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hydraulic unit (full) keeps popping the overload on the mag switch

metalmagpie

Titanium
Joined
May 22, 2006
Location
Seattle
My grinder is a K.O. Lee S718HG from the late '70s. It gets occasional use. I'm doing a small job right now and right in the middle of it the hydraulic unit shut off like I'd turned off the switch. Eventually I figured out the mag switch and pushed the reset button on one of the heaters and everything worked again. However, this now keeps happening, about every 20 minutes. The fluid is between the min and max lines and is very clean - you can just barely see it on the stick. Note that I am not asking the hydraulic system to move anything - I'm cranking by hand because of the finicky nature of the job. I have to keep it running during manual operation, though, because it pumps fluid to the table ways for lubrication.

When the hydraulic unit is running it sounds normal to me.

Got any ideas what's going on?

metalmagpie
 
Assuming you've run this machine regularly in the past and this is a new development, first thing I'd do is to check the current on all 3 legs and see if there's an imbalance. If that is good, try swapping the heaters and see if the problem follows. If it moves to the new heater, be a good idea to check your motor for electrical leakage. If it follows the same heater, replace it.
 
Thanks, Mod. Good thinking.

There is a coolant pump whose power goes through the overload relays of the mag switch that controls the hydraulic unit. I got to wondering if maybe that coolant pump was drawing excessive power and essentially tripping the overload relay back in the hydraulic unit mag switch. So I ran the hydraulic system by itself, the coolant pump not even turned on. I came back to check some time later and it had popped the overload relay again even without the coolant pump. So for now I'm going to rule that pump out.

I'm not too sure about measuring current inline, but I certainly can swap overload relays. The overload relays have heaters bolted to them and they are literally little pieces of some kind of wire that heats up. I doubt there is anything wrong with the actual heater element - it's the overload relay I'm suspecting right now.

Time will tell.
 
Usually pretty easy to measure the current as long as you have a current clamp. If you don't have one, might be worth considering. Very handy item. Moving this to the electrical section to get some more eyes on it too.
 
You don't have to measure anything yet.
If the heater unit has a -85% - 115% knob you can adjust up a little.
That's all it would take. Same stuff happens here.
 
You don't have to measure anything yet.
If the heater unit has a -85% - 115% knob you can adjust up a little.
That's all it would take. Same stuff happens here.
I wish. Plain old Allen Bradley N21 heaters. On plain old AB 709 series mag switch.
 
I wish. Plain old Allen Bradley N21 heaters. On plain old AB 709 series mag switch.
The 20 minutes of operation means you are "Close to the edge, down by the river".
I have had power-off events after less than 5 minutes and just a small knob adjustment CW made it right.

Never taken apart a OL unit with a fine adjust knob. Wonder if it can be hacked on a OL like yours.
The OL units I looked at in the past did not have disassembly screws. Not made to take apart.


Notice the message about the contacts and not filing them.
I would debate about cleaning. Nothing wrong with clean.
 
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I wish. Plain old Allen Bradley N21 heaters. On plain old AB 709 series mag switch.
Post your two motor tags, and then we could tell what heater sizes would be correct for your application. Does your overload relay have two or three heater elements?
 
You are not stuck with the heater arrangement. Those can be changed or you can get
another OL that has an adjustment dial. I sure would like to know how that adjustment dial works.
It's just a potentiometer with no active components.
 
Are you running an RPC? How well balanced are the line voltages? I'm having the same problem on my Gorton mill after about an hour of run time, it also has an AB contactor and N21 heaters, just one heater trips. I have the artificial leg running thru center tap on contactor, but suspect problem is somehow related to artificial leg running high. Watching this thread in hopes of some insight to my problem.
 
Post your two motor tags, and then we could tell what heater sizes would be correct for your application. Does your overload relay have two or three heater elements?

The schematic shows three breaker/heater units, but the mag switch only has 2. The breaker units have little buttons that stick out. At the ends they are white and look like Ds. You can easily see there are only 2 installed:

ab709TOA.jpg


Here's the drive motor nameplate:

driveMotorNameplate.jpg


And the motor on the hydraulic unit itself:

hydMotorNameplate.jpg


I ordered a pair of the correct breakers. I will put my N21 heaters on them. The breakers are new. I am fervently hoping that solves the problem. I got down on the floor and started to swap the breakers to see if the problem moves with it or not, but gave up partway into it and put it back together. If I'm going to do all that work I'm going to put new ones in.

metalmagpie
 
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Are you running an RPC? How well balanced are the line voltages? I'm having the same problem on my Gorton mill after about an hour of run time, it also has an AB contactor and N21 heaters, just one heater trips. I have the artificial leg running thru center tap on contactor, but suspect problem is somehow related to artificial leg running high. Watching this thread in hopes of some insight to my problem.

I have line-to-line voltmeters in the cabinet of my rotary phase converter. The voltages aren't identical but they're good enough for the girls I run with. Also, they look just like they always have, nothing different here.

rpcGauges.jpg


I will let you know if replacing the breaker (not the N21 heater) fixes the problem because if mine went wonky yours may well have also.

metalmagpie
 
Is it a 1 Hp model like this?

See above, but in short, yes.

That vendor is fulla bulla. He claims that machine has hydraulic feeds on both X and Y. Funny it doesn't have the controls for those, then. (It doesn't have hydraulic feeds.) If it did have hydraulics then the table would be lubricated with hydraulic fluid like mine is so why have a one-shot lubricator? Also, he says the model is S718HG which would indicate hydraulic feeds but since they obviously aren't there and never were, that's the wrong model number. And KO Lee never made a surface grinder with max X travel of 19". The cigarette crushed out on the mag chuck (which isn't electromagnetic, by the way, it has a regular handle even if the lever is missing) is a real bad look.

Thanks for the chuckle. And the help!

metalmagpie
 
I wish. Plain old Allen Bradley N21 heaters. On plain old AB 709 series mag switch.
N21 heaters are rated at3.95A
You have two motors connected for a total of 7.46A
You need N28 Heaters rated at 7.63A
Your overload relay is doing what it is supposed to do and is working properly.
The heaters you have are only sized for one motor, not two.
I will post the chart for you and some additional details a little later tonight.

208V 1HP 3.26A 1.0SF
200V 3/4HP 4.2A 1.25SF
Your motors have lower voltage ratings than what your supplying, and different service factors.
I used the higher service factor numbers to be sure to eliminate nuisance tripping.
3.26A + 4.2A = 7.46 full load amps of both motors. That would cover the higher service factor motor.
 

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  • AB Type N Heater Element Tables.pdf
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I'd be awfully surprised if they were running both motors through one set of heaters...
metalmagpie
There is a coolant pump whose power goes through the overload relays of the mag switch that controls the hydraulic unit.

Two sets of motor leads on the starter, a fuller picture we would be able to tell better. But he has the heater table now, if he needs to select an alternate size, it would be best if he could measure the total load on the overload block since the motor nameplate ratings and the supplied voltage don't match.
20170203_124913.jpg
 
Unless I'm mistaken, the coolant pump's nameplate is not in the picture... It's probably very low fractional horsepower. Might be enough to push the heater over the limit, except for the test that he mentioned running...

When I commented about being surprised if they were running both motors through one set of heaters, I meant the depicted motors that you added the nameplate ratings together for, which I believe are hydraulic pump and spindle motor.
 
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Swap the heater advise is easy to do and you know after 20 minutes what it really is.

Swap the heater. See if the event follows the heater.
Swap the phase wires and account for the motor to reverse. Does the event happen on the same side?
 
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