TRANSISTORIZED DIRECT CURRENT MOTOR CONTROL

Warren R . Sheets

THE DOW CHEMICAL COMPANY ROCKY FLATS DIVISION

P. 0 . BOX 888 GOLDEN, COLORADO 80401

U. S. ATOMIC ENERGY COMMISSION CONTRACT AT(29-1)-1106

DISCLAIMER

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September 10, 1968

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TRANSISTORIZED DIRECT CURRENT .

MOTOR CONTROL

Warren R . Sheets

THE DOW CHEMICAL COMPANY ROCKY FLATS DIVISION

p. 0 . BOX 888 GOLDEN, COLORADO 80401

U. S. ,ATOMIC ENERGY COMMISSION

. CONTRACT AT(29-1).11O6

RFP-iOOor UC-38 ENGINEERING

AND EQUIPMENT

TID-4500

RFP-10007

1

1.

1

1 '

.,

'I

ii

C O N T E N T S

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

. . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

. . Astable Multivibrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . : . ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Monostable Multivibrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Power Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

. RFP- 1000

A C K N O W L E D G M E N T S

For suggesting the problem, Douglas C . Hunt of the

Nuclear Safety Group i s gratefully acknowledged.

Appreciation . i s expressed a l so t 0 . D . E. Payne of the Instrument Shop for aid in installation and fabrication.

TRANSISTORIZED DIRECT CURRENT MOTOR CONTROL

Warren R . Sheets

Abstract. A t ransis tor ized direct current motor control i s descr ibed. T h e control h a s been ins ta l l ed on a n electric, platform-lift t ruck t o permit continuous speed adjustment of both the ho is t and t ravel motors. T h e control i s des igned t o supply a maximum of 350 amperes from a 12-volt bat tery t o a load cons i s t ing of a direct .current mulor and current-limiting resistor. T o a d j u s t the s p e e d of the two motors, potentiometers are used . T h e control c ircui t eff ic iency w a s found to exceed 8 0 percent.

INTRODUCTION

Trans i s to rs Q, and Q, perform th i s funct ion. A resistor-capacitor network located a t the base of Q, genera tes posi t ive and negat ive p u l s e s from the as tab le multivibrator s igna l . Only the posi t ive pu lses a re used t o operate the monostable multi- vibrator once e a c h period. .

Monostable Multivibrator: i

Transis tor Q,.is an emitter-follower and operates the nlonostable multivibrator with the posi t ive p u l s e s a s described.

T h e monostable multivibrator c o n s i s t s of T r a n s i s t o r s . The transis tor ized direct ,current (DC) motor control Q,, Q 5 , and Q,, and h a s a s t a b l e and quas i - s tab le operates on a duty-cycle principle. Current flow t o s t a t e . T h e time spen t in the quas i - s tab le s t a t e i s the motor i s interrupted by a n electronic switch with determined by the 0.05-microfarad capaci tor , the adjustable rat io of time on t o the time of one period. '

4700'-ohm res i s to r and the lOOK (K = 1 0 0 0 ohms) Thus , cont inuous control of motor speed i s permitted.

potentiometer connected between the em.itter.of .

An a s t a b l e multivibrator and a monostable m u l t i ~ vibrator define the rat io of on time t o to tal period time. T h e a s t a b l e multivibrator operates a t 1 0 0 Hertz (Hz), generat ing a period of 1 0 mil l iseconds. The monostable multivibrator permits ad jus t ing the

on time from 5 t o 9 5 percent of the period t ime. T h e adjustment i s performed with a smal l potentiometer.

, 1 l h e t rans i s to rs used in the driver and power-switch s e c t i o n s a r e operated in two modes, e i ther saturated or off, ensuring minimum power d i ss ipa t ion . T h e majority of power required by the motor control i s d i ss ipa ted in the base-bias r e s i s t o r s of the driver and the power-switch s e c t i o n s . When supplying power t o a load, the efficiency of the motor control circuit i s greater than 80 percent ( s e e T a b l e I).

CIRCUIT DETAIL

The motor control s y s t e m c o n s i s t s of four bas ic b locks , a s noted in Figure 1. E a c h a re explained individually, and a schemat ic diagram i s given in Figure 2.

