The circuit in Figure 1 solves the problem with two PUTs (programmable unijunction transistors), one connected to each SCR. Performance is good because the circuit does not 'fold back' as inexpensive ...

This 12V SCR battery charger circuit differs from the norm in a number of ways, all of which make it difficult to understand.

Standard features include overtemperature protection; phase loss inhibit; on-board led indicators; 5V and 15V outputs for customer control circuits; and fault signals.