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Monarch 10ee drive system - repair or replace ?

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Posted by Edson on January 09, 01 (from the WWWMachine Shop forum)

I have a fully tooled 1954 Monarch 10 EE toolroom lathe that has been sitting dormant in my shop for the past 12 years with serious dc motor control problems. The controller is of the tube variety (state of the ark.) Recently I have been motivated to get the old girl operational again. I am trying to locate a modern solid state unit which can replace the existing controller. Somebody must be making them as there are lot of 10EE's still in existence

Posted by Forrest Addy

Your Monarch EE has a Ward leonard drive. This is a very sophisticated electrical/mechanical control designed to produce a constant HP output from the DC motor shaft over a wide range of RPM - 700 (motor base RPM) to 2500 (max motor RPM) in the case of your EE.

Several regulars on HSM have considerable hands on experience getting their EE's up and running. Maybe they will sign on with their hard won experience.

You best bet is to get your existing control system to work.

If you were to replace your present control system with a solid state drive you'd need one which incorporates variable voltage from min motor RPM to motor base RPM and field weakening therafter to the motor's max rated RPM. Other required features include full plug reversibility, accel and decel control, dynamic braking, and motor overcurrent protection. These drives are not cheap and will likely have to be engineered for your application.

Caution: do not listen to anyone suggesting the use of a low cost DC drive designed for DC motors. Low cast DC drives do not incorporate field weakening nor will they provide full motor HP between base RPM and max RPM. If you cave in and purchase one of these drives, your EE will perform poorly expecially at low RPM developing very low torque.

I also reccommend against exchanging your DC motor for an AC motor VFD drive without major input from an EE with experience in constant HP machine tool spindle drives. If your motor is shot economics may force this option on you.

Do your research carefully, there are serveral options that appear plausible but are actually both expensive and unsatisfactory.

Posted by len

Forrest,

As usual, you provide the authorative answer, but I want to add my 2 cents.

If I couldn't get a replacement drive, which I agree is best, I would consider a PM DC motor and a good DC drive package. One reason the Monarch control is complicated is that shunt motors have little torque below about 500 RPM due to armature reaction. A PM DC motor has linear torque/speed characteristics down to zero speed. This means that your controller can be simpler.

As for constant power output, I would use speed feedback from the motor shaft and use either a regulated power supply or build a (fairly) simple PWM control circuit that used the feedback.

Posted by Forrest Addy

I dunno Len, I cant agree with your remarks. I hope I don't upset you by seeming to nitpick your posting but the following considerations are crutial to the legendary operability, speed, and power of the Monarch EE.

We agree that repairing the original drive would be best but parts and know-how may be scarce plus if there is a problem requiring rewind of the motor or MG set... that's a big and expensive problem.

"One reason the Monarch control is complicated is that shunt motors have little torque below about 500 RPM due to armature reaction."

- I've never had that problem. I've run shunt motors to zero RPM at full torque on a double dyno we used to test hydraulic variable pump/motor transmissions for replenshment at sea winches. This was a pure DC system.

A flux integrated PWM DC drive may pose torque problems due to armature reaction. I don't know. I'm not the smart on that aspect of the technology. I do know older technlogy 3 phase SCR drives run small and large DC motors from zip to full load everyday in the shop where I used to work.

"A PM DC motor has linear torque/speed characteristics down to zero speed."

- True

"This means that your controller can be simpler."

- False. A PM motor will not work in a constant HP regime because it's essentially constant torque. In a Ward Leonard drive the drive motor output HP is constant between base 700 RPM (full armature voltage and full field) and Max 2500 RPM (full armature voltage and fully weakened field). Motor torque is an inverse function of motor RPM in this regime.

"As for constant power output, I would use speed feedback from the motor shaft and use either a regulated power supply or build a (fairly) simple PWM control circuit that used the feedback."

- This isn't an issue of maintaining constant RPM. Are you suggesting a PM motor? Won't work. They're constant field/constant torque.

If you wished your PM motor to have 3 HP at 700 RPM at reduced voltage it would still have to be wound for 2500 RPM at full drive voltage meaning in order for the motor to develop 3 HP at 700 RPM the motor would have to develop X hp at full RPM or 700 RPM/3HP : 2500 RPM/X HP or X = 10.7 HP

If you used a DC drive on the stock motor, how would you manage the motor field current? A good variable power supply works wonderfully well from 0 RPM to motor base RPM but how would you get from 700 RPM to 2500 RPM? Variable field?

How about above 700 RPM base speed? Would you incorporate a field weakening power supply and interconnect their controls so the EE spindle motor varies smoothly from zip to max as in the Ward leonard drive? If so, that's a great way to duplicate the Ward/Leonard functionality. I've seen many DC planer drives modernized with well integrated solid state systematized components the same way.

In 1983 I watched while two very capable electricians who consulted with a Reliant DC drive expert and arrived at a plan of action. They gutted the drive from a Monarch EE which had a history of drive troubles. They installed a 3 HP PM motor and variable voltage drive that rendered the machine practically impotent. It would stall at 700 RPM in high gear by merely drilling a 1/2" hole in aluminum.

They had to go back to square one and engineer a wide range field weakening constant HP solid state drive with an expensive new wound field DC motor (they scrapped the old one).

Monarch installed the expensive Ward-Leonard drive in the EE for a good reason: wide ranging flexible power unattainable from a straight variable voltage DC drive which was widely available even at the time.
 








 
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