T-7 overheated!

[Herman Trivilino]

It says at idling it actually reaches its highest temperature.
Does this mean the motor is actually under greatest stress when there is no load?

The faster the motor spins, the greater the so-called back EMF. Back EMF is a voltage produced by the motor, and it opposes the voltage of the source. Therefore the current in the motor's windings is smaller when the motor is spinning faster. Less current means lower temperature in the windings.

On the other hand, higher rotation speeds mean there is more friction, which means a higher temperature.

So, just because the temperature is higher at high speeds doesn't mean the motor is under less load. It just means more mechanical energy is being converted to thermal energy via friction.

[SharpenADullWitt]

I can see some issues with tylers suggestion about swapping it.
If the retailer did the swap, I would expect they would do it there.  If not, then you have the possible issue of the number being registered already (and being able to modify the registry).  That leads to some questions about the models such as Ken's stolen one (if someone decides to register it).
Personally, I have never seen a "refurbished" Tormek for sale.  Typically they go for less on a refurbished item, and I would have seen one, I thought, in my searches over the years.

A modification of tylers idea would be to send a new unit, sans stone, via mail (if requested and typically this involves a temporary charge to a CC when done with a hard drive), and the old unit gets sent back in that packing.  Then it could be swapped back the same way.

[Jan]

I measured the electric current which flows to the T7 induction motor with an ammeter. I have found that the current is more or less independent from the regime of the motor. It means there is more or less no difference in the size of the AC current through the stator of the motor in an idling or an standard honing regime.

Of courese, if you try to stop the wheel, the current will increase.

The electric power transferred to the motor is proportional to the current. Part of the electric energy transferred to the motor is converted to heat. The rate of heat generation determines the temperature of the motor.

[tylers]

I like the way you think Sharpen. I would be happy with any response from either the retailer, wholesaler, or Tormek, but I have not received any response to my email.
Grepper, I no longer have access to an SEM, but I do have a nice Meiji stereo scope, but no mount for a camera...I may try to photo with just a camera and see what I get. Down the list of things to do though.

[Jan]

I have heard that the newest T7 are equipped with motors of the duty type S6-40%. S6 means continuous-operation periodic duty. Duty cycle is usually 10 min.  Hence S6-40% means 4 min load and 6 min no–load. S6 should guarantee that there is no temperature rise when the motor is loaded at its rated output.

[SharpenADullWitt]

I have heard that the newest T7 are equipped with motors of the duty type S6-40%. S6 means continuous-operation periodic duty. Duty cycle is usually 10 min.  Hence S6-40% means 4 min load and 6 min no–load. S6 should guarantee that there is no temperature rise when the motor is loaded at its rated output.

Heard where?  Without any proof, this sounds like either a competitor's rumor, or just gossip, which would go against the advertised (currently) stuff, that Tormek has to legally adhere to:
http://tormek.com/international/en/machine-models/tormek-t-7/
Motor: Industrial single phase, 200 W (input)
230 V, 50 Hz or 115 V, 60 Hz. Continuous duty, Maintenance free.
Silent running, 52 dB. 25,000 hour life

[Jan]

Yes Sharpen, it is an important issue. My good friend informed me about the duty type of T7 motors already in the autumn last year, but I did not care about it too much.
Only recently, during the discussion concerning the overheated Tyler's machine, I looked at the label of my T7 motor and found that it is ATB motor type name SRBF 0,18/4  - B41, equipped with a 4 microFarad capacitor, which is the duty type S6-40%.

[Jan]

Because the type name SRBF 0,18/4 – B41, 220-240 V is not uniquely defining the ATB motor I am attaching photo of the name plate from the motor.

[grepper]

So, the advertising is basically true:

S6: Continuous operation with intermittent load    
Sequential, identical cycles of running with constant load and running with no load. No rest periods.

I could be wrong, but I'm guessing that because it is only 4uF, that capacitor spec is for its run capacitor, not the start capacitor.

[Fineline]

I have heard that the newest T7 are equipped with motors of the duty type S6-40%. S6 means continuous-operation periodic duty. Duty cycle is usually 10 min.  Hence S6-40% means 4 min load and 6 min no–load. S6 should guarantee that there is no temperature rise when the motor is loaded at its rated output.

Hi Jan,
From your knowledge, is this change for the better or for the worse in terms of durability, reliability or performance?
If it is for the worse, it could be for cost reduction
Regardless, there should be a reason for the change but perhaps only Tormek knows.

[Jan]

Hi Grapper,
yes, S6 is continuous duty with no rest period.
The motor data sheet is not free available. We have to ask Tormek to make it available for us.

Hi Fineline,
the Continuous duty S1 is the best rating of a motor. All other duties, called periodic duties S2 – S10, are usually used to economize the size of the machine and yet meet the load demands.

[Fineline]

Thanks for your reply, Jan. 
Now I'm curious.
What type of motor was it for the older version; S1?

[Stickan]

The motor is rated at S6 – 60% duty which is defined in the EN60034-1 standard as 'Continuous-operation periodic duty'. This means a sequence of identical duty cycles, each cycle consisting of a time of operation at constant load and a time of operation at no-load. There is no time at rest and de-energized. Unless otherwise specified, the time for a duty cycle is 10mins.

Periodic duty implies that thermal equilibrium is not reached during the time on load.

As stated the motors are duty rated S6 60%. Therefore for S6 60% the motor can run 6 minutes under load followed by 4 minutes at no-load. I hope this explains things.

We have had the same motor since early 80`s.

Stig

[Jan]

Thank you Stig for your statement and clarification. 

1) I would like to ask you kindly, to provide this forum with data sheet for the T7 motors. This would enable us to consider some design questions and also to get details concerning temperature classification. Also the capacitor regime may be important, especially during the idle running.

2) My question is, why on the name plate from my T7 motor is indicated duty S6-40%.

Regards
Jan

[Stickan]

Jan,
1) Maybe a good idea, however, I don't think many of us thinks about it, if you are not an electrician. So personally, I don´t find it very important. We do give the information that is acquired from us. I will take it up for discussion though.

2) We have been using S6-40% motors since we started using motors in the early 80´s, and still are, the first Tormek models were driven by a drill back when we started in 1973. But I learned today that the S6-60% is a motor we recently started to use, along with S6-40% .

Stig