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Discussion Starter · #1 ·
I have just built a voltage sensor relay that fits easily in an 8 pin octal enclosure (1.5"x1.5"x2"), with DPDT contacts rated at 8 amps 240 VAC. It draws only about 12-15 mA from the signal, which can be AC or DC. It is only programmed to turn on the relay at 160 VAC and off at 140 VAC, to detect the line voltage which could be 120 VAC nominal or 208/240 VAC nominal. It's a fairly simple circuit which fits on a 1.2"x1.75" PCB, and the parts are less than $20 (including $10 for the enclosure).

Since it uses a PIC, it could be programmed to provide voltage sensing of other levels as well as provide timing and other functions. For instance, it could be connected to a battery pack under charge, and turn off the charger when the voltage reaches a preset limit, or after a period of time. The contacts (in parallel) could handle a 3600W charger (240V 15A).

The basic circuit should work down to about 60 volts, and components could be changed (mostly the 48 VDC relay) for lower voltages down to 12 VDC. This was designed for a specific purpose, but if anyone is interested I can supply the details (and possibly PC boards). I'll post more later but let me know if you have any suggestions for possible uses in the DIY EV field.
 

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I have just built a voltage sensor relay that fits easily in an 8 pin octal enclosure (1.5"x1.5"x2"), with DPDT contacts rated at 8 amps 240 VAC. It draws only about 12-15 mA from the signal, which can be AC or DC. It is only programmed to turn on the relay at 160 VAC and off at 140 VAC, to detect the line voltage which could be 120 VAC nominal or 208/240 VAC nominal. It's a fairly simple circuit which fits on a 1.2"x1.75" PCB, and the parts are less than $20 (including $10 for the enclosure).

Since it uses a PIC, it could be programmed to provide voltage sensing of other levels as well as provide timing and other functions. For instance, it could be connected to a battery pack under charge, and turn car parts off the charger when the voltage reaches a preset limit, or after a period of time. The contacts (in parallel) could handle a 3600W charger (240V 15A).

The basic circuit should work down to about 60 volts, and components could be changed (mostly the 48 VDC relay) for lower voltages down to 12 VDC. This was designed for a specific purpose, but if anyone is interested I can supply the details (and possibly PC boards). I'll post more later but let me know if you have any suggestions for possible uses in the DIY EV field.
Can you design more voltage sensor relay? Send me some pics, diagram and working details. We can make good deal
 

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Discussion Starter · #4 ·
Here is a simulation of the VRLY circuit. The only thing missing is the PIC12F675, which is powered from the 5VDC and drives a transistor to control the 48 VDC relay (which is simulated by the 5k resistor R4:



If you want to use this as a backup battery pack controller, you could set the trip voltage to whatever is the peak charge, and the relay will energize to shut off the charge. But it may be better to reverse the logic so the relay is on until peak voltage is reached, at which point the relay will turn off, and the current draw will be reduced to about 2 mA. ;)

It is also possible to add a timer function. :)
 

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Discussion Starter · #5 ·
I made a video of the operation of the voltage relay, and images of the circuit as built on a perfboard.

 
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