DC Motor Drive 2 - Construction

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Motors and Drives

This page is intended as a construction guide for the DC Drive Kit on DIYAudio.com .

It will be progressively updated as I work through the construction of the actual kit.

Firstly, here are the circuits for the final version of the controller board and the adjustment board.

Controller Circuit, click for full size

 

 

Adjustment circuit.

 

Controller layout - this is the actual silkscreen for the board house.

 

 

Adjustment board

First the errors: The switch S1 is shown as pads due to limitations in the layout software. Unfortunately these pads are smaller than expected so the switch does not fit very well. The holes should not be redrilled as this destroys the through plating. They can be slotted with a 1mm drill or the pins on the switch can be reduced. I did this by cutting them at a shallow angle with a pair of snips.

The L200 is shown as the vertical version (L200CV) as that's what the software had.The connector X6 was drafted in reverse so it and X3 must be wired so they reverse polarity.

I have drafted in two sets of adjustment potentiometers - one pair (VR2, VR3) are 3/4 inch horizontal multiturn types which would be accessible through holes in the front panel (this is what will be supplied). The other pair (VR4, VR5) are shown as three pin connectors. If you want single turn adjustment from the front panel you can mount 9mm single turn pots (eg Spectrol 248-7-10 or similar) in the positions shown as VR4, VR5.

DO NOT mount two sets of pots, they don't work very well in parallel.

Here is a parts list for the components which go on the boards. The number following the Dale resistor description is the Dale code (value1 value2 value3 exponent). 4k75 is 475 x 10^1 so will be coded 4751. Note for kits: due to an ordering error one of the 1k resistors will actually be a Welwyn R55C.

Part Value Device Package
C1 1000uF Rubycon ZL 25V E5-13
C2 220nF Wima MKP 100V C5B7.2
C3 220nF Wima MKP 100V C5B7.2
C4 220nF Wima MKP 100V C5B7.2
C5 1000uF Rubycon ZL 16V E5-10,5
C6 1000uF Rubycon ZL 16V E5-10,5
C7 470uF Rubycon ZL 16V E3,5-8
C8 470uF Rubycon ZL 16V E3,5-8
C9 470uF Rubycon ZL 16V E3,5-8
C10 470uF Rubycon ZL 16V E3,5-8
C11 100nF Wima MKP 100V C5B5
C12 100nF Wima MKP 100V C5B5
C13 100nf Wima MKP 100V C5B5
C14 100pF Wima MKP 100V C5B3
D1 1N4004 1N4004 DO41-10
IC1 L200C Nat. Semi L200 C L200S
IC2 OPA2277 BB OPA 2277PA DIL08
IC3 REF02 BB REF02AP DIL08
IC4 OPA2277 BB OPA 2277PA DIL08
JP2 JP2E 2.54mm 3 pin header
Q1 BC557 BC557 TO92
Q2 BD140 BD140 TO126
Q3 BC337 BC337 TO92
Q4 BC337 BC337 TO92
Q5 BC547 BC547 TO92
Q6 BC557 BC557 TO92
Q7 BC557 BC557 TO92
Q8 BD139 BD139 TO126
R1 750R Dale RN55 1/8 watt 1% 7500 0309/12
R2 3k Dale RN55 1/8 watt 1% 3011 0309/12
R3 0R75 Dale RS1A1watt 1% 0617/22
R4 4R0 Dale RS1A1watt 1% 0617/22
R5 4k75 Dale RN55 1/8 watt 1% 4751 0309/12
R6 4R99 Dale RN55 1/8 watt 1% 4R99 0309/12
R7 49R9 Dale RN55 1/8 watt 1% 49R9 0309/12
R8 100R Dale RN55 1/8 watt 1% 1000 0309/12
R9 100R Dale RN55 1/8 watt 1% 1000 0309/12
R10 4k75 Dale RN55 1/8 watt 1% 4751 0309/12
R11 1k Dale RN55 1/8 watt 1% 1001 0309/12
R12 4k75 Dale RN55 1/8 watt 1% 4751 0309/12
R13 1k Dale RN55 1/8 watt 1% 1001 0309/12
R14 4k75 Dale RN55 1/8 watt 1% 4751 0309/12
R15 475R Dale RN55 1/8 watt 1% 4750 0309/12
R16 680R WelwynR55C 1/8 watt 1% 681R 0309/12
R17 10k Dale RN55 1/8 watt 1% 1002 0309/12
R18 10k Dale RN55 1/8 watt 1% 1002 0309/12
R19 1k Dale RN55 1/8 watt 1% 1001 0309/12
R20 10k Dale RN55 1/8 watt 1% 1002 0309/12
R21 1k Dale RN55 1/8 watt 1% 1001 0309/12
R22 1k Dale RN55 1/8 watt 1% 1001 0309/12
R23 475k Dale RN55 1/8 watt 1% 4753 0309/12
R24 47k5 Dale RN55 1/8 watt 1% 4752 0309/12
VR1 50k Spectrol 1/2" vertical multiturn RJ9W
X1 AK300/2 2 pin 5.08mm AK300/2
X2 AK300/3 3 pin 5.08mm AK300/3
X3 L03P 3pin 2.54mm polarised L03P
X4 L02P 2 pin 2.54mm polarised L02P
X5 AK300/2 2pin 5.08mm AK300/2
R25 2k49 Dale RN55 1/8 watt 1% 2491 0309/12
R26 4k75 Dale RN55 1/8 watt 1% 4751 0309/12
R27 10k Dale RN55 1/8 watt 1% 1002 0309/12
R28 20k Dale RN55 1/8 watt 1% 2002 0309/12
R29 20k Dale RN55 1/8 watt 1% 2002 0309/12
R30 10k Dale RN55 1/8 watt 1% 1002 0309/12
R31 4k75 Dale RN55 1/8 watt 1% 4751 0309/12
R32 2k49 Dale RN55 1/8 watt 1% 2491 0309/12
R33 2k49 Dale RN55 1/8 watt 1% 2491 0309/12
R34 4k75 Dale RN55 1/8 watt 1% 4751 0309/12
R35 10k Dale RN55 1/8 watt 1% 1002 0309/12
R36 20k Dale RN55 1/8 watt 1% 2002 0309/12
R37 20k Dale RN55 1/8 watt 1% 2002 0309/12
R38 10k Dale RN55 1/8 watt 1% 1002 0309/12
R39 4k75 Dale RN55 1/8 watt 1% 4751 0309/12
R40 2k49 Dale RN55 1/8 watt 1% 2491 0309/12
S2 SW_DIP-8 8switch DIP 2.54mm EDG-08
S3 SW_DIP-8 8switch DIP 2.54mm EDG-08
SW1 DPDT C&K horizontal DPDT LSP13
VR2 5k 3/4" Bourns horizontal multiturn PT-SPIN
VR3 5k 3/4" Bourns horizontal multiturn PT-SPIN
VR4 5k optional
VR5 5k optional
X6 L03P 3pin 2.54mm polarised L03P

