prob with high power dc motor control

[nipun]

i made a control circuit based on µc for PWM speed control of a 48V 0.5 Ω PMDC motor using mosfets.it worked fine but the next day when i again tried it mosfets blew. im still not aable to find out any reason plz help what can b the prob.earlier when it was working mosfets didnt heat at all but even after replacing them they blow up every time.

 

[fuzzycontrolfreak]

Hi,
It sems your motor is draining a lot of current, the mosfets don't need to heat up in order to get fried. One way to check up is to connect your motor directly to a power supply thoraugh an ammeter, and check your current, at starting, no load and full load...
Normal mosfets would withstand currents upto 4 or 5 amperes max, special mosfets would be needed for higher currents. Starting current is the most dangerous, so you'll have to multiply your full load current by a factor of atleast 3 to get your mosfet rating.
Check the TIP 147 mosfets, they can handle upto 10 amperes continuous load. Make sure you equip your circuit with a reversed diode in order to handle reverse currents.

 

[nipun]

im using two mosfets in parallel each rated 55A my motor cant take more than 96 A starting since its 48V 0.5Ω so I is 96 max,dnt know wats the prob. can it be related transients.

 

[babatundeawe]

hi pal, i will suggest you something that could handle much higher current at start up. consider first the current rating of your motor at start (starting current) which i presume should be on the name plate. using mosfet might not really give you the high current you require. i would rather suggest that you try thyristors or a much better component IGBT (insulated gate bipolar transistor) they can handle more current than mosfet but they can be quite expensive. but i can assure you will get the value for the money. here is a link that compares mosfet and IGBT
**broken link removed**

you can also try out some search in google or other search engines. good luck

 

[docel]

1. PMDC motors Dont stop at 2xI(A) at startup, unless forced to do so, by external circuitry.
2. The "break" voltage will far exceed the applied voltage. Since you have not specified the FET type, it is difficult to analyse the problem.
3. Parallel components are 'dangerous':!::!: Unless you have done something to 'equalise ' the drive ....! even assuming the internal protection diodes are present, one transistor may " hog' more current/drive than the other...(and fail..)