RS-50A / RS-50M / RM-50A / RM
Contents
1. 99 T ayol ving vot AQVL TGA IY ocr to 688 0 wee BY ssosos MSM ras ME ore rid T2ZEN2 zam 1010 7 153 1531 NE 03123195 39 Y 1172612 SOVUVIOUIIN SHOLID dv NY 2 WHO NI 4 39 MS O SHOISISSH 11 1 3104 3SIMY3HLO SS3INN 3 ase ase 022 A006 2 2 gt gt vor Page 142. rocker switch Transformer Astron 8401 Panel meter 0 15 Astron model 1 15 1mADC V130LA10A MOV 10 amp 130 volt GE Note Other manufacturer s equivalent capacitors and resistors with the same specifications may be substituted for those specified above Industry standard semiconductors from several manufacturers may be used for replacement Page 11 SECTION 6 PARALLEL 6 1 PARALLEL OPERATION Two units may be set up in parallel to double the current capacity by using the following procedure Connect the negative output terminals of two power supplies using 10 gauge or large wire depending on the distance between the units Connect the positive output terminals using the same gauge and same length wire The output voltage of each unit must be set to the same voltage Connect a wire from the red terminal marked FOR PARALLEL OPERATION ONLY on power supply A to the same red terminal on power supply B Connect the negative load to the negative output terminal of power supply A and connect the positive load to the positive output terminal of power supply B This will allow the power supplies to track and share the load equally Page 12 VOLTAGE REFERENCE BUFFER CURRENT SERIES PASS CIRCUIT OUTPUT OUTPUT SIMPLIFIED SCHEMATIC Page 13 9 5 08 59 VINHOJNTYO ANH SY 96 12 ILYA N oen de
3. to the power supply should the crowbar circuit trigger which will place a virtual short circuit across the battery The battery should be disconnected when servicing the power supply to prevent accidental shorting of the battery voltage Page 3 SECTION 2 CIRCUIT DESCRIPTIONS 2 1 LINE CIRCUIT AND RECTIFIERS Refer to RM 50M RS 50M Schematic on page 14 The 115 VAC line voltage is supplied to transformer 8401 via the 10 amp back panel mounted fuse F1 and front mounted switch SW1 When the switch is on the indicator lamp indicates the presence or absence of 115 VAC VR1 MOV provides protection against short duration high voltage line transients Diodes CR101 and CR102 in conjunction with capacitor C5 form a high current rectifier circuit for the power supply load CR1 CR2 and C1 provide DC voltage for the voltage regulator crowbar and series pass drive circuits CR6 provides over voltage protection for the regulator CR7 protects the power transistors against over voltage when power is turned off and an external battery is connected across the load 2 2 SERIES PASS POWER CIRCUIT The series pass power circuit is made up of two banks of four 2N3771 transistors operating in parallel as illustrated in the circuit showing Q101 and Q102 Resistors R101 R102 are provided in the emitter circuits for balancing the load among the eight transistors CR7 provides protection against reverse voltage across the transistors Q109 provides b
4. ASTRON CORPORATION SERVICE MANUAL FOR RM 50A RM 50M RS 50A RS 50M Originally had a 2009 schematic that did not match the parts list Transcribed and updated by Robert W Meister WA1MIK August 2015 ASTRON CORPORATION 9 AUTRY IRVINE CA 92618 PH 949 458 7277 FAX 949 458 0826 SECTION 1 GENERAL INFORMATION 1 1 INTRODUCTION The ASTRON 50 series are heavy duty power supplies capable of supplying 37 amps continuous at 13 8 VDC from 115 VAC line voltage The output voltage is adjustable from approximately 11 15 VDC These supplies are protected against overload and short circuits by fold back current limiting The load is protected against over voltage by a crowbar circuit which initiates latched current limiting upon over voltage dropping the output voltage to a safe level The RS 50A and 50 are identical to the RS 50M and RM 50M except the A models do not have meters Two meters on the RM 50M and RS 50M front panel provide measurement of voltage and current being supplied to the load The current meter is calibrated for 0 50 amps and the voltmeter reads 0 15 VDC The power switch on the front panel controls AC power to the supply and indicates the presence of AC power when in the ON position AC line surge protection is provided internally and a 10 amp AC line fuse is accessible at the rear panel Page 1 1 2 SPECIFICATIONS Input Output Voltage factory adjust Current Ripple Regulation Ove
5. Q1 while the voltage at the base of the transistor is determined by the voltage divider R8 and R10 As the output voltage increases the voltage at the emitter of Q1 increases by the same amount while the base voltage increases according to the ratio of R8 and R10 At 16 5 volts the base becomes more negative than the emitter to the extent that Q1 conducts producing a voltage across R11 sufficient to trigger SCR1 When triggered SCR1 acts as a virtual short circuit causing current limiting and subsequent low voltage output Once triggered on the SCR will continue to conduct until power is turned off Capacitors C6 and C102 in the gate circuit of SCR1 prevent false triggering from voltage transients Page 6 2 5 METER CIRCUITS The current meter uses R102 as a meter shunt for measuring relative current Although only one eighth of the current is measured the meter is calibrated at full load by adjustment of R103 and therefore accurately indicates the full load current The voltmeter is calibrated by R104 after setting the supply output voltage to 13 8 VDC with a calibrated external meter SECTION 3 INSTALLATION 3 1 GENERAL The RM 50A RM 50M is supplied in a rack mount configuration and may be mounted in any standard 19 rack mount cabinet with suitable ventilation The power supply generates appreciable heat when operated at full load and requires an adequate airflow for cooling It should always be mounted with adequate clearance ab
6. ase current drive to the eight series pass transistors It in turn is driven by the voltage regulator circuitry contained on the PC board Page 4 2 3 VOLTAGE REGULATOR The uA723 LM723 1 in conjunction with associated circuitry performs the function of voltage regulator fold back current limiting and provides drive current for the series pass circuit See manufacturer s data book for details on the internal operation of the uA723 LM723 Refer to Simplified schematic on page 13 Voltage regulation is accomplished within the IC by comparing the scaled down supply output voltage from the wiper of R5 to an internal 7 2 volt reference voltage The reference voltage pin 6 is connected to the non inverting input pin 5 of an internal op amp The scaled down power supply voltage from R5 is connected to the op amp inverting input pin 2 providing negative feedback If the power supply output voltage attempts to change the IC output at pin 10 changes in the opposite direction thus maintaining the output voltage constant for a given setting of R5 The IC internal op amp maintains null between its two inputs i e the inverting input through negative feedback is maintained equal to the 7 2 volt reference Therefore the output supply voltage will go up or down to accommodate a change in the setting of R5 This allows the output voltage to be adjusted to any value between 11 and 15 volts with the voltage division ratio provide
7. d by the combination of R5 R6 and R7 The current from the 723 IC is amplified by Q2 and applied to the base of the 2N3771 series pass drive transistor As noted in the voltage chart on the schematic the regulator output voltage increases as power supply loading increases to compensate for the increased voltage drop across R1 R1X and the series pass circuit Page 5 At full load the voltage at the current limit input of the IC pin 2 is around 14 volts as determined by the ratio of R4 and R3 R3X which sets the point at which current limiting begins As the load is increase above full load the differential between pins 2 and 3 current sense input increases until the internal current sense transistor begins to conduct at 52 amps factory set by R3X Fold back current limiting then occurs and the load current and output voltage decrease with decreasing load resistance until the short circuit current of 4 amps is reached The short circuit current is factory set by selecting the value of resistor R1X Diodes CR3 and CR6 prevent damage to the circuits by capacitive discharge or an external battery when power is turned off CR4 stabilizes current in the limiting mode preventing overheating due to current drift 2 4 CROWBAR CIRCUIT The power supply load is protected from over voltage by the crowbar circuit which triggers at 16 5 volts Zener diode CR4 maintains a voltage 5 6 volts lower than the power supply voltage at the emitter of
8. d in the following sections 4 3 1 TEST EQUIPMENT REQUIRED Voltmeter DC 0 25 volts sensitivity min 20K ohms volt Ammeter DC 0 100 amps Variable load 0 100 ohms rated at 70 amps minimum 4 3 2 OUTPUT VOLTAGE R5 controls the output voltage and may be adjusted to set it to exactly 13 8 volts If calibration of the front panel meter is suspect use a known accurate voltmeter for this adjustment then calibrate the front panel meter by adjusting R104 Page 8 4 3 3 OUTPUT CURRENT Output current at rated load may be checked by connecting the ammeter in series with the load and adjusting the load for 37 amps If the panel mounted current meter does not read 37 amps it may be recalibrated by adjusting R103 4 3 4 FOLD BACK CURRENT To check the fold back current limiting point connect the load to the output and adjust for 52 amps Decreasing the resistance of the load should cause current to begin decreasing to 4 amps when the load reaches zero resistance Resistor R3 in parallel with R3X factory selected determines the current limit point i e the point where fold back begins Resistor R1 in parallel with R1X determines the short circuit limit of 4 amps In the event of component replacement it may be necessary to change the values of R3X and R1X to reset these currents to design limits Increasing the value of either network decreases their respective current values 4 3 5 CROWBAR VOLTAGE To test for proper operation of th
9. e crowbar circuit momentarily short across resistor R7 This causes the output voltage to rise to approximately 17 volts and should trigger the crowbar circuit Page 9 4 4 TROUBLESHOOTING Refer to RM 50M RS 50M Schematic on page 14 Remove the top cover to gain access to the inside of the power supply and check for proper operation of the transformer primary and secondary circuits including the power rectifier circuit CR101 CR102 and capacitor C5 large chassis mounted electrolytic capacitors A check of voltage present at the I O pins of IC A1 uA723 LM723 voltage regulator as compared to the A1 voltage chart shown on the schematic should provide an indication of the nature of the problem If the voltage regulator is suspect it can be replaced by removing the two PC board mounting screws and replacing the IC in the socket provided Since the heat sink mounted series pass power transistors operate at high junction temperatures a failure in this area is most probable Junctions may be checked for shorts or opens by disconnecting one end of the 0 05 ohm balancing resistors R101 R102 in their emitter circuits Note that due to the use of R102 as a meter shunt to measure relative current rather than absolute current a failure of Q102 will cause false current readings An open series pass transistor may not be apparent in terms of the current reading but may be detected by a significant drop in its case temperature A shorted transis
10. ove and below to provide convective cooling Forced air cooling may be required if other equipment generating relatively high levels of heat is enclosed in the came cabinet DC output wiring should be of sufficient gauge to carry the current without excessive voltage drop CAUTION If a battery is used for standby operation and is connected directly across the power supply output always connect a fuse and a blocking diode between the power supply and the battery Failure to follow this practice could result in battery destruction and or damage to the power supply should the crowbar circuit trigger which will place a virtual short circuit across the battery The battery should be disconnected when servicing the power supply to prevent accidental shorting of the battery voltage Page 7 SECTION 4 SERVICING 4 1 1 PRECAUTIONS See Section 1 3 4 1 2 TECHNICAL BULLETINS From time to time Technical Bulletins may be issued to enable updating of equipment provide information or to meet specific operational requirements 4 2 MECHANICAL Access to the inside of the power supply for servicing may be obtained by removing the six screws holding the top lid in place 4 3 TEST AND ADJUSTMENT All power supply parameters previously defined are factory adjusted and normally will not require field adjustment However if certain components are replaced or a malfunction is suspected it may be necessary to perform test and adjustment as define
11. rload Protection Current limit Fold back current Over voltage Protection Operating Temperature Range Dimensions Height Depth Width Weight Chassis Type 105 125 VAC 60 Hz 13 8 VDC 0 05 volts 37 amps continuous 50 amps ICS 5 mv maximum full load low line 0 5 over load and line ranges 55 amps 4 amps 16 5 VDC 10 to 40 deg C for rated output RM 50A RM 50M RS 50A RS 50M 5 25 inches 6 00 inches 12 5 inches 13 5 inches 19 0 inches 11 0 inches 50 pounds 46 pounds Rack Mount Desk Top Page 2 1 3 PRECAUTIONS WARNING HAZARDOUS VOLTAGES The RM 50M RS 50M contains voltages that may be lethal The case of the supply should not be removed without first disconnecting the AC supply Servicing should be done only by qualified technicians CAUTION HANDLE WITH CARE The weight of the RM 50M is 50 Ibs so care is needed when removing it from the rack mount CAUTION HEAT SINK TEMPERATURE Under some conditions the power supply heat sinks may reach high temperatures Handle with extreme care after prolonged operation CAUTION VENTILATION Do not operate this power supply in a concealed cabinet CAUTION EXTERNAL BATTERY FUSING If a battery is used for standby operation and is connected directly across the power supply output always connect a fuse and a blocking diode between the power supply and the battery Failure to follow this practice could result in battery destruction and or damage
12. tor will cause either current limiting or crowbar triggering SECTION 5 PARTS LIST Editor s Note Some of the parts have been replaced as the power supplies went through design revisions The parts list below closely matches the 1996 schematic at the end of this file but think the manual was written prior to 1990 The schematic that originally came with the file was dated 2009 Page 10 Designation CR1 CR2 CR101 CR102 CR3 CR4 CR5 CR6 CR7 Q101 Q109 Q2 R101 R108 R113 R114 R115 R5 RXXX SCR1 SWw1 T1 VM VR1 Description LM723CN voltage regulator TI Motorola 2 200 uF 35V radial electrolytic capacitor 2 200 uF 16V electrolytic capacitor 0 33 uF 50V ceramic capacitor 0 1 uF 50V capacitor 0 001uF 100V capacitor 100 uF 25V electrolytic capacitor 50 000 uF 25V computer grade electrolytic cap 1N5404 rectifier diode 1N1184A rectifier diode 40 amp 100 volt 1N4148 small signal diode 1N5232B zener diode 1N4002 diode 1 amp 100 volt P6KE39A 39 volt 600 watt transient suppressor MR751 rectifier diode 6 amp 100 volt 10 amp 250 volt MDL fuse should be 12 amp Panel meter 0 50 Astron model 1 50 1mADC 2N3906 PNP transistor 2N3771 NPN transistor 30 amp 40 volt TIP29 NPN transistor Motorola 0 05 ohm 5W wire wound 4 7 ohm 2W 500 ohm 0 5W pot 1T 20k 0 5W pot 1T 1k 0 5W pot 1T All other resistors 0 5W 5 CF SO565J 50 amp 50 volt SCR LRA211RSB 125N illuminated AC
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