Astable Multivibrator:

Trans i s to r Q,, and the b a s e of Trans i s to r Q , . It i s during the quasi-s table s t a t e that power i s appl ied to the motors. T h e power on time i s ad jus tab le from 5 t o 95 percent of the period time.

Trans i s to rs Q, and Q, form'an emitter-follower circuit with 1ow:output impedance.

T A B L E I . T y p i c a l Operating Data .

Average Percent T o t a l Power

of Load Current Input Power (pounds) (amperes) (watts ) - -

1.80 22 .

5' 80 { n n e c t e d 28.0 l s 2 186 343

Etf ic iency (percent)

Power Diss ipated

( P D ) (watts ) in Control

87 85' 81 8 7 86

' 82 9 0 8 7 83

An a s t a b l c multivibrator s e t s the operation frequency to 1 0 0 Hz , and therefore the period of one .cyc le i s 10 mil l iseconds.

NOTE: Battery-Terminal Voltage = 12.2 volts;

Powerdiss ipated Percent Eff ic iency = x 100.

" ~ ~ ~ i n p u t

FIGURE 1 . Block Diagram of Direct Current Motor Control.

12 volts BATTERY +

Driver:

CURRENT LIMITING

T r a n s i s t o r s Q, and Q,, del iver a 25-ampere current pu lse t o t h e power-switch s e c t i o n . T h e vo l tage pulse from T r a n s i s t o r Q, i s fed through a 22-ohm r e s i s t o r t o bias Il'rans,istor Q, on during the quasi- s t a b l e s t a t e of the monostable multivibrator.

rlllll POWER SWITCH

RESISTOR

- -

DRIVER 0 - -

T r a n s i s t o r s Q i and Q,, have a current ga in of npproximatcly 140 .

ASTABLE MULTIVIBRATOR

The power s w i t c h c o n s i s t s of s e v e n 60-ampere ra ted t rans i s to rs (Qll through Q,,), connected in paral le l . T h e 25-ampere current pu lse from T r a n s i s t o r Qlo s a t u r a t e s t h e s e t rans i s to rs and allows'maximum current flow t o the motor load during the q ~ i a s i - s t a b l e state'kif the monostable multivibrator. T h e average current (Iiv) suppl ied to the motor load i s determined by:

MONOSTABLE SPEED MULTIVIBRATOR CONTROL

Iaverage = Imcwimum x (G) Where,

I,,, = peak current . . t ' = time monostable vibrator 'is in

the quas i - s tab le s t a t e T = period of a s t a b l e multivibrator

T h e power output and s p e e d of the motor i s controlled by changing the duty cyc le ( t /T) of the monostable multivibrator. A current-limiting res i s to r used in the original control c ircui t i s re tained in the fina1,circuit.

Current through the load dur ing .OFF perinrls is less than 1 milliampere, A diode is nserl a c r o s s the ' l o id t o s t o p . a n y inductive back vol tage from damaging T r a n s i s ~ i w s Qll through Q,,.

CONCLUSION

T e s t s performed us ing different loads on the platform-

lift truck show complete control of both the t ravel and ho is t s p e e d s permitting safe' and smooth operat ions.

Table I g i v e s typical operating da ta for the sys tem. . T h e eff ic iency va lues given a re for the control unit only and d o not include motor l o s s c s . T h c c o s t s of the s y s t e m amounted to $130 for components and. for construct ion, a to ta l of 6 0 man-hours.

T h e lift t ruck i s now being used in t ransfer opera- tions which occur in the plutonium-metal c r i t i ca l ,

mass experiments . No contamination r e l e a s e a s a resul t of abrupt t rans fe rs h a s been experienced.

Transistors: Legend

Capacitors: Resistors: Q, - Q, 2N414 S - Solenoids 1 , 2 , e t c . '

Q, - Q. 2N1306 .P - Potentiometers 1 , 2 , e t c . u n i t s in microfarads (mf), Units in ohms (a), -"

- 2NJ055 F - F i e l d s (armature) u n l e s s noted otherwise. K = 1000 ohms. Q~,, - Q,, Mp504 RY - Relay ( c o i l s ) U n l e s s shown, resistors are

pf - picofarads, a s noted .0.5 watts ( W ) .

FIGURE 2 . Schematic Diagram of Direct Current Motor Control.