| ??? 04/02/07 18:52 Modified: 04/02/07 18:58 Read: times |
#136434 - I would use a MOSFET instead of relay Responding to: ???'s previous message |
Ajay said:
Please anyone, guide me how to make a high current DC motor controller using 8051. the idea i have thought so far is to use a relay connected to a pin of port of 8051 and DC motor connected to relay. if current is too large, will the relay work?? or any other method for it... From your post I understand, that you only want to switch your motor on/off. In such a case I would use a MOSFET, or better MOSFET array (to enhance the current drivability) to turn-on the motor. A relay will suffer from contact erosion due to the switching sparks and is less suited. So, I would give the following circuit a try: 
How does it work? When P1.1 goes low, the output of 74HC04 goes high and the four BUZ11 MOSFETs are turning-on, connecting the motor to the motor supply. When P1.1 goes high again, the output of 74HC04 goes low and the four BUZ11 are turning-off, disconnecting the motor from the motor supply. When the MOSFETs are turned-off, the inductance of motor will produce a huge inductive kick, unless free wheeling diodes are present. In this circuit two BYV79-50 are used as free wheeling diodes. The fast acting fuse shall prevent a disaster, when something goes wrong. You can switch currents of up to 40A with this circuit, about 10A per MOSFET. Motor supply voltage may be up to +24V. I know, there are much better MOSFETs available today, but the BUZ11 should be easily available where you live. The same is true of the BYV79-50. Keep in mind, that MOSFETs want to be driven by steep and clean edges. Because of this a 74HCMOS gate is used to drive the gates. The 100R gate resistors dampen resonances caused by unavoidable gate inductances and assures, that the MOSFETs turn-on without showing oscillations. Take care, that no high motor currents flow along ground connections within your microcontroller circuit. The schematic shows how to achieve this: Keep the ground wiring of microcontroller circuit and motor separated. Also, use a solid ground plane for the microcontroller circuit to minimize the current loop area of 74HC04's and BUZ11 gates' currents. Otherwise the turning-on/off of MOSFETs can interfere your micro and cause strange performance. In any case, use a proper reset chip (e.g. MAX1232), which resets the micro, whenever the supply voltage falls below nominal voltage!!! This is extremely important, because otherwise your motor can accidentally turn-on, when you do not expect it!!! For the same reason, the MOSFETs are only turned-on, when P1.1 is emitting low level. This guarantees that a reseted micro (which has P1.1 emitting high level!) or a micro that is just powered-on (reset active time!) will not make the motor to start to run! Kai |
| Topic | Author | Date |
| High current Dc motor controller | 01/01/70 00:00 | |
| More detail required | 01/01/70 00:00 | |
| try these ics | 01/01/70 00:00 | |
| for drivers, there is, in my opinion, ONE source | 01/01/70 00:00 | |
| I would use a MOSFET instead of relay | 01/01/70 00:00 | |
| more details | 01/01/70 00:00 | |
| Well i think that Relay is Best Solution for you, | 01/01/70 00:00 | |
| Not suitable - no speed control! | 01/01/70 00:00 | |
| 800 A ??? | 01/01/70 00:00 | |
| Are you sure? | 01/01/70 00:00 | |
| High is relative | 01/01/70 00:00 | |
| you need a H-bridge as has been mentioned | 01/01/70 00:00 | |
| Topology is simple | 01/01/70 00:00 | |
| Tutorial | 01/01/70 00:00 | |
| good info | 01/01/70 00:00 | |
| The +1 karma point came from me,... | 01/01/70 00:00 | |
| relay will work ,but | 01/01/70 00:00 | |
| better power amp | 01/01/70 00:00 | |
READ the question | 01/01/70 00:00 |