dc motor starting with high load 4

[garyp]

I have a problem starting a 12v DC Motor

When I start it from my 12v DC line it drags the line down to 10 volts. But due to some voltage checking circuitry in the starter for the motor it stops the motor if the line drops below 12v.
Would I be right in assuming that if I placed a large enough Capacitor (1 farad) in parallel with the motor this would act to stop the line being dragged down & hence enable me to start the motor?
The motor runs a compressor so it is a high inertia load & I expect it to need an assisted start will this work?

 

[cbarn24050]

Hi, a large capacitor would make things worse, the psu would have to charge the cap as well as start the motor. What you need to do is put some current limiting in the system or put a time delay in the fault detecting circuit.

 

[djs]

Hello;
Placing a resistor in series with the armature during start will help. After the motor is running at a constant speed, short out the resistor.
As an alternative, an electronic DC motor controller can be used.

 

[electricshock]

the high starting current results in temprarory voltage drop across armature which reaches its almost normal value once the motor picks up speed.the motor should pick up rated speed in about 7-8 seconds. if you could increase the time delay for undervoltage protection it would serve the purpose. you havnt mentioned whether its series or shunt motor. a series motor very high torque in the begginning,and even if you put 10% of armature resistance in stator ckt during starting it will give 80 % of starting torque. in case of shunt motor resistance may dropdown the starting torque below the required level,so one has to select the resistance carefully. moreover it needs to be cutoff.
capacitor though will not let the voltage fall but will be an added item which will keep on discharging to the armatature whenever motor is stopped.

 

[gjones33]

Hi garyp,

In reply to your question, yes, you could put a capacitor in parallel with the supply BEFORE the motor start circuit. The capacitor would then be charged before you start the motor and provided it is of sufficient capacity it would hold the voltage up during starting. As a rule of thumb you need about 1000 uf per amp.

Cheers,
G

 

[jbartos]

Suggestion: A reostast in series with the armature will enable your motor a smooth start.

 

[garyp]

Cheers
I shall look into some of the suggestions.