AC/DC control voltage

[watana]

what happened that if the control voltage is suspected of feeding a original design 24VDC but wrongly connected to a 24VAC, how to ensure the voltage is DC or AC by a muttimeter?

what will happened to the circuit?

Need help!!

[Reeferjon]

worst case:
as the ac part goes negative, any semiconductor componants will be reverse connected and will probably destroy them.


OOPS.

[Gibson]

Could you be more specific watana? Provide more details?
What are you servicing? Is there a step down transformer? Is there any info stamped on it?
What is the line voltage?
What do you read with the voltmeter on AC? What do you read with the voltmeter on DC?

[watana]

the control is for the frequency inverter of condenser fan motor, and using a pressure transducer sensing the condenser pressure to increase & decrease the fan speed, I just saw a ordinary transformer of 220/24V step down transformer without a diode to convert AC to DC, the controller nameplate show 24V-- with a solid line on top of dash line, is it the sign of DC voltage.

as the main problem is the fan motor while run at normal speed, it is not overload, if the condenser pressure is lowering due to cooler weather or less load, the motor overload.

another question is the inverter calling the motor to run at lower frequency (lower speed), is the motor current drawing higher or lower?

would seek the colleagues to advise.

thank you

[Gibson]

watana, could you provide the specifics of the motor you are trying to control? Voltage? Phase? Sleeve or ball bearing? Condition of the motor? PSC?

Is the condenser fan speed control an add on, or from the (OEM) original equipment manufacturer? Are there any control settings on the controller?

All of the low voltage add on controls we can buy here are 24v AC. Most fan speed controllers I have used are selected for the motor voltage.

Can you provide a manufacturer's name and part number?

The current should never rise above the motor nameplate rating more than the service factor allows. In my experience, the current draw should rise and lower with the fan speed.

[watana]

hi, Gibson,

the condenser fan motor is squirrel cage motor of 11KW, 960RPM, 380V/3ph/50Hz, FLA 24.4AAmp, bearing type unknown, how to check?

this is part of a remote air-cooled condenser of packaged chiller which is customed built, using "HISON" axial fan of air flow rate 68,000cu.m/hr, using a frequency inverter to start the fan and control the fan speed by sensing the condenser pressure thru' a pressure transducer then pass the 0-10VDC signal to pressure transmitter, next to form a 0-10VDC supply to the inverter in order to increase or decrease the fan speed.

the frequency inverter and the pressure transmitter make is "CAREL" of Italy origin

by meaure the supply voltage to pressure transmitter is 23VAC, but shown on the nameplate is 24VDC, measure with VDC band of multimeter, 0VDC shown; the voltage of the pressure transducer to the transmitter is 10.8VDC.

i always suspect that AC fed in DC circuit will make the system not working properly, how to prove, since i get the VDC at the transducer connection

now the ambient is about 18deg C, the condenser pressure is low as 200psi, which swing too quick with the fan speed change quickly, also cause liquid flood back to crankcase, the pressure is 160psi, the fan need to stop, but in short time the pressure rise to 240psi, the fan start again, start stop too frequent.

Now there is 2 problems, one is AC/DC control voltage, second is the setting of the start fan /stop fan parameter to prevent short cyclling.

would like to have advise from everone.

many thanks