Speed control with feedback for collector AC motors

Most of the world's manufacturers of professional angular grinders (Bulgarians) such as Bosch, Metabo, Makita, DeWalt and others use two types of speed control with feedback.

With the help of a tachogenerator

At the end of the armature of the motor is mounted a ring magnet with a slot or cut, and on Board regulator is installed the coil or the Hall sensor. Such a controller provides highly accurate stabilization of the engine speed when the load changes.

Based on the measurement of the voltage drop on the electric motor

In this case, the measured voltage drop across the motor and the control circuit changes the duration of opening of the power key. Such a controller if it is configured correctly, also provides good stabilization of the engine speed when the load changes.

All industrial controllers, assembled on microcontrollers, fully filled with epoxy resin and as a result, they are not suitable for repair, and price for the new controller is quite large and accounts for approximately 20-30% of the cost of the power tool.

В поиске специализированных микросхем для решения данной задачи мне приглянулись регуляторы Phase Control фирмы Atmel. Например, простой вариант регулятора на ми­кросхеме U2008B. Рассмотрим схему регулятора на ИМС U2008B приведенную на рис.1. В данном регуляторе можно использовать обратную связь по току или режим плавного пуска, однако в нём нет защиты от перегрузки. Если исполь­зовать плавный пуск тогда нужны только элементы С1, R4 и перемычку Х1 не ставим, а если нужна обратную связь – тог­да все наоборот.

As IC U2008B can work in the soft start mode and feedback, it is not suitable for our problem. In Fig.2 shows a regulator circuit on the chip U2010B, which has a feedback voltage, over current, overload protection and smooth start at the same time. Led D2 indicates the overload of the motor. Switch SA1 "Mode" enables selection of action in case of overload on the motor in three modes: Position A — overload indication and the subsequent reset to minimum speed. To restore the operating speed, you must turn off the tool.

The Situation In — overload indication, the subsequent reset to the minimum rpm after the removal of load from the tool restores the set speed, i.e. there is a auto start.

The Situation only the indication, without shutting down the engine and protect.

The selection of the capacitance of the capacitor of Sz from 1 to 10 UF can change the duration and smoothness of the engine start-up.

Regulator setting.

In the technical description of the IC U2010B in the connection diagram is indicated by a voltage drop on R6 250 mV and does not state how it must be this resistor.

Calculate the resistance R6 can be based on engine power by the formula:

R6 = U_R6/(R_MOT/U_Pit),

Where is:
in the_R6 – напряжение на R6 (250 мВ),
P_MOT – мощность двигателя,
in the_PETE – напряжение питания сети.

For example, engine power 750 W calculate: R6= 0,25/(750/220) = 0.07 Ω.

The values of the resistors R6 and R11, depending on the power of the electric motor shown in table.

R11 Power, W	R6*, Ohm	Nichrome, D 1 mm	Nichrome, D 0.8 mm	R11*, room
250	0,22	30	19	180-270
300	0,18	27	17	180-220
550	0,1	25	16	180
700	0,08	20	14	160
850	0,07	17	11	150
1000	0,055	15	10	100-120
1200	0,047	13	9	90-110
1500	0,04	12	8	80-100
1800	0,03	10	7	70-100
2000	0,028	8	6	65-90
2200	0,025	7	5	65-90

The main thing to choose the resistor R6 under engine power. The above formula is correct, but in practice may need some correction on the behavior of the engine under load. If the resistor is too big, the engine starts quite abruptly (i.e. there is a large payment burden than necessary), and then turned off, and if the resistor is small, it will not provide compensation of the load.

In the Datasheet for IC U2010B the capacitance of the capacitor C2 is specified to 0.01 UF, but it is designed for 60 Hz network and the use of IMS in a network of 50 Hz for the period was given some impulse control. In the end, the revolutions of the motor is practically not regulated and the engine was at full power. For a network with frequency of 50 Hz we need the capacitance of the capacitor C2 to increase to 0.015 UF.

The first launch

Variable resistor R1 (the speed controller) should be installed at a minimum engine speed, according to the scheme of the potentiometer should be rotated to the side of the resistor R13. Then rigged a resistor R10 (compensation of load) set to the middle position and the place of R11 (overload) temporarily solder a permanent resistor 62 kOhm. Then insert the controller into a network of 220 V / 50 Hz and adjusted the resistor R8 to set the minimum engine speed.

You need to make it so that when you turn the motor begins to rotate at minimum speed. If you configure the device so that no voltage at the motor, then it becomes too non-linear dependence of the control resistor R1 when you first turn the engine spinning and then abruptly starts without soft start.

Next you need to connect a voltmeter with a measuring range of 300 V to the motor terminal, start the engine and at medium speed, clamping the shaft or the drive motor through the cloth by hand, to put such a provision of the resistor R10, so that the revolutions of the motor has not changed if you change the load on its shaft. Simultaneously, you need to look at the voltmeter connected to the engine. As the load increases on the motor shaft, the regulator adds the voltage, and the motor revolves with the same speed, regardless of load.

And in the last turn configures the resistor R11 (overload). A constant resistor 62 kOhm giving to drink and instead put a fixed or variable resistor of 220 ohms. The engine speed is slightly more than the minimum, strongly clamping the shaft or the drive of the engine, almost trying to jam the motor shaft, and gradually change the value of resistor R11 until you start to trigger the protection, and will not glow VD2. Then measure the resistance of the variable resistor tester and sealed to the device corresponding resistor. The table shows the approximate resistance values R11,

Details of the regulator

Купить микросхемы U2008B, U2010B можно через сайт AliExpress (www.ru.aliexpress.com) в Китае с бесплатной до­ставкой на Украину, а далее посылка бесплатно отправляется через «Укрпочту» в любое почтовое отделение на тер­ритории Украины. Доставка на Украину производится на про­тяжении 25-40 дней. Например, цена 1 шт. микросхемы U2010B зависит от корпуса исполнения, примерно 0,9 USD в корпусе S016 и 1,2 USD в корпусе DIP16, а симистора ВТА24-800 – 0,4 USD.

Printed circuit Board device made of one-sided foil fiberglass thickness of 1 mm.

Triac VS1 is better to use with a non-slip pad under the radiator series VTA, such as BTA12-800, BTA16-800, BTA24-800, or use other. With engine power of 400 watts, VS1 can not install on the radiator. All SMD parts of size 1206, they can solder a normal soldering iron with a fine tip.

Подстроенные резисторы – типа СП3-19а или другой ма­логабаритный. Переменный резистор Р1 любой на 47-50 кОм, можно малогабаритные СП4-1, СП3-9. Резистор R1 мощностью не менее 2 Вт, например, типа MЛT-2 или др. Резистор R6 изготовлен из нихромовой проволоки диаметром 0,7 – 1 мм. Автор использовал нихромовый провод из старого блока сопротивлений для зажигания автомобилей ГАЗ с маркировкой 1402.3729. Все электролитические конденса­торы на напряжение не менее 50 В. Диод D1 – типа 1N4007 или КД208, также можно использовать диод в SMD исполне­нии. Светодиод D2 любой малогабаритний диаметром 3-5 мм красного света. Переключатель SA1 любой малогабаритный 3-х позиционный. Если нужен только один режим перегруз­ки, тогда вместо него можно установить перемычку.

Literature:

1. Бирюков С. Автомат плавного пуска коллекторных эле­ктродвигателей. // Радио. – 1997. – №7. – С.40-42.

Printed circuit Board for the circuit shown in figure 2:

[hidepost]Download[/hidepost]

Author: Valentin Siplec, Uzhgorod