DC Motor (PMDC Blower Motor for Automotive HVAC) Speed Control (Resistor Blower)

How about just above the full load current for the motor, so as to prevent its catching fire from an overload situation?

You can monitor current vs temprature to find

the characterisics of resistor and measure the

fusing current for different valuesof resitors.

Kishore K Gupta

pyn@airtelmail.in

New delhi INDIA

This is OK but is there any calculation available for the same with which i can get the resistor blower resistance values along with fusing charecteristics.

HELLO NITIN

ACCORDING TO ME...

FOR A COIL TYPE RESISTOR,WE NEED CURRENT,TIME AND TEMPERATURE AT WHICH THE COIL MUST BLOW OFF.

i.e AT SPECIFIC CURRENT VALUE WITH IN SPECIFIED RANGE OF TIME.

NOW BOTH OF ABOVE PARAMETERS CAN BE ACHIEVED BY MOTOR CHARACTERISTICS. i.e.

FOR CURRENT:- GET WHAT IS NORMAL CURRENT AT WHICH COIL MUST NOT BLOW OFF FOR DIFFERENT SPEEDS AND WHAT IS BLOCKED ROTOR CURRENT AT WHICH COIL MUST BLOW OFF,AND NOW FUSING CURRENT WILL BE HIGHER THAN (AT MOST 2 TIMES)NORMAL CURRENT AND LITTLE LESSER THAN BLOCKED ROTOR CURRENT,DEPENDING ON SAFETY YOU CAN SELECT THE FUSING CURRENT (90-95% BLOCKED ROTOR CURRENT)

FOR TIME:- SELECT TIME SUCH THAT IN SPECIFIED MAX. TIME MOTOR MUST NOT GET DAMAGED AND ALL PLASTIC PARTS WITHSTAND THAT HEAT FOR SPECIFIED TIME.NO TYPE OF DAMAGE AND DEFORMATION MUST ALLOWED OR YOU CAN SPECIFY THE ACCEPTANCE CRITRIA.

ADDITIONAL REFER MOTOR CHARACTERISTICS,ALSO OF RESISTANCE WIRE YOU CHOOSE.

HOPE THE ABOVE WILL GIVE SOME HELP IN DECIDING THE FUSING CHARACTERISTICS

Thanks for the same.

Actully i have designed one resistor blower and according to the Blocked rotor current i have decided the fusing requirment.

Motor current for High speed was 22-23 A.

i have taken after iteration for resistance value 0.20 ohm 28 amp fusing current and it should blow off within 10-30 sec when blown off with the locked rotor.

As you have mentioned fusing current will be around 2 times but if the same will be 2 times then we will be having lot of field failures.

it came after lot of iteration.

Do you have any calculation specific for the fusable coils through which we can approch the fusing values approximatly close enough.

If you know or workign on that we can both share the data and find out the calculations for the same.

thanks for your assitance.