How To Wire A Universal Motor For Reversing (switches)

[JimDawson]

When I get out to the shop today I'll dig out a schematic of the switching for a universal motor, it's different (and a little more complex) than a brushed DC motor. I did this for the power draw bar on Alloy's Shizouka. The problem I see is that an instant reverse at the end of stroke. The table needs to accel, run at speed, then decel to a stop before reversing. This could be accomplished, sort of, by setting a delay before reversing, at least allowing the motor to coast to a stop before switching direction. It's going to take a little electrical hardware the get it right.

An air cylinder would work pretty well since it is ''squishy'' on the start and stop, and could be well controlled by another dampening cylinder that is filled with light oil.

I am going to do the same thing and have been scrounging parts for some time. I have the parts on the shelf now, but I haven't had time for that project yet. Hydraulics work but I hate hydraulics. My DoAll is all hydraulic and that hardware is going to be removed and servo control installed.

 

[bvd1940]

I'm leaning towards a hydraulic or pneumatic cylinder I have one with about a 3/4" bore, but it's only a foot or so stroke. Not sure about the effect, if any, on the reciprocating action of the table. Mine has plain vee ways, so I'm wondering about where to do the mount, and if it will try to twist or lift the table. If I can get it all worked out, I can have variable length and speed. I'll get a longer cylinder if I get that far. I've thought about using a sprocket on the handwheel shaft tied to the cylinder by a #35 chain or so.....and an extension spring on the "free end" of the chain to anchor it.

Too many ways to approach it.

Now that chain and cylinder is food for thought, with a flow control and a soft stop/reverse that should work good but you still need hyd/air to run it.

 

[bvd1940]

I would think that you are fine at typical milling speeds. If you are doing a rapid traverse, just pop the switch to the center off position until the table stops and then reverse. I used a transistor switched control and early in its life, I did flip the switch under full power and blew the transistors. Since then, I make it a practice to only switch at low power and have not blown a transistor in twenty five years. Here are some possible candidates for your switch.
http://www.digikey.com/product-search/en?pv783=247&pv783=263&pv783=382&pv783=239&pv783=238&pv783=400&pv783=262&pv783=219&FV=fff40011,fff80064,2080004,3ac0003&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

Bob

This is not a mill it is a surface grinder and I just need about 13 inches of travel at a very low speed, the switch will need to be tripped by the table ,s back and forth movement unattended. I may have to go to steppers but did not want all the extra electronics +$$ and programming.

 

[bvd1940]

When I get out to the shop today I'll dig out a schematic of the switching for a universal motor, it's different (and a little more complex) than a brushed DC motor. I did this for the power draw bar on Alloy's Shizouka. The problem I see is that an instant reverse at the end of stroke. The table needs to accel, run at speed, then decel to a stop before reversing. This could be accomplished, sort of, by setting a delay before reversing, at least allowing the motor to coast to a stop before switching direction. It's going to take a little electrical hardware the get it right.

An air cylinder would work pretty well since it is ''squishy'' on the start and stop, and could be well controlled by another dampening cylinder that is filled with light oil.

I am going to do the same thing and have been scrounging parts for some time. I have the parts on the shelf now, but I haven't had time for that project yet. Hydraulics work but I hate hydraulics. My DoAll is all hydraulic and that hardware is going to be removed and servo control installed.

I appreciate any help with this as I am feed up running the table by hand, I can put a fine tooth pawl on cross feed then very little arm movement will be involved. Also do like they do on my shaper for down feed. (dream on old fool)
Thanks to all for imput as you are making my gray cells wake up
I will take a pic of the motor mounted on the grinder & you will see why I would like to use this setup.

 

[bvd1940]

Well here ar the pics of the Mtr and mount, see if that helps.

 

[JimDawson]

I found the schematic I was looking for, I'm trying to simplify it now. If I posted it as it is, it would just confuse the issue. I did find this name plate diagram on line so a good starting point. I needed to confirm that it is wired the way I thought is was.

 

[bvd1940]

I found the schematic I was looking for, I'm trying to simplify it now. If I posted it as it is, it would just confuse the issue. I did find this name plate diagram on line so a good starting point. I needed to confirm that it is wired the way I thought is was.

View attachment 115957

that is the setup I have just need to know what type switch to use to have the table trip it both ways for reversing the mtr.

 

[British Steel]

Dual-pole, Dual-throw, rated well above the motor current, no "centre-off" position - that should do it.
If you were very keen you could use a contactor or two so the switch wasn't handling the motor current (just the contactor coil current), but with such a small motor? not a lot of point IMHO. If you're using a DC feed to the motor, it's a lot harder for the contacts and I'd go with a contactor.

Remember you need to maintain the field current AT ALL TIMES, reversing-switch the armature (brush) current! And a Main Switch that feeds both the field and the reversing switch when the work's done...

Dave H. (the other one)

 

[John Hasler]

Remember you need to maintain the field current AT ALL TIMES, reversing-switch the armature (brush) current!

It's a series motor.

I'd use a couple of microswitches and a latching relay. The relay would need DPDT contacts plus an NO contact for latching.

 

[bvd1940]

Dual-pole, Dual-throw, rated well above the motor current, no "centre-off" position - that should do it.
If you were very keen you could use a contactor or two so the switch wasn't handling the motor current (just the contactor coil current), but with such a small motor? not a lot of point IMHO. If you're using a DC feed to the motor, it's a lot harder for the contacts and I'd go with a contactor.

Remember you need to maintain the field current AT ALL TIMES, reversing-switch the armature (brush) current! And a Main Switch that feeds both the field and the reversing switch when the work's done...

Dave H. (the other one)

hope to use 115 volt AC trough a speed controller.