Decision Time.

Before you start you need to decide which version of the controller you want to try. If you want the error amplifer function for greatest stability and lowest noise, use all components and set JP2 to the forward position. If you wish you can decide not to use any or all of the six smoothing capacitors (C5 - C10 inclusive). This increases noise slightly and speeds up the current compensation circuit.

If you wish to run without the error amplifier, do not insert IC4 into its socket. In its place use a jumper wire between pins 2 and 3 of the socket. In this configuration at least three of the smoothing capacitors (C5, 7 and 9) must be installed. You can decide to run with reference return to ground (JP2 at rear postion) or with reference return to motor return (JP2 at forward position).

Construction:

Pack the board in order of height, soldering as you go:

Resistors

IC sockets and diode (mount diode proud of board)

small signal transistors

connectors

small capacitors

large capacitors.

The pads for the resistors are quite small so you will need good soldering technique to get a reliable joint - keep the tip clean, heat the lead and the pad with iron, touch the solder to the pad so it wicks into the joint.

I recommend attaching the L200C and the two larger transistors to an angle bracket (I used a 125mm length of 20mm x 25mm aluminium angle 3mm thick) before they are soldered to the board. Drill three holes in line 10mm in from the angle edge with centres spaced at 1.5" (my apologies for the mixture of units but the board software I used defaults to inch)

Tap these holes for the hardware in use (I use 3mm ISO screws). Attach the transistors and the L200C to this and bend the transistor leads so they are in line with the inner set of leads on the L200C. Insert all the leads through the PCB holes and solder.

Board and heatsink connection.

Because the power dissipation in this circuit is so low (less than 3 watts when running without charging) the small piece of aluminium angle as above is all the heatsink it needs. Using the angle as a support on the back panel of the enclosure gives more than enough heatsinking.

Wiring Up.

