Help establishing armature connection diagram of an electric motor.

[jwet]

I'm really impressed with your tenacity! Hopefully, the bearings are something standard. Good luck- you've earned my respect. Please post any updates on the final conclusion of whether it was worthwhile, etc.

 

[Flynth]

That's pretty impressive, @Flynth. Congratulations!

I'm really impressed with your tenacity! Hopefully, the bearings are something standard. Good luck- you've earned my respect. Please post any updates on the final conclusion of whether it was worthwhile, etc.

Thank you both. These are very common metric bearings (627zz). So common my local farmer's supply store has them so I already got them. I thought they are regular ball bearings, but they are deep groove ball bearings. So I have no idea why they failed so soon. I briefly considered replacing them with sealed bearings, but the seal causes a bit more drag which I wasn't sure will be good for such a small motor. So I'm replacing them with the same type (just made by a better brand - Enzo).

 

[jwet]

Bearings are something you can spend $2 to $200 on and they look pretty much the same. For a fast rotating spindle, I might go a little above the minimum- cheap bearings usually run hot.

 

[Flynth]

Bearings are something you can spend $2 to $200 on and they look pretty much the same. For a fast rotating spindle, I might go a little above the minimum- cheap bearings usually run hot.

Yes, me too. Here I had a couple of brands to choose cheapest possible for around $0.3 a piece(these are small bearings) , then Enzo (mada in Japan) for about $1.5 (those I bought) and more expensive bearings to order. I was told those enzos are pretty good for the price.

So I have my table feed put together and installed on the machine now. I used it briefly and it seems to run fine. For full piece of mind I just need to measure the current consumed during rapid traverse to make sure the motor isn't driven too hard.

The control board even on top setting gives the motor half of the AC waveform, but during rapid traverse it essentially shorts AC to the motor. Now the question becomes, did they design the motor for 95% of use (at half of the voltage) and they are overvolting it during rapids hoping people would only use it for few seconds at a time? Or did they design the motor for the rapids (5% of use) basically over sizing the motor for 95% of use?
The former sounds much more likely to me, but I have no proof until I measure current consumption at full voltage while moving the table. Also, it seems they are running bearings over their rated speed due rapid traverse too.

According to skf bearing top speed formula those bearings 7*22mm deep groove. Can run at top speed of 34k rpm if oil lubricated and only 22k rpm when grease lubed. They are using grease and the motor sure sounds like running definitely over 30-few k rpm during rapids.

Edit: After thinking about it for a while I decided to add a diode into the rapid travel circuit. This means rapids will be half as fast (same as top speed setting on the dial), but I'll be much more confident about it lasting a lot longer.

 

[jwet]

This is top secret but they always do what's cheapest. The diode is cheap insurance. Remember that even with just a .7 volt drop at a few amps, that diode will dissipate a bit of power= IV, easy few watts. These types of motors are all designed for intermittent use so the 95/5 probably doesn't matter much. Run the table 2 full cycles of back and forth- the longest credible run and see how hot it gets. Hand test- 70 C is uncomfortable to touch, 100 c will leave a red spot, 125 will leave skin behind, use a wet finger. I'm very impressed once again.

 

[jwet]

Also, measure leakage current just to be safe. Lift the third prong of the plug and put an AC ammeter in there. The will be some current, capacitive coupling etc but should be <<1 mA.

 

[jwet]

One other thing that I thought of is use a spdt pushbutton for the rapid button. The NC connection lets the wiper connection go to the pot wiper. The wiper goes to the NC and wiper control input goes to the com of the switch. The top of the pot (full speed wiper position) is connected to the NO position of the pushbutton. When pushed, it gives the input to the control what the full wiper would give. No diodes. This is pretty easy if things aren't all mounted on a PCB. Hope this makes sense. I can post a sketch. Take care.

 

[Flynth]

One other thing that I thought of is use a spdt pushbutton for the rapid button. The NC connection lets the wiper connection go to the pot wiper. The wiper goes to the NC and wiper control input goes to the com of the switch. The top of the pot (full speed wiper position) is connected to the NO position of the pushbutton. When pushed, it gives the input to the control what the full wiper would give. No diodes. This is pretty easy if things aren't all mounted on a PCB. Hope this makes sense. I can post a sketch. Take care.

Thank you for an alternate idea

However, the pot doesn't control the motor directly. As far as I understand the circuit, the pot forms a voltage divider with a large 10W resistor. Then this voltage is sent to the gate of an scr.

The scr then starts conducting sooner or later(depending on the gate voltage) during each half wave cycle. The rapids switch shorts the scr. So by putting a diode in line of the switch it will mean the motor never sees the full AC with minimal mods.

There is a pcb, but it is very cramped there. There is a section of the switch wire that is loose inside the case. I plan to put the diode there and to wrap it in self vulcanising rubber isolation tape. I did a pv installation last year. I added a diode in line with a wire like this to each panel(I forgot why they recommend it) and they are all still holding up well.

 

[jwet]

Got it- I guess I'm imagining a different circuit for the speed control. Carry on.