ac 3 phase motor spikes with uC

[garg29]

motor spikes

Dear friends,
i'm working on a project in which i have to run a motor with a 89c51 microcontroller. the microcontroller counts the rotations on 4 digit display. i'm using a 12v relay. when the realy starts the motor the microcontroller gets reset or hangs up. Please help me. thanku

 

[nicleo]

resistor ac motor 220 volt

Well, you need to isolate (using optocoupler) the 89C51 microcontroller from high power circuit that drives the motor. Or, you can add capacitor to filter out the noise. Pls tell what is the role of 89C51 in your system.

 

[jourval]

motor spikes

As a rule you receive spikes via your ground line
Optocoupler will not help if you have the same gnd
for power driver and your control unit
Try to use optocouplers for in/out + floating power supply placed close to uC
it will work for sure.
try to connect two gnd's via 0.1u capacitor, sometimes it is better
than "absolutly" floating power

 

[albert22]

threepole ac motor figure

I had a similar problem with a PIC driving a relay. It produced a spike in the Unregulated side of the power supply. That sneaked into the regulated +5 to the pic. I cured it by adding a small series resistor and a couple of capacitors to gnd.
(.1uF and 10uF in parallel). To filter the relay supply.

 

[IanP]

3 phase 220v capacitor filter 10uf

Please see posts on Microcontroller for noisy environment" in this forum.

 

[garg29]

optocouplers with 89c51

Thanks everybody for replying. "albert22" can you please tell me how to add series resistor and of what value. "jourval" can you explain a bit more. thanks

 

[albert22]

12vac 3 phase motor

The resistor depends on the current needed by the coil of the relay. Too large and the relay will not operate. I used a 22 to 39 ohms for a 100mA coil. There was a dropout on the resistor but I was using a +V a little higher than 12volts.

I assume that you are using a NPN transistor to gnd to drive the coil (low side drvr). And that you placed a diode in parallel with the coil to absorb the spike produced in the disconnection. One end of the coil goes to the collector and the other to +V.

Open the +V lead, conect there the series resistor and place the caps between the coil and gnd (the lead of the coil that was connected to +V).

I read the post suggested by IanP and it is very interesting. Specially the reset issues. With correct practices in power supply filtering, propper gnds and reset circuits, this patch probably woudnt be needed at all

Hope that this helps
K

 

[nicleo]

Possible to give more info:

1) Motor rating?
2) What is the power source of your system? Battery?
3) PWM control?

I guess the microcontroller, driver, relay, and motor in your system share the same power source (e.g. 12V). When the relay is triggered, the motor draws a huge amount of current. This inrush current might cause the positive supply rail to drop momentarily. Also, when the relay contact closes, there will be mechanical bouncing, which will be translated into voltage pulses (spikes) and conducted to the microcontroller circuit as noise.

Circuit shown in Figure 1 is suggested by 'albert22' (pls correct if it's not correct or complete). The circuit in Figure 2 is more complex and expensive but it will work.

 

[garg29]

thanks for replying. i'm using a 3-phase 220 volt ac motor and a three pole relay 12 volts. i am using 12-0-12 step down transformer. actually nicleo my spikes are coming from ground line. if i use two seprate power supplies, one for microcontroller and other for relay and join both the grounds with 10k resistor then they work fine but i want to use only one power supply. please tell me details of isolated dc/dc. and how can i isolate the two grounds using single power supply

 

[nicleo]

i'm using a 3-phase 220 volt ac motor and a three pole relay 12 volts. i am using 12-0-12 step down transformer. actually nicleo my spikes are coming from ground line. if i use two seprate power supplies, one for microcontroller and other for relay and join both the grounds with 10k resistor then they work fine but i want to use only one power supply. please tell me details of isolated dc/dc. and how can i isolate the two grounds using single power supply

Option 1
Well, you can design the DC-DC converter yourself. But if you have extra budget, probably you can buy off-the-self DC-DC converter, for example, PT4243 or DCP021205 from Texas Instrument.

220VAC -> Step Down Transformer -> Rectifier -> 12VDC
12VDC -> Relay primary coil
12VDC -> Isolated DC/DC converter -> +5V -> Microcontroller + Optocoupler


Option 2
Probably you can get another lower rating 220VAC -> 9VAC or 6VAC step down transformer. After the 9VAC and rectifier, use a voltage regulator to give +5V output, which is required to power up the microcontroller and optocoupler. By doing this, you already isolate the power/gnd from that of motor.


Option 3
As you have 220VAC -> 12-0-12 VAC step download transformer already, you just need to buy an optocoupler. One of the 12VAC output of the transformer is used to power the primary coil of relay. The other 12VAC output is connected to a rectifier. The output of the rectifier is then connected to a voltage regulator to get +5V output to power the microcontroller and optocoupler circuit.

 

[IanP]

If you still have all these problems you should use solid state relays ..