Transformer malfunction can be the result of organic ageing, premature shorting of adjoining coil wires, or overheating harm. The most typical reason for transformer overheating and burnout is the consequence of misuse, connecting the charger to a battery system of lower voltage than specified for the charger. This is generally caused when service is conducted on a battery system consisting of several 6-volt batteries attached in series to generate a higher system voltage. During service, one or more batteries are installed reverse polarity lowering the system voltage, driving the charge current to stay high without tapering.
Testing the transformers needs energising the transformer primary with the specified voltage and frequency AC power and recording the AC voltage calculated at the transformer secondary leads that connect to the diodes. This voltage is (1) determined with a good capacitor attached and (2) assessed with the capacitor disconnected. Always test and verify the capacitor is good before functioning transformer tests. All fuse links of the fuse assembly should test well and/or connect a jumper lead across the transformer leads attached to the fuse assembly.
- To electrically isolate the transformer output for these tests, disconnect the transformer secondary coil leads (TAN sleeking) from the diode terminals. Connect the meter leads to these kinds of transformer leads and adjust the meter in the beginning to an AC range of three (3) times the DC voltage rating specified by the charger nameplate.
- Examine to make sure for individual protection that no leads have been accidentally allowed to short before applying input power to the transformer primary for test.
- With the resonant capacitor attached , the AC voltage determined across the transformer secondary leads disconnected from the diodes should read approximately two and one half ( 2 .5 ) times the DC voltage rating of the charger . With the resonant capacitor disconnected, the measured voltage should decrease to two-thirds (2/3) of that measured with the capacitor connected.
The voltage readings are approximate and transformer malfunction is indicated when the calculated AC voltages are considerably below the calculated values. Voltage measurements less than 10 volts with the capacitor disconnected usually confirm a failed transformer that must be changed. Because of no-load transformer instabilities and peculiar wave shapes, transformer secondary voltage readings made with the resonant capacitor connected can create noticeably higher voltage readings. This is especially true when using digital meters. Transformer malfunction is confirmed when the measured voltages are significantly lower than calculated.