hartjies

Thank very much, I will start on this project as soon as possable. You have been a great help. Regards

Thank you very much. Will a BC557 work for the top transistor. I did the math - if I make R1 2.2K and R2 500 ohm, I will get exactly 13.5 vdc. Is it possible to replace R2 with a 1K pot (variable carbon resistor) or would it be better to put a 47E pot in serie with R2 for finetuning? If R2 is fixed on 500 ohm, what would R3 be? Based on your instruction I understand something like this: 100 x ((2200 x 500) / (2200 + 500)) = 40740 ohm Thank You

Sorry for the confusion. The Cole Hersee solenoid will take about 5 amp to switch. But to switch the relay will take about 100mA. Thanks

Thanks for the reply. The relay needs to switch a Cole Hersee solenoid or a battery isolation relay. I need the Cole Hersee to switch an auxiliary battery to put in charging mode. Basically the auxiliary battery must only start to charge when the main battery voltage is above 13.5vdc. Thanks

Hi guys Could someone help me on a diagram how to build a module that switch a 12 vdc relay when the battery voltage is above 13 vdc. When the battery's voltage is below 13 vdc, the relay must remain normaly open. Thanks in advance