Help with Varipak 26758000 DC Drive

[allscott]

That's kind of the conclusion I am coming too. All of the numbers seem to add up, it just seems as though the motor isn't big enough for what he is trying to do.

Jacker, if you want I can find and or calculate how much torque that motor "should" be able to produce. If you happen to have a torque wrench we should be able to rig up some sort of means to see how much torque the motor is actually producing. Then you'll know for sure. I won't bother unless your interested.

 

[rsdoran]

.33HP should be 1ft-lb or 12in-lbs when running at 1750rpm.

Alot depends on the drive, if HP can remain constant then torque would increase as the motor slows i.e. a .33hp motor running at 875rpm would provide approximately 24in-lbs

 

[jacker]

Okay, here is more info:

Motor:
Reliance T56H1031AB-TU,
Type-TPR, 1/3 HP, 1725 RPM,
Cont. duty, 90V, 3.00A.
Motor connectors are A1, A2, P1, P2 and the latter two are identified as Thermal Protection and safed off/not being used.

Controller:
VARIPAK/CAMCO/KB ELECTRICS
PN 2675-8000 REV B DATE BL
1/5 - 1 HP
Input: 120V 50/60HZ 14A Max
Output 90V 10A Max

rsdoran - I owe you some more photos, I'll get the full board, back of cover, etc., shots up later today. This controller has KB's name on it.

input voltage - there was a factory label inside saying the unit is wired for 115V, markings on outside (see above) agree with that. Fuses on both input and output are 15A which is consistent with a 115V controller, no?

Have not tested the potentiometer. More on that in next post.

allscot - The DC motor says it is 1/3 HP, the AC motor it replaced was 1/2. My thinking was that the motor should be producing more power and enough for my needs. But the motor came used and might be suspect.

And I have some torque wrenches, give me an idea what I can do with them. I think I can measure from about 20 in/lbs up to 150 ft/lbs.

I've got a lot of experience on lathes, milling machines, drill presses, and the like and working mostly in metal. And experience with both AC and DC motors. This drill press, as it is now, falls way short of my experience and expectations for 1/3 HP AC or DC. It has a lot less power now than it did with the 1/2 HP Taiwanese AC motor that was removed.

If I have the wrong controller or motor or a bad controller or motor, I'd like to fix that and appreciate the help I'm getting here.

Jack

 

[rsdoran]

They are confusing with who builds what, this thing looks exactly like a Focus 1 (Emerson/Control Technology unit) http://www.emersonct.com/products_usa/focus1_frame.htm

I have looked at every DC drive manual they both offer though and have not come up with a match....YET.

BTW: http://www.camcoindex.com/varipak.htm

 

[jacker]

Whoops! I screwed that up! It is an Emerson made controller, *not* a KB electrics.

Jack

 

[milldrone]

If I have the wrong controller or motor or a bad controller or motor, I'd like to fix that and appreciate the help I'm getting here. Jack

IMHO
Because your controller will only output 55 volts, it is suspect. It should output 90 volts at full speed with a motor connected (light load). Also I believe your motor is too small, the bulk of variable speed controllers are constant torque devices so the torque remains constant throughout the RPM range. What is generally desired with a drill press is to have more torque at lower speed. The only way to achieve this is to have a very special drive (not recomended) or just oversize the drive to begin with. As I mentioned before I'm using an AC inverter. The pulleys are set up to give me 446 rpm at the spindle with 1750 rpm at the motor. This gives me all my torque below 500 RPM(right where I need it). Then as the motor goes overspeed (I use 240 hz as my top speed) the torque drops off. Yeah I know thats 7200 rpm at the motor (1740 RPM at the spindle) but my run time at that speed is less than 20 minutes a month. Sometimes I feel like shouting "MORE POWER! Arg! arg!" like Tim The Tool Man Taylor would.

 

[rsdoran]

Technically not sure you need a motor attached for testing. If you apply power, turn speed pot to 100%, and start it then 90v should be on A1-A2.

This is a DC drive but one thing to note, the reason it shows switches on the terminal is this is/was an indexer drive.

