By Grant Laidlaw
Problem Page
This leads to warranty claims and some ill feelings as this type of burnout is not covered by warranty. Make one hundred percent sure connections are correct prior toor Experiencing problems of a technical nature, drop usyour a line at editorial@ptmg.co.za starting theincompressor. In line. addition do not supply power acra@netactive.co.za with problem page the subject to a hermetic / semi hermetic compressor whilst the system is in deep vacuum, electrical damage may occur. Hermetic compressor cut away showing windings
Welcome to the PROBLEM PAGE. We find many people request assistance in the practical aspects of the industry. In response we will investigate the problem and endeavour to present the best possible solution. Thank you for all your questions sent in. Send your problems (and sometimes your creative solutions) to editorial@ptmg.co.za or acra@netactive.co.za with problem page in the subject line. You may include pictures. P Botha from Krugersdorp asks: Nobody seems to be able to tell me what is the best storage temperature for frozen chicken, can you help. The correct storage temperature for frozen chicken is minus 32˚C. The recommended maximum storage at this temperature is 12 months after which protein breakdown begins to occur. In addition the chicken should be frozen as quickly as possible and be tightly wrapped in plastic to prevent moisture loss and subsequent freezer burn. The following chart gives more detail: Storage Times (Suggested times for maximum quality) Refrigerator (4°C)
Freezer (-32°C)
Whole Chicken
Two to Three Days
Twelve Months
Chicken Parts
Two to Three Days
Nine Months
Giblets
One Day
Three Months
Ground Chicken
One Day
Three Months
Cooked Chicken
Three to Four Days
Three to Four Months
P Carletts from Braamfontien asks: I do not have much electrical knowledge and find that in many cases the problems I encounter are electrical in nature. Please could you shed some light on the connection of a single phase compressor with a start relay and how does a three speed motor found in the indoor units of most air conditioning systems operate? Thanks for the interesting question, speaking to some of the industries suppliers this appears to be a common problem. Unfortunately the incorrect wiring of a single phase compressor will almost certainly result in damage / burnt windings.
You should have a multimeter and an insulation tester available (MEGA). A multimeter does not normally have the functionality to perform insulation tests. A clamp type tong tester used to test amperes is in addition a very useful tool when testing motors Using a multimeter set on the ohms scale and the compressor electrically disconnected, test the motor windings for continuity, see figure below. PLEASE NOTE: THE READINGS GIVING ARE AN EXAMPLE. THE R TO C READING WILL GIVE THE LOWEST READING. THE S TO C WILL GIVE THE MIDDLE READING AND R TO S WICH REPRESENTS BOTH WINDINGS TOGETHER WILL GIVE THE HIGHEST READING. At the risk of repeating myself: different compressor makes and sizes will have different readings but the running winding will always have a lower resistance than the starting winding. The two readings added together give the total resistance. This reading identifies the common connection. The resistance of the running and starting windings when added together must be the same as the total resistance. If not the windings are damaged and the compressor will have to be replaced. EXAMPLE: R = Running winding S = Starting winding C = Common winding E = Earth terminal R to C = 3,5 ohms
S to C = 10,2 ohms R to S = 13,7 ohms 3,5 + 10,2 = 13,7 ohms Note: T h e
The connections shown are for low speed. For higher speeds switch the input from “A” to B, C or D. The capacitor in series with the motor windings serves a dual function; it improves starting torques and provides better running efficiency. resistance of some undamaged windings can be as low as 0.5 ohm. Zero resistance indicates a shorted winding and an infinite or very high resistance indicates an open winding. Use an insulation tester when checking for a grounded winding. (Current is passed through the weakness / breakdown in the insulation material to the other winding or to earth) Unless you have specific information indicating otherwise, any hermetic motor of one horsepower or under can be considered suspect if the resistance between the windings and the housing is less than 0,5 meg-ohm. Test as follows; E to R = less than 0,5 meg ohm E to S = less than 0,5 meg ohm E to C = less than 0,5 meg ohm If all the readings test correct the compressor can be run. Using a tong tester take the ampere reading while it is running. The amp reading should correspond with the ampere rating on the compressor whilst under operating conditions. The above is very important and I would recommend that you check all compressors (even new) prior to connecting the power supply. If a fault is found prior to installation of the compressor the warranty claim should be simplified. With regard to the second part of you question: The function of a multiple-winding motor is to provide a selection of running torques which, when driving a load such as a blower wheel, will result in varying speeds and thus affects air flow volumes.
Shawn Erasmus asks: It would be interesting to know what all the information on a three phase motor name plate means. Thanks for the interest Shawn. The name plate or data contains all the information required for the installer. You may find some variation between manufactures so always check. Meaning of information Ser. No. Vd 5157/74 = is the serial number of the motor. Frame T.E.F.C. / D132S TEFC = Totally enclosed fan cooled D132S =Indicates the distance between the mounting and the shaft centre kW = indicates total motor output at sea level Volts = 380 Working Volts of motor. Amps 12,6 = When motors at full load it draws12,6amps RPM 1450 = 1450 Revolutions per minute Conn = Star connection or Delta connection Brgs 6208 D = Bearing drive end = size/type 6208 6206 ND = Bearing non drive end Duty: S1 C.M.R. S1 or C.M.R. = This motor can run continuously without having to stop to cool down S2 = This motor can run for up to 60 minutes before stopping to cool down S3 = This motor can only run for 2.5 minutes and then must cool down for 7,5 minutes. 3 Ph 50 Hz = a motor operating with a 3 phase supply at 50 Hertz Ins: E 80 This indicates the insulation materials maximum operating temperatures. A = 105ºC E = 120ºC B = 130ºC H = 180ºC F = 155°C Therefore E 80 indicates a motor normally running at 80°C with a maximum operating temperature of 120˚C. REFERENCES: USFDA / FEMCO Thanks to all for writing in with interesting questions. Looking forward to hearing from you – Grant Laidlaw