Need imput on stalling...

[Dave W]

First off I have a Jet 1642 1.5 hp, not the American Beauty I dream of.

Now to cover the usual suspects: Tools sharp √, Voltage consistent √, Belt in low and tensioned properly √, understanding of basic woodturning principals √, sanity 😱


Lately when I have a bowl blank lets say 15 x 4, I've been having issues with getting bigger cuts done. With the belt on the low side and trying to take a cut of 1/4", I'm seeing a drop in rpm of 50-200 rev's or more. When trying to take a 3/8-1/2" cut I am capable of bringing the wood to a total stop real quick. This isn't with much force on my behalf. I should mention this happens with both really green or dry wood. When I first purchased the lathe all of these cuts were achievable, unless I fed the gouge to fast. It's like I'm loosing the torque in the motor. I've watched through the door, and it appears that the motor is actually stopping, not just the belt slipping.

Another issue that has come up in the past week is with the power switch. I'll be turning (whatever) and hit the switch to bring things to a stop. And then when I pull the switch back on some times it starts, some times it does not. Yesterday I had a couple times where it took 3 or 4 pulls to get it to kick in.

One thing I decided to do is check the parameter settings of the vfd with the manual. Just check, no code entered. I discovered something interesting in the motor parameters. Under Pr. 7-00, Motor Rated Current the manual says the factory setting is d.85. On my lathe it is showing d.120. My understanding is that this is the percentage of power the motor is running at (correct me if I am wrong). I naturally suspect that if this is the correct setting, I may have done damage to the motor by running it at 120% for the past 2 years. I did call Jet, and I am awaiting a return call. It seems they don't know how to change the parameters, let alone which setting is the correct one.

So the questions be, has anyone else with the Jet 1642 1.5 hp run into anything similar with this lathe, or do you have any input to my dilemma?

 

[Bill Boehme]

I think that perhaps you are confusing rated current with service factor. Rated current is stamped on the nameplate and is the maximum full load current. The rating will appear in the box labeled "FLC". For most general purpose TEFC AC induction motors that have been manufactured in the last couple years, the SF is typically 1.0 to 1.15. Service factor basically is a rating that says how long that the motor can be operated above its rated load torque without significantly shortening its life.

I think that the number that you are reading as "d.85" may actually be "6.85". You could check the motor nameplate to see what the FLC says. It is possible that the no-load current may be about 6.12 Amps, but you do not normally find that on the nameplate.

It is hard to diagnose problems long-distance, but some of the things you describe sound like a failing motor. I do not know about Jet, but I do know that some lathes with VFD drives use motors that are not rated for inverter duty. Sometimes the nameplate will say so and sometimes you can go to the motor manufacturer website to find out if it is an American made motor, If it is from a Pacific Rim country, then you may not be able to find out anything about it. However, you can check the insulation class listed on the nameplate and if it says "F" or "H" then it would most likely be rated for inverter duty. If it says "B", then maybe not although some US made motors with an insulation class rating of B or B4 can be used for inverter duty under certain limited conditions.

Generally, lathe operation is not a heavy duty full load condition for a motor, but I suppose that it could be if relentlessly pushing the motor to its limits for extended periods of time without letting the motor cool down. Has the motor ever gotten really hot when used? Just to humor me, could you confirm that the belt is on the large spindle pulley and the small motor pulley?

Without getting into the technical nitty-gritty, inverters (VFD's) synthesize three phase AC output with a scheme called pulse-width modulation. An unavoidable byproduct of this scheme is that there is a lot of "hash" (or high amplitude, high frequency power line noise) also created. This hash can have voltage spikes of well over a thousand volts -- sufficient to punch through the enamel insulation on normal motor winding wires. If this happens, the motor performance will experience an insidious gradual degradation in output performance that may take years before it becomes apparent. I suspect that this could be your problem, but this is just a guess and may not be the case at all.

If it turns out to be a bad motor, you might consider biting the bullet and getting a higher quality motor rated for inverter duty, but be prepared for sticker shock. Of course, Robust is standing by waiting for your order. 😀

The best thing to do at this point is to contact Jet support and ask about the VFD parameter settings. Whether your style of turning had anything to do with the problem is something that would be very hard to say and besides knowing that isn't going to fix the problem at hand. FWIW, it is probably better to finesse the cuts rather than a full frontal assault. At least, that is my philosophy, but your mileage may vary. All of the above is just my humble opinion and not warranted to be for for any useful purpose.

 

[Dave W]

Bill,

The d stands for decimal in everything I have read. This is straight from the manual.



Even though I've been doing this for 7 or 8 years, I'll humor you 🙂



And it looks like Taiwan is the winner.



The only time I get aggressive is when I'm hogging down a bowl blank. Keep in mind I start them all out round off the band saw.

I know about the cost of a new motor. I had given thought of taking it and the inverter to a larger point a few months ago. If anything, I'd rather put it towards the next lathe.

