor to the gizmo that counts the revs (what ever thats called)

As for the motor I do not have a clue if its permanent magnet or not, I have included a picture of one (PIC4) Note this is not my motor it is a stock picture of the 120v version but the spec is the same otherwise, if that helps at all

still trying to trace a schematic, I have sent a request to Delta but not holding my breath on that one

The ironic thing is that this problem has been getting worse as time goes on But I have to say that since the machine has been put back together (4 days now) and has had approx 25-30 hours running time the problem has only occurred three or four times, as if something has had a jolt and is behaving better (AT THE MOMENT)

hope some of that garble helps some.

Dave

[EIEIO]

good info. You can feel the magnet grab abd release as you turn a PM motor by hand. This motor has brushes so it is not a permanent magnet motor. The brushes are to switch the magnetic field on the rotor, so there is no permanent magnet. It is labeled 120V so it seems like an AC motor and the controller is switching a 120V DC supply to make a square AC waveform of variable frequency. The motor speed will follow the freq of the square wave.

Your original photo at lower right has 2 bigger TO-220 packaged devices - maybe MOSFET transistors that do the switching? The transformer (230V) may be just a step down to get to the 120 VAC used in the US. The rectifier to its left would make high voltage DC (120 average, 169 peak) from the 120V side of the transformer.

Can you get  photo of the back of the board? Maybe we can make our own schematic.

[daveo]

Ray
sorry for the confusion, but I did point out that the picture of the motor is not my motor and is a stock photo of the 120v version, my motor is the 230v version, sorry about that.
I will try and strip the machine down again tomorrow and get as many shots of the board as I can.
Dave

[EIEIO]

Have you looked for a replacement controller board? It might not be too expensive and save you a lot of trouble trying to fix it yourself.
Simple schematic: from http://c.searspartsdirect.com/lis_png/PLDM/50024044-00002.png


Another schematic from http://media.toolpartsdirect.com/media/schematic/files/images/1/4/1418958_fig3.png

[daveo]

Ray
the only replacement boards would reach me at around $600
and no good any way as they are 120v and I need the 230V of which are obselete

Dave

[EIEIO]

ouch - don't want to go there. I wish there was more that I could do to help.

Do you have a digital voltmeter? If so, while the motor is running, measure the voltage across its terminals. It could be DC or AC (measure both), and might be at 120V so measure with care.

The other is to try to reproduce the schematic from the top and bottom photos. And try to read the labels on the DIP parts (the intergrated circuits on the board) and the TO-220 parts (3-terminal, may be on a heat sink). 

[dirtrider73068]

Have you tried once the motor is on then stops, turning the switch off rotate the motor slightly then turn the switch back on to confirm bad spots on the motor? 600 bucks for a control board is going price for a 16 inch excalibur. I have a craftsman 16 inch sitting in my shed collecting dust, if its the same board I could send it to you and give a try. I am in the usa if that makes any difference on parts, it might be the same parts just different branded saw.