Old Okamoto Grinder 3Phase Switches

I am restoring this Okamoto OMA 350. I got it with the wiring removed. I have the manual with the wiring diagram and new normally open/normally closed push buttons.
However, I see no motor contactors for switching the three phase for the grinding wheel or the dust extractor. Nothing shows up on the wiring diagram... What am I missing???

It appears you are missing the contactor!

Welcome to the forum.

Stuart

There must be a more detailed schematic somewhere. Each motor requires a start contactor and a heater for thermal protection.

ewlsey said:

There must be a more detailed schematic somewhere. Each motor requires a start contactor and a heater for thermal protection.

Click to expand...

Not necessarily.

If the motor is under 1 HP, it can use a built-in thermal. The blower may be well under that.

If you look, the "switch" is actually a "manual motor starter", with overload protector. The additional motor etc can run from that line if motors are considerably smaller, and have their own internal overload.

OK. I've never seen a 3 phase motor with internal thermal protection. But, I guess I have not studied small 3 phase motors.

My 5hp 3 phase Marathon motor has a built in thermo switch. Set to be in series with LV contactor wiring, in this case wired to the VFD.

The diagram shows a manual push button contactor with heaters, No primary wiring. I had a Harig grinder wired the same way. I use the same on my air compressor, toggle 3phase switch with heaters. These type components are pricey new, ebay is where I buy that stuff. Often find NOS for fraction of new.

ewlsey said:

OK. I've never seen a 3 phase motor with internal thermal protection. But, I guess I have not studied small 3 phase motors.

Click to expand...

I have a 1 HP of that type. Therm-O-Disc overload in the wye point, easy, cheap..

O.K.

I contacted Okamoto Service in Illinois and this is what they said

"This is only a 200 v machine and does not use a contactor , power goes through the switch’s as it shows in the diagram."

I still don't get it... What does the forum think... Ever seen 3 Phase motors set up like this? If it's not clear, the push buttons are NOT ganged together.

It is a manual motor starter. Just like a contactor except you push the button. Provides overload etc. It's just how it works.... basically an "on" button to run it, no drama. Perfectly fine for that type machine.

3 Phase Manual Motor Starter

Here is a couple examples of an enclosed manual 3Φ motor starters. Similar to what your drawing shows.

3 Pole maintained contactor on the top and a 3 pole overload relay on the bottom.

The one in your drawing shows no overload relay section, as these examples do. Therefore your motors should contain their own thermal overload switch internally.

Square D 251 MCG3 Pushbutton Manual Motor Starter 1HP, 6VAC, 25VDC, 3-Pole | eBay



Allen Bradley Manual Motor Starter | eBay



And here's a manual operated, HP rated 3 pole, snap switch, that has no overload relay section.

Leviton MS33-DS 3 Amp 6 Volt, Three-Pole, Three Phase AC Motor Starter, Suitable as Motor Disconnect, Toggle, Industrial Grade, Non-Grounding, Black - Wall Light Switches - Amazon.com



SAF Ω

You are correct..... I did not look closely at the pic.... that's a stop button shown..... when I looked at the pic, I saw it as being the overload symbol..... Woops......

Yes, that explains the multi motors... they all have to have their own overloads.

Someone who knows old Okamoto grinders

I'm still at it.

I appreciate your responses.

You are showing me a lot of switches and telling me about a lot of switches that are NOT listed in the parts list
OR shown in the schematic. And am not wondering about the overheat... Just getting the thing to stay on when I press the start.

However.... Let me restate the problem.

There is a normally open/spring loaded start button.
There is a normally closed/spring loaded stop button.
There is NO contactor shown in the schematic.
Therefore... There is no way to seal-in the start circuit.

I assume that a contactor with an electromagnetic hold-in has to be used in this circuit.

Why does it not show up??

Does anyone know someone who has an Okamoto like this??
Can you take a look at it for me and see how the start circuit is held in until the stop button is pressed?

Let's restate the solution. As Okamoto told you.

In the original diagram, there is no contactor or spring loaded buttons. Because you received some buttons with the gutted machine controls, doesn't mean that that's what the diagram shows. All the diagram shows, is a manual motor starter with maintained start/stop with 3 pole contacts. There are no momentary pushbutton contacts or 3 pole contactor shown. Your just making the wrong assumption, likely because you have some momentary buttons on hand.

I showed you three types of manual maintained motor rated switches, two with maintained start stop buttons. The two shown with maintained buttons, happens to have an overload relay section, which your drawing does not include, but the manual starter is exactly what your diagram shows.

If you want to use the momentary buttons you have, then you need to provide your own contactor with an auxiliary contact for the seal in circuit and wire it in yourself. But that's not how the machine came from its maker, as they explained to you, and as the print shows.

Here is a diagram of some momentary buttons and a seal in circuit for the control connections.



SAF Ω

I just got a used Okamoto OMA-450 which I think is almost identical to the 350 but it is 6x18 instead of 6x12. I haven't got too far into it yet but I did push the start and stop buttons (no power applied). The start button does feel like a momentary contact button, but I think it does push in a set of contacts that are held in place while the button springs back. The stop button then releases the contacts and opens it's own contacts for redundancy to stop the grinder. I could be wrong but I'm pretty sure that is the way that start switch works.It would be very easy to check with an ohm meter without needing to take the switch apart.
I'll be using a VFD to run the one that I got but I may still use the original switch to send a start and stop command to the VFD.

I do have a question that I'm hoping someone here can answer. The oil pump is like nothing I've ever seen before, it is a solenoid valve with a spring loaded hollow plunger and check valve to pump the oil. The solenoid coil is bad on this pump so I ordered another pump but it has not arrived. My question is, shouldn't the power to the solenoid be pulsed in order for it to work? If you look at the diagram in post #1 it shows it connected to constant power which is how my OMA-450 is wired. I disassembled the one that I am replacing and the wires go straight to the coil, so it gets constant power.I'm assuming there must be something in the (plunger, check valve, and springs)that allow the plunger to cycle up and down with the coil under constant power. If anyone knows how they work please let me know.

Also to the OP Jericho, I don't have a manual for my grinder and I think your manual would be very close to being the right manual for my grinder.
If there is any way that I could get a copy please let me know, thanks.

Dwight

There is no “requirement” for a contactor or even an overload relay. The requirement is that the motor have a way to turn it on and off, and it needs protection. The protection can be in the form of integral thermal protection inside of the motor and at small HP sizes, that is absolutely possible. As JST said, it is often just a simple thermal disc (often called a “Klixon” for a common brand name) inside of the windings at the internal Wye point so if the motor overloads, it clicks open and disconnects power flow. I have seen them in up to 2HP but usually they are only offered at 1HP and under.

If the total HP is really low, as in the two motors totaling less than 1-1/2HP, it’s legally possible to use a pair of maintained Start-Stop push buttons. Some of the options are the market carry HP ratings so using 3 sets of contacts you can directly switch up to 1-1/2 HO at 230V 3 phase.

So. Ottom line it is entirely possible that the diagram shown is complete, so long as the components agree with these restrictions.

I got the manual on ebay for $59 from this guy.

Sylvester Ceramix
[email protected]

Jericho said:

I got the manual on ebay for $59 from this guy.

Sylvester Ceramix
[email protected]

Click to expand...

Thanks.

Dwight

Thanks.

Dwight