 

[Bill Boehme]

Thanks for the information, Dave. It appears that the way that the inverter is set up, the motor current parameter is a setting for the maximum percentage of the FLA of the motor, so that 120% would allow it to be operated at over the normal FLA. Most newer design motors allow operation up to 115% of the rated current. This implies that there is another setting that gives the exact current rating, but it might not be on a user accessible menu. The letter "d" doesn't stand for decimal -- see page 4-2 of the inverter manual, when the letter "d" appears in the display, it is showing the actual stored value of the selected parameter.

I'm glad that you humored me by taking a picture of the drive belt. 😉

Earlier I had calculated the approximate FLA for a 1.5 HP motor so that is why I thought that the FLA was in the neighborhood of 6.5 Amps. I was somewhat startled to see the picture of the nameplate where it shows a FLA of 4.6 Amps and a mechanical output power of 1.5 HP. This means that the motor has to be more than 100% efficient, making power out of thin air. 😀 I am appalled that importers are able to get away with such stuff when they are supposed to be in compliance with the same standards that US manufacturers must meet.

Here is how to get a close approximation of output power:

• Multiply voltage by FLA current to get the input power. 230 X 4.6 = 1058 watts
• Multiply the input power by the motor efficiency. For new motors that must meet high efficiency requirements, efficiency would be about 82% to 88%, so 85% would be a good average. The Jet motor is not marked s being high efficiency so it probably has an efficiency of 68% to 75%. Let's be generous and assume that it is 75% efficient. This gives us 1058 X 0.75 = 793.5 watts output mechanical power.
• In the US, we use Horsepower rather than watts. One horsepower is 746 watts, so 793.5 / 746 = 1.064 HP, if we are lucky.

So there you have it -- your 1.5 HP motor has suddenly been demoted to one horsepower. Sorry about the demotion. Maybe they were counting on operating the motor at 120% service factor to make up for the shortfall in output power. However, that still leaves the motor quite a bit short of 1.5 HP output power and it is being rather dishonest in claiming a nonexistent service factor as justification for a claimed output power. Well, all this is besides the point. The real question is what is wrong with the motor. My suspicion is that it is dying and that nothing has changed with the inverter unless they had it programmed to drive a real 1.5 HP motor. Since the motor was built three years ago, maybe it is still in warranty or maybe they will replace it anyway. Wouldn't hurt to twist their tail about it anyway.

 

[Bill Boehme]

A couple more thoughts. Check the bearings for friction. Remove the drive belt and see if the spindle turns freely and quietly. Do the same with the motor shaft.

Also, check the model number of the inverter. Does it start with VFD007S11 or VFD015S11. Check for any loose wires from the inverter to the motor or to the switches and pot. The starting thing could be a bad switch. I noticed that the lathe has a five year warranty.

 

[robo hippy]

Well, I don't know about all the electrical engineering, but if it doesn't cut like it used to, and it isn't the belt, then it could be problems with the motor. I did turn on one of those a few times, and found it to be kind of whimpy compared to my old PM3520A and my Robust. Stalling a 15 inch diameter blank isn't difficult, well, at least not for me.

robo hippy

 

[Dave W]

Reed,

I agree it's a bit whimpy for the bigger stuff, great for the spindle work. I know I've improved over the years, but my approach to shaping out a bowl has not changed much. I don't know how else to put it, I just don't feel like it has all the torque it once use to. In all my searching of the net, I've come across a couple threads, mind you years ago, where there were complaints of the same issue. They ended up having a new motor shipped under warranty. I'm still waiting for a call back from Jet.

As far as the parameters of the VFD, There is some talk out there on the powermatic's, but not much when it comes to the Jet. My curiosity is mainly about the Motor Rated Current and why the huge difference between the manual and the actual setting in the VFD. If it's suppose to be d.120 then I leave it where it is, but if in fact it's suppose to be d.85 I want to change it. Also knowing if running at d.120 has had any chance of doing damage or not, would be helpful.


Bill,

Bearings all appear to be good. VFD: VFD007S11A Haven't gotten to the wires as of yet. I'll be looking at them soon.

 

[Bill Boehme]

Bill,

Bearings all appear to be good. VFD: VFD007S11A Haven't gotten to the wires as of yet. I'll be looking at them soon.

Aha, as I suspected. That model VFD is a 1 HP model ... to match the 1 HP motor that Jet advertizes as 1.5 HP. I don't doubt what you say about performance decreasing, but as Reed suggests, heavy cuts on a 15" diameter bowl can slow down the motor.

Sounds like it is time to start saving up for a Robust AB. 😀

 

[Odie]

An alternative thought.......

I have a 1 1/2 hp Leeson motor on my 16" Woodfast lathe with Minarak controller. It's fairly easy to bog down a large bowl when taking big cuts.....

.......but, how much time is really saved by the necessity of taking smaller cuts in the long run? 10 minutes?

What I've found is shallower cuts generally lead to a higher quality of the cut......a finer cut, with a better curve. Maybe it's not the physics involved with the tool acting with the wood, but the ability of my physical body to move the cut in a controlled fashion.......? This observation has led me to take my time a little more on smaller bowls where I really don't have to take smaller cuts.......I just choose to!

Anyway, it just seems to lead to better things by concentrating on how well the cut is controlled.......rather than how much wood can be removed. This could als be seen as enhancing the ability to contemplate what you are doing, before you no longer have choices........:cool2:

ooc