NOTE WELL: There is no on board reverse polarity protection. If the circuit is connected to a power source with reversed polarity it will be destroyed. If you can't trust yourself to get it right, install protection diodes at the appropriate terminals. Reversed polarity at the power supply will take out the supply capacitor and the L200C chip. Reversed polarity at the battery will destroy the op-amps, the reference chip, both the power transistors and most likely three of the driver transistors. Don't do it.

The kit does not include wire as the length required depends on enclosure etc.

Built and wired, note this version uses single turn adjustment pots.

The main board and the adjustment board are attached to each other using a three core cable between X3 on the drive board and X6 on the adjustment board. NOTE: due to an error in drafting the three pin connectors should be mounted so that the cable reverses orientation eg pin 1 on one board becomes pin 3 on the other. The plugs use crimp connectors.

The 2.1mm DC connector is wired to X1 with the positive to the rear terminal (eg closer to the regulator IC) Positive is usually the centre pin but check your power supply BEFORE you power up.

The Batt- terminal at the front of X2 is connected to the negative terminal of the battery. The Batt+ (centre) terminal is taken to a switch. The Charge + (rear) terminal is taken to another switch. The other sides of the two switches are taken to the positive terminal of the battery. I choose to wire the two switches so that "both up" is charge / motor off and "both down" is no charge / motor on. The two switches are independent so that if the supply is switched off for long periods the charge circuit can be disconnected from the battery so that the battery does not drain through the charge circuit (charge off / motor off).

The motor is wired to X5, the polarity given will give correct direction for the Maxon motor for a belt system. Wire from X5 to the two pin JDEC microphone socket and from the equivalent plug to the motor will allow the controller to be disconnected when required. The JDEC connector plug has a fixing screw on top. Remove this screw then remove the plug insert from the body (bayonet release). Solder the motor wires then reconnect. I use heatshrink to give the cable clamp some purchase.

X4 connects the indicator LED, pin 1 to the shorter lead.

Left side showing wiring layout.

 

Niceties

If you want to you can include some charge status LEDs. Here is one scheme:

The red LED indicates current limited charge (CL). The amber LED indicates trickle charge (TC). When the charger is connectoed to the battery the red LED will light. As the battery voltage comes up to the trickle voltage (13.8V) the red LED will start for fade and the yellow LED will start to glow. When the trickle voltage is reached the red LED will be completely out and the yellow completely on.

The green LED indicates battery OK (> 11.4 volts, dims below 12V). If the blue satus LED is on but the green is off or dim the battery needs charging.

 

I wired the LEDS to the switches for the battery / charger like this:

Adjustment.

Before setting the voltage adjust VR1 all the way down (anticlockwise). For very low current motors such as the Maxon motor it is recommended to bypass the motor terminals with a resistance of approximately 1 k to give the Widlar current mirror some idle current which improves its linearity.

Use the dip switches and resistors to select the working range of the potentiometer to suit the voltage adjustment required for the motor speed. The circuit is arranged so that the two sets are selected via the toggle switch, the toggle of which "points" to the selected adjustment potentiometer. The left hand pot uses the rear set of resistors / DIP switches, the right hand pot uses the front. The DIP switches short the resistors in the "on" position. If all the resistors are shunted the potentiometer has a working range of 100%. If resistors are selected in to give a total of 50k the potentiometer has a working range of 10% thus giving finer speed control.

To set the range, select resistors to give the centre point of the potentiometer at the required voltage, the full scale output of the controller being 10.0 volts. For say 7.5 volts we would need the pot centred at 12.5k / 37.5k so we would select 10k plus half the pot above the set point and 20k,10k, 4k75 plus half the pot below. The DIP switches would thus be set to 1,0,1,1,1,0,0,0.

Before adjusting the current compensation measure the resistance of the motor as presented at the terminals on the board (including any shunt resistance as above). Take an appropriate adjustable resistance (eg a 100 ohm multiturn trimpot) and make a compensation resistance by adjusting the value as close to the resistance of the motor as you can get, using the same measurement device. Disconnect one lead of the motor wiring from the terminal, turn the controller on, measure and note the output voltage at the board terminals. For best accuracy this should be done with an output voltage above 5 volts. Turn the controller off.

Insert the compensation resistance in series between the (disconnected) board terminal and motor lead. Turn the controller on and measure the voltage present at the motor. Adjust VR1 until this voltage equals the voltage noted in step 1 above. For best accuracy this should be done with the motor loaded with a consistent load (eg running the turntable) and the board terminal voltage must be below 10 volts. Turn the controller off, remove the compensation resistance and reattach the motor wiring to the board terminal.