DC motor protection
DC motor protection
(OP)
Hello ,
I'm a fresh control systems graduate , and I admit I severely lack practical experience , I have an old milling machine that I want to fix , it has dc motors , unfortunately I can't find any manuals or information about it online , its plate has the following information : V=170V , Ieff=33A , Icap=300A , does I eff mean rated current , and I cap mean stalling current?
and I can see people taking about the case of a motor short circuit , does that mean the case when the motor stalls , so its back emf drops to zero , or is there another case that makes this short circuit conditions?
when I inspected the old controller of the machine , I found different overloads and fuses , so what is the difference between circuit breakers , overloads and fuses , and why would they put fuses if they have overloads?
and what protection methods do I need for such motor ? and would they be fast enough to protect the control electronics ? or would the electronics need faster way of protection?
thanks
I'm a fresh control systems graduate , and I admit I severely lack practical experience , I have an old milling machine that I want to fix , it has dc motors , unfortunately I can't find any manuals or information about it online , its plate has the following information : V=170V , Ieff=33A , Icap=300A , does I eff mean rated current , and I cap mean stalling current?
and I can see people taking about the case of a motor short circuit , does that mean the case when the motor stalls , so its back emf drops to zero , or is there another case that makes this short circuit conditions?
when I inspected the old controller of the machine , I found different overloads and fuses , so what is the difference between circuit breakers , overloads and fuses , and why would they put fuses if they have overloads?
and what protection methods do I need for such motor ? and would they be fast enough to protect the control electronics ? or would the electronics need faster way of protection?
thanks






RE: DC motor protection
When the back emf drops to zero, the rotor is not rotating; this is known as a locked or blocked rotor condition. This occurs on startup and means inrush current will be large until the back emf is produced as the rotor increases in speed.
Overloads protect the wiring from an overtemperature condition due to prolonged operation at elevated operating current, and have a time delay that will prevent them from tripping during starting inrush current. Fuses or circuit breakers are sized to protect the wiring from short-circuit conditions like when a line-line or line-ground fault occurs, but to allow starting inrush currents to pass through so they don't trip on startup. Neither is there to protect the equipment, e.g., the control electronics, they are there to prevent fires caused by overheated wiring. Equipment would need its own fuses to protect it.
xnuke
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RE: DC motor protection
This is engineering tips, not electrical apparatus 101, 201, and 301.
Bill
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