I have run into situations like this a few times. I think the key right now is to determine why you are not getting full output voltage. Not sure you will be happy with the 1/3HP unit even if you do get it running properly, especially if working with metal.

A few years back I automated a Mill, have too find my notes on it. I know we used a single phase in 3 phase out frequecy drive with a 2Hp motor (I think).

 

[allscott]

allscot - The DC motor says it is 1/3 HP, the AC motor it replaced was 1/2. My thinking was that the motor should be producing more power and enough for my needs. But the motor came used and might be suspect.

And I have some torque wrenches, give me an idea what I can do with them. I think I can measure from about 20 in/lbs up to 150 ft/lbs.

Jack

Your DC motor will produce approximately 33% less torque than the AC motor you removed assuming the AC motor was also a 4 pole 1750ish RPM unit. AC or DC it doesn't matter HP is a function of torque and speed, that's it.

Since you can stall the motor with your hand I was thinking of having you put the shaft of a bolt in your chuck. Put the torque wrench on the head and start the motor at 0 speed (I am also assuming if you turn the rheostat all the way down the motor doesn't turn).

Keep the motor stalled and turn the rheostat up, hopefully you have a "needle" style torque wrench and not a "click" kind. You will be measuring your spindle torque. Multiply that by the pulley ratio and you have the torque of the motor at the shaft. This isn't actually the rated torque it's the blocked rotor torque but at least it will give us an idea of what your motor is doing.

DISCLAIMER, DON'T BREAK YOUR ARM BLAH BLAH BLAH!, and don't keep it stalled for more than a few seconds, get a buddy to help etc....

 

[jacker]

allscott - I have a clicker torque wrench so I measured starting torque, not running, with reostat at 5 on 10 scale. The motor was peaking at 0.7A starting load yesterday and then settling back to a little over 0.5A running.

I started at 10 in/lbs and got clicks every time until I got up to about 45 in/lbs, then no more clicks. Did it three times and it was consistent. Hope that helps.

milldrone - I had a Linley jig borer for some years (think of a light but precise vertical mill) and used it in my gunsmithing business. It had a Dayton 1/2 HP DC motor and matching controller. It was 90V and drew 9.0 Amps max per the specs. With a 3:1 motor:spindle pulley setup it could pull chips in steel right down to stalling speeds with a six flute counterbore and do it absolutely chatter free (good lube, light feed). So I think I'd like to see how this motor (even though only 1/3 HP and 3.0A) works with 90V before I give up on it. I can and will play with the pulley ratios, I understand the joys of doing that, thanks for the input.

rsdoran - "..If you apply power, turn speed pot to 100%, and start it then 90v should be on A1-A2..."

That is what is happening except that I only get 55V. With the motor not attached, I get 53V and it slowly creeps up to 55V.

The photos - here is the front of the controller with the plastic cover removed from the heatshrink:

Here is the interior, cover open:

Here is the circuit board:

Tell me if you want closeups of any areas. The only trimpots are the IR COMP and MAX SPEED at right center. There is a moveable black wire HI or LO jumper above IR COMP. The wire can be moved to either pin. It is as I got it, on HI, I tried it on LO and it did not change anything.

The reostat in the right cover is marked "3533-0502 625-0338" and was checked with Ohmmeter. Using the center lug as the common and turning the knob, I get 0-4,700 Ohms on one side and 5,000-0 on the other. The two outer legs read open to each other.

Here are the sides of the bridge(?) thing on the back of the heat sink:

That is marked "Gentron PowerTherm 372004, 75030 010984-889". The six 1/4" male terminals on the Gentron are marked:
AC1 G1 -
AC2 G2 +

What next please. :>)

Jack

 

[milldrone]

I may be wrong, but this doesn't seem right.

Using the center lug as the common and turning the knob, I get 0-4,700 Ohms on one side and 5,000-0 on the other. The two outer legs read open to each other.

Do you feel comfortable with the power on and the pot exposed for testing? If you do, can you test the pot while the unit is running? test for DC voltage on the outside legs of the pot. Then test with the speed at the slowest setting one outside leg to the middle or wiper leg. We are looking for the outside leg to middle leg combination that gives us 0 volts at 0 speed. When you find the right pair then increase the speed to full and record the DC voltage.

 

[rsdoran]

The "bridge" thing is an SCR power module: http://www.nteinc.com/specs/5700to5799/NTE5700.html

The dial on the front is a potentiometer, which is a voltage divider while a rheostat (or using 2 terminals of a pot) makes it a variable resistor. http://en.wikipedia.org/wiki/Potentiometer

The center tap on a potentiometer should be the wiper and using an ohmmeter you should se the resistance vary as you described BUT the 2 outside posts should read the full resistance (ohms) of the potentiometer, in this case it appears to be 5k which is kind of standard. I also did not like the fact you did not get zero-5000 on the one side, that could mean the pot is weak and breaking down when in operation. These are cheap and if the watt rating matches you can get from Radio Shack.
http://www.radioshack.com/product/index.jsp?productId=2102789&cp=2032058.2032230.2032275&parentPage=family

With power disconnected naturally, test that pot again. Try turning it back and forth a few times (in case of rust) then test it throughly from center to both sides and between the 2 outside terminals.

If all that is good then it gets a little more difficult to find, it could be something on the board not properly triggering the SCR, the SCR could be bad, the on-board speed pot could be bad.

There are many things it could be, lets look at the obvious first.

 

[jacker]

milldrone - On the test you asked about, the center to right outside leg read 0.0 with the potentiometer set to "0", when I turn that to "10" the voltage read 7.8 Volts.

rsdoran - I did the readings on the pot again after running the up and down a few times.

With pot at "0", center to right leg is 0.002 Ohms, it goes to 4.69 kOhms with pot at "10".

With pot at "0", center to left leg is 5.05 kOhms, it goes to 0.002 Ohms with pot at "10".

The outer legs read 5.05 kOhms when the pot is at "0" and 4.69 kOhms when the pot is at "10".

Kind of makes me wonder if I made a mistake when I said it read open across the outside legs before.

So I'll check radio shack for that pot. The one that is on there is marked Clarostat but that brand name and the numbers on it (3533-0502 625-0338) do not come up at Mouser or anywhere that I can find. The Radio Shack pot is 1/2 Watt, maybe that's enough.

Jack

 

[milldrone]

Hmmm, sounds a little low!

when I turn that to "10" the voltage read 7.8 Volts.

Jacker, we also need the voltage on the two outside legs to compare with the voltage from the wiper reading. This way we can tell if the pot is bad.

 

[DickDV]

It is unlikely that the pot is bad if it reads 5K end to end and sweeps 0-5k as it is rotated.

More likely is a low power supply voltage across the pot end to end since there is only 7.8V max on the wiper.

Power up the drive and check the DC voltage across the ends of the pot. Check this voltage with the pot swung around to zero speed and also with the pot at max speed. A defect in the analog input fed by the pot could be loading down the power supply voltage as full speed but not at min speed.

 

[jacker]

"..we also need the voltage on the two outside legs to compare with the voltage from the wiper reading. This way we can tell if the pot is bad.."

Things appear to have changed again. Last night I got that 7.8V reading from the wiper to the right leg. And the motor would start, run, and and respond to pot changes in what looked like a normal manner.

But when I checked again a while ago there was 0VDC there with the pot at "0" and it stayed at 0VDC with the pot at "10". I checked that twice and am certain of the readings.

And the motor did not run with the pot in any position. That was different too.

And when I tried to check the voltage across the outside legs of the pot (Fluke 77 on VDC) it tripped the ground fault breaker on that leg of the garage wiring.

There was a slight noise out of the drill press as the breaker tripped, I think the motor got some momentary voltage as I touched the two outside legs and the breaker tripped.

With the controller disconnected from the line and off, the pot now reads a direct short from center to both legs and across the outside legs. It is a dead parrot for sure, no?

I'm going to disconnect that pot from the controller and see what readings I get from it. And then go to Radio Shack and see if they have that 5K pot.

The fuses in the controller survived through it all